Collagen Matrix Remodeling Research Articles

Adipose-derived stem cells apoptosis rejuvenate radiation-impaired skin in mice via remodeling and rearranging dermal collagens matrix

BackgroundChronic radiation dermatitis (CRD) is a late consequence of radiation with high incidence in patients receiving radiotherapy. Conventional therapies often yield unsatisfactory results. Therefore, this study aimed to explore the therapeutic potential and mechanism of adipose-derived stem cells (ADSCs) for CRD, paving the way for novel regenerative therapies in clinical practice.MethodsClinical CRD skin biopsies were analyzed to character the pathological changes of CRD skin and guided the animal modeling scheme. Subsequently, an in vivo analysisusing mouse CRD models was conducted to explore their effects of ADSCs on CRD, monitoring therapeutic impact for up to 8 weeks. Transcriptome sequencing and histologic sections analysis were performed to explore the potential therapeutic mechanism of ADSCs. Following observing extensive apoptosis of transplanted ADSCs, the therapeutic effect of ADSCs were compared with those of apoptosis-inhibited ADSCs. Multiphoton imaging and analysis of collagen morphologic features were employed to explain how translated ADSCs promote collagen remodeling at the microscopic level based on the contrast of morphology of collagen fibers.ResultsFollowing injection into CRD-afflicted skin, ADSCs therapy effectively mitigated symptoms of CRD, including acanthosis of the epidermis, fibrosis, and irregular collagen deposition, consistent with the possible therapeutic mechanism suggested by transcriptome sequencing. Notably, in vivo tracking revealed a significant reduction in ADSCs number due to extensive apoptosis. Inhibiting apoptosis in ADSCs partially tempered their therapeutic effects. Mechanically, analysis of collagen morphologic features indicated that translated ADSCs might promote dermal extracellular matrix remodeling through enlarging, lengthening, crimping, and evening collagen, counteracting the atrophy and rupture caused by irradiation.ConclusionsThis study demonstrated that ADSCs underwent substantial apoptosis upon local skin transplantation, and paradoxically, this apoptosis is essential for their efficacy in promoting the regeneration of late radiation-impaired skin. Mechanically, transplanted ADSCs could promote the remodeling and rearrangement of radiation-damaged dermal collagen matrix.

Abstract 5571: Collagen stabilization directs immune suppression in the head and neck squamous cell carcinoma hypoxic subtype

Abstract Head & neck squamous cell carcinoma (HNSCC) show limited clinical benefit to immune checkpoint inhibitors (ICI). Interactions between extracellular matrix (ECM), tumor, and immune cells underly the mechanisms leading to immunosuppression and resistance to ICIs. Collagen matrix remodeling within tumor stroma can influence accessibility and function of immune cells. Specifically, telopeptidyl lysine residues in fibrillar collagen can be hydroxylated by Lysyl hydroxylase 2 (LH2) prior to cross-linking which leads to stiffened, stable collagen. We previously showed that this LH2-modified tumor microenvironment (TME) drives HNSCC invasion and metastasis. Here, we elucidate the interplay between LH2-modified collagen and the immune landscape within TME of hypoxic and immunosuppressive HNSCC. Bioinformatics analyses of RNAseq datasets were performed to assess pathways regulating collagen deposition and stabilization. Tissue microarray having 81 primary, 28 recurrent primary, and 3 lymph node metastases tumor cores was analyzed. Cores were classified according to our published Hypoxia-Immune signature (Chaudhary R. et al. 2023, Can Res Comm). We performed Second Harmonic Generation imaging of H&E stained TMA section to analyze the orientation and length of collagen fibrils. Picrosirius red (PSR) staining allowed quantification of total collagen and collagen maturation was assessed by polarized light imaging of birefringence. Further, we performed multiplex immunofluorescence staining for CD3+ (T-cell); CD14+ (Monocyte & Macrophage); CD11c+ (Dendritic); Pax5+ (B-cell); Pan-Cytokeratin+ (tumor), and LH2. Low (0-1) LH2 expression was seen in 29.5% of analyzed cores whereas 70.5% of cores scored high (2-3) for LH2 expression. Cores classified under the hypoxia subtype exhibit high LH2 and enrichment of collagen stability signature. Late-stage tumors have highly oriented collagen fibers compared to normal tissue or early-stage tumors which have randomly distributed fibers. CT-Fire-based measurements revealed that LH2hi cores have significantly increased fiber length and lower coefficient of variance for fiber angles. The area of collagen measured by PSR staining had no correlation with tumor stage or subtype indicating that collagen deposition is similarly high in HNSCCs. However, birefringence measurements showed that a higher fraction of mature fibrillar collagen is associated with late-stage LH2hi tumors. Interestingly, LH2 expression positively correlated with increased CD3+ T cells in stroma suggesting that anti-tumor T cells are physically obstructed by the presence of LH2-stabilized and stiffened collagen fibers. LH2 expression influences the quality of collagen but not the quantity. Understanding the effect of LH2-mediated collagen modifications on the TIME may have implications for therapeutic strategies to enhance anti-tumor immune response in HNSCC. Citation Format: Sonal Srivastava, John Powers, Ritu Chaudhary, Sadegh Marzban, Robbert J. Slebos, Jeffrey West, Xiaofei Song, Jose A. Guevara-Patino, Christine H. Chung, Antonio L. Amelio. Collagen stabilization directs immune suppression in the head and neck squamous cell carcinoma hypoxic subtype [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5571.

The role of cell-matrix adhesion and cell migration in breast tumor growth and progression.

During breast cancer progression, there is typically increased collagen deposition resulting in elevated extracellular matrix rigidity. This results in changes to cell-matrix adhesion and cell migration, impacting processes such as the epithelial-mesenchymal transition (EMT) and metastasis. We aim to investigate the roles of cell-matrix adhesion and cell migration on breast tumor growth and progression by studying the impacts of different types of extracellular matrices and their rigidities. We embedded MCF7 spheroids within three-dimensional (3D) collagen matrices and agarose matrices. MCF7 cells adhere to collagen but not agarose. Contrasting the results between these two matrices allows us to infer the role of cell-matrix adhesion. We found that MCF7 spheroids exhibited the fastest growth rate when embedded in a collagen matrix with a rigidity of 5.1kPa (0.5mg/mL collagen), whereas, for the agarose matrix, the rigidity for the fastest growth rate is 15kPa (1.0% agarose) instead. This discrepancy is attributable to the presence of cell adhesion molecules in the collagen matrix, which initiates collagen matrix remodeling and facilitates cell migration from the tumor through the EMT. As breast tumors do not adhere to agarose matrices, it is suitable to simulate the cell-cell interactions during the early stage of breast tumor growth. We conducted further analysis to characterize the stresses exerted by the expanding spheroid on the agarose matrix. We identified two distinct MCF7 cell populations, namely, those that are non-dividing and those that are dividing, which exerted low and high expansion stresses on the agarose matrix, respectively. We confirmed this using Western blot which showed the upregulation of proliferating cell nuclear antigen, a proliferation marker, in spheroids grown in the 1.0% agarose (≈13kPa). By treating the embedded MCF7 spheroids with an inhibitor or activator of myosin contractility, we showed that the optimum spheroids' growth can be increased or decreased, respectively. This finding suggests that tumor growth in the early stage, where cell-cell interaction is more prominent, is determined by actomyosin tension, which alters cell rounding pressure during cell division. However, when breast tumors begin generating collagen into the surrounding matrix, collagen remodeling triggers EMT to promote cell migration and invasion, ultimately leading to metastasis.

Poster 136: Augmented Meniscus Radial Tear Healing via Local Transforming Growth Factor-beta 1 (TGF- β1) Gene Therapy in a Rat Model

Objectives: Meniscus tears cause significant musculoskeletal impairment and are among the most common knee injuries. Tears in the inner third of the meniscus have intrinsically poor healing capacity due to insufficient blood supply. In an effort to improve healing, use of biologic augments is a promising area of investigation. Tissue engineering strategies, such as growth factor gene therapy, have emerged as encouraging approaches to improving meniscal healing. Transforming Growth Factor-Beta 1 (TGF-β1) gene therapy has shown promise in vitro and ex vivo as a therapeutic strategy, but its effects on meniscus healing in vivo remain unknown. This study aimed to determine whether local delivery of viral vectors carrying the TGF-β1 gene could improve the healing of a meniscus tear involving the avascular zone in vivo in a rat model. Methods: Recombinant adenoviruses were generated using the AdEasy system. Briefly, the coding regions of mouse TGFβ1 were PCR amplified and cloned into an adenoviral shuttle vector and subsequently used to generate recombinant adenoviruses in HEK293 cells. The resulting adenoviruses were designated as Adv-TGF-β1. An analogous adenovirus expressing only GFP (Adv-GFP) was used as mock virus controls. To achieve local delivery of viral vectors to the injury site, we utilized a thermoresponsive biodegradable polydiolcitrate-gelatin delivery scaffold (PPCNg). A full-thickness radial tear was made in the medial meniscus of the left hind leg of twelve Wistar rats. Rats were divided into two groups: one receiving a mixture of PPCNg+TGF-β1 (n = 3) and the other receiving PPCNg+GFP (n = 3). A 4ºC pre-chilled solution of PPCNg seeded with Adv-TGF-β1 or Adv-GFP at 1011 infectious viral particles/injection was administered at the site of the induced meniscus tear. After 3 weeks, rats were euthanized, and the menisci were histologically evaluated by hematoxylin and eosin (H&E) staining. The histologic assessment and scoring of meniscus tissue wound healing were done by one blinded and one unblinded observer, each using selected wound healing parameters as described in Table 1, and the results were averaged. The intra-class correlation coefficient (ICC) was computed based on a mean rating (k=2), absolute agreement, and two-way random effects model to assess the agreement between the wound healing score rating of the two observers. Statistical significance between groups was determined using the Mann-Whitney Wilcoxon rank sum test. A value of p < 0.05 was considered statistically significant. All animal procedures were performed according to an Institutional Animal Care and Use Committee protocol at the home institution. Results: Immediately after and 3 weeks post-surgery, there was no evidence of infection, dehiscence, or functional deficit. Histologic evaluation of the sections (n = 8/group) of harvested rat menisci (n = 2/group) revealed improved healing of tears in the PPCNg+TGF-β1 group compared to the control group (5.7 ± 0.48 vs. 5.0 ± 0.89, p = 0.011) (Figure 1B). The lesion area demonstrated significantly greater neovascularization (2.75 ± 0.45 vs. 2.06 ± 0.68, p = 0.004), better collagen organization (1.94 ± 0.25 vs. 1.62 ± 0.50, p = 0.038), and increased hypercellularity (1.0 ± 0.00 vs. 1.3 ± 0.48, p = 0.018) in the PPCNg+TGF-β1 group compared to the controls (Figure 1C). Moderate absolute agreement between the two raters was observed in their wound healing score ratings (ICC = 0.615). Conclusions: Our results indicate that PPCNg-mediated delivery of Adv-TGF-β1 enhanced the early (3 weeks) healing of the meniscus lesion in rats compared with control (Adv-GFP) gene therapy. Further, localized administration of Adv-TGF-β1 induced greater neovascularization, better organization of collagen fibers, and increased hypercellularity at the injury site in the Adv-TGFβ-1 rat group compared with controls at 3 weeks post-injury. These results together suggest that TGF-β1 gene therapy may enhance meniscus healing by inducing more cellular proliferation and infiltration and greater neovascularization at the injury site to serve as nourishment for the establishment of new wound matrix, leading to more significant deposition and remodeling of mature collagen matrix. Further study that includes larger sample sizes, confirmation of successful gene transfer to meniscal cells around the tear site, and investigations of both later time points of wound healing and the mechanisms by which local TGF-β1 gene therapy may modulate augmented meniscus healing in this rat model of meniscal defect is necessary to better determine the potential future clinical utility of local TGF-β1 gene therapy to treat of meniscus tears with poor healing capacity. [Table: see text]

Development of a novel senolysis approach targeting the senescent fibroblast marker HTR2A via antibody-dependent cellular cytotoxicity.

Abnormal remodeling of collagen and extracellular matrix caused by the accumulation of senescent fibroblasts in the dermis is the most likely cause of skin aging. Therefore, the application of "senolysis," in which only senescent cells are cleared from the body, has a potential in the development of antiaging treatments for skin. However, markers that label senescent fibroblasts only reflect the state of senescence, and it is important to develop markers as therapeutic targets to aid senolysis application. We investigated the potential of serotonin 2A receptor (HTR2A), which is involved in melanin production in response to UV light, as a senescent cell marker. The results showed that HTR2A is upregulated in aging dermal fibroblasts but is expressed at low levels in proliferating young cells. Flow cytometry demonstrated the presence of many HTR2A-positive cells in the aging cell population and few in the young cells. Furthermore, antibody-dependent cytotoxicity assays revealed that HTR2A preferentially sensitizes senescent fibroblasts and specifically damages only senescent cells by NK cells that recognize it. In conclusion, selective labeling of the novel senescent cell marker, HTR2A, could preferentially eliminate senescent cells and may contribute to the future development of novel skin senolysis approaches.

Exposure to oxLDL impairs TGF-β activity in human tendon cells

BackgroundPrevious studies have shown that patients with hypercholesterolemia experience elevated levels of oxidized LDL (oxLDL), a molecule which triggers inflammation and collagenase activity. In this study we discovered novel mechanistic effects of oxLDL on tendon cells and the mediators regulating matrix remodeling by analyzing the expression and activity of related proteins and enzymes. These effects may contribute to tendon damage in patients with high cholesterol.MethodsIsolated human tendon cells (male and female donors age 28 ± 1.4 age 37 ± 5.7, respectively) were incubated in the presence or absence of oxLDL. The influence of oxLDL on the expression level of key mRNA and proteins was examined using real time quantitative PCR, ELISA and Western blots. The activities of enzymes relevant to collagen synthesis and breakdown (lysyl oxidase and matrix metalloproteinases) were quantified using fluorometry. Finally, the isolated human tendon cells in a 3D construct were exposed to combinations of oxLDL and TGF-β to examine their interacting effects on collagen matrix remodeling.ResultsThe one-way ANOVA of gene expression indicates that key mRNAs including TGFB, COL1A1, DCN, and LOX were significantly reduced in human tendon cells by oxLDL while MMPs were increased. The oxLDL reduced the activity of LOX at 50 µg/ml, whereas conversely MMP activities were induced at 25 µg/ml (P ≤ 0.01). COL1A1 synthesis and TGF-β secretion were also inhibited (P ≤ 0.05). Adding recombinant TGF-β reversed the effects of oxLDL on the expression of collagens and LOX. OxLDL also impaired collagen matrix remodeling (P ≤ 0.01), and adding TGF-β restored the native phenotype.ConclusionExposure to oxLDL in patients with hypercholesterolemia may adversely affect the mechanical and structural properties of tendon tissue through a direct action of oxLDL on tendon cells, including impairment of TGF-β expression. This impairment leads to disturbed matrix remodeling and synthesis, thereby potentially leading to increased risk of acute or chronic tendon injury. Our discovery may provide an opportunity for developing effective treatments for tendon injury in hypercholesterolemia patients by targeting the TGF-β pathway.

In vitro vascularization of hydrogel-based tissue constructs via a combined approach of cell sheet engineering and dynamic perfusion cell culture

The bioengineering of artificial tissue constructs requires special attention to their fast vascularization to provide cells with sufficient nutrients and oxygen. We addressed the challenge of in vitro vascularization by employing a combined approach of cell sheet engineering, 3D printing, and cellular self-organization in dynamic maturation culture. A confluent cell sheet of human umbilical vein endothelial cells (HUVECs) was detached from a thermoresponsive cell culture substrate and transferred onto a 3D-printed, perfusable tubular scaffold using a custom-made cell sheet rolling device. Under indirect co-culture conditions with human dermal fibroblasts (HDFs), the cell sheet-covered vessel mimic embedded in a collagen gel together with additional singularized HUVECs started sprouting into the surrounding gel, while the suspended cells around the tube self-organized and formed a dense lumen-containing 3D vascular network throughout the gel. The HDFs cultured below the HUVEC-containing cell culture insert provided angiogenic support to the HUVECs via molecular crosstalk without competing for space with the HUVECs or inducing rapid collagen matrix remodeling. The resulting vascular network remained viable under these conditions throughout the 3 week cell culture period. This static indirect co-culture setup was further transferred to dynamic flow conditions, where the medium perfusion was enabled via two independently addressable perfusion circuits equipped with two different cell culture chambers, one hosting the HDFs and the other hosting the HUVEC-laden collagen gel. Using this system, we successfully connected the collagen-embedded HUVEC culture to a dynamic medium flow, and within 1 week of the dynamic cell culture, we detected angiogenic sprouting and dense microvascular network formation via HUVEC self-organization in the hydrogel. Our approach of combining a 3D-printed and cell sheet-covered vascular precursor that retained its sprouting capacity together with the self-assembling HUVECs in a dynamic perfusion culture resulted in a vascular-like 3D network, which is a critical step toward the long-term vascularization of bioengineered in vitro tissue constructs.

Electrospun Chitosan-Polyvinyl Alcohol Nanofiber Dressings Loaded with Bioactive Ursolic Acid Promoting Diabetic Wound Healing.

The design and development of novel dressing materials are urgently required for the treatment of chronic wounds caused by diabetic ulcers in clinics. In this study, ursolic acid (UA) extracted from Chinese herbal plants was encapsulated into electrospun nanofibers made from a blend of chitosan (CS) and polyvinyl alcohol (PVA) to generate innovative CS-PVA-UA dressings for diabetic wound treatment. The as-prepared CS-PVA-UA nanofiber mats exhibited randomly aligned fiber morphology with the mean fiber diameters in the range of 100–200 nm, possessing great morphological resemblance to the collagen fibrils which exist in the native skin extracellular matrix (ECM). In addition, the CS-PVA-UA nanofiber mats were found to possess good surface hydrophilicity and wettability, and sustained UA release behavior. The in vitro biological tests showed that the high concentration of UA could lead to slight cytotoxicity. It was also found that the CS-PVA-UA nanofiber dressings could significantly reduce the M1 phenotypic transition of macrophages that was even stimulated by lipopolysaccharide (LPS) and could effectively restore the M2 polarization of macrophages to shorten the inflammatory period. Moreover, the appropriate introduction of UA into CS-PVA nanofibers decreased the release levels of TNF-α and IL-6 inflammatory factors, and suppressed oxidative stress responses by reducing the generation of reactive oxygen species (ROS) as well. The results from mouse hepatic hemorrhage displayed that CS-PVA-UA nanofiber dressing possessed excellent hemostatic performance. The in vivo animal experiments displayed that the CS-PVA-UA nanofiber dressing could improve the closure rate, and also promote the revascularization and re-epithelization, as well as the deposition and remodeling of collagen matrix and the regeneration of hair follicles for diabetic wounds. Specifically, the mean contraction rate of diabetic wounds using CS-PVA-UA nanofiber dressing could reach 99.8% after 18 days of treatment. In summary, our present study offers a promising nanofibrous dressing candidate with multiple biological functions, including anti-inflammation, antioxidation, pro-angiogenesis, and hemostasis functions, for the treatment of hard-to-heal diabetic wounds.

Involvement of Lysyl Oxidase in the Pathogenesis of Arterial Stiffness in Chronic Kidney Disease

RationaleIncreased vascular stiffness is a key mediator of cardiovascular disease (CVD) in patients with chronic kidney disease (CKD). Increased vascular stiffness in CKD is thought to be the consequence of long‐standing hypertension and vascular calcification. However, vascular stiffness is increased early in patients with CKD, even before metabolic complications develop. Lysyl Oxidase (LOX) is a key mediator of collagen crosslinking and matrix remodeling. Up‐regulation of LOX has been associated with increased tissue stiffness in cancer and wound healing. We hypothesize that increased LOX might be a key mechanism for increased vascular stiffness in CKD. β‐aminopropionitrile (BAPN), a LOX inhibitor, was used to test the hypothesis.Methods5/6 nephrectomy (Nx) or Sham surgery was performed in 8‐weeks old male C57BL/6 mice. 2‐weeks after Nx, mice were randomized to BAPN (300 mg/kg/day in water) or vehicle for 4‐weeks. Vascular stiffness was assessed by pulse wave velocity (PWV). LOX levels were measured by ELISA and qPCR. Collagen crosslinking was measured by mass spectrometry. Comparisons between groups were made using one‐way ANOVA, p‐Value <0.05 was accepted as significant.ResultsNx resulted in decreased renal function at 8 weeks but no change in blood pressure or calcification. (~2‐3‐fold increase in creatinine, urea, and cystatin C) compared to control mice. Nx surgery resulted in increase in PWV (Con:179±32, Nx: 306 ± 47 cm/s, p<0.001). This was associated with an increased LOX in aorta (Con:118±8, Nx: 311±13 pg/mg dry weight, p<0.001). Mice with Nx surgery had an increased total collagen contents (183%, p<0.001) as well as cross‐linked collagen (DPD; 83%, p<0.05, PYD: 270% p<0.01). BAPN treatment significantly attenuates PWV (211± 49 cm/s, p<0.01), LOX (256±21 pg/mg dry weight, p<0.05) and total collagen contents (23%, p<0.01). BAPN treatment reduced the crosslinked collagens (DPD and PYD) but this did not reach statistical significance.ConclusionOur findings suggest: a) Increased vascular stiffness in CKD is independent of BP and calcification b) LOX mediated changes in extracellular matrix are at least in part responsible for the pathogenesis of arterial stiffness in CKD. Inhibition of excessive LOX may have therapeutic potential in alleviating increased vascular stiffness in CKD.

Integrin α11β1 in tumor fibrosis: more than just another cancer-associated fibroblast biomarker?

There is currently an increased interest in understanding the role of the tumor microenvironment (TME) in tumor growth and progression. In this context the role of integrins in cancer-associated fibroblasts (CAFs) will need to be carefully re-evaluated. Fibroblast-derived cells are not only in the focus in tumors, but also in tissue fibrosis as well as in inflammatory conditions. The recent transcriptional profiling of what has been called “the pan-fibroblast cell lineage” in mouse and human tissues has identified novel transcriptional biomarker mRNAs encoding the secreted ECM proteins dermatopontin and collagen XV as well as the phosphatidylinositol-anchored membrane protein Pi16. Some of the genes identified in these fibroblasts scRNA-seq datasets will be useful for rigorous comparative characterizations of fibroblast-derived cell subpopulations. At the same time, it will be a challenge in the coming years to validate these transcriptional mRNA datasets at the protein-(expression) and at tissue-(distribution) levels and to find useful protein biomarker reagents that will facilitate fibroblast profiling at the cell level. In the current review we will focus on the role of the collagen-binding integrin α11β1 in CAFs, summarizing our own work as well as published datasets with information on α11 mRNA expression in selected tumors. Our experimental data suggest that α11β1 is more than just another biomarker and that it as a functional collagen receptor in the TME is playing a central role in regulating collagen assembly and matrix remodeling, which in turn impact tumor growth and metastasis.

Contributions of Myocardial Hypertrophy and Stiffening to Right‐Ventricular Remodeling in a Rat Model of Pulmonary Arterial Hypertension

Pulmonary Arterial Hypertension (PAH) is a progressive vasculopathy which increases pulmonary vascular stiffness and induces a pressure overload on the right ventricle (RV). In patients with PAH, the RV remodels in response to increased pulmonary pressure, including myocardial hypertrophy and RV geometric remodeling, but can result in intractable right heart failure. Given that the underlying mechanisms of RV remodeling are not well understood,1 we carried out invasive RV catherization in the sugen-hypoxia (SuHx) rat model to assess systolic and diastolic chamber function during the progression of PAH. To distinguish the relative contributions of RV geometric remodeling from myocardial material remodeling to changes in RV function, a biomechanics model was fitted to measured RV pressure-volume relations and morphology after three, five, and eight weeks of sugen injections. After an initial decrease in RV ejection fraction (66±10% to 44±6%, p<0.01), systolic function stabilized (subsequent 2% change in EF through the end of the study, p>0.05), despite progressive increases to RV end-systolic pressure. The model attributed these changes to RV myocardial hypertrophic wall-thickening, with only minor increases in myocyte force generating capacity at week 5 (Figure 1). After RV systolic function stabilized, end-diastolic pressure increased significantly (p<0.05), with maintained RV diastolic volumes. Unlike end systole, RV end-diastolic volume was maintained due to stiffening of myocardium resting properties (Figure 1, panel 2-3). These passive stiffness findings are in agreement with previously identified increases in diastolic chamber and myocardial stiffening in both PAH animals and patients occurring before the onset of severe systolic dysfunction2,3. While significant myocardial passive stiffness was found in this study, there was no evidence of changes in total collagen content (p>0.05) or collagen type I to III ratio (p>0.05). This points towards possible collagen matrix remodeling such as collagen fiber structure, tortuosity, or cross-linking, or changes in titin isoforms or phosphorylation. This progressive increase in RV myocardial passive stiffness that occurs after RV hypertrophy has stabilized systolic function may be a compensatory mechanism to delay or prevent RV dilation but may also eventually contribute to diastolic dysfunction. [1] Van de Veerdonk MC et al. Heart Fail Rev. 2016. [2] Vélez-Rendón D et al. J Biomech Eng. 2019. [3] Rain S et al. Circ Heart Fail. 2016.

The Role of Kruppel‐like Factor 6 in Prolidase Regulation

Prolidase, also known as peptidase D (PEPD), is a hydrolase that cleaves dipeptides containing C-terminal proline or hydroxyproline. These dipeptides are generated largely during collagen turnover, therefore prolidase catalysis is an essential rate-limiting step during collagen biosynthesis. Consequently, prolidase plays a significant role in collagen metabolism, matrix remodeling, and wound healing. Defective wound healing is one of the hallmarks of Prolidase Deficiency, a rare autosomal recessive disorder characterized by the excretion of prolidase substrates in the urine. Although prolidase is implicated in wound healing, its molecular and cellular regulation remains understudied. Our initial in silico analysis of the PEPD promoter (PEPDpro) identified key regulatory elements upstream of the transcription start site. We identified Kruppel-like factor 6 (KLF6), a zinc-finger transcription factor associated with vascular injury, wound healing, and collagen metabolism. To study the interaction between KLF6 and prolidase, we amplified the promoter from the human genome and inserted it into a luciferase reporter construct. Our preliminary data demonstrate that KLF6 enhances PEPD promoter activity in a dose-dependent manner. Additionally, KLF6 is regulated by transforming growth factor β1 (TGFβ1), and our data illustrate that TGFβ1 drives PEPD promoter activity. These results will generate new knowledge on the molecular regulation of prolidase and aid in developing therapeutic approaches to regulate prolidase expression in various physiological and pathological conditions such as wound healing.

Mueller polarimetric imaging for fast macroscopic mapping of microscopic collagen matrix remodeling by smooth muscle cells

Smooth muscle cells (SMCs) are critical players in cardiovascular disease development and undergo complex phenotype switching during disease progression. However, SMC phenotype is difficult to assess and track in co-culture studies. To determine the contractility of SMCs embedded within collagen hydrogels, we performed polarized light imaging and subsequent analysis based on Mueller matrices. Measurements were made both in the absence and presence of endothelial cells (ECs) in order to establish the impact of EC-SMC communication on SMC contractility. The results demonstrated that Mueller polarimetric imaging is indeed an appropriate tool for assessing SMC activity which significantly modifies the hydrogel retardance in the presence of ECs. These findings are consistent with the idea that EC-SMC communication promotes a more contractile SMC phenotype. More broadly, our findings suggest that Mueller polarimetry can be a useful tool for studies of spatial heterogeneities in hydrogel remodeling by SMCs.

Tendon Extracellular Matrix Assembly, Maintenance and Dysregulation Throughout Life.

In his Lissner Award medal lecture in 2000, Stephen Cowin asked the question: "How is a tissue built?" It is not a new question, but it remains as relevant today as it did when it was asked 20years ago. In fact, research on the organization and development of tissue structure has been a primary focus of tendon and ligament research for over two centuries. The tendon extracellular matrix (ECM) is critical to overall tissue function; it gives the tissue its unique mechanical properties, exhibiting complex non-linear responses, viscoelasticity and flow mechanisms, excellent energy storage and fatigue resistance. This matrix also creates a unique microenvironment for resident cells, allowing cells to maintain their phenotype and translate mechanical and chemical signals into biological responses. Importantly, this architecture is constantly remodeled by local cell populations in response to changing biochemical (systemic and local disease or injury) and mechanical (exercise, disuse, and overuse) stimuli. Here, we review the current understanding of matrix remodeling throughout life, focusing on formation and assembly during the postnatal period, maintenance and homeostasis during adulthood, and changes to homeostasis in natural aging. We also discuss advances in model systems and novel tools for studying collagen and non-collagenous matrix remodeling throughout life, and finally conclude by identifying key questions that have yet to be answered.

Paeoniflorin promotes angiogenesis and tissue regeneration in a full-thickness cutaneous wound model through the PI3K/AKT pathway.

The treatment of wounds remains a clinical challenge because of poor angiogenesis under the wound bed, and increasingly, the patients' need for functional and aesthetically pleasing scars. For the wound healing process, new blood vessels which can deliver nutrients and oxygen to the wound area are necessary. In this study, we investigated the pro-angiogenesis ability and mechanism in wound healing of paeoniflorin (PF), which is a traditional Chinese medicine. In our in vitro results, the ability for proliferation, migration and in vitro angiogenesis in human umbilical vein endothelial cells was promoted by coculturing with PF (1.25-5 μM). Meanwhile, molecular docking studies revealed that PF has excellent binding abilities to phosphatidylinositol-3-kinase (PI3K) and protein kinase B (AKT), and consistent with our western blot results, that PF suppressed PI3K and AKT phosphorylation. Furthermore, to investigate the healing effect of PF in vivo, we constructed a full-thickness cutaneous wound model in rats. PF stimulated the cellular proliferation status, collagen matrix deposition and remodeling processes in vitro and new blood vessel formation at the wound bed resulting in efficient wound healing after intragastric administration of 10 mg·kg-1 ·day-1 in vivo. Overall, PF performed the pro-angiogenetic effect in vitro and accelerating wound healing in vivo. In summary, the capacity for angiogenesis in endothelial cells could be enhanced by PF treatment via the PI3K/AKT pathway in vitro and could accelerate the wound healing process in vivo through collagen deposition and angiogenesis in regenerated tissue. This study provides evidence that application of PF represents a novel therapeutic approach for the treatment of cutaneous wounds.

Honey loaded silk fibroin 3D porous scaffold facilitates homeostatic full-thickness wound healing

Dermal reconstruction in acute and chronic wounds needs highly vascularized dermal tissue engineered skin substitutes which has the potentiality to provide physical cues as well as biological cues for scarless regenerative wound healing. Herein, we have investigated blends of silk fibroin and honey as a wound healing substrate that able to facilitate keratinocyte and fibroblast adhesion, migration and proliferation. Honey-silk fibroin (HSF) three dimensional (3D) scaffolds were fabricated by freeze drying and characterized in detailed for their physico-chemical, mechanical, swelling and degradable properties. Interestingly, in vitro studies showed better adhesion, proliferation and homogenous distribution of fibroblasts within blended scaffolds especially with 4% honey concentration (HSF4). Also, its structural composition with pores size ~ 139 µm and porosity 87% further confirms the superiority over the counterparts and other blended scaffolds. The in vitro cytotoxic studies illustrated the biocompatibility, proliferation and proper infiltration of primary fibroblasts within HSF4 scaffolds, validated by in vivo studies. Fascinatingly, in vivo cutaneous wound healing studies demonstrated the attainment of normal homeostasis with proper re-epithelialization, collagen matrix remodeling having high collagen I expression in respect to collagen III with minimal scar under HSF4 scaffold implantation. Taken together, this study suggests the potentiality of incorporation of honey component as a payload which not only augmented the scarless healing also modified the physical properties of scaffold in order to provide the suitable micro-ambience for healing and these material scaffold proved to be a potential dermal substitute for acute as well as chronic wounds. Statement of SignificanceThe 3D honey based porous scaffolds are increasingly getting attention in the field of biomedicine and wound healing due to their ability to mimic the architecture of native microenvironment and could provide the controlled release of honey at the affected area for fast regeneration. In this work we demonstrated that the addition of honey in SF scaffold not only enhanced the biological activity of scaffold also modulated the physico-chemical properties which ultimately helps in attaining fast homeostatic wound healing. The synergy of pore size, porosity and mechanical strength of scaffold having 4% honey concentration showed its potentiality in augmenting proper re-epithelialization, collagen matrix deposition and skin appendages formation which presents this scaffold as potential candidate in skin tissue engineering applications.

Osteopontin regulates type I collagen fibril formation in bone tissue

Osteopontin (OPN) is a non-collagenous protein involved in biomineralization of bone tissue. Beyond its role in biomineralization, we show that osteopontin is essential to the quality of collagen fibrils in bone. Transmission electron microscopy revealed that, in Opn−/− tissue, the organization of the collagen fibrils was highly heterogeneous, more disorganized than WT bone and comprised of regions of both organized and disorganized matrix with a reduced density. The Opn−/− bone tissue also exhibited regions in which the collagen had lost its characteristic fibrillar structure, and the crystals were disorganized. Using nanobeam electron diffraction, we show that damage to structural integrity of collagen fibrils in Opn−/- bone tissue and their organization causes mineral disorganization, which could ultimately affect its mechanical integrity. Statement of SignificanceThis study presents new evidence about the role of osteopontin (OPN) – a non-collagenous protein – on the structure and organization of the organic and mineral matrix in bone. In previous work, osteopontin has been suggested to regulate the nucleation and growth of bone mineral crystals and to form sacrificial bonds between mineralized collagen fibrils to enhance bone's toughness. Our findings show that OPN plays a crucial role before mineralization, during the formation of the collagen fibrils. OPN-deficient bones present a lower collagen content compared to wild type bone and, at the tissue level, collagen fibrils organization can be significantly altered in the absence of OPN. Our results suggest that OPN is critical for the formation and/or remodeling of bone collagen matrix. Our findings could lead to the development of new therapeutic strategies of bone diseases affecting collagen formation and remodeling.

Honey Loaded Silk Fibroin 3D Porous Scaffold Facilitates Homeostatic Full-Thickness Wound Healing

Dermal reconstruction in acute and chronic wounds needs highly vascularized dermal tissue engineered skin substitutes which has the potentiality to provide physical cues as well as biological cues for scarless regenerative wound healing. Herein, we have investigated blends of silk fibroin and honey as a wound healing substrate that able to facilitate keratinocyte and fibroblast adhesion, migration and proliferation. Honey-silk fibroin (HSF) three dimensional (3D) scaffolds were fabricated by freeze drying and characterized in detail for their physico-chemical, mechanical, swelling and degradable properties. Interestingly, in vitro studies showed better adhesion, proliferation and homogenous distribution of fibroblasts within blended scaffolds especially with 4% honey concentration (HSF4). Also, its structural composition with interconnected pores in the range of 108-152µm and porosity 82-92% further confirms the superiority over the counterparts and other blended scaffolds. The in vivo cytotoxic studies validated the biocompatibility of HSF4 scaffolds and the infiltration of both types of cells from the neighboring tissue. Fascinatingly, in vivo cutaneous wound healing studies demonstrated the attainment of normal homeostasis with proper re-epithelialization, collagen matrix remodeling having high collagen I expression with minimal scar under HSF4 scaffolds implantation. Taken together, this study suggests the potentiality of incorporation of honey component as a payload which not only augmented the scarless healing also modified the physical properties of scaffold in order to provide the suitable micro-ambience for healing and these material scaffold proved to be a potential dermal substitute for acute as well as chronic wounds.

Stress Distribution and Collagen Remodeling of Periodontal Ligament During Orthodontic Tooth Movement.

Periodontal ligament (PDL), as a mechanical connection between the alveolar bone and tooth, plays a pivotal role in force-induced orthodontic tooth movement (OTM). However, how mechanical force controls remodeling of PDL collagenous extracellular matrix (ECM) is largely unknown. Here, we aimed to evaluate the stress distribution and ECM fiber remodeling of PDL during the process of OTM. An experimental tooth movement model was built by ligating a coil spring between the left maxillary first molar and the central incisors. After activating the coil spring for 7 days, the distance of tooth movement was 0.324 ± 0.021 mm. The 3D finite element modeling showed that the PDL stress obviously concentrated at cervical margin of five roots and apical area of the mesial root, and the compression region was distributed at whole apical root and cervical margin of the medial side (normal stress < −0.05 MPa). After force induction, the ECM fibers were disordered and immature collagen III fibers significantly increased, especially in the apical region, which corresponds to the stress concentration and compression area. Furthermore, the osteoclasts and interleukin-1β expression were dramatically increased in the apical region of the force group. Taken together, orthodontic loading could change the stress distribution of PDL and induce a disordered arrangement and remodeling of ECM fibers. These findings provide orthodontists both mechanical and biological evidences that root resorption is prone to occur in the apical area during the process of OTM.

Biomolecular Analysis of Beta Dose-Dependent Cutaneous Radiation Injury in a Porcine Model.

While cutaneous radiation injury (CRI) is generally referenced as a consequence of a nuclear attack, it can also be caused by less dangerous events such as the use of dirty bombs, industrial radiological accidents, or accidental overexposure of beta (β) particle or gamma (γ) radiation sources in medical procedures. Although the gross clinical consequences of these injuries have been well documented, relatively little is known about the molecular changes underlying the progression of pathology. Here we describe a porcine model of cutaneous radiation injury after skin was exposed to strontium-90 b particle at doses of 16-42 Gy and characterize the anatomical and molecular changes over 70 days. The results show that irradiated sites displayed dosedependent increases in erythema and moist desquamation that peaked between days 35 and 42. Dose-dependent histopathological changes were observed, with higher doses exhibiting increased inflammation and epidermal hyperplasia beyond day 35. Furthermore, immunohistochemistry showed that exposure to 37 Gy β-particle radiation decreased epidermal cell proliferation and desmosomal junction proteins at day 70, suggesting compromised epidermal integrity. Metabolomic analysis of biopsies revealed dose- and time-dependent changes as high as 252-fold in several metabolites not previously linked to CRI. These alterations were seen in pathways reflecting protein degradation, oxidative stress, eicosanoid production, collagen matrix remodeling, mitochondrial stress, cell membrane composition and vascular disruption. Taken together, these data show that exposure to high doses of β particle damaged the molecular processes underlying skin integrity to a greater extent and for a longer period of time than has been shown previously. These findings further understanding of radiation-induced skin injury and serve as a foundation for the development and testing of potential therapeutics to treat CRI.