Platelet Recruitment Promotes Keratocyte Repopulation following Corneal Epithelial Abrasion in the Mouse

Corneal abrasion not only damages the epithelium but also induces stromal keratocyte death at the site of injury. While a coordinated cascade of inflammatory cell recruitment facilitates epithelial restoration, it is unclear if this cascade is necessary for keratocyte recovery. Since platelet and neutrophil (PMN) recruitment after corneal abrasion is beneficial to epithelial wound healing, we wanted to determine if these cells play a role in regulating keratocyte repopulation after epithelial abrasion. A 2 mm diameter central epithelial region was removed from the corneas of C57BL/6 wildtype (WT), P-selectin deficient (P-sel^-/-), and CD18 hypomorphic (CD18^hypo) mice using the Algerbrush II. Corneas were studied at 6h intervals out to 48h post-injury to evaluate platelet and PMN cell numbers; additional corneas were studied at 1, 4, 14, and 28 days post injury to evaluate keratocyte numbers. In WT mice, epithelial abrasion induced a loss of anterior central keratocytes and keratocyte recovery was rapid and incomplete, reaching ~70% of uninjured baseline values by 4 days post-injury but no further improvement at 28 days post-injury. Consistent with a beneficial role for platelets and PMNs in wound healing, keratocyte recovery was significantly depressed at 4 days post-injury (~30% of uninjured baseline) in P-sel^-/- mice, which are known to have impaired platelet and PMN recruitment after corneal abrasion. Passive transfer of platelets from WT, but not P-sel^-/-, into P-sel^-/- mice prior to injury restored anterior central keratocyte numbers at 4 days post-injury to P-sel^-/- uninjured baseline levels. While PMN infiltration in injured CD18^hypo mice was similar to injured WT mice, platelet recruitment was markedly decreased and anterior central keratocyte recovery was significantly reduced (~50% of baseline) at 4–28 days post-injury. Collectively, the data suggest platelets and platelet P-selectin are critical for efficient keratocyte recovery after corneal epithelial abrasion.     

FOXP3+ T Cells Recruited to Sites of Sterile Skeletal Muscle Injury Regulate the Fate of Satellite Cells and Guide Effective Tissue Regeneration

Muscle injury induces a classical inflammatory response in which cells of the innate immune system rapidly invade the tissue. Macrophages are prominently involved in this response and required for proper healing, as they are known to be important for clearing cellular debris and supporting satellite cell differentiation. Here, we sought to assess the role of the adaptive immune system in muscle regeneration after acute damage. We show that T lymphocytes are transiently recruited into the muscle after damage and appear to exert a pro-myogenic effect on muscle repair. We observed a decrease in the cross-sectional area of regenerating myofibers after injury in Rag2^-/- γ-chain^-/- mice, as compared to WT controls, suggesting that T cell recruitment promotes muscle regeneration. Skeletal muscle infiltrating T lymphocytes were enriched in CD4⁺CD25⁺FOXP3⁺ cells. Direct exposure of muscle satellite cells to in vitro induced Treg cells effectively enhanced their expansion, and concurrently inhibited their myogenic differentiation. In vivo, the recruitment of Tregs to acutely injured muscle was limited to the time period of satellite expansion, with possibly important implications for situations in which inflammatory conditions persist, such as muscular dystrophies and inflammatory myopathies. We conclude that the adaptive immune system, in particular T regulatory cells, is critically involved in effective skeletal muscle regeneration. Thus, in addition to their well-established role as regulators of the immune/inflammatory response, T regulatory cells also regulate the activity of skeletal muscle precursor cells, and are instrumental for the proper regeneration of this tissue.     

Leukemia inhibitory factor restores the hypertrophic response to increased loading in the LIF(-/-) mouse

Cytokines and growth factors are thought to contribute to skeletal muscle hypertrophy. Leukemia inhibitory factor (LIF), a cytokine, enhances skeletal muscle regeneration; however the role of LIF in skeletal muscle hypertrophy remains uncertain. We examined the hypertrophic ability of the plantaris and soleus muscles in wild-type mice (WT) and LIF knock-out mice [LIF(-/-)] in response to increased mechanical load. Using the functional overload model to induce increases in mechanical load on the plantaris and soleus muscle, WT mice demonstrated increases in plantaris and soleus mass after 7, 21, and 42 days of loading. However, the LIF(-/-) mice had no significant increases in plantaris muscle mass at any time point, while the soleus muscle exhibited a delayed hypertrophic response. Systemic delivery of LIF to the LIF(-/-) mice returned the hypertrophic response to the same levels as the WT mice after 21 days of functional overload. These data demonstrate for the first time that LIF expression in loaded skeletal muscle is critical for the development of skeletal muscle hypertrophy in the functional overload model.     

Mest but Not MiR-335 Affects Skeletal Muscle Growth and Regeneration

When skeletal muscle fibers are injured, they regenerate and grow until their sizes are adjusted to surrounding muscle fibers and other relevant organs. In this study, we examined whether Mest, one of paternally expressed imprinted genes that regulates body size during development, and miR-335 located in the second intron of the Mest gene play roles in muscle regeneration. We generated miR-335-deficient mice, and found that miR-335 is a paternally expressed imprinted microRNA. Although both Mest and miR-335 are highly expressed during muscle development and regeneration, only Mest^+/- (maternal/paternal) mice show retardation of body growth. In addition to reduced body weight in Mest^+/-; DMD-null mice, decreased muscle growth was observed in Mest^+/- mice during cardiotoxin-induced regeneration, suggesting roles of Mest in muscle regeneration. Moreover, expressions of H19 and Igf2r, maternally expressed imprinted genes were affected in tibialis anterior muscle of Mest^+/-; DMD-null mice compared to DMD-null mice. Thus, Mest likely mediates muscle regeneration through regulation of imprinted gene networks in skeletal muscle.     

TDAG51 Is Not Essential for Fas/CD95 Regulation and Apoptosis In Vivo

Fas/CD95 is a key regulator of apoptotic signaling, which is crucial for the maintenance of homeostasis in peripheral lymphoid organs. TDAG51 has been shown to play critical roles in the up-regulation of Fas gene expression and T-cell apoptosis in vitro. In order to identify the role of TDAG51 in vivo, we generated TDAG51-deficient (TDAG51-/-) mice. Northern blotting revealed no expression of TDAG51 in TDAG51-/- mice, indicating that the TDAG51 gene was successfully targeted. TDAG51-/- mice were healthy and showed no gross developmental abnormalities. While Fas-deficient mice display marked lymphadenopathy, splenomegaly, and lymphocytosis, TDAG51-/- mice had no apparent defects in secondary lymphoid organs. Although TDAG51 is required for up-regulation of Fas expression in T-cell hybridomas, TDAG51-/- mice expressed normal levels of Fas and had normal T-cell apoptosis. Therefore, we conclude that TDAG51 is not essential for Fas up-regulation and T-cell apoptosis in vivo. There are several known homologs of TDAG51, and these homologs may substitute for TDAG51 in TDAG51-/- mice.     

Urokinase-type plasminogen activator plays essential roles in macrophage chemotaxis and skeletal muscle regeneration

Although macrophages are thought to play important roles in tissue repair, the molecular mechanisms involved remain to be elucidated. Mice deficient in urokinase-type plasminogen activator (uPA-/-) exhibit decreased accumulation of macrophages following muscle injury and severely impaired muscle regeneration. We tested whether macrophage-derived uPA plays essential roles in macrophage chemotaxis and skeletal muscle regeneration. Macrophage uPA was required for chemotaxis, even when invasion through matrix was not necessary. The mechanism by which macrophage uPA promoted chemotaxis was independent of receptor binding but appeared to depend on proteolytic activity. Exogenous uPA restored chemotaxis to uPA-/- macrophages and rescued muscle regeneration in uPA-/- mice. Macrophage depletion in wild-type (WT) mice using clodronate liposomes resulted in impaired muscle regeneration, confirming that macrophages are required for efficient healing. Furthermore, transfer of WT bone marrow cells to uPA-/- mice restored macrophage accumulation and muscle regeneration. In this rescue, transferred WT cells appeared to contribute to IGF-1 expression but did not fuse to regenerating fibers. These data indicate that WT leukocytes, including macrophages, that express uPA were sufficient to rescue muscle regeneration in uPA-/- mice. Overall, the results indicate that uPA plays a fundamental role in macrophage chemotaxis and that macrophage-derived uPA promotes efficient muscle regeneration.     

Receptor-Interacting Protein Kinase 3 Deficiency Delays Cutaneous Wound Healing

Wound healing consists of a complex, dynamic and overlapping process involving inflammation, proliferation and tissue remodeling. A better understanding of wound healing process at the molecular level is needed for the development of novel therapeutic strategies. Receptor-interacting protein kinase 3 (RIPK3) controls programmed necrosis in response to TNF-α during inflammation and has been shown to be highly induced during cutaneous wound repair. However, its role in wound healing remains to be demonstrated. To study this, we created dorsal cutaneous wounds on male wild-type (WT) and RIPK3-deficient (Ripk3 ^-/-) mice. Wound area was measured daily until day 14 post-wound and skin tissues were collected from wound sites at various days for analysis. The wound healing rate in Ripk3 ^-/- mice was slower than the WT mice over the 14-day course; especially, at day 7, the wound size in Ripk3 ^-/- mice was 53% larger than that of WT mice. H&E and Masson-Trichrome staining analysis showed impaired quality of wound closure in Ripk3 ^-/- wounds with delayed re-epithelialization and angiogenesis and defected granulation tissue formation and collagen deposition compared to WT. The neutrophil infiltration pattern was altered in Ripk3 ^-/- wounds with less neutrophils at day 1 and more neutrophils at day 3. This altered pattern was also reflected in the differential expression of IL-6, KC, IL-1β and TNF-α between WT and Ripk3 ^-/- wounds. MMP-9 protein expression was decreased with increased Timp-1 mRNA in the Ripk3 ^-/- wounds compared to WT. The microvascular density along with the intensity and timing of induction of proangiogenic growth factors VEGF and TGF-β1 were also decreased or delayed in the Ripk3 ^-/- wounds. Furthermore, mouse embryonic fibroblasts (MEFs) from Ripk3 ^-/- mice migrated less towards chemoattractants TGF-β1 and PDGF than MEFs from WT mice. These results clearly demonstrate that RIPK3 is an essential molecule to maintain the temporal manner of the normal progression of wound closure.     

VEGFR1-Positive Macrophages Facilitate Liver Repair and Sinusoidal Reconstruction after Hepatic Ischemia/Reperfusion Injury

Liver repair after acute liver injury is characterized by hepatocyte proliferation, removal of necrotic tissue, and restoration of hepatocellular and hepatic microvascular architecture. Macrophage recruitment is essential for liver tissue repair and recovery from injury; however, the underlying mechanisms are unclear. Signaling through vascular endothelial growth factor receptor 1 (VEGFR1) is suggested to play a role in macrophage migration and angiogenesis. The aim of the present study was to examine the role of VEGFR1 in liver repair and sinusoidal reconstruction after hepatic ischemia/reperfusion (I/R). VEGFR1 tyrosine kinase knockout mice (VEGFR1 TK^-/- mice) and wild-type (WT) mice were subjected to hepatic warm I/R, and the processes of liver repair and sinusoidal reconstruction were examined. Compared with WT mice, VEGFR1 TK^-/- mice exhibited delayed liver repair after hepatic I/R. VEGFR1-expressing macrophages recruited to the injured liver showed reduced expression of epidermal growth factor (EGF). VEGFR1 TK^-/- mice also showed evidence of sustained sinusoidal functional and structural damage, and reduced expression of pro-angiogenic factors. Treatment of VEGFR1 TK^-/- mice with EGF attenuated hepatoceullar and sinusoidal injury during hepatic I/R. VEGFR1 TK^-/- bone marrow (BM) chimeric mice showed impaired liver repair and sinusoidal reconstruction, and reduced recruitment of VEGFR1-expressing macrophages to the injured liver. VEGFR1-macrophages recruited to the liver during hepatic I/R contribute to liver repair and sinusoidal reconstruction. VEGFR1 activation is a potential therapeutic strategy for promoting liver repair and sinusoidal restoration after acute liver injury.     

Eccentric exercise facilitates mesenchymal stem cell appearance in skeletal muscle

Eccentric, or lengthening, contractions result in injury and subsequently stimulate the activation and proliferation of satellite stem cells which are important for skeletal muscle regeneration. The discovery of alternative myogenic progenitors in skeletal muscle raises the question as to whether stem cells other than satellite cells accumulate in muscle in response to exercise and contribute to post-exercise repair and/or growth. In this study, stem cell antigen-1 (Sca-1) positive, non-hematopoetic (CD45^-) cells were evaluated in wild type (WT) and α7 integrin transgenic (α7Tg) mouse muscle, which is resistant to injury yet liable to strain, 24 hr following a single bout of eccentric exercise. Sca-1⁺CD45⁻ stem cells were increased 2-fold in WT muscle post-exercise. The α7 integrin regulated the presence of Sca-1⁺ cells, with expansion occurring in α7Tg muscle and minimal cells present in muscle lacking the α7 integrin. Sca-1⁺CD45⁻ cells isolated from α7Tg muscle following exercise were characterized as mesenchymal-like stem cells (mMSCs), predominantly pericytes. In vitro multiaxial strain upregulated mMSC stem cells markers in the presence of laminin, but not gelatin, identifying a potential mechanistic basis for the accumulation of these cells in muscle following exercise. Transplantation of DiI-labeled mMSCs into WT muscle increased Pax7⁺ cells and facilitated formation of eMHC⁺DiI⁻ fibers. This study provides the first demonstration that mMSCs rapidly appear in skeletal muscle in an α7 integrin dependent manner post-exercise, revealing an early event that may be necessary for effective repair and/or growth following exercise. The results from this study also support a role for the α7 integrin and/or mMSCs in molecular- and cellular-based therapeutic strategies that can effectively combat disuse muscle atrophy.     

Troponin T3 expression in skeletal and smooth muscle is required for growth and postnatal survival: Characterization of Tnnt3tm2a(KOMP)Wtsi mice

The troponin complex, which consists of three regulatory proteins (troponin C, troponin I, and troponin T), is known to regulate muscle contraction in skeletal and cardiac muscle, but its role in smooth muscle remains controversial. Troponin T3 (TnnT3) is a fast skeletal muscle troponin believed to be expressed only in skeletal muscle cells. To determine the in vivo function and tissue‐specific expression of Tnnt3, we obtained the heterozygous Tnnt3+/flox/lacZ mice from Knockout Mouse Project (KOMP) Repository. Tnnt3^lacZ/+ mice are smaller than their WT littermates throughout development but do not display any gross phenotypes. Tnnt3^lacZ/lacZ embryos are smaller than heterozygotes and die shortly after birth. Histology revealed hemorrhagic tissue in Tnnt3^lacZ/lacZ liver and kidney, which was not present in Tnnt3^lacZ/+ or WT, but no other gross tissue abnormalities. X‐gal staining for Tnnt3 promoter‐driven lacZ transgene expression revealed positive staining in skeletal muscle and diaphragm and smooth muscle cells located in the aorta, bladder, and bronchus. Collectively, these findings suggest that troponins are expressed in smooth muscle and are required for normal growth and breathing for postnatal survival. Moreover, future studies with this mouse model can explore TnnT3 function in adult muscle function using the conditional‐inducible gene deletion approach genesis 51:667–675. © 2013 Wiley Periodicals, Inc.     

Irgm 1参与动脉粥样硬化斑块的形成

目的:探讨免疫相关GTP酶1(Irgm 1)对小鼠血管动脉粥样硬化(AS)斑块形成的影响。方法:高脂饲料喂养野生型(WT)、ApoE~(-/-)Irgm 1~(+/+)和ApoE~(-/-)Irgm1~(+/-)小鼠3个月,建立AS模型;取小鼠主动脉弓,免疫荧光染色方法观察WT和ApoE~(-/-)Irgm 1~(+/+)小鼠血管AS斑块中Irgm 1的表达情况及部位;Western blot方法检测WT和ApoE~(-/-)Irgm 1~(+/+)小鼠血管AS斑块中Irgm 1蛋白表达情况;Q-PCR方法检测WT和ApoE~(-/-)Irgm 1~(+/+)小鼠血管AS斑块中Irgm 1 m RNA表达情况;油红O染色观察ApoE~(-/-)Irgm1~(+/+)和ApoE~(-/-)Irgm1~(+/-)小鼠血管AS斑块形成情况;结果:与WT组相比,ApoE~(-/-)Irgm 1~(+/+)组小鼠主动脉弓AS斑块中Irgm 1+细胞明显增多,Irgm 1+细胞主要位于血管AS斑块的表面;与WT组相比,ApoE~(-/-)Irgm 1~(+/+)组小鼠血管AS斑块中Irgm 1蛋白表达显著增多(P0.001),Irgm 1 m RNA表达显著增多(P0.01);与ApoE~(-/-)Irgm1~(+/-)组相比,ApoE~(-/-)Irgm1~(+/+)组小鼠主动脉弓AS斑块面积显著增大(P0.01);结论:Irgm 1能够促进血管AS斑块的形成。     

Calcineurin-A alpha activation enhances the structure and function of regenerating muscles after myotoxic injury

Calcineurin signaling is essential for successful muscle regeneration. Although calcineurin inhibition compromises muscle repair, it is not known whether calcineurin activation can enhance muscle repair after injury. Tibialis anterior (TA) muscles from adult wild-type (WT) and transgenic mice overexpressing the constitutively active calcineurin-A alpha transgene under the control of the mitochondrial creatine kinase promoter (MCK-CnA alpha*) were injected with the myotoxic snake venom Notexin to destroy all muscle fibers. The TA muscle of the contralateral limb served as the uninjured control. Muscle structure was assessed at 5 and 9 days postinjury, and muscle function was tested in situ at 9 days postinjury. Calcineurin stimulation enhanced muscle regeneration and altered levels of myoregulatory factors (MRFs). Recovery of myofiber size and force-producing capacity was hastened in injured muscles of MCK-CnA alpha* mice compared with control. Myogenin levels were greater 5 days postinjury and myocyte enhancer factor 2a (MEF2a) expression was greater 9 days postinjury in muscles of MCK-CnA alpha* mice compared with WT mice. Higher MEF2a expression in regenerating muscles of MCK-CnA alpha* mice 9 days postinjury may be related to an increase of slow fiber genes. Calcineurin activation in uninjured and injured TA muscles slowed muscle contractile properties, reduced fatigability, and enhanced force recovery after 4 min of intermittent maximal stimulation. Therefore, calcineurin activation can confer structural and functional benefits to regenerating skeletal muscles, which may be mediated in part by differential expression of MRFs.     

Enhanced Activation of Canonical Wnt Signaling Confers Mesoderm-Derived Parietal Bone with Similar Osteogenic and Skeletal Healing Capacity to Neural Crest-Derived Frontal Bone

Bone formation and skeletal repair are dynamic processes involving a fine-tuned balance between osteoblast proliferation and differentiation orchestrated by multiple signaling pathways. Canonical Wnt (cWnt) signaling is known to playing a key role in these processes. In the current study, using a transgenic mouse model with targeted disruption of axin2, a negative regulator of cWnt signaling, we investigated the impact of enhanced activation of cWnt signaling on the osteogenic capacity and skeletal repair. Specifically, we looked at two calvarial bones of different embryonic tissue origin: the neural crest-derived frontal bone and the mesoderm-derived parietal bone, and we investigated the proliferation and apoptotic activity of frontal and parietal bones and derived osteoblasts. We found dramatic differences in cell proliferation and apoptotic activity between Axin2 ^-/- and wild type calvarial bones, with Axin2 ^-/- showing increased proliferative activity and reduced levels of apoptosis. Furthermore, we compared osteoblast differentiation and bone regeneration in Axin2 ^-/- and wild type neural crest-derived frontal and mesoderm-derived parietal bones, respectively. Our results demonstrate a significant increase either in osteoblast differentiation or bone regeneration in Axin2 ^-/- mice as compared to wild type, with Axin2 ^-/- parietal bone and derived osteoblasts displaying a “neural crest-derived frontal bone-like” profile, which is typically characterized by higher osteogenic capacity and skeletal repair than parietal bone. Taken together, our results strongly suggest that enhanced activation of cWnt signaling increases the skeletal potential of a calvarial bone of mesoderm origin, such as the parietial bone to a degree similar to that of a neural crest origin bone, like the frontal bone. Thus, providing further evidence for the central role played by the cWnt signaling in osteogenesis and skeletal-bone regeneration.     

Adaptive changes in structure of skeletal muscles from adult <Emphasis Type="Italic">Sod1</Emphasis> homozygous knockout mice

Cu/Zn superoxide dismutase (SOD1), which is localized cytoplasmically and in the mitochondrial intermembrane space, is an enzyme that is critically important for superoxide free-radical elimination. Compared with age-matched wild-type littermates (Sod1 ^+/+ ), SOD1 homozygous knockout (Sod1 ^-/- ) mice have smaller body masses, heart and skeletal muscle masses, and muscle cross-sectional areas. At the light-microscopic level, cross sections of skeletal muscles from Sod1 ^-/- mice show no gross structural abnormalities. Following the staining of muscles of Sod1 ^-/- mice for succinate dehydrogenase (SDH) enzymatic activity, a grouping of SDH-positive fibers has been observed. Immunostaining for neural cell adhesion marker in the gastrocnemius muscle of Sod1 ^-/- mice has revealed a small number of atrophic denervated muscle fibers. No denervated fibers are observed in extensor digitorum longus (EDL), tibialis anterior, or plantaris muscles. An increase in mRNA expression levels of myogenin and acetylcholine receptor alpha has been detected in muscles in Sod1 ^-/- mice, but no changes in MyoD expression occur. Compared with fast oxidative fibers in EDL muscles of Sod1 ^+/+ mice, those of Sod1 ^-/- mice show increased accumulations of sub-sarcolemmal mitochondria. We conclude that the lack of SOD1 in adult Sod1 ^-/- mice does not result in extensive denervation of skeletal muscle fibers, although the distribution of fiber types is modified, and that fast oxidative fibers develop alterations in the amount and spatial distribution of sub-sarcolemmal mitochondria. This study was supported by NIA grant PO1-AG20591, by the Nathan Shock Center Contractility Core (NIA grant P30-AG13283), and by a Nathan Shock Center Pilot Award (to T. Kostrominova).     

Urinary Retention,Incontinence, and Dysregulation of Muscarinic Receptors in Male Mice Lacking Mras

Here we show that male, but not female mice lacking expression of the GTPase M-Ras developed urinary retention with distention of the bladder that exacerbated with age but occurred in the absence of obvious anatomical outlet obstruction. There were changes in detrusor morphology in Mras ^-/- males: Smooth muscle tissue, which exhibited a compact organization in WT mice, appeared disorganized and became increasingly ‘layered’ with age in Mras ^-/- males, but was not fibrotic. Bladder tissue near the apex of bladders of Mras ^-/- males exhibited hypercontractility in response to the cholinergic agonist carbachol in in vitro, while responses in Mras ^-/- females were normal. In addition, spontaneous phasic contractions of detrusors from Mras ^-/- males were increased, and Mras ^-/- males exhibited urinary incontinence. We found that expression of the muscarinic M2 and M3 receptors that mediate the cholinergic contractile stimuli of the detrusor muscle was dysregulated in both Mras ^-/- males and females, although only males exhibited a urinary phenotype. Elevated expression of M2R in young males lacking M-Ras and failure to upregulate M3R with age resulted in significantly lower ratios of M3R/M2R expression that correlated with the bladder abnormalities. Our data suggests that M-Ras and M3R are functionally linked and that M-Ras is an important regulator of male bladder control in mice. Our observations also support the notion that bladder control is sexually dimorphic and is regulated through mechanisms that are largely independent of acetylcholine signaling in female mice.     

Application of VEGFA and FGF-9 Enhances Angiogenesis,Osteogenesis and Bone Remodeling in Type 2 Diabetic Long Bone Regeneration

Although bone regeneration is typically a reliable process, type 2 diabetes is associated with impaired or delayed healing processes. In addition, angiogenesis, a crucial step in bone regeneration, is often altered in the diabetic state. In this study, different stages of bone regeneration were characterized in an unicortical bone defect model comparing transgenic type 2 diabetic (db^-/db^-) and wild type (WT) mice in vivo. We investigated angiogenesis, callus formation and bone remodeling at early, intermediate and late time points by means of histomorphometry as well as protein level analyses. In order to enhance bone regeneration, defects were locally treated with recombinant FGF-9 or VEGFA. Histomorphometry of aniline blue stained sections indicated that bone regeneration is significantly decreased in db^-/db^- as opposed to WT mice at intermediate (5 days post operation) and late stages (7 days post operation) of bone regeneration. Moreover, immunohistochemical analysis revealed significantly decreased levels of RUNX-2, PCNA, Osteocalcin and PECAM-1 in db^-/db^- defects. In addition, osteoclastogenesis is impaired in db^-/db^- indicating altered bone remodeling. These results indicate significant impairments in angiogenesis and osteogenesis in type 2 diabetic bones. Importantly, angiogenesis, osteogenesis and bone remodeling could be reconstituted by application of recombinant FGF-9 and, in part, by VEGFA application. In conclusion, our study demonstrates that type 2 diabetes affects angiogenesis, osteogenesis and subsequently bone remodeling, which in turn leads to decreased bone regeneration. These effects could be reversed by local application of FGF-9 and to a lesser degree VEGFA. These data could serve as a basis for future therapeutic applications aiming at improving bone regeneration in the type 2 diabetic patient population.     

Role of integrin-β3 protein in macrophage polarization and regeneration of injured muscle

Following injury, skeletal muscle achieves repair by a highly coordinated, dynamic process resulting from interplay among numerous inflammatory, growth factors and myogenic regulators. To identify genes involved in muscle regeneration, we used a microarray analysis; there was a significant increase in the expression of a group of integrin genes. To verify these results, we used RT-PCR and Western blotting and found that 12 integrins were up-regulated from 3 h to 15 days following injury. Following muscle injury, integrin-β3 was initially expressed, mainly in macrophages. In integrin-β3 global KO mice, the expression of myogenic genes was decreased and muscle regeneration was impaired, whereas fibrosis was enhanced versus events in wild type (WT) mice. The mechanism for these responses in integrin-β3 KO mice included an infiltration of macrophages that were polarized into the M2 phenotype. These macrophages produced more TGF-β1 and increased TGF-β1/Smad signaling. In vitro, we confirmed that M2 macrophages lacking integrin-β3 produced more TGF-β1. Furthermore, transplantation of bone marrow cells from integrin-β3 KO mice into WT mice led to suppression of the infiltration and accumulation of macrophages into injured muscles. There was also impaired muscle regeneration with an increase in muscle fibrosis. Our results demonstrate that integrin-β3 plays a fundamental role in muscle regeneration through a regulation of macrophage infiltration and polarization leading to suppressed TGF-β1 production. This promotes efficient muscle regeneration. Thus, an improvement in integrin-β3 function could stimulate muscle regeneration.