Activity Of Progenitor Cells Research Articles

Toll-like receptor bioactivity in endothelial progenitor cells

Cardiovascular disease is the main cause of death globally that can be mitigated by the modulation of angiogenesis. To achieve this goal, the application of endothelial progenitor cells and other stem cell types is useful. Following the onset of cardiovascular disease and pro-inflammatory conditions as seen during bacterial sepsis, endothelial progenitor cells enter systemic circulation in response to multiple cytokines and activation of various intracellular mechanisms. The critical role of Toll-like receptors has been previously identified in the dynamics of various cell types, in particular, immune cells. To our knowledge, there are a few experiments related to the role of Toll-like receptors in endothelial progenitor cell activity. Emerging data point of endothelial progenitor cells and other stem cells having the potential to express Toll-like receptors to control different activities such as multipotentiality and dynamics of growth. In this review article, we aim to collect data related to the role of Toll-like receptors in endothelial progenitor cells bioactivity and angiogenic potential.

The Role of Interferon, Inflammation and Infection in Aplastic Anemia

Bone marrow failure (BMF) syndromes are a group of acquired and inherited diseases characterized by failed production of blood and immune cells, and profound bone marrow aplasia. Acquired BMF, including severe aplastic anemia (SAA), has been linked to radiation, chemical exposure, and infection, and the precise mechanisms of disease likely differ on a case-by-case basis. Inflammation and immune-mediated destruction of the marrow is a key driver of SAA, thus disease management centers on immunosuppressive therapy (IST) and, especially in young patients, bone marrow transplantation (BMT). However, not all patients are good transplant candidates and IST responsiveness varies, therefore, more specific treatments are necessary. HSC loss is a key feature of SAA, though it has been unclear if inflammation depletes HSCs directly or does so through the microenvironment. Interferons (IFNs) are proteins produced in response to microbial infections that play key roles in limiting pathogen spread and eradicating infections. While transient inflammatory responses and IFN production are often necessary for appropriate host defense, elevated levels of IFN-gamma (IFNγ) have long been associated with BMF syndromes, and type I IFNs (alpha and beta) are well documented to cause bone marrow aplasia during viral infection 1. In models of infection and inflammation IFNs can activate HSCs to proliferate and differentiate, but can also impair proliferation, and in both cases result in restricting HSC self-renewal 2-5. The precise mechanisms whereby IFNs mediate SAA and whether IFNs act directly on HSCs have remained elusive. In a mouse model of SAA driven by T cell-derived IFNγ we found that IFNγ-dependent HSC loss was associated with reduced marrow stromal cells, but a marked preservation of bone marrow-resident macrophages (MΦs) 6. Our data were consistent with findings from SAA patient marrow that also demonstrates MΦ persistence, despite significant reductions in nearly all other stromal and hematopoietic cell types 7. Moreover, we found that IFNγ was necessary for the maintained pool of MΦs. Depleting MΦs using Clodronate-loaded liposomes, or abrogating IFNγ signaling specifically in MΦs was shown to rescue HSCs and reduce SAA-associated mortality. Targeting MΦs during SAA improved thrombocytopenia, increased BM megakaryocytes, preserved platelet-primed HSCs, and increased the platelet-repopulating capacity of transplanted HSCs 6. During SAA IFNγ and MΦs were required for elevated levels of particular chemokines in the bone marrow, including CCL3, CCL4, and CCL5, which were further identified as downstream targets for mitigating SAA pathogenesis. The identification of MΦ function as a key determinant of IFNγ-dependent HSC loss in SAA furthers our understanding of disease pathogenesis and illustrates an important role for the microenvironment in SAA. These studies may reveal potential therapeutic strategies to complement current treatments for SAA that avoid generalized immunosuppression and potentially improve long-term outcomes. Smith JN, Kanwar VS, MacNamara KC. Hematopoietic Stem Cell Regulation by Type I and II Interferons in the Pathogenesis of Acquired Aplastic Anemia. Frontiers in immunology. 2016;7:330. Baldridge MT, King KY, Boles NC, Weksberg DC, Goodell MA. Quiescent haematopoietic stem cells are activated by IFN-gamma in response to chronic infection. Nature. 2010;465(7299):793-797. de Bruin AM, Demirel O, Hooibrink B, Brandts CH, Nolte MA. Interferon-gamma impairs proliferation of hematopoietic stem cells in mice. Blood. 2013;121(18):3578-3585. MacNamara KC, Jones M, Martin O, Winslow GM. Transient activation of hematopoietic stem and progenitor cells by IFNgamma during acute bacterial infection. PLoS One. 2011;6(12):e28669. Matatall KA, Jeong M, Chen S, et al. Chronic Infection Depletes Hematopoietic Stem Cells through Stress-Induced Terminal Differentiation. Cell reports. 2016;17(10):2584-2595. McCabe A, Smith JNP, Costello A, Maloney J, Katikaneni D, MacNamara KC. Hematopoietic stem cell loss and hematopoietic failure in severe aplastic anemia is driven by macrophages and aberrant podoplanin expression. Haematologica. 2018;103(9):1451-1461. Park M, Park CJ, Jang S, et al. Reduced expression of osteonectin and increased natural killer cells may contribute to the pathophysiology of aplastic anemia. Appl Immunohistochem Mol Morphol. 2015;23(2):139-145. Disclosures No relevant conflicts of interest to declare.

Fenofibrate Reverses Dysfunction of EPCs Caused by Chronic Heart Failure.

The enhanced activity of endothelial progenitor cells (EPCs) by AMP-activated protein kinase (AMPK) agonists might explain the reversal of chronic heart failure (CHF)-mediated endothelial dysfunction. We studied baseline circulating EPC numbers in patients with heart failure and clarified the effect of fenofibrate on both circulating angiogenic cell (CAC) and late EPC activity. The numbers of circulating EPCs in CHF patients were quantified by flow cytometry. Blood-derived mononuclear cells were cultured, and CAC and late EPC functions, including fibronectin adhesion, tube formation, and migration, were evaluated. We focused on the effect of fenofibrate, an AMPK agonist, on EPC function and Akt/eNOS cascade activation in vitro. The number of circulating EPCs (CD34+/KDR+) was significantly lower in CHF patients (ischemic cardiomyopathy (ICMP): 0.07%, dilated cardiomyopathy (DCMP): 0.068%; p < 0.05) than in healthy subjects (0.102% of the gating region). In CACs, fibronectin adhesion function was reversed by fenofibrate treatment (p < 0.05). Similar results were also found for tube formation and migration in late EPCs, which were significantly improved by fenofibrate in an AMPK-dependent manner (p < 0.05), suggesting that fenofibrate reversed CACs and late EPC dysfunction in CHF patients. The present findings reveal the potential application of the AMPK agonist fenofibrate to reverse endothelial dysfunction in CHF patients.

HMGB2 is a negative regulator of telomerase activity in human embryonic stem and progenitor cells.

High-mobility group box (HMGB)1 and HMGB2 proteins are the subject of intensive research because of their involvement in DNA replication, repair, transcription, differentiation, proliferation, cell signaling, inflammation, and tumor migration. Using inducible, stably transfected human embryonic stem cells (hESCs) capable of the short hairpin RNA-mediated knockdown (KD) of HMGB1 and HMGB2, we provide evidence that deregulation of HMGB1 or HMGB2 expression in hESCs and their differentiated derivatives (neuroectodermal cells) results in distinct modulation of telomere homeostasis. Whereas HMGB1 enhances telomerase activity, HMGB2 acts as a negative regulator of telomerase activity in the cell. Stimulation of telomerase activity in the HMGB2-deficient cells may be related to activation of the PI3K/protein kinase B/ glycogen synthase kinase-3β/β-catenin signaling pathways by HMGB1, augmented TERT/telomerase RNA subunit transcription, and possibly also because of changes in telomeric repeat-containing RNA (TERRA) and TERRA-polyA+ transcription. The impact of HMGB1/2 KD on telomerase transcriptional regulation observed in neuroectodermal cells is partially masked in hESCs by their pluripotent state. Our findings on differential roles of HMGB1 and HMGB2 proteins in regulation of telomerase activity may suggest another possible outcome of HMGB1 targeting in cells, which is currently a promising approach aiming at increasing the anticancer activity of cytotoxic agents.-Kučírek, M., Bagherpoor, A. J., Jaroš, J., Hampl, A., Štros, M. HMGB2 is a negative regulator of telomerase activity in human embryonic stem and progenitor cells.

P3475Dabigatran inhibits the activation of endothelial progenitor cells induced by thrombin

Abstract Introduction Thrombin is a coagulation serine protease, which also activates various cell types, including endothelial cells. Late-outgrowth endothelial cells (OECs) are a type of endothelial progenitor cells that contribute to endothelial regeneration and angiogenesis. Dabigatran is a direct oral anticoagulant that inhibits thrombin's action and is widely used in everyday clinical practice. Purpose We investigated the effect of dabigatran on thrombin-induced activation of OECs, using the membrane expression of adhesion molecule ICAM-1 as activation marker. Control experiments were conducted in mature human umbilical vein endothelial cells (HUVECs). Methods CD34+ cells were isolated from cord blood mononuclear cells, using human CD34 Microbead Kit and appropriately cultured for OEC formation. HUVECs were purchased from Lonza. Confluent OECs and HUVECs were incubated with 10 or 20 μM dabigatran for 10 min, before activation with 8 U/mL thrombin, for 24 h. The effect of dabigatran on ICAM-1 expression (anti-CD54-PE) was evaluated in both cell types as % gated CD31+/CD54+ cells, using flow cytometry. Results Thrombin induced ICAM-1 membrane expression by 33±15% on OECs and by 123±22% on HUVECs, compared with respective untreated cells (p&lt;0.05 for both comparisons, from 6 different experiments). Dabigatran at 10 μM significantly inhibited ICAM-1 expression by 36±7% on OECs and 57±8% on HUVECs, as well as at 20 μM by 51±8% on OECs and 79±7% on HUVECs (p&lt;0.05 for all comparisons, from 4 different experiments). Conclusions We show for the first time that dabigatran at concentrations relevant to those existing in vivo after oral administration, inhibits the thrombin-induced membrane expression of the adhesion molecule ICAM-1 on OECs, a phenomenon that is also observed on mature endothelial cells. The significance of this effect regarding the pathophysiological role of OECs and mature endothelial cells at the clinical level remains to be established. Acknowledgement/Funding Operational Program “Human Resources Development, Education and Lifelong Learning”. Co-financed by the European Union and Greek national funds

Hematopoietic stem cell response to acute thrombocytopenia requires signaling through distinct receptor tyrosine kinases

AbstractAlthough bone marrow niche cells are essential for hematopoietic stem cell (HSC) maintenance, their interaction in response to stress is not well defined. Here, we used a mouse model of acute thrombocytopenia to investigate the cross talk between HSCs and niche cells during restoration of the thrombocyte pool. This process required membrane-localized stem cell factor (m-SCF) in megakaryocytes, which was regulated, in turn, by vascular endothelial growth factor A (VEGF-A) and platelet-derived growth factor-BB (PDGF-BB). HSCs and multipotent progenitors type 2 (MPP2), but not MPP3/4, were subsequently activated by a dual-receptor tyrosine kinase (RTK)–dependent signaling event, m-SCF/c-Kit and VEGF-A/vascular endothelial growth factor receptor 2 (VEGFR-2), contributing to their selective and early proliferation. Our findings describe a dynamic network of signals in response to the acute loss of a single blood cell type and reveal the important role of 3 RTKs and their ligands in orchestrating the selective activation of hematopoietic stem and progenitor cells (HSPCs) in thrombocytopenia.

Activation of Skeletal Stem and Progenitor Cells for Bone Regeneration Is Driven by PDGFRβ Signaling.

Bone repair and regeneration critically depend on the activation and recruitment of osteogenesis-competent skeletal stem and progenitor cells (SSPCs). Yet, the origin and triggering cues for SSPC propagation and migration remain largely elusive. Through bulk and single-cell transcriptome profiling of fetal osterix (Osx)-expressing cells, followed by lineage mapping, cell tracing, and conditional mouse mutagenesis, we here identified PDGF-PDGFRβ signaling as critical functional mediator of SSPC expansion, migration, and angiotropism during bone repair. Our data show that cells marked by a history of Osx expression, including those arising in fetal or early postnatal periods, represent or include SSPCs capable of delivering all the necessary differentiated progeny to repair acute skeletal injuries later in life, provided that they express functional PDGFRβ. Mechanistically, MMP-9 and VCAM-1 appear to be involved downstream of PDGF-PDGFRβ. Our results reveal considerable cellular dynamism in the skeletal system and show that activation and recruitment of SSPCs for bone repair require functional PDGFRβ signaling.

Evaluation of related variables on endothelial progenitor cells in first transient ischemic attack

Background and aims: In a transient ischemic attack (TIA), the activation of the endothelial progenitor cells (EPCs) has a prominent role in the formation of collateral vessels. The aim of this study was to evaluate the role of effective variables (e.g., hypertension, diabetes, hyperlipidemia, cardiovascular diseases, a family history of cardiovascular diseases, and statin therapy on the level of EPCs in TIA. Methods: Thirty patients suffering from the first attack of TIA, without having a history of acute cerebral injury, surgery or trauma, and blood disorders were enrolled in this cross-sectional study. Then, flow cytometry was utilized to estimate the level of EPCs CD34 and CD309 and the results were evaluated based on the t test or the Mann-Whitney test. Finally, the Pearson or Spearman correlation was used to establish the relationship between the variables. The level of P&lt;0.05 was considered statistically significant in this study. Results: The mean±SD number of CD309 in patients with hyperlipidemia was less than those with no hyperlipidemia (3.35±2.77 vs. 5.59±3.85, P=0.02) and diabetic patients had a significantly higher number of CD309 compared to non-diabetics (6.14±4.89 vs, 3.5± 3.49, P=0.05). Conversely, the mean number of CD34 in groups with or without the studied variables was not statistically significant. The results further revealed that the average total of CD309 and CD34 was significantly lower in patients with hyperlipidemia as compared to those with no sign of hyperlipidemia (9.44± 3.05 vs. 6.67±4.6, P=0.02). Using logistic regression, the intended variables demonstrated no significant effects on endothelial cells, and the relationship between age and the number of progenitor cells was not significant. Conclusion: In our study, only hyperlipidemia acted as a factor influencing the numbers of EPCs. Therefore, more studies with larger sample sizes are required to discover the role of these variables on progenitor cells in TIA.

The effects of microenergy acoustic pulses on animal model of obesity-associated stress urinary incontinence. Part 2: In situ activation of pelvic floor and urethral striated muscle progenitor cells.

To investigate the possibility and mechanism of microenergy acoustic pulses (MAP) for activating tissue resident stem/progenitor cells within pelvic and urethral muscle and possible mechanism. The female Zucker Lean and Zucker Fatty rats were randomly divided into four groups: ZL control, ZLMAP, ZF control, and ZFMAP. MAP was applied at 0.033 mJ/mm2 , 3 Hz for 500 pulses, and the urethra and pelvic floor muscles of each rat was then harvested for cell isolation and flow cytometry assay. Freshly isolated cells were analyzed by flow cytometry for Pax-7, Int-7α, H3P, and EdU expression. Meanwhile, pelvic floor muscle-derived stem cells (MDSCs) were harvested through magnetic-activated cell sorting, MAP was then applied to MDSCs to assess the mechanism of stem cell activation. Obesity reduced EdU-label-retaining cells and satellite cells in both pelvic floor muscle and urethra, while MAP activated those cells and enhanced cell proliferation, which promoted regeneration of striated muscle cells of the pelvic floor and urethral sphincter. Activation of focal adhesion kinase (FAK)/AMP-activated protein kinase (AMPK) /Wnt/β-catenin signaling pathways by MAP is the potential mechanism. MAP treatment activated tissue resident stem cells within pelvic floor and urethral muscle in situ via activating FAK-AMPK and Wnt/β-catenin signaling pathway.

Ceramide 1-Phosphate Protects Endothelial Colony-Forming Cells From Apoptosis and Increases Vasculogenesis In Vitro and In Vivo.

Ceramide 1-phosphate (C1P) is a bioactive sphingolipid highly augmented in damaged tissues. Because of its abilities to stimulate migration of murine bone marrow-derived progenitor cells, it has been suggested that C1P might be involved in tissue regeneration. In the present study, we aimed to investigate whether C1P regulates survival and angiogenic activity of human progenitor cells with great therapeutic potential in regenerative medicine such as endothelial colony-orming cells (ECFCs). Approach and Results: C1P protected ECFC from TNFα (tumor necrosis factor-α)-induced and monosodium urate crystal-induced death and acted as a potent chemoattractant factor through the activation of ERK1/2 (extracellular signal-regulated kinases 1 and 2) and AKT pathways. C1P treatment enhanced ECFC adhesion to collagen type I, an effect that was prevented by β1 integrin blockade, and to mature endothelial cells, which was mediated by the E-selectin/CD44 axis. ECFC proliferation and cord-like structure formation were also increased by C1P, as well as vascularization of gel plug implants loaded or not with ECFC. In a murine model of hindlimb ischemia, local administration of C1P alone promoted blood perfusion and reduced necrosis in the ischemic muscle. Additionally, the beneficial effects of ECFC infusion after ischemia were amplified by C1P pretreatment, resulting in a further and significant enhancement of leg reperfusion and muscle repair. Our findings suggest that C1P may have therapeutic relevance in ischemic disorders, improving tissue repair by itself, or priming ECFC angiogenic responses such as chemotaxis, adhesion, proliferation, and tubule formation, which result in a better outcome of ECFC-based therapy.

Effects of astragaloside IV on activity and proliferative function of endothelial progenitor cells

Objective The objective is to probe into the effects of astragaloside Ⅳ (AS-Ⅳ) on activity and proliferative function of endothelial progenitor cells (EPCs), which lays a foundation for further study on the effects of AS-Ⅳ on vascular neovascularization mediated by endothelial progenitor cells. Methods The mononuclear cells were isolated by the density gradient centrifugation in umbilical cord blood of full-term healthy infants, and EPCs were obtained by subculture and cell identification when the cells presented spindle shapes. The obtained EPCs were randomly divided into the experimental group and the control group. In the experimental group, EPCs were cultured by AS-Ⅳ with different concentration gradients (25 mg/L, 50 mg/L, 100 mg/L, 200 mg/L and 400 mg/L), while in the control group, they were treated with the same amount of phosphate buffer saline (PBS) solutions. The effects of AS-Ⅳ on the proliferation of endothelial progenitor cells was studied by cell counting kit-8 (CCK-8) cell proliferation experiment, and the activity rate of EPCs cells was measured at the optimum concentration of EPCs proliferation. Results EPCs were successfully obtained after confirming nuclear staining test of CD31 antibody and 4′, 6-diamidino-2-phenylindole (DAPI). Further study showed that AS-Ⅳ can promote the proliferation of EPCs, and its optimal concentration of EPCs proliferation is 100 mg/L. Compared with the normal control group, the activity rate of endothelial progenitor cells after intervention of AS-Ⅳ was 98.7%, higher than 98.12% in the control group, with significant difference (χ2=49.59, P<0.01). Conclusions AS-Ⅳ can enhance the activity of human EPCs and promote their proliferation in vitro. Key words: Astragalus membranaceus; Saponins; Endothelial progenitor cells; Cell proliferation; Cell survival; In vitro

Nodular Regenerative Hyperplasia: Expression Pattern of Glutamine Synthetase and a Potential Role for Hepatic Progenitor Cells.

Nodular regenerative hyperplasia (NRH) is one of the most frequent causes of noncirrhotic intrahepatic hypertension, but is a difficult histologic diagnosis. The expression of glutamine synthetase (GS) and cytokeratin 7 (CK7) has been reported to be increased in other regenerative/vascular conditions, while CK7 and BerEP4 are also markers of hepatic progenitor cells. The aims of this study were to investigate the use of GS, CK7, and BerEP4 as the potential markers for NRH. This is a retrospective case series of NRH at Centre Hospitalier de l'Universite de Montreal between 1993 and 2013. Normal liver from partial hepatectomies for tumors were used as controls. GS, CK7, CK19, and BerEP4 immunohistochemical stains were performed on all specimens. Immunohistochemical staining patterns were scored from 0 to 3+. NRH was identified in 46 samples obtained from 26 patients. Liver chemistry profile was cholestatic in 45% of the patients. In 93% of the NRH cases, there was abnormal zone 2 expression of GS. Weak panacinar GS staining was seen in all the NRH cases. Aberrant CK7 expression was present in all cases of NRH, but were not associated with cholestasis. BerEP4 was overexpressed in 47% of the NRH cases (P<0.05); all cases with diffuse BerEP4 staining also showed extensive CK7 expression (P<0.01). NRH showed increased immunohistochemical GS staining that may support its morphologic diagnosis. Our findings suggest that there is an activation of hepatic progenitor cells in NRH.

Dicer1 facilitates liver regeneration in a manner dependent on the inhibitory effect of miR-21 on Pten and Rhob expression

AimsTamoxifen-induced liver-specific Dicer1 deletion (iDicer1−/−) in mature mice may provide clues demonstrating the genuine effects of acute loss of Dicer1 and miRNAs in the liver regeneration process. Main methodsIn this study, mice with tamoxifen-induced Dicer1 deletion through the Cre/LoxP system were constructed and then underwent classic 70% partial hepatectomy or CCl4-induced liver injury. To rescue the inhibitory effect of Dicer1 ablation on liver regeneration, miR-21 agomir was injected into the tail vein of iDicer1−/− mice. Key findingsUnlike constitutive embryonic deletion of Dicer1, tamoxifen-induced Dicer1 deletion did not result in severe liver injury or lesions, providing an ideal model for investigating acute loss of Dicer1 and miRNAs in liver regeneration. Dicer1 deletion led to impaired liver regeneration through the inhibitory effect of miR-21 on PTEN and Rhob expression. SignificanceIn our previous study, we found that embryonic loss of Dicer1 impairs hepatocyte survival and leads to chronic inflammation and progenitor cell activation, while the role of Dicer1 in liver regeneration remains largely unknown. We clearly identified the promotion effect of Dicer1 on liver regeneration by increasing miR-21 expression, which inhibits the expression of two negative cell proliferation regulators, Pten and Rhob.

Enzyme-Aided Extraction of Fucoidan by AMG Augments the Functionality of EPCs through Regulation of the AKT/Rheb Signaling Pathway.

The purpose of the present study is to improve the endothelial progenitor cells (EPC) activation, proliferation, and angiogenesis using enzyme-aided extraction of fucoidan by amyloglucosidase (EAEF-AMG). Enzyme-aided extraction of fucoidan by AMG (EAEF-AMG) significantly increased EPC proliferation by reducing the reactive oxygen species (ROS) and decreasing apoptosis. Notably, EAEF-AMG treated EPCs repressed the colocalization of TSC2/LAMP1 and promoted perinuclear localization of mTOR/LAMP1 and mTOR/Rheb. Moreover, EAEF-AMG enhanced EPC functionalities, including tube formation, cell migration, and wound healing via regulation of AKT/Rheb signaling. Our data provided cell priming protocols to enhance therapeutic applications of EPCs using bioactive compounds for the treatment of CVD.

Exogenous FGF-2 improves biological activity of endothelial progenitor cells exposed to high glucose conditions

Purpose: To investigate the effects of exogenous basic fibroblast growth factor -2 (FGF-2) on the biological activity of endothelial progenitor cells (EPCs) exposed to high glucose conditions.Materials and Methods: 1) Bone marrow EPCs from C57BL/6 mice were isolated and cultured in vitro. EPC purity was identified by flow cytometry and immunofluorescence staining. 2) Apoptosis was detected by TUNEL assay. Migration and tube formation ability was detected by Transwell chamber and Matrigel assays, respectively. The expression and activation of β-catenin was detected by Western blot. 3) Doppler flowmetry was used to detect the effect of FGF2 on blood flow recovery in ischemic hind limbs of mice.Results: 1) FGF-2 treatment reversed high glucose induced growth inhibition of EPCs. FGF-2 treatment also increased migration and tube formation ability of EPCs even in high glucose conditions. 2) Western blot analysis demonstrated that the percentage of activated β-catenin/total β-catenin in the high glucose group were significantly lower than that in the control group, while FGF-2 treatment reversed high glucose induced β-catenin inhibition. 3) In vivo experiments demonstrated that the blood flow recovery in ischemic hind limbs of mice was significantly improved after FGF-2 treatment.Conclusion: Exogenous FGF-2 could play a role in the functional repair of damaged EPC exposed to high glucose conditions, via the activation of the Wnt/β-catenin signaling pathway.

Dual role of FGF in proliferation and endoreplication of Drosophila tracheal adult progenitor cells.

Adult progenitor cells activation is a key event in the formation of adult organs. In Drosophila, formation of abdominal adult trachea depends on the specific activation of tracheal adult progenitors (tracheoblasts) at the Tr4 and Tr5 spiracular branches. Proliferation of these tracheoblasts generates a pool of tracheal cells that migrate toward the posterior part of the trachea by the activation of the branchless/fibroblast growth factor (Bnl/FGF) signaling to form the abdominal adult trachea. Here, we show that, in addition to migration, Bnl/FGF signaling, mediated by the transcription factor Pointed, is also required for tracheoblast proliferation. This tracheoblast activation relies on the expression of the FGF ligand bnl in their nearby branches. Finally, we show that, in the absence of the transcription factor Cut (Ct), Bnl/FGF signaling induces endoreplication of tracheoblasts partially by promoting fizzy-related expression. Altogether, our results suggest a dual role of Bnl/FGF signaling in tracheoblasts, inducing both proliferation and endoreplication, depending on the presence or absence of the transcription factor Ct, respectively.

Potential therapeutic use of relaxin in accelerating closure of cranial bone defects in mice.

Bone fractures are associated with considerable morbidity and increased mortality. A major limitation to healing is lack of bone blood flow, which is impaired by physical disruption of intraskeletal and/or periosteal vasculature by the fracture. Thus, pharmacological interventions are needed to improve osseous blood flow, thereby accelerating bone fracture closure. Relaxin is secreted by the ovary and circulates in rodents and humans during pregnancy. Because relaxin might benefit bone fracture healing by stimulating angiogenesis, vasculogenesis (and potentially osteogenesis) through mobilization and activation of bone marrow progenitor cells, and by increasing blood flow via vasodilation, we investigated whether relaxin administration would accelerate closure of a calvarial defect in mice. Whether administered systemically by osmotic pump or locally by collagen scaffolds for ~2 week period after lesioning, relaxin did not accelerate bone healing. Despite implementing relaxin doses that reached plasma concentrations spanning the physiological to supraphysiological range, testing the closure of two different sizes of calvarial lesions, allowing for different intervals of time from instigation of cranial lesion to euthanasia, and investigating mice of different ages, we did not observe a significant benefit of relaxin in bone lesion healing. Nor did we observe stimulation of blood vessel formation in the bone lesion by the hormone. An incidental finding was that relaxin appeared to enhance trabecular bone growth in an uninjured control bone (femur). Although the results of this study were not supportive of a therapeutic benefit for relaxin on calvarial defect closure, future investigation is needed employing different animal species and experimental models of bone fracture.

Hepatic progenitor cell activation is induced by the depletion of the gut microbiome in mice.

The homeostasis of the gut microbiome is crucial for human health and for liver function. However, it has not been established whether the gut microbiome influence hepatic progenitor cells (HPCs). HPCs are capable of self‐renewal and differentiate into hepatocytes and cholangiocytes; however, HPCs are normally quiescent and are rare in adults. After sustained liver damage, a ductular reaction occurs, and the number of HPCs is substantially increased. Here, we administered five broad‐spectrum antibiotics for 14 days to deplete the gut microbiomes of male C57BL/6 mice, and we measured the plasma aminotransferases and other biochemical indices. The expression levels of two HPC markers, SRY‐related high mobility group‐box gene 9 (Sox9) and cytokeratin (CK), were also measured. The plasma aminotransferase activities were not affected, but the triglyceride, lactate dehydrogenase, low‐density lipoprotein, and high‐density lipoprotein concentrations were significantly altered; this suggests that liver function is affected by the composition of the gut microbiome. The mRNA expression of Sox9 was significantly higher in the treated mice than it was in the control mice (p < 0.0001), and a substantial expression of Sox9 and CK was observed around the bile ducts. The mRNA expression levels of proinflammatory factors (interleukin [IL]‐1β, IL‐6, tumor necrosis factor [TNF]‐α, and TNF‐like weak inducer of apoptosis [Tweak]) were also significantly higher in the antibiotic‐treated mice than the levels in the control mice. These data imply that the depletion of the gut microbiome leads to liver damage, negatively impacts the hepatic metabolism and function, and activates HPCs. However, the underlying mechanisms remain to be determined.

The alliance between nerve fibers and stem cell populations in bone marrow: life partners in sickness and health.

The bone marrow (BM) is the central hematopoietic organ in adult mammals, with great potential to be used as a tool to improve the efficacy of the body's response to a number of malignancies and stressful conditions. The nervous system emerges as a critical regulatory player of the BM both under homeostatic and pathologic settings, with essential roles in cellular anchorage and egress, stem cell differentiation, and endothelial cell permeability. This review collects the current knowledge on the interplay between the nervous system and the BM cell populations, with a focus on how the nervous system modulates hematopoietic stem and progenitor cell, mesenchymal stromal cell, and endothelial progenitor cell activity in BM. We have also highlighted the pathologies that have been associated with disturbances in the neuronal signaling in BM and discussed if targeting the nervous system, either by modulating the activity of specific neuronal circuits or by pharmacologically leveling the activity of sympathetic and sensorial signaling-responsive cells in BM, is a promising therapeutic approach to tackling pathologies from BM origin.-Leitão, L., Alves, C. J., Sousa, D. M., Neto, E., Conceição, F., Lamghari, M. The alliance between nerve fibers and stem cell populations in bone marrow: life partners in sickness and health.

Calcium Activity Dynamics Correlate with Neuronal Phenotype at a Single Cell Level and in a Threshold-Dependent Manner.

Calcium is a ubiquitous signaling molecule that plays a vital role in many physiological processes. Recent work has shown that calcium activity is especially critical in vertebrate neural development. Here, we investigated if calcium activity and neuronal phenotype are correlated only on a population level or on the level of single cells. Using Xenopus primary cell culture in which individual cells can be unambiguously identified and associated with a molecular phenotype, we correlated calcium activity with neuronal phenotype on the single-cell level. This analysis revealed that, at the neural plate stage, a high frequency of low-amplitude spiking activity correlates with an excitatory, glutamatergic phenotype, while high-amplitude spiking activity correlates with an inhibitory, GABAergic phenotype. Surprisingly, we also found that high-frequency, low-amplitude spiking activity correlates with neural progenitor cells and that differentiating cells exhibit higher spike amplitude. Additional methods of analysis suggested that differentiating marker tubb2b-expressing cells exhibit relatively persistent and predictable calcium activity compared to the irregular activity of neural progenitor cells. Our study highlights the value of using a range of thresholds for analyzing calcium activity data and underscores the importance of employing multiple methods to characterize the often irregular, complex patterns of calcium activity during early neural development.