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Background Polarization of microglia, the resident retinal immune cells, plays important roles in mediating both injury and repair responses post-retinal ischemia–reperfusion (I/R) injury, which is one of the main pathological mechanisms behind ganglion cell apoptosis. Aging could perturb microglial balances, resulting in lowered post-I/R retinal repair. Young bone marrow (BM) stem cell antigen 1-positive (Sca-1 + ) cells have been demonstrated to have higher reparative capabilities post-I/R retinal injury when transplanted into old mice, where they were able to home and differentiate into retinal microglia. Methods Exosomes were enriched from young Sca-1 + or Sca-1 − cells, and injected into the vitreous humor of old mice post-retinal I/R. Bioinformatics analyses, including miRNA sequencing, was used to analyze exosome contents, which was confirmed by RT-qPCR. Western blot was then performed to examine expression levels of inflammatory factors and underlying signaling pathway proteins, while immunofluorescence staining was used to examine the extent of pro-inflammatory M1 microglial polarization. Fluoro-Gold labelling was then utilized to identify viable ganglion cells, while H&E staining was used to examine retinal morphology post-I/R and exosome treatment. Results Sca-1 + exosome-injected mice yielded better visual functional preservation and lowered inflammatory factors, compared to Sca-1 − , at days 1, 3, and 7 days post-I/R. miRNA sequencing found that Sca-1 + exosomes had higher miR-150-5p levels, compared to Sca-1 − exosomes, which was confirmed by RT-qPCR. Mechanistic analysis found that miR-150-5p from Sca-1 + exosomes repressed the mitogen-activated protein kinase kinase kinase 3 (MEKK3)/JNK/c-Jun axis, leading to IL-6 and TNF-α downregulation, and subsequently reduced microglial polarization, all of which contributes to reduced ganglion cell apoptosis and preservation of proper retinal morphology. Conclusion This study elucidates a potential new therapeutic approach for neuroprotection against I/R injury, via delivering miR-150-5p-enriched Sca-1 + exosomes, which targets the miR-150-5p/MEKK3/JNK/c-Jun axis, thereby serving as a cell-free remedy for treating retinal I/R injury and preserving visual functioning.

Reduced quantity and quality of stem cells in aged individuals hinders cardiac repair and regeneration after injury. We used young bone marrow (BM) stem cell antigen 1 (Sca‐1) cells to reconstitute aged BM and rejuvenate the aged heart, and examined the underlying molecular mechanisms. BM Sca‐1+ or Sca‐1− cells from young (2–3 months) or aged (18–19 months) GFP transgenic mice were transplanted into lethally irradiated aged mice to generate 4 groups of chimeras: young Sca‐1+, young Sca‐1−, old Sca‐1+, and old Sca‐1−. Four months later, expression of rejuvenation‐related genes (Bmi1, Cbx8, PNUTS, Sirt1, Sirt2, Sirt6) and proteins (CDK2, CDK4) was increased along with telomerase activity and telomerase‐related protein (DNA‐PKcs, TRF‐2) expression, whereas expression of senescence‐related genes (p16INK4a, P19ARF, p27Kip1) and proteins (p16INK4a, p27Kip1) was decreased in Sca‐1+ chimeric hearts, especially in the young group. Host cardiac endothelial cells (GFP−CD31+) but not cardiomyocytes were the primary cell type rejuvenated by young Sca‐1+ cells as shown by improved proliferation, migration, and tubular formation abilities. C‐X‐C chemokine CXCL12 was the factor most highly expressed in homed donor BM (GFP+) cells isolated from young Sca‐1+ chimeric hearts. Protein expression of Cxcr4, phospho‐Akt, and phospho‐FoxO3a in endothelial cells derived from the aged chimeric heart was increased, especially in the young Sca‐1+ group. Reconstitution of aged BM with young Sca‐1+ cells resulted in effective homing of functional stem cells in the aged heart. These young, regenerative stem cells promoted aged heart rejuvenation through activation of the Cxcl12/Cxcr4 pathway of cardiac endothelial cells. Reconstitution of aged bone marrow with young Sca‐1+ cells results in effective homing of functional stem cells and rejuvenation of the aged heart. Host cardiac endothelial cells are the primary cell type rejuvenated by young Sca‐1+ cells with improved angiogenic abilities. Cxcl12 is a key modulator of the interaction between homed Sca‐1+ cells and the Cxcr4 receptor in host cardiac endothelial cells which leads to the activation of the senescence‐suppressing pathway AKT‐FoxO3a‐P27.

The injection of minimally expanded exogenous mesenchymal stromal cells (MSCs) into a mouse model of human age‐related osteoporosis led to long‐term engraftment and markedly increased bone formation. This led to improved bone quality and turnover and sustained microarchitectural competence, establishing proof of concept that MSC transplantation may be used to prevent or treat human age‐related osteoporosis. Age‐related osteoporosis is driven by defects in the tissue‐resident mesenchymal stromal cells (MSCs), a heterogeneous population of musculoskeletal progenitors that includes skeletal stem cells. MSC decline leads to reduced bone formation, causing loss of bone volume and the breakdown of bony microarchitecture crucial to trabecular strength. Furthermore, the low‐turnover state precipitated by MSC loss leads to low‐quality bone that is unable to perform remodeling‐mediated maintenance—replacing old damaged bone with new healthy tissue. Using minimally expanded exogenous MSCs injected systemically into a mouse model of human age‐related osteoporosis, we show long‐term engraftment and markedly increased bone formation. This led to improved bone quality and turnover and, importantly, sustained microarchitectural competence. These data establish proof of concept that MSC transplantation may be used to prevent or treat human age‐related osteoporosis. Significance This study shows that a single dose of minimally expanded mesenchymal stromal cells (MSCs) injected systemically into a mouse model of human age‐related osteoporosis display long‐term engraftment and prevent the decline in bone formation, bone quality, and microarchitectural competence. This work adds to a growing body of evidence suggesting that the decline of MSCs associated with age‐related osteoporosis is a major transformative event in the progression of the disease. Furthermore, it establishes proof of concept that MSC transplantation may be a viable therapeutic strategy to treat or prevent human age‐related osteoporosis.

Abstract Diabetic neuropathy is a major complication of diabetes mellitus that occurs during the early stages of the disease. Many pathogenic mechanisms are related and induced by hyperglycemia. However, even if these factors improve, diabetic neuropathy cannot go into remission and progresses slowly. Furthermore, diabetic neuropathy often progresses even with proper glycemic control. Recently, bone marrow-derived cells (BMDCs) were reported to be involved in the pathogenesis of diabetic neuropathy. BMDCs expressing proinsulin and TNFα migrate to the dorsal root ganglion and fuse with neurons, and this neuronal-hematopoietic cell fusion induces neuronal dysfunction and apoptosis. The CD106-positive lineage–sca1+c-kit+ (LSK) stem cell fraction in the bone marrow is strongly involved in cell fusion with neurons, leading to diabetic neuropathy. Surprisingly, when CD106-positive LSK stem cells obtained from diabetic mice were transplanted into nondiabetic mice, they fused with dorsal root ganglion neurons and induced neuropathy in non-hyperglycemic normal mice. The transplanted CD106-positive LSK fraction inherited the trait even after transplantation; this “progeny effect” may explain the irreversibility of diabetic neuropathy and is a significant finding for determining the target of radical treatments and provides new directions for developing therapeutic methods for diabetic neuropathy. Graphical Abstract Graphical Abstract

Aims Neointimal hyperplasia remains a major obstacle in vascular regeneration. Sca-1-positive progenitor cells residing within the vascular adventitia play a crucial role in the assemblage of vascular smooth muscle cell (VSMC) and the formation of the intimal lesion. However, the underlying mechanisms during vascular injury are still unknown. Methods and results Aneointimal formation rat model was prepared by carotid artery injury using 2F-Forgaty. After vascular injury, Meox1 expressions time-dependently increased during the neointima formation, with its levels concurrently increasing in the adventitia, media, and neointima. Meox1 was highly expressed in the adventitia on the first day after vascular injury compared to the expression levels in the media. Conversely, by the 14th day post-injury, Meox1 was extensively expressed more in the media and neointima than the adventitia. Analogous to the change of Meox1 in injured artery, Sca-1+ progenitor cells increased in the adventitia wall in a time-dependent manner and reached peak levels on the 7th day after injury. More importantly, this effect was abolished by Meox1 knockdown with shRNA. The enhanced expression of SDF-1α after vascular injury was associated with the markedly enhanced expression levels of Sca1+ progenitor cell, and these levels were relatively synchronously increased within neointima by the 7th day after vascular injury. These special effects were abolished by the knockdown of Meox1 with shRNA and inhibition of CXCR4 by its inhibitor, AMD3100. Finally, Meox1 concurrently regulated SDF-1α expressions in VSMC via activating CDC42, and CDC42 inhibition abolished these effects by its inhibitor, ZCL278. Also, Meox1 was involved in activation of the CXCR4 expression of Sca-1+ progenitor cells by CDC42. Conclusions Spatio-temporal model of Meox1 expression regulates theSca-1+progenitor cell migration during the formation of the neointima through the synergistic effect of Rho/CDC42 and SDF-1α/CXCR4.

The immense regenerative power of hematopoietic tissue stems from the activation of the immature stem cells and the progenitor cells. After partial damage, hematopoiesis is reconstituted through a period of intense regeneration when blood cell production originates from erythro-myeloid progenitors in the virtual absence of stem cells. Since the damaged hematopoiesis can also be reconstituted from transplanted hematopoietic cells, we asked whether this also leads to the transient state when activated progenitors initially execute blood cell production. We first showed that the early reconstitution of hematopoiesis from transplanted cells gives rise to extended populations of developmentally advanced but altered progenitor cells, similar to those previously identified in the bone marrow regenerating from endogenous cells. We then identified the cells that give rise to these progenitors after transplantation as LSK CD48 – cells. In the submyeloablative irradiated host mice, the transplanted LSK CD48 – cells preferably colonized the spleen. Unlike the endogenous hematopoiesis reconstituting cells, the transplanted whole bone marrow cells and sorted LSK CD48 – cells had greater potential to differentiate to B-lymphopoiesis. Separate transplantation of the CD150 – and CD150 + subsets of LSK CD48 – cells suggested that CD150 – cells had a greater preference to B-lymphopoiesis than CD150 + cells. In the intensively regenerating hematopoiesis, the CD71/Sca-1 plot of immature murine hematopoietic cells revealed that the expanded populations of altered myeloid progenitors were highly variable in the different places of hematopoietic tissues. This high variability is likely caused by the heterogeneity of the hematopoiesis supporting stroma. Lastly, we demonstrate that during the period when active hematopoiesis resumes from transplanted cells, the hematopoietic tissues still remain highly permissive for further engraftment of transplanted cells, particularly the stem cells. Thus, these results provide a rationale for the transplantation of the hematopoietic stem cells in successive doses that could be used to boost the transplantation outcome.

Introduction Accumulation of vascular smooth muscle cells (VSMCs) within the neointimal region is a hallmark of atherosclerosis and vessel injury. Evidence has shown that Sca-1-positive (Sca-1+) progenitor cells residing in the vascular adventitia play a crucial role in VSMC assemblages and intimal lesions. However, the underlying mechanisms, especially in the circumstances of vascular injury, remain unknown. Methods and results The neointimal formation model in rats was established by carotid artery balloon injury using a 2F-Forgaty catheter. Most Sca-1+ cells first appeared at the adventitia of the vascular wall. S100B expressions were highest within the adventitia on the first day after vessel injury. Along with the sequentially increasing trend of S100B expression in the intima, media, and adventitia, respectively, the numbers of Sca-1+ cells were prominently increased at the media or neointima during the time course of neointimal formation. Furthermore, the Sca-1+ cells were markedly increased in the tunica media on the third day of vessel injury, SDF-1α expressions were obviously increased, and SDF-1α levels and Sca-1+ cells were almost synchronously increased within the neointima on the seventh day of vessel injury. These effects could effectually be reversed by knockdown of S100B by shRNA, RAGE inhibitor (SPF-ZM1), or CXCR4 blocker (AMD3100), indicating that migration of Sca-1+ cells from the adventitia into the neointima was associated with S100B/RAGE and SDF-1α/CXCR4. More importantly, the intermediate state of double-positive Sca-1+ and α-SMA cells was first found in the neointima of injured arteries, which could be substantially abrogated by using shRNA for S100B or blockade of CXCR4. S100B dose-dependently regulated SDF-1α expressions in VSMCs by activating PI3K/AKT and NF-κB, which were markedly abolished by PI3K/AKT inhibitor wortmannin and enhanced by p65 blocker PDTC. Furthermore, S100B was involved in human umbilical cord-derived Sca-1+ progenitor cells’ differentiation into VSMCs, especially in maintaining the intermediate state of double-positive Sca-1+ and α-SMA. Conclusions S100B triggered neointimal formation in rat injured arteries by maintaining the intermediate state of double-positive Sca-1+ progenitor and VSMCs, which were associated with direct activation of RAGE by S100B and indirect induction of SDF-1α by activating PI3K/AKT and NF-κB.

In adults, bone hematopoietic cells are responsible for the lifelong production of all blood cells. It is affected in aging, with progressive loss of physiological integrity leading to impaired function by cellular intrinsic and extrinsic factors. However, intervention measures, which directly inhibit the aging of hematopoietic cells, remain to be investigated. In the present study, 10 µmol/l ginsenoside Rg1 (Rg1) markedly alleviated the aging phenotypes of Sca-1+ hematopoietic cells following in vitro exposure. In addition, the protective effects of ginsenoside Rg1 on the aging of Sca-1+ hematopoietic cells was confirmed using a serial transplantation assay in C57BL/6 mice. The mechanistic investigations revealed that Rg1-mediated Sca-1+ hematopoietic cell aging alleviation was linked to a series of characteristic events, including telomere end attrition compensation, telomerase activity reconstitution and the activation of genes involved in p16-Rb signaling pathways. Based on the above results, it was concluded that ginsenoside Rg1 is a potent agent, which acts on hematopoietic cells to protect them from aging, which has implications for therapeutic approaches in hemopoietic diseases.

Inhibition of the prolyl-4-hydroxylase domain (PHD) enzymes, leading to the stabilization of hypoxia-inducible factor (HIF) α as well as to the stimulation of erythropoietin (Epo) synthesis, is the functional mechanism of the new anti-anemia drug roxadustat. Little is known about the effects of roxadustat on the Epo-producing cell pool. To gain further insights into the function of PHD inhibitors, we characterized the abundance of mesenchymal stem cell (MSC)-like cells after roxadustat treatment of mice. The number of Sca-1+ mesenchymal cells following roxadustat treatment increased exclusively in the kidneys. Isolated Sca-1+ cells demonstrated typical features of MSC-like cells, including adherence to tissue culture plates, trilineage differentiation potential, and expression of MSC markers. Kidney-derived Sca-1+ MSC-like cells were cultured for up to 21 days. Within the first few days in culture, cells stabilized HIF-1α and HIF-2α and temporarily increased Epo production upon incubation in hypoxia. In summary, we have identified a Sca-1+ MSC-like cell population that is involved in renal Epo production and might contribute to the strong anti-anemic effect of the PHD inhibitor roxadustat.

Although vaccination has been an effective way of preventing infections ever since the eighteenth century, the generation of therapeutic vaccines and immunotherapies is still a work in progress. A number of challenges impede the development of these therapeutic approaches such as safety issues related to the administration of whole pathogens whether attenuated or inactivated. One safe alternative to classical vaccination methods gaining recognition is the use of nanoparticles, whether synthetic or naturally derived. We have recently demonstrated that the papaya mosaic virus (PapMV)-like nanoparticle can be used as a prophylactic vaccine against various viral and bacterial infections through the induction of protective humoral and cellular immune responses. Moreover, PapMV is also very efficient when used as an immune adjuvant in an immunotherapeutic setting at slowing down the growth of aggressive mouse melanoma tumors in a type I interferon (IFN-I)-dependent manner. In the present study, we were interested in exploiting the capacity of PapMV of inducing robust IFN-I production as treatment for the chronic viral infection model lymphocytic choriomeningitis virus (LCMV) clone 13 (Cl13). Treatment of LCMV Cl13-infected mice with two systemic administrations of PapMV was ineffective, as shown by the lack of changes in viral titers and immune response to LCMV following treatment. Moreover, IFN-α production following PapMV administration was almost completely abolished in LCMV-infected mice. To better isolate the mechanisms at play, we determined the influence of a pretreatment with PapMV on secondary PapMV administration, therefore eliminating potential variables emanating from the infection. Pretreatment with PapMV led to the same outcome as an LCMV infection in that IFN-α production following secondary PapMV immunization was abrogated for up to 50 days while immune activation was also dramatically impaired. We showed that two distinct and overlapping mechanisms were responsible for this outcome. While short-term inhibition was partially the result of interleukin-1 receptor-associated kinase 1 degradation, a crucial component of the toll-like receptor 7 signaling pathway, long-term inhibition was mainly due to interference by PapMV-specific antibodies. Thus, we identified a possible pitfall in the use of virus-like particles for the systemic treatment of chronic viral infections and discuss mitigating alternatives to circumvent these potential problems.