Comparison of Three Antagonists of Hedgehog Pathway to Promote Skeletal Muscle Regeneration after High Dose Irradiation

The current geopolitical context has brought the radiological nuclear risk to the forefront of concerns. High-dose localized radiation exposure leads to the development of a musculocutaneous radiation syndrome affecting the skin and subcutaneous muscles. Despite the implementation of a gold standard treatment based on an invasive surgical procedure coupled with autologous cell therapy, a muscular defect frequently persists. Targeting the modulation of the Hedgehog (Hh) signaling pathway appears to be a promising therapeutic approach. Activation of this pathway enhances cell survival and promotes proliferation after irradiation, while inhibition by Cyclopamine facilitates differentiation. In this study, we compared the effects of three antagonists of Hh, Cyclopamine (CA), Vismodegib (VDG) and Sonidegib (SDG) on differentiation. A stable cell line of murine myoblasts, C2C12, was exposed to X-ray radiation (5 Gy) and treated with CA, VDG or SDG. Analysis of proliferation, survival (apoptosis), morphology, myogenesis genes expression and proteins production were performed. According to the results, VDG does not have a significant impact on C2C12 cells. SDG increases the expression/production of differentiation markers to a similar extent as CA, while morphologically, SDG proves to be more effective than CA. To conclude, SDG can be used in the same way as CA but already has a marketing authorization with an indication against basal cell cancers, facilitating their use in vivo. This proof of concept demonstrates that SDG represents a promising alternative to CA to promotes differentiation of murine myoblasts. Future studies on isolated and cultured satellite cells and in vivo will test this proof of concept.

IGF-1 Therapy Improves Muscle Size and Function in Experimental Peripheral Arterial Disease

Lower-extremity peripheral arterial disease (PAD) has increased in prevalence, yet therapeutic development has remained stagnant. Skeletal muscle health and function has been strongly linked to quality of life and medical outcomes in patients with PAD. Using a rodent model of PAD, this study demonstrates that treatment of the ischemic limb with insulin-like growth factor (IGF)-1 significantly increases muscle size and strength without improving limb hemodynamics. Interestingly, the effect size of IGF1 therapy was larger in female mice than in male mice, highlighting the need to carefully examine sex-dependent effects in experimental PAD therapies.

AAV-mediated expression of PFKFB3 in myofibers, but not endothelial cells, improves ischemic muscle function in mice with critical limb ischemia

6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) is a powerful driver of angiogenesis through its modulation of glycolytic metabolism within endothelial cells. Recent work has demonstrated that PFKFB3 modulates the response to muscle ischemia, however the cell specificity of these effects is not fully understood. In this study, we tested the impact of viral mediated expression of PFKFB3, driven by gene promoters specific for myofibers or endothelial cells, on ischemic hindlimb revascularization and muscle function. We hypothesized that both endothelium- and muscle-specific expression of PFKFB3 would attenuate limb pathology following femoral artery ligation. Male and female BALB/cJ mice were injected with adeno-associated virus encoding the either a green fluorescent protein (GFP) or PFKFB3 driven by either the human skeletal actin (ACTA1) or cadherin-5 (Cdh5) promoters. Four weeks after AAV treatment, mice were subjected to unilateral femoral artery ligation and limb perfusion and muscle function were assessed. Both endothelium- and muscle-specific PFKFB3 expression resulted in significantly more perfused capillaries within the ischemic limb muscle, but neither changed myofiber size/area. Muscle-, but not endothelium-specific, PFKFB3 expression significantly improved maximal force production in ischemic muscle (P=0.0005). Notably, there was a significant effect of sex on maximal force levels in both cohorts of mice (P=0.0075 and P=0.0481), indicating that female mice had higher ischemic muscle strength compared to male mice, regardless of treatment group. Taken together, these data demonstrate that while both muscle- and endothelium-specific expression of PFKFB3 enhanced ischemic revascularization, only muscle-specific PFKFB3 expression improved muscle function.

Pro-angiogenic approach for skeletal muscle regeneration

The angiogenesis process is a phenomenon in which numerous molecules participate in the stimulation of the new vessels' formation from pre-existing vessels. Angiogenesis is a crucial step in tissue regeneration and recovery of organ and tissue function. Muscle diseases affect millions of people worldwide overcome the ability of skeletal muscle to self-repair. Pro-angiogenic therapies are key in skeletal muscle regeneration where both myogenesis and angiogenesis occur. These therapies have been based on mesenchymal stem cells (MSCs), exosomes, microRNAs (miRs) and delivery of biological factors. The use of different calls of biomaterials is another approach, including ceramics, composites, and polymers. Natural polymers are use due its bioactivity and biocompatibility in addition to its use as scaffolds and in drug delivery systems. One of these polymers is the natural rubber latex (NRL) which is biocompatible, bioactive, versatile, low-costing, and capable of promoting tissue regeneration and angiogenesis. In this review, the advances in the field of pro-angiogenic therapies are discussed.

Sonic hedgehog is expressed in human brain arteriovenous malformations and induces arteriovenous malformations in vivo

Abnormalities in arterial versus venous endothelial cell identity and dysregulation of angiogenesis are deemed important in the pathophysiology of brain arteriovenous malformations (AVMs). The Sonic hedgehog (Shh) pathway is crucial for both angiogenesis and arterial versus venous differentiation of endothelial cells, through its dual role on the vascular endothelial growth factor/Notch signaling and the nuclear orphan receptor COUP-TFII. In this study, we show that Shh, Gli1 (the main transcription factor of the Shh pathway), and COUP-TFII (a target of the non-canonical Shh pathway) are aberrantly expressed in human brain AVMs. We also show that implantation of pellets containing Shh in the cornea of Efnb2/LacZ mice induces growth of distinct arteries and veins, interconnected by complex sets of arteriovenous shunts, without an interposed capillary bed, as seen in AVMs. We also demonstrate that injection in the rat brain of a plasmid containing the human Shh gene induces the growth of tangles of tortuous and dilated vessels, in part positive and in part negative for the arterial marker αSMA, with direct connections between αSMA-positive and -negative vessels. In summary, we show that the Shh pathway is active in human brain AVMs and that Shh-induced angiogenesis has characteristics reminiscent of those seen in AVMs in humans.

The Hedgehog Signaling Pathway in Ischemic Tissues

Hedgehog (Hh) proteins are prototypical morphogens known to regulate epithelial/mesenchymal interactions during embryonic development. In addition to its pivotal role in embryogenesis, the Hh signaling pathway may be recapitulated in post-natal life in a number of physiological and pathological conditions, including ischemia. This review highlights the involvement of Hh signaling in ischemic tissue regeneration and angiogenesis, with particular attention to the heart, the brain, and the skeletal muscle. Updated information on the potential role of the Hh pathway as a therapeutic target in the ischemic condition is also presented.

Exercise and Cardiovascular Progenitor Cells

Autologous stem/progenitor cell-based methods to restore blood flow and function to ischemic tissues are clinically appealing for the substantial proportion of the population with cardiovascular diseases. Early preclinical and case studies established the therapeutic potential of autologous cell therapies for neovascularization in ischemic tissues. However, trials over the past ∼15 years reveal the benefits of such therapies to be much smaller than originally estimated and a definitive clinical benefit is yet to be established. Recently, there has been an emphasis on improving the number and function of cells [herein generally referred to as circulating angiogenic cells (CACs)] used for autologous cell therapies. CACs include of several subsets of circulating cells, including endothelial progenitor cells, with proangiogenic potential that is largely exerted through paracrine functions. As exercise is known to improve CV outcomes such as angiogenesis and endothelial function, much attention is being given to exercise to improve the number and function of CACs. Accordingly, there is a growing body of evidence that acute, short-term, and chronic exercise have beneficial effects on the number and function of different subsets of CACs. In particular, recent studies show that aerobic exercise training can increase the number of CACs in circulation and enhance the function of isolated CACs as assessed in ex vivo assays. This review summarizes the roles of different subsets of CACs and the effects of acute and chronic exercise on CAC number and function, with a focus on the number and paracrine function of circulating CD34+ cells, CD31+ cells, and CD62E+ cells. © 2019 American Physiological Society. Compr Physiol 9:767-797, 2019.

Inhibition of microRNA-92a increases blood vessels and satellite cells in skeletal muscle but does not improve duchenne muscular dystrophy-related phenotype in mdx mice

INTRODUCTION

The vasculature and blood flow in muscle are perturbed in Duchenne muscular dystrophy (DMD) and its mdx mouse model. MicroRNA-92a (miR-92a) is enriched in endothelial cells, especially during ischemic injury.

METHODS

Because antagonizing miR-92a was shown to result in increased proliferation and migration of endothelial cells and recovery from ischemia, we assessed the effects of Antagomir-92a in vitro in muscle stem cell culture and in vivo in mdx mice.

RESULTS

miR-92a was found to be highly expressed in muscle endothelial cells and satellite cells. Treatment with Antagomir-92a increased capillary density and tissue perfusion, which was accompanied by an increase in satellite cells. However, Antagomir-92a-treated mdx mice showed no histological improvement and had worse muscle function. Antagomir-92a suppressed myogenic differentiation in satellite cell culture.

DISCUSSION

AntagomiR-92a improves the vasculature but not the muscle in mdx mice, possibly due to its side effects on satellite cell differentiation. Muscle Nerve 59:594-594, 2019.

Sonic Hedgehog Signaling Pathway in Endothelial Progenitor Cell Biology for Vascular Medicine

The Hedgehog (HH) signaling pathway plays an important role in embryonic and postnatal vascular development and in maintaining the homeostasis of organs. Under physiological conditions, Sonic Hedgehog (SHH), a secreted protein belonging to the HH family, regulates endothelial cell growth, promotes cell migration and stimulates the formation of new blood vessels. The present review highlights recent advances made in the field of SHH signaling in endothelial progenitor cells (EPCs). The canonical and non-canonical SHH signaling pathways in EPCs and endothelial cells (ECs) related to homeostasis, SHH signal transmission by extracellular vesicles (EVs) or exosomes containing single-strand non-coding miRNAs and impaired SHH signaling in cardiovascular diseases are discussed. As a promising therapeutic tool, the possibility of using the SHH signaling pathway for the activation of EPCs in patients suffering from cardiovascular diseases is further explored.

Hh signaling in regeneration of the ischemic heart

Myocardial infarction (MI) is caused by the occlusion of a coronary artery due to underlying atherosclerosis complicated by localized thrombosis. The blockage of blood flow leads to cardiomyocyte (CM) death in the infarcted area. Adult mammalian cardiomyocytes have little capacity to proliferate in response to injury; however, some pathways active during embryogenesis and silent during adult life are recruited in response to tissue injury. One such example is hedgehog (Hh) signaling. Hh is involved in the embryonic development of the heart and coronary vascular system. Pathological conditions including ischemia activate Hh signaling in adult tissues. This review highlights the involvement of Hh signaling in ischemic tissue regeneration with a particular emphasis on heart regeneration and discusses its potential role as a therapeutic agent.

Tetramethylpyrazine attenuates sinusoidal angiogenesis via inhibition of hedgehog signaling in liver fibrosis

Accumulating evidence indicates that hedgehog signaling plays a pivotal role in pathological angiogenesis and is involved in wound-healing responses in a number of adult tissues, including the liver. We previously demonstrated that hedgehog signaling promoted proliferation and inhibited apoptosis in hepatic stellate cells. This study was aimed to evaluate the effect of tetramethylpyrazine (TMP) on hedgehog signaling and to further examine the molecular mechanisms of TMP-induced antiangiogenesic effects in liver fibrosis. We found that TMP ameliorated the expression of proangiogenic markers vascular endothelial growth factor A (VEGF-A), vascular endothelial growth factor receptor 2 (VEGF-R2), platelet-derived growth factor BB (PDGF-BB), platelet-derived growth factor-β receptor (PDGF-βR) and hypoxia inducible factor 1α (HIF-1α), concomitant with reduced abundance of endothelial markers platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31), CD34 and von willebrand factor in vivo and in vitro. Interestingly, TMP attenuated the abundance of sonic hedgehog, smoothened (Smo) and glioblastoma but increased the expression of hedgehog-interacting protein in liver sinusoidal endothelial cells, which was underlying mechanism for the antiangiogenesic activity of TMP. Downregulation of Smo activity, using selective Smo inhibitor cyclopamine, lead to a synergistic effect with TMP, whereas Smo overexpression plasmid impaired the induction of antiangiogenesic effects of TMP. Overall, these results provide novel implications to reveal the molecular mechanism of TMP-inhibited liver sinusoidal angiogenesis, by which points to the possibility of using TMP-based antiangiogenic drugs for the treatment of liver fibrosis. © 2017 IUBMB Life, 69(2):115-127, 2017.

Targeting brain microvascular endothelial cells: a therapeutic approach to neuroprotection against stroke

Brain microvascular endothelial cells form the interface between nervous tissue and circulating blood, and regulate central nervous system homeostasis. Brain microvascular endothelial cells differ from peripheral endothelial cells with regards expression of specific ion transporters and receptors, and contain fewer fenestrations and pinocytotic vesicles. Brain microvascular endothelial cells also synthesize several factors that influence blood vessel function. This review describes the morphological characteristics and functions of brain microvascular endothelial cells, and summarizes current knowledge regarding changes in brain microvascular endothelial cells during stroke progression and therapies. Future studies should focus on identifying mechanisms underlying such changes and developing possible neuroprotective therapeutic interventions.

Role of Growth Factors in Modulation of the Microvasculature in Adult Skeletal Muscle

Post-natal skeletal muscle is a highly plastic tissue that has the capacity to regenerate rapidly following injury, and to undergo significant modification in tissue mass (i.e. atrophy/hypertrophy) in response to global metabolic changes. These processes are reliant largely on soluble factors that directly modulate muscle regeneration and mass. However, skeletal muscle function also depends on an adequate blood supply. Thus muscle regeneration and changes in muscle mass, particularly hypertrophy, also demand rapid changes in the microvasculature. Recent evidence clearly demonstrates a critical role for soluble growth factors in the tight regulation of angiogenic expansion of the muscle microvasculature. Furthermore, exogenous modulation of these factors has the capacity to impact directly on angiogenesis and thus, indirectly, on muscle regeneration, growth and performance. This chapter reviews recent developments in understanding the role of growth factors in modulating the skeletal muscle microvasculature, and the potential therapeutic applications of exogenous angiogenic and anti-angiogenic mediators in promoting effective growth and regeneration, and ameliorating certain diseases, of skeletal muscle.

Sonic Hedgehog signaling regulates vascular differentiation and function in human CD34 positive cells: vasculogenic CD34(+) cells with Sonic Hedgehog

Identification of pivotal factors potentially present in the in situ environment and capable of influencing the function of CD34(+) cells, which can be used for autologous cell therapy, is of paramount interest. SHh is one of the morphogens essential for embryonic vascular development as well as postnatal neovascularization, and the activation of SHh signaling with angiogenic and vascular differentiation responses in CD34(+) cells by SHh treatment differed depending on the G-CSF treatment or the background disease. SHh enhanced the migration, proliferation, adhesion, and EPC colony forming capacities of G-CSF mobilized CD34(+) cells, increasing the vasculogenic/angiogenic potential for neovascularization. An increase in the differentiation potential of CD34(+) cells toward vascular lineages was demonstrated with SHh treatment involving TGFβ signaling pathway. The SHh-activated G-CSF mobilized CD34(+) cells directly contributed to vascular regeneration while non-activated CD34(+) cells showed a lower regenerative capacity in a mouse ischemic hindlimb model. SHh signaling regulates human CD34(+) cell fate and function, and may potentiate the therapeutic effect of G-CSF mobilized CD34(+) cells on ischemic diseases.

Salidroside exerts angiogenic and cytoprotective effects on human bone marrow-derived endothelial progenitor cells via Akt/mTOR/p70S6K and MAPK signalling pathways

BACKGROUND AND PURPOSE

With the increase of age, increased susceptibility to apoptosis and senescence may contribute to proliferative and functional impairment of endothelial progenitor cells (EPCs). The aim of this study was to investigate whether salidroside (SAL) can induce angiogenic differentiation and inhibit oxidative stress-induced apoptosis in bone marrow-derived EPCs (BM-EPCs), and if so, through what mechanism.

EXPERIMENTAL APPROACH

BM-EPCs were isolated and treated with different concentrations of SAL for up to 4 days. Cell proliferation, migration and tube formation ability were detected by DNA content quantification, transwell assay and Matrigel-based angiogenesis assay. Gene and protein expression were assessed by qRT-PCR and Western blot respectively.

KEY RESULTS

Treatment with SAL promoted cellular proliferation and angiogenic differentiation of BM-EPCs, and increased VEGF and NO secretion, which in turn mediated the enhanced angiogenic differentiation of BM-EPCs. Furthermore, SAL significantly attenuated hydrogen peroxide (H₂O₂)-induced cell apoptosis, reduced the intracellular level of reactive oxygen species and restored the mitochondrial membrane potential of BM-EPCs. Moreover, SAL stimulated the phosphorylation of Akt, mammalian target of rapamycin and p70 S6 kinase, as well as ERK1/2, which is associated with cell migration and capillary tube formation. Additionally, SAL reversed the phosphorylation of JNK and p38 MAPK induced by H₂O₂ and suppressed the changes in the Bax/Bcl-xL ratio observed after stimulation with H₂O₂.

CONCLUSIONS AND IMPLICATIONS

These findings identify novel mechanisms that regulate EPC function and suggest that SAL has therapeutic potential as a new agent to enhance vasculogenesis as well as protect against oxidative endothelial injury.

The effect of CXCL12 on endothelial progenitor cells: potential target for angiogenesis in intracerebral hemorrhage

Endothelial progenitor cells (EPCs) may contribute to vascular repair and angiogenesis. Chemokine (C-X-C motif) ligand 12 (CXCL12/SDF-1) is known to play an important role in the mobilization and recruitment of progenitor cells. Therefore, we assessed the function of CXCL12 as a stimulating molecule of angiogenesis in EPCs and the underlying mechanism after intracerebral hemorrhage (ICH). Isolated EPCs from male Sprague-Dawley rats, stimulate with various doses of CXCL12. Then, 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay was used to assess the proliferation of EPCs, and cell migration and adhesion were analyzed by transwell chamber assay. Furthermore, mRNA levels of endothelial markers von Willebrand Factor (vWF), Tie-2, and vascular endothelial cadherin (VE-cadherin) were explored by real-time polymerase chain reaction. Capillary tube and vessel formation in vitro and in vivo were detected after pretreatment with the C-X-C chemokine receptor type 4 (CXCR4) inhibitor AMD3100. Following stimulation with various doses of CXCL12, an obvious dose-dependent increase in the proliferation, migration, and adhesion of EPCs was confirmed. Furthermore, the mRNA levels of endothelial markers vWF, Tie-2, and VE-cadherin were also demonstrated in CXCL12-treated EPCs, indicating that CXCL12 could regulate EPC differentiation to endothelial cells. Importantly, these increases depended on the activation of CXCR4 signaling, as pretreatment with CXCR4 inhibitor AMD3100 dramatically dampened the CXCL12-induced effects. Additionally, blocking CXCR4 signaling dampened CXCL12-induced angiogenic activity both in vitro and in vivo. Following construction of a rodent ICH model, scaffolds delivering CXCL12 together with EPCs resulted in an evident increase in blood vessel formation; however, this increase in blood vessels was attenuated with delivery of AMD3100. CXCL12 stimulates EPCs to induce angiogenesis though the CXCR4 pathway after ICH. Consequently, our findings provide a potential target for angiogenesis in ICH.

Smooth muscle progenitor cells from peripheral blood promote the neovascularization of endothelial colony-forming cells

Proangiogenic cell therapy using autologous progenitors is a promising strategy for treating ischemic disease. Considering that neovascularization is a harmonized cellular process that involves both endothelial cells and vascular smooth muscle cells, peripheral blood-originating endothelial colony-forming cells (ECFCs) and smooth muscle progenitor cells (SMPCs), which are similar to mature endothelial cells and vascular smooth muscle cells, could be attractive cellular candidates to achieve therapeutic neovascularization. We successfully induced populations of two different vascular progenitor cells (ECFCs and SMPCs) from adult peripheral blood. Both progenitor cell types expressed endothelial-specific or smooth muscle-specific genes and markers, respectively. In a protein array focused on angiogenic cytokines, SMPCs demonstrated significantly higher expression of bFGF, EGF, TIMP2, ENA78, and TIMP1 compared to ECFCs. Conditioned medium from SMPCs and co-culture with SMPCs revealed that SMPCs promoted cell proliferation, migration, and the in vitro angiogenesis of ECFCs. Finally, co-transplantation of ECFCs and SMPCs induced robust in vivo neovascularization, as well as improved blood perfusion and tissue repair, in a mouse ischemic hindlimb model. Taken together, we have provided the first evidence of a cell therapy strategy for therapeutic neovascularization using two different types of autologous progenitors (ECFCs and SMPCs) derived from adult peripheral blood.

Sonic hedgehog gene therapy increases the ability of the dystrophic skeletal muscle to regenerate after injury

The Hedgehog (Hh) pathway is a crucial regulator of muscle development during embryogenesis. We have previously demonstrated that Sonic hedgehog (Shh) regulates postnatal myogenesis in the adult skeletal muscle both directly, by acting on muscle satellite cells, and indirectly, by promoting the production of growth factors from interstitial fibroblasts. Here, we show that in mdx mice, the murine equivalent of Duchenne muscular dystrophy in humans, progression of the dystrophic pathology corresponds to progressive inhibition of the Hh signaling pathway in the skeletal muscle. We also show that the upregulation of the Hh pathway in response to injury and during regeneration is significantly impaired in mdx muscle. Shh treatment increases the proliferative potential of satellite cells isolated from the muscles of mdx mice. This treatment also increases the production of proregenerative factors, such as insulin-like growth factor-1 and vascular endothelial growth factor, from fibroblasts isolated from the muscle of mdx mice. In vivo, overexpression of the Hh pathway using a plasmid encoding the human Shh gene promotes successful regeneration after injury in terms of increased number of proliferating myogenic cells and newly formed myofibers, as well as enhanced vascularization and decreased fibrosis.

Angiogenesis as a novel therapeutic strategy for Duchenne muscular dystrophy through decreased ischemia and increased satellite cells

Duchenne muscular dystrophy (DMD) is the most common hereditary muscular dystrophy caused by mutation in dystrophin, and there is no curative therapy. Dystrophin is a protein which forms the dystrophin-associated glycoprotein complex (DGC) at the sarcolemma linking the muscle cytoskeleton to the extracellular matrix. When dystrophin is absent, muscle fibers become vulnerable to mechanical stretch. In addition to this, accumulating evidence indicates DMD muscle having vascular abnormalities and that the muscles are under an ischemic condition. More recent studies demonstrate decreased vascular densities and impaired angiogenesis in the muscles of murine model of DMD. Therefore, generation of new vasculature can be considered a potentially effective strategy for DMD therapy. The pro-angiogenic approaches also seem to be pro-myogenic and could induce muscle regeneration capacity through expansion of the satellite cell juxtavascular niche in the mouse model. Here, we will focus on angiogenesis, reviewing the background, vascular endothelial growth factor (VEGF)/VEGF receptor-pathway, effect, and concerns of this strategy in DMD.

Accelerated functional recovery after skeletal muscle ischemia-reperfusion injury using freshly isolated bone marrow cells

BACKGROUND

Relatively little information exists regarding the usefulness of bone marrow-derived cells for skeletal muscle ischemia-reperfusion injury (I/R), especially when compared with I/R that occurs in other tissues. The objectives of this study were to evaluate the ability of freshly isolated bone marrow cells to home to injured skeletal muscle and to determine their effects on muscle regeneration.

MATERIALS AND METHODS

Freshly isolated lineage-depleted bone marrow cells (Lin(-) BMCs) were injected intravenously 2 d after I/R. Bioluminescent imaging was used to evaluate cell localization for up to 28 d after injury. Muscle function, the percentage of fibers with centrally located nuclei, and the capillary-to-fiber ratio were evaluated 14 d after delivery of either saline (Saline) or saline containing Lin(-) BMCs (Lin(-) BMCs).

RESULTS

Bioluminescence was higher in the injured leg than the contralateral control leg for up to 7 d after injection (P < 0.05) suggestive of cell homing to the injured skeletal muscle. Fourteen days after injury, there was a significant improvement in maximal tetanic torque (40% versus 22% deficit; P < 0.05), a faster rate of force production (+dP/dt) (123.6 versus 94.5 Nmm/S; P < 0.05), and a reduction in the percentage of fibers containing centrally located nuclei (40 versus 17%; P < 0.05), but no change in the capillary-to-fiber ratio in the Lin(-) BMC as compared with the Saline group.

CONCLUSIONS

The homing of freshly isolated BMCs to injured skeletal muscle after I/R is associated with an increase in functional outcomes.

Gli3 regulation of myogenesis is necessary for ischemia-induced angiogenesis

RATIONALE

A better understanding of the mechanism underlying skeletal muscle repair is required to develop therapies that promote tissue regeneration in adults. Hedgehog signaling has been shown previously to be involved in myogenesis and angiogenesis: 2 crucial processes for muscle development and regeneration.

OBJECTIVE

The objective of this study was to identify the role of the hedgehog transcription factor Gli3 in the cross-talk between angiogenesis and myogenesis in adults.

METHODS AND RESULTS

Using conditional knockout mice, we found that Gli3 deficiency in endothelial cells did not affect ischemic muscle repair, whereas in myocytes, Gli3 deficiency resulted in severely delayed ischemia-induced myogenesis. Moreover, angiogenesis was also significantly impaired in HSA-Cre(ERT2); Gli3(Flox/Flox) mice, demonstrating that impaired myogenesis indirectly affects ischemia-induced angiogenesis. The role of Gli3 in myocytes was then further investigated. We found that Gli3 promotes myoblast differentiation through myogenic factor 5 regulation. In addition, we found that Gli3 regulates several proangiogenic factors, including thymidine phosphorylase and angiopoietin-1 both in vitro and in vivo, which indirectly promote endothelial cell proliferation and arteriole formation. In addition, we found that Gli3 is upregulated in proliferating myoblasts by the cell cycle-associated transcription factor E2F1.

CONCLUSIONS

This study shows for the first time that Gli3-regulated postnatal myogenesis is necessary for muscle repair-associated angiogenesis. Most importantly, it implies that myogenesis drives angiogenesis in the setting of skeletal muscle repair and identifies Gli3 as a potential target for regenerative medicine.

Co-transplantation of bone marrow-derived endothelial progenitor cells improves revascularization and organization in islet grafts

Bone marrow-derived early endothelial progenitor cells (BM-EPCs) are a clinical tool for enhancing revascularization. However, the therapeutic efficacy of co-transplantation of BM-EPC with islets has not been investigated. In this study, marginal mass islets were co-transplanted with or without BM-EPCs under the kidney capsules of syngeneic streptozotocin-induced diabetic mice. Using green fluorescent protein transgenic (GFP-Tg) mice as BM-EPC and islet donors or recipients, the role of EPCs in revascularization was assessed for graft morphology, vascular density and fate of EPCs by immunohistochemistry. Islet-EPC co-transplantation improved the outcome of islet transplantation as measured by glucose tolerance, serum insulin level and diabetes reversal rate, compared with transplantation of islets alone. Between groups, the morphology of islet grafts showed significant differences in size and composition of grafted endocrine tissues. Significantly more vessel density derived from donors and recipients was detected with islet-EPC co-transplantation. Abundant GFP-Tg mice-derived BM-EPCs (GFP-EPCs) were observed in or around islet grafts and incorporated into CD31-positive capillaries. Remaining GFP-EPCs expressed VEGF. In conclusion, co-transplantation of islets with BM-EPCs could improve the outcome of marginal mass islet transplantation by promoting revascularization and preserving islet morphology.