A major therapeutic challenge is how to replace bone once it is lost. Bone loss is a characteristic of chronic inflammatory and degenerative diseases such as rheumatoid arthritis and osteoporosis. Cells and cytokines of the immune system are known to regulate bone turnover by controlling the differentiation and activity of osteoclasts, the bone resorbing cells. However, less is known about the regulation of osteoblasts (OB), the bone forming cells. This study aimed to investigate whether immune cells also regulate OB differentiation. Using in vitro cell cultures of human bone marrow-derived mesenchymal stem cells (MSC), it was shown that monocytes/macrophages potently induced MSC differentiation into OBs. This was evident by increased alkaline phosphatase (ALP) after 7 days and the formation of mineralised bone nodules at 21 days. This monocyte-induced osteogenic effect was mediated by cell contact with MSCs leading to the production of soluble factor(s) by the monocytes. As a consequence of these interactions we observed a rapid activation of STAT3 in the MSCs. Gene profiling of STAT3 constitutively active (STAT3C) infected MSCs using Illumina whole human genome arrays showed that Runx2 and ALP were up-regulated whilst DKK1 was down-regulated in response to STAT3 signalling. STAT3C also led to the up-regulation of the oncostatin M (OSM) and LIF receptors. In the co-cultures, OSM that was produced by monocytes activated STAT3 in MSCs, and neutralising antibodies to OSM reduced ALP by 50%. These data indicate that OSM, in conjunction with other mediators, can drive MSC differentiation into OB. This study establishes a role for monocyte/macrophages as critical regulators of osteogenic differentiation via OSM production and the induction of STAT3 signalling in MSCs. Inducing the local activation of STAT3 in bone cells may be a valuable tool to increase bone formation in osteoporosis and arthritis, and in localised bone remodelling during fracture repair.

Regenerative medicine using mesenchymal stem cells for the purposes of tissue repair has garnered considerable public attention due to the potential of returning tissues and organs to a normal, healthy state after injury or damage has occurred. To achieve this, progenitor cells such as pericytes and bone marrow-derived mesenchymal stem cells can be delivered exogenously, mobilised and recruited from within the body or transplanted in the form organs and tissues grown in the laboratory from stem cells. In this review, we summarise the recent evidence supporting the use of endogenously mobilised stem cell populations to enhance tissue repair along with the use of mesenchymal stem cells and pericytes in the development of engineered tissues. Finally, we conclude with an overview of currently available therapeutic options to manipulate endogenous stem cells to promote tissue repair.

The embryonic epicardium, originating from the proepicardial organ (PEO), provides a source of multipotent progenitors for cardiac lineages, including pericytes, fibroblasts, and vascular smooth muscle cells. Maximizing the regenerative capacity of the adult epicardium depends on recapitulating embryonic cell fates. The potential of the epicardium to contribute coronary endothelium is unclear, due to conflicting Cre-based lineage trace data. Controversy also surrounds when epicardial cell fate becomes restricted. Here, we systematically investigate expression of five widely used epicardial markers, Wt1, Tcf21, Tbx18, Sema3d, and Scx, over the course of development. We show overlap of markers in all PEO and epicardial cells until E13.5, and find no evidence for discrete proepicardial sub-compartments that might contribute coronary endothelium via the epicardial layer. Our findings clarify a number of prevailing discrepancies and support the notion that epicardium-derived cell fate, to form fibroblasts or mural cells, is specified after epithelial-mesenchymal transition, not pre-determined within the PEO. RESULTSWt1, Sema3d, Tbx18, Scx, and Tcf21 Overlap in the PEO, but Their Expression Domains Are Not Confined to This Tissue First, we used multiplexed single-molecule RNA in situ hybridization (RNAscope) on E9.5 sagittal mouse sections to simultaneously detect expression of the PEO markers:

The lipid compositions and associated antioxidant capacities of spermatozoa and seminal plasma from bulls were examined at the beginning, middle and end of their reproductive period. The reduction in concentration and motility of spermatozoa associated with ageing was accompanied by a large decrease in lipid concentrations within the seminal plasma; this change in lipid concentration was accompanied by an increase in the proportion of phospholipid. By contrast, the proportion of phospholipids in the spermatozoa was significantly reduced. The major phospholipid fractions within both the spermatozoa and seminal plasma were phosphatidyl choline and phosphatidyl ethanolamine. With increasing age there was a large decrease in the proportion of phosphatidyl ethanolamine and a commensurate increase in that of phosphatidyl choline within the spermatozoa and seminal plasma. These major changes in phospholipids were accompanied by a decrease in the amount of phosphatidyl inositol and an increase in that of cardiolipin in both spermatozoa and seminal plasma. The reductions in the proportions of phosphatidyl ethanolamine were accompanied by extensive reductions in the content of the major polyunsaturated fatty acids, arachidonic 20:4 (n-6) and docosahexaenoic 22:6 (n-3); there was a decrease also in the concentration of 22:6 (n-3) in phosphatidyl choline. The changes in lipid composition owing to ageing were associated with a marked reduction within the seminal plasma of the major antioxidant enzyme systems, glutathione peroxidase and superoxide dismutase.

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Pharmacological mobilization of hematopoietic progenitor cells (HPCs) is used clinically to harvest HPCs for bone marrow transplants. It is now widely accepted that the CXCR4:CXCL12 chemokine axis plays a critical role in the retention of HPCs in the bone marrow, and CXCR4 antagonists have been developed for their mobilization. The first of this class of drugs to be US Food and Drug Administration-approved was the bicyclam AMD3100. In addition to mobilizing HPCs and leukocytes in naïve mice, AMD3100 has been shown to mobilize mesenchymal progenitor cells (MPCs) in vascular endothelial growth factor (VEGF-A) pretreated mice. AMD3100 binds to the transmembrane region of CXCR4 and is thought to mobilize HPCs by reversing the gradient of CXCL12 across the bone marrow endothelium. Consistent with this hypothesis, our data show that selective neutralization of CXCL12, with chalcone 4-phosphate (C4P), inhibited AMD3100-stimulated mobilization of HPCs and leukocytes in naïve mice and MPCs in VEGF-A pretreated mice. In contrast it is shown here that the CXCR4 antagonist KRH3955 that binds to the extracellular loop of CXCR4 does not reverse the CXCL12 chemokine gradient. However, this drug efficiently mobilizes HPCs, a response that is not inhibited by C4P. In contrast, KRH3955 does not mobilize MPCs in VEGF-A pretreated mice. These data suggest that CXCR4 antagonists that bind to distinct regions of the receptor mobilize progenitor cells by distinct molecular mechanisms

The survival of ischaemic cardiomyocytes after myocardial infarction (MI) depends on the formation of new blood vessels. However, endogenous neovascularization is inefficient and the regulatory pathways directing coronary vessel growth are not well understood. Here we describe three independent regulatory pathways active in coronary vessels during development through analysis of the expression patterns of differentially regulated endothelial enhancers in the heart. The angiogenic VEGFA-MEF2 regulatory pathway is predominantly active in endocardial-derived vessels, whilst SOXF/RBPJ and BMP-SMAD pathways are seen in sinus venosus-derived arterial and venous coronaries, respectively. Although all developmental pathways contribute to post-MI vessel growth in the neonate, none are active during neovascularization after MI in adult hearts. This was particularly notable for the angiogenic VEGFA-MEF2 pathway, otherwise active in adult hearts and during neoangiogenesis in other adult settings. Our results therefore demonstrate a fundamental divergence between the regulation of coronary vessel growth in healthy and ischemic adult hearts.

Vascular stability and tone are maintained by contractile smooth muscle cells (VSMCs). However, injury-induced growth factors stimulate a contractile-synthetic phenotypic modulation which increases susceptibility to abdominal aortic aneurysm (AAA). As a regulator of embryonic VSMC differentiation, we hypothesised that Thymosin β4 (Tβ4) may function to maintain healthy vasculature throughout postnatal life. This was supported by the identification of an interaction with Low density lipoprotein receptor related protein 1 (LRP1), an endocytic regulator of PDGF-BB signaling and VSMC proliferation. LRP1 variants have been implicated by genome-wide association studies with risk of AAA and other arterial diseases. Tβ4-null mice displayed aortic VSMC and elastin defects, phenocopying LRP1 mutants, and their compromised vascular integrity predisposed to Angiotensin II-induced aneurysm formation. Aneurysmal vessels were characterised by enhanced VSMC phenotypic modulation and augmented platelet-derived growth factor (PDGF) receptor (PDGFR)β signaling. In vitro, enhanced sensitivity to PDGF-BB, upon loss of Tβ4, associated with dysregulated endocytosis, with increased recycling and reduced lysosomal targeting of LRP1-PDGFRβ. Accordingly, the exacerbated aneurysmal phenotype in Tβ4-null mice was rescued upon treatment with the PDGFRβ antagonist, Imatinib. Our study identifies Tβ4 as a key regulator of LRP1 for maintaining vascular health and provides insights into the mechanisms of growth factor-controlled VSMC phenotypic modulation underlying aortic disease progression.