Resident Progenitor Cells Research Articles

Lung Immune Cell Niches and the Discovery of New Cell Subtypes.

Immune cells in the lungs are important for maintaining lung function. The importance of immune cells in defending against lung diseases and infections is increasingly recognized. However, a primary knowledge gaps in current studies of lung immune cells is the understanding of their subtypes and functional heterogeneity. Increasing evidence supports the existence of novel immune cell subtypes that engage in the complex crosstalk between lung-resident immune cells, recruited immune cells, and epithelial cells. Therefore, further studies on how immune cells respond to perturbations in the pulmonary microenvironment are warranted. This review explores the processes behind the formation of the immune cell niche during lung development, and the characteristics and cell interaction modes of several major lung-resident immune cells. It indicates that distinct lung microenvironments or inflammatory niches can mediate the formation of different cell subtypes. These findings summarize and clarify paths to identify new cell subtypes that originate from resident progenitor cells and recruited peripheral cells, which are remodeled by the pulmonary microenvironment. The development of new techniques combining transcriptome analysis and location information is essential for identifying new immune cell subtypes and their relative immune niches, as well as for uncovering the molecular mechanisms of immune cell-mediated lung homeostasis.

Epigenetic Cross-Talk Between Sirt1 and Dnmt1 Promotes Axonal Regeneration After Spinal Cord Injury in Zebrafish.

Though spinal cord injury (SCI) causes irreversible sensory and motor impairments in human, adult zebrafish retain the potent regenerative capacity by injury-induced proliferation of central nervous system (CNS)-resident progenitor cells to develop new functional neurons at the lesion site. The hallmark of SCI in zebrafish lies in a series of changes in the epigenetic landscape, specifically DNA methylation and histone modifications. Decoding the post-SCI epigenetic modifications is therefore critical for the development of therapeutic remedies that boost SCI recovery process. Here, we have studied on Sirtuin1 (Sirt1), a non-classical histone deacetylase that potentially plays a critical role in neural progenitor cells (NPC) proliferation and axonal regrowth following SCI in zebrafish. We investigated the role of Sirt1 in NPC proliferation and axonal regrowth in response to injury in the regenerating spinal cord and found that Sirt1 is involved in the induction of NPC proliferation along with glial bridging during spinal cord regeneration. We also demonstrate that Sirt1 plays a pivotal role in regulating the HIPPO pathway through deacetylation-mediated inactivation of Dnmt1 and subsequent hypomethylation of yap1 promoter, leading to the induction of ctgfa expression, which drives the NPC proliferation and axonal regrowth to complete the regenerative process. In conclusion, our study reveals a novel cross-talk between two important epigenetic effectors, Sirt1 and Dnmt1, in the context of spinal cord regeneration, establishing a previously undisclosed relation between Sirt1 and Yap1 which provides a deeper understanding of the underlying mechanisms governing injury-induced NPC proliferation and axonal regrowth. Therefore, we have identified Sirt1 as a novel, major epigenetic regulator of spinal cord regeneration by modulating the HIPPO pathway in zebrafish.

MTORC1 Signaling in Brain Endothelial Progenitors Contributes to CCM Pathogenesis.

Cerebral vascular malformations (CCMs) are primarily found within the brain, where they result in increased risk for stroke, seizures, and focal neurological deficits. The unique feature of the brain vasculature is the blood-brain barrier formed by the brain neurovascular unit. Recent studies suggest that loss of CCM genes causes disruptions of blood-brain barrier integrity as the inciting events for CCM development. CCM lesions are proposed to be initially derived from a single clonal expansion of a subset of angiogenic venous capillary endothelial cells (ECs) and respective resident endothelial progenitor cells (EPCs). However, the critical signaling events in the subclass of brain ECs/EPCs for CCM lesion initiation and progression are unclear. Brain EC-specific CCM3-deficient (Pdcd10BECKO) mice were generated by crossing Pdcd10fl/fl mice with Mfsd2a-CreERT2 mice. Single-cell RNA-sequencing analyses were performed by the chromium single-cell platform (10× genomics). Cell clusters were annotated into EC subtypes based on visual inspection and GO analyses. Cerebral vessels were visualized by 2-photon in vivo imaging and tissue immunofluorescence analyses. Regulation of mTOR (mechanistic target of rapamycin) signaling by CCM3 and Cav1 (caveolin-1) was performed by cell biology and biochemical approaches. Single-cell RNA-sequencing analyses from P10 Pdcd10BECKO mice harboring visible CCM lesions identified upregulated CCM lesion signature and mitotic EC clusters but decreased blood-brain barrier-associated EC clusters. However, a unique EPC cluster with high expression levels of stem cell markers enriched with mTOR signaling was identified from early stages of the P6 Pdcd10BECKO brain. Indeed, mTOR signaling was upregulated in both mouse and human CCM lesions. Genetic deficiency of Raptor (regulatory-associated protein of mTOR), but not of Rictor (rapamycin-insensitive companion of mTOR), prevented CCM lesion formation in the Pdcd10BECKO model. Importantly, the mTORC1 (mTOR complex 1) pharmacological inhibitor rapamycin suppressed EPC proliferation and ameliorated CCM pathogenesis in Pdcd10BECKO mice. Mechanistic studies suggested that Cav1/caveolae increased in CCM3-depleted EPC-mediated intracellular trafficking and complex formation of the mTORC1 signaling proteins. CCM3 is critical for maintaining blood-brain barrier integrity and CCM3 loss-induced mTORC1 signaling in brain EPCs initiates and facilitates CCM pathogenesis.

Neuronally differentiated macula densa cells regulate tissue remodeling and regeneration in the kidney.

Tissue regeneration is limited in several organs, including the kidney, contributing to the high prevalence of kidney disease globally. However, evolutionary and physiological adaptive responses and the presence of renal progenitor cells suggest an existing remodeling capacity. This study uncovered endogenous tissue remodeling mechanisms in the kidney that were activated by the loss of body fluid and salt and regulated by a unique niche of a minority renal cell type called the macula densa (MD). Here, we identified neuronal differentiation features of MD cells that sense the local and systemic environment and secrete angiogenic, growth, and extracellular matrix remodeling factors, cytokines and chemokines, and control resident progenitor cells. Serial intravital imaging, MD nerve growth factor receptor and Wnt mouse models, and transcriptome analysis revealed cellular and molecular mechanisms of these MD functions. Human and therapeutic translation studies illustrated the clinical potential of MD factors, including CCN1, as a urinary biomarker and therapeutic target in chronic kidney disease. The concept that a neuronally differentiated key sensory and regulatory cell type responding to organ-specific physiological inputs controls local progenitors to remodel or repair tissues may be applicable to other organs and diverse tissue-regenerative therapeutic strategies.

Age-Related Changes in Kidney and Loss of Resistance to Damage: The Role of the Decrease in the Number of Kidney Progenitor Cells during Aging

Many organs undergo negative changes during aging that affect their functions and ability to regenerate. In particular, the kidneys become more susceptible to acute injury and are more likely to develop chronic kidney disease with age. One of the reasons for this may be a decrease in the number of kidney resident progenitor cells. This review addresses age-related changes that occur in the kidneys at the histological and molecular levels, including those related to the cell cycle, mitochondrial function, oxidative stress, and chronic inflammation. This review describes the available studies on resident kidney stem cells, their niches, morphology, possible markers, and the dynamics of their numbers during the aging process. The reasons for the age-related decline in renal regenerative potential are considered based on molecular and cellular mechanisms.

CD8 T cell response and its released cytokine IFN-γ are necessary for lung alveolar epithelial repair during bacterial pneumonia.

Alveolar epithelial regeneration depends on the activity of resident quiescent progenitor cells. Alveolar epithelial type II (AT2) cells are known as the alveolar epithelial progenitor cells. They exit quiescent state, proliferate rapidly in response to injury and differentiate into alveolar epithelial type I (AT1) cells to regenerate the damaged alveolar epithelium. Although AT2 cell plasticity has been a very intense field of research, the role of CD8 T cell response and their released cytokine IFN-γ, in regulating AT2 cell plasticity and alveolar epithelial repair and regeneration after injury remains largely unknown. We used flow cytometry to quantify the amount of CD8 T cells in mouse lungs after bacterial pneumonia caused by Streptococcus pneumoniae. To determine whether CD8 T cells and their released cytokine IFN-γ are necessary for AT2 cell activity during alveolar epithelial regeneration, we performed loss of function studies using anti-CD8 or anti-IFN-γ monoclonal antibody (mAb) treatment in vivo. We assessed the effects of CD8 T cells and cytokine IFN-γ on AT2 cell differentiation capacity using the AT2- CD8 T cell co-culture system in vitro. We detected a transient wave of accumulation of CD8 T cells in mouse lungs, which coincided with the burst of AT2 cell proliferation during alveolar epithelial repair and regeneration in mice following bacterial pneumonia caused by Streptococcus pneumoniae. Depletion of CD8 T cells or neutralization of cytokine IFN-γ using anti-CD8 or anti-IFN-γ monoclonal antibody significantly reduced AT2 cell proliferation and differentiation into AT1 cells in mice after bacterial pneumonia. Furthermore, co-culture of CD8 T cells or cytokine IFN-γ with AT2 cells promoted AT2-to-AT1 cell differentiation in both murine and human systems. Conversely, blockade of IFN-γ signaling abrogated the increase in AT2-to-AT1 cell differentiation in the AT2- CD8 T cell co-culture system. Our data demonstrate that CD8 T-cell response and cytokine IFN-γ are necessary for promoting AT2 cell activity during alveolar epithelial repair and regeneration after acute lung injury caused by bacterial pneumonia.

Age-Related Changes and Loss of Damage Resistance of Kidney Tissue: The Role of a Decrease in the Number of Kidney Resident Progenitor Cells

Age-Related Changes and Loss of Damage Resistance of Kidney Tissue: The Role of a Decrease in the Number of Kidney Resident Progenitor Cells

Oligodendrocyte progenitor cells differentiation induction with MAPK/ERK inhibitor fails to support repair processes in the chronically demyelinated CNS.

Remyelination failure is considered a major obstacle in treating chronic-progressive multiple sclerosis (MS). Studies have shown blockage in the differentiation of resident oligodendrocyte progenitor cells (OPC) into myelin-forming cells, suggesting that pushing OPC into a differentiation program might be sufficient to overcome remyelination failure. Others stressed the need for a permissive environment to allow proper activation, migration, and differentiation of OPC. PD0325901, a MAPK/ERK inhibitor, was previously shown to induce OPC differentiation, non-specific immunosuppression, and a significant therapeutic effect in acute demyelinating MS models. We examined PD0325901 effects in the chronically inflamed central nervous system. Treatment with PD0325901 induced OPC differentiation into mature oligodendrocytes with high morphological complexity. However, treatment of Biozzi mice with chronic-progressive experimental autoimmune encephalomyelitis with PD0325901 showed no clinical improvement in comparison to the control group, no reduction in demyelination, nor induction of OPC migration into foci of demyelination. PD0325901 induced a direct general immunosuppressive effect on various cell populations, leading to a diminished phagocytic capability of microglia and less activation of lymph-node cells. It also significantly impaired the immune-modulatory functions of OPC. Our findings suggest OPC regenerative function depends on a permissive environment, which may include pro-regenerative inflammatory elements. Furthermore, they indicate that maintaining a delicate balance between the pro-myelinating and immune functions of OPC is of importance. Thus, the highly complex mission of creating a pro-regenerative environment depends upon an appropriate immune response controlled in time, place, and intensity. We suggest the need to employ a multi-systematic therapeutic approach, which cannot be achieved through a single molecule-based therapy.

Engineered neurogenesis in naïve adult rat cortex by Ngn2-mediated neuronal reprogramming of resident oligodendrocyte progenitor cells.

Adult tissue stem cells contribute to tissue homeostasis and repair but the long-lived neurons in the human adult cerebral cortex are not replaced, despite evidence for a limited regenerative response. However, the adult cortex contains a population of proliferating oligodendrocyte progenitor cells (OPCs). We examined the capacity of rat cortical OPCs to be re-specified to a neuronal lineage both in vitro and in vivo. Expressing the developmental transcription factor Neurogenin2 (Ngn2) in OPCs isolated from adult rat cortex resulted in their expression of early neuronal lineage markers and genes while downregulating expression of OPC markers and genes. Ngn2 induced progression through a neuronal lineage to express mature neuronal markers and functional activity as glutamatergic neurons. In vivo retroviral gene delivery of Ngn2 to naive adult rat cortex ensured restricted targeting to proliferating OPCs. Ngn2 expression in OPCs resulted in their lineage re-specification and transition through an immature neuronal morphology into mature pyramidal cortical neurons with spiny dendrites, axons, synaptic contacts, and subtype specification matching local cytoarchitecture. Lineage re-specification of rat cortical OPCs occurred without prior injury, demonstrating these glial progenitor cells need not be put into a reactive state to achieve lineage reprogramming. These results show it may be feasible to precisely engineer additional neurons directly in adult cerebral cortex for experimental study or potentially for therapeutic use to modify dysfunctional or damaged circuitry.

"Slow walk" mimetic tensile loading maintains human meniscus tissue resident progenitor cells homeostasis in photocrosslinked gelatin hydrogel.

Meniscus, the cushion in knee joint, is a load-bearing tissue that transfers mechanical forces to extracellular matrix (ECM) and tissue resident cells. The mechanoresponse of human tissue resident stem/progenitor cells in meniscus (hMeSPCs) is significant to tissue homeostasis and regeneration but is not well understood. This study reports that a mild cyclic tensile loading regimen of ∼1800 loads/day on hMeSPCs seeded in 3-dimensional (3D) photocrosslinked gelatin methacryloyl (GelMA) hydrogel is critical in maintaining cellular homeostasis. Experimentally, a "slow walk" biomimetic cyclic loading regimen (10% tensile strain, 0.5Hz, 1h/day, up to 15 days) is applied to hMeSPCs encapsulated in GelMA hydrogel with a magnetic force-controlled loading actuator. The loading significantly increases cell differentiation and fibrocartilage-like ECM deposition without affecting cell viability. Transcriptomic analysis reveals 332 mechanoresponsive genes, clustered into cell senescence, mechanical sensitivity, and ECM dynamics, associated with interleukins, integrins, and collagens/matrix metalloproteinase pathways. The cell-GelMA constructs show active ECM remodeling, traced using a green fluorescence tagged (GFT)-GelMA hydrogel. Loading enhances nascent pericellular matrix production by the encapsulated hMeSPCs, which gradually compensates for the hydrogel loss in the cultures. These findings demonstrate the strong tissue-forming ability of hMeSPCs, and the importance of mechanical factors in maintaining meniscus homeostasis.

How can early life adversity still exert an effect decades later? A question of timing, tissues and mechanisms.

Exposure to any number of stressors during the first 1000 days from conception to age 2 years is important in shaping an individual's life trajectory of health and disease. Despite the expanding range of stressors as well as later-life phenotypes and outcomes, the underlying molecular mechanisms remain unclear. Our previous data strongly suggests that early-life exposure to a stressor reduces the capacity of the immune system to generate subsequent generations of naïve cells, while others have shown that, early life stress impairs the capacity of neuronal stem cells to proliferate as they age. This leads us to the "stem cell hypothesis" whereby exposure to adversity during a sensitive period acts through a common mechanism in all the cell types by programming the tissue resident progenitor cells. Furthermore, we review the mechanistic differences observed in fully differentiated cells and suggest that early life adversity (ELA) may alter mitochondria in stem cells. This may consequently alter the destiny of these cells, producing the lifelong "supply" of functionally altered fully differentiated cells.

Mesenchymal progenitor cells from non-inflamed versus inflamed synovium post-ACL injury present with distinct phenotypes and cartilage regeneration capacity

BackgroundOsteoarthritis (OA) is a chronic debilitating disease impacting a significant percentage of the global population. While there are numerous surgical and non-invasive interventions that can postpone joint replacement, there are no current treatments which can reverse the joint damage occurring during the pathogenesis of the disease. While many groups are investigating the use of stem cell therapies in the treatment of OA, we still don’t have a clear understanding of the role of these cells in the body, including heterogeneity of tissue resident adult mesenchymal progenitor cells (MPCs).MethodsIn the current study, we examined MPCs from the synovium and individuals with or without a traumatic knee joint injury and explored the chondrogenic differentiation capacity of these MPCs in vitro and in vivo.ResultsWe found that there is heterogeneity of MPCs with the adult synovium and distinct sub-populations of MPCs and the abundancy of these sub-populations change with joint injury. Furthermore, only some of these sub-populations have the ability to effect cartilage repair in vivo. Using an unbiased proteomics approach, we were able to identify cell surface markers that identify this pro-chondrogenic MPC population in normal and injured joints, specifically CD82LowCD59+ synovial MPCs have robust cartilage regenerative properties in vivo.ConclusionsThe results of this study clearly show that cells within the adult human joint can impact cartilage repair and that these sub-populations exist within joints that have undergone a traumatic joint injury. Therefore, these populations can be exploited for the treatment of cartilage injuries and OA in future clinical trials.

Redistribution of the chromatin remodeler Brg1 directs smooth muscle-derived adventitial progenitor-to-myofibroblast differentiation and vascular fibrosis.

Vascular smooth muscle-derived Sca1+ adventitial progenitor (AdvSca1-SM) cells are tissue-resident, multipotent stem cells that contribute to progression of vascular remodeling and fibrosis. Upon acute vascular injury, AdvSca1-SM cells differentiate into myofibroblasts and are embedded in perivascular collagen and the extracellular matrix. While the phenotypic properties of AdvSca1-SM-derived myofibroblasts have been defined, the underlying epigenetic regulators driving the AdvSca1-SM-to-myofibroblast transition are unclear. We show that the chromatin remodeler Smarca4/Brg1 facilitates AdvSca1-SM myofibroblast differentiation. Brg1 mRNA and protein were upregulated in AdvSca1-SM cells after acute vascular injury, and pharmacological inhibition of Brg1 by the small molecule PFI-3 attenuated perivascular fibrosis and adventitial expansion. TGF-β1 stimulation of AdvSca1-SM cells in vitro reduced expression of stemness genes while inducing expression of myofibroblast genes that was associated with enhanced contractility; PFI blocked TGF-β1-induced phenotypic transition. Similarly, genetic knockdown of Brg1 in vivo reduced adventitial remodeling and fibrosis and reversed AdvSca1-SM-to-myofibroblast transition in vitro. Mechanistically, TGF-β1 promoted redistribution of Brg1 from distal intergenic sites of stemness genes and recruitment to promoter regions of myofibroblast-related genes, which was blocked by PFI-3. These data provide insight into epigenetic regulation of resident vascular progenitor cell differentiation and support that manipulating the AdvSca1-SM phenotype will provide antifibrotic clinical benefits.

Abstract 363: Resident Vascular Adventitial Progenitor Cells Of Smooth Muscle Cell-lineage Adopt Profibrotic Phenotype And Contribute To Cardiac Fibrosis.

Cardiac myofibroblasts are the major contributors to ECM deposition in pathological cardiovascular fibrosis, which is the characteristic feature of cardiovascular diseases. However, due to potential heterogeneity of myofibroblasts, the origin of these cells remains controversial. Using highly specific smooth muscle cell lineage-tracing mouse models, we discovered the smooth muscle cell origin of a subpopulation of resident vascular adventitial progenitor cells, defined by the expression of the stem cell marker Sca1 (AdvSca1-SM cells), which rapidly proliferate and adopt a myofibroblast phenotype in response to acute vascular injury. Further, we identified a specific gene signature of active hedgehog/Wnt/β-catenin/Klf4 signaling in AdvSca1-SM cells and validated a Gli1-CreERT2-ROSA26-YFP (Gli1) reporter mouse model to be a faithful lineage tracing system for AdvSca1-SM cells. However, the function of AdvSca1-SM cells in cardiac fibrosis is unknown. Using immunofluorescent staining and label-free second harmonic generation (SHG) imaging, we observed the expansion and migration of AdvSca1-SM cells in close association with perivascular and interstitial cardiac fibrosis in pressure overload-induced cardiac fibrosis in Gli1 reporter mice. By integrating single cell RNA sequencing (scRNA-seq) with spatial transcriptomics, we identified a AngII-driven spatiotemporal profibrotic differentiation trajectory of AdvSca1-SM cells in mouse cardiac tissue. The trajectory, characterized by loss of expression of stemness genes, such as Klf4 , the lncRNA, Meg3 , and up-regulation of myofibroblast genes, was recapitulated in human RNA-seq data and of translational significance. Connectivity map analysis of the scRNA-seq data identified statins as potential candidates for inhibition of the profibrotic transition of AdvSca1-SM cells. In agreement, simvastatin induced the expression of stemness genes and inhibited TGFβ-induced up-regulation of αSMA and down-regulation of KLF4 in cultured AdvSca1-SM cells. Lentiviral-mediated up-regulation of Meg3 also rescued TGFβ-induced suppression of stemness genes. Our findings support the further development of anti-fibrotic therapeutics targeting AdcSca1-SM cells.

Elevated Serum Alpha-fetoprotein Levels in Non-alcoholic Steatohepatitis: Possible Molecular Mechanisms and Potential Clinical Significance

With the improvement of living standards in recent years, up to 90% of obese patients have nonalcoholic fatty liver disease (NAFLD). The number of nonalcoholic steatohepatitis (NASH)-related deaths will gradually increase, and NASH is expected to be the most common cause of liver-related deaths in the future. Therefore, there is an urgent need to find effective and reliable serum biomarkers to distinguish simple hepatic steatosis (SS) from NASH. Liver cell regeneration, oxidative stress-induced DNA methylation, and biliary epithelial cell proliferation were reported to increase serum alpha-fetoprotein (AFP) levels. AFP has long been used as a tool to monitor liver cancer. However, the function of AFP in NAFLD, especially NASH, has not been clarified. Moreover, whether an elevated AFP level indicates the occurrence of NASH or serves as a serum biomarker remains to be elucidated. The miRNA-122 pathway, DNA methylation and DNA damage, and activation of resident stem cells and/or progenitor cells in the liver, as well as necrosis, regeneration, and repair of liver cells, may contribute to slight increases in AFP levels in the development of NASH in patients with NAFLD. Furthermore, mildly elevated AFP levels may indicate the development of NASH. This review explores the role of elevated AFP levels in the development of NASH, with a specific focus on the underlying molecular mechanisms and the clinical significance.

Abstract 1129: Targeting tissue-resident macrophage progenitors restores anti-tumor immunity and suppresses tumor growth

Abstract Macrophages are innate immune cells that accumulate rapidly in tumors, where they promote immune suppression, tumor growth and resistance to checkpoint inhibitor therapy. As these cells play critical roles in tumor progression, they are the focus of efforts to develop novel cancer therapeutics. Strategies to inhibit macrophage accumulation to suppress tumor growth by blocking their recruitment from circulation have been only partially effective. In this project, we examined the origins of tumor associated macrophages using lineage tracing, flow cytometry, and single cell sequencing. We found that large proportions of macrophages in subcutaneous and genetically engineered mouse tumors do not derive from Ly6C+ or Ly6C- or CCR2+ monocytes. Instead, a large population of CCR2-Ly6C-F4/80hi macrophages that are CD206+MerTK+ are profoundly immune suppressive resident macrophages that arise from a transcriptionally related proliferative progenitor subpopulation rather than by trafficking from the circulation. By comparing gene expression profiles of resident and recruited macrophages in subcutaneous, alveolar, central nervous and renal normal and tumor tissues, we identified generic tissue resident macrophage and recruited signatures that reveal that resident macrophages are more immune suppressive than recruited macrophages and are associated with worse outcomes in cancer patients. Tissue resident macrophages express signatures of Myc-driven proliferation, cholesterol metabolism and profound immune suppression while bone marrow derived macrophages express mixed signatures of inflammation and immune suppression. Genetic and pharmacological inhibition of c-Kit/mCsf1R, cMyc and cyclin-dependent kinases suppressed the expansion of these macrophages, thereby limiting their accumulation in tumors, promoting anti-tumor adaptive immunity and inhibiting tumor progression in mouse models of cancer. We identified a novel cKit/Csf1r/Cdk19 inhibitor that suppressed tissue resident macrophage accumulation and potently inhibited tumor growth. These results identify tissue resident macrophage progenitor cells as key targets for the development of therapeutic strategies to stimulate anti-cancer immunity. Citation Format: Hui Chen, Marc Paradise, Ryan Shepard, Guangfang Wang, Mark Onaitis, Judith Varner. Targeting tissue-resident macrophage progenitors restores anti-tumor immunity and suppresses tumor growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1129.

Oligodendrocyte death initiates synchronous remyelination to restore cortical myelin patterns in mice.

Myelin degeneration occurs in neurodegenerative diseases and aging. In these conditions, resident oligodendrocyte progenitor cells (OPCs) differentiate into oligodendrocytes that carry out myelin repair. To investigate the cellular dynamics underlying these events, we developed a noninflammatory demyelination model that combines intravital two-photon imaging with a single-cell ablation technique called two-photon apoptotic targeted ablation (2Phatal). Oligodendrocyte 2Phatal in both sexes results in a myelin degeneration cascade that triggers rapid forms of synchronous remyelination on defined axons. This remyelination is driven by oligodendrocytes differentiated from a subset of morphologically distinct, highly branched OPCs. Moreover, remyelination efficiency depends on the initial myelin patterns, as well as the age of the organism. In summary, using 2Phatal, we show a form of rapid synchronous remyelination, mediated by a distinct subset of OPCs, capable of restoring the original myelin patterning in adulthood but not aging.

A single-cell transcriptional atlas reveals resident progenitor cell niche functions in TMJ disc development and injury

The biological characteristics of the temporomandibular joint disc involve complex cellular network in cell identity and extracellular matrix composition to modulate jaw function. The lack of a detailed characterization of the network severely limits the development of targeted therapies for temporomandibular joint-related diseases. Here we profiled single-cell transcriptomes of disc cells from mice at different postnatal stages, finding that the fibroblast population could be divided into chondrogenic and non-chondrogenic clusters. We also find that the resident mural cell population is the source of disc progenitors, characterized by ubiquitously active expression of the NOTCH3 and THY1 pathways. Lineage tracing reveals that Myh11+ mural cells coordinate angiogenesis during disc injury but lost their progenitor characteristics and ultimately become Sfrp2+ non-chondrogenic fibroblasts instead of Chad+ chondrogenic fibroblasts. Overall, we reveal multiple insights into the coordinated development of disc cells and are the first to describe the resident mural cell progenitor during disc injury.

Distinctive role of inflammation in tissue repair and regeneration.

Inflammation is an essential host defense mechanism in response to microbial infection and tissue injury. In addition to its well-established role in infection, inflammation is actively involved in the repair of damaged tissues and restoration of homeostatic conditions after tissue injury. The intensity of the inflammatory response and types of cells involved in inflammation have a significant impact on the quality of tissue repair. Numerous immune cell subtypes participate in tissue repair and regeneration. In particular, immune cell-derived secretants, including cytokines and growth factors, can actively modulate the proliferation of resident stem cells or progenitor cells to facilitate tissue regeneration. These findings highlight the importance of inflammation during tissue repair and regeneration; however, the precise role of immune cells in tissue regeneration remains unclear. In this review, we summarize the current knowledge on the contribution of specific immune cell types to tissue repair and regeneration. We also discuss how inflammation affects the final outcome of tissue regeneration.

Single-cell RNA sequencing reveals resident progenitor and vascularization-associated cell subpopulations in rat annulus fibrosus.

One of the main causes of low back pain is intervertebral disc degeneration (IDD). Annulus fibrosus (AF) is important for the integrity and functions of the intervertebral disc (IVD). However, the resident functional cell components such as progenitors and vascularization-associated cells in AF are yet to be fully identified. Identification of functional AF cell subpopulations including resident progenitors and vascularization-associated cells. In this study, the single-cell RNA sequencing data of rat IVDs from a public database were analyzed using Seurat for cell clustering, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) for functional analysis, StemID for stem cell identification, Monocle and RNA velocity for pseudotime differentiation trajectory validation, single-cell regulatory network inference and clustering (SCENIC) for gene regulatory network (GRN) analysis, and CellChat for cell-cell interaction analysis. Immunostaining on normal and degenerated rat IVDs, as well as human AF, was used for validations. From the data analysis, seven AF cell clusters were identified, including two newly discovered functional clusters, the Grem1 + subpopulation and the Lum +​subpopulation. The Grem1 + subpopulation had progenitor characteristics, while the Lum +​subpopulation was associated with vascularization during IDD. The GRN analysis showed that Sox9 and Id1 were among the key regulators in the Grem1 + subpopulation, and Nr2f2 and Creb5 could be responsible for the vascularization function in the Lum +​subpopulation. Cell-cell interaction analysis revealed highly regulated cellular communications between these cells, and multiple signaling networks including PDGF and MIF signaling pathways were involved in the interactions. Our results revealed two new functional AF cell subpopulations, with stemness and vascularization induction potential, respectively. These findings complement our knowledge about IVDs, especially the AF, and in return provide potential cell source and regulation targets for IDD treatment and tissue repair. The existence of the cell subpopulations was also validated in human AF, which strengthen the clinical relevance of the findings.