OBJECTIVETo determine whether skeletal muscle‐derived stem cells (MDSCs) convert into smooth muscle cells (SMCs) both in vitro and in vivo, and in so doing ameliorate the erectile dysfunction (ED) of aged rats, and whether endogenous stem cells are present in the rat corpora cavernosa.MATERIALS AND METHODSMDSCs were obtained from mouse muscle, and shown by immunocytochemistry for α‐smooth muscle actin (αSMA) to originate in vitro in myofibroblasts and SMCs, discriminating SMCs by calponin 1 expression. In vivo these MDSCs, labelled with 4′,6‐diamidino‐2‐phenylindole, were implanted into the corpora cavernosa of young adult (5‐month old) and aged (20‐month old) rats for 2 and 4 weeks. Histological changes were assessed by immunohistochemistry and quantitative Western blot. Functional changes were determined by electrical field stimulation (EFS) of the cavernosal nerve.RESULTSThe exogenous cells replicated and converted into SMCs, as shown in corporal tissue sections by confocal immunofluorescence microscopy for proliferating cell nuclear antigen (PCNA), αSMA, and smoothelin, and also by Western blot for αSMA and PCNA. MDSC differentiation was confirmed by the activation of the αSMA promoter‐linked β‐galactosidase in transfected cells, both in vitro and after implantation in the corpora. Putative endogenous stem cells were shown in corporal tissue sections and Western blots by detecting CD34 and a possible Sca1 variant. EFS showed that implanted MDSCs raised in aged rats the maximal intracavernosal pressure/mean arterial pressure levels above (2 weeks) or up to (4 weeks) those of young adult rats.CONCLUSIONSMDSCs implanted into the corpora cavernosa of aged rats converted into SMCs and corrected ED, and endogenous cells expressing stem cell markers were also found in untreated tissue. This suggests that exogenous stem cell implantation and/or endogenous stem cell modulation might be viable therapeutic approaches for ageing‐related ED.

Tissue fibrosis, the excessive deposition of collagen/extracellular matrix combined with the reduction of the cell compartment, defines fibroproliferative diseases, a major cause of death and a public health burden. Key cellular processes in fibrosis include the generation of myofibroblasts from progenitor cells, and the activation or switch of already differentiated cells to a fibrotic synthetic phenotype. Myostatin, a negative regulator of skeletal muscle mass, is postulated to be involved in muscle fibrosis. We have examined whether myostatin affects the differentiation of a multipotent mesenchymal mouse cell line into myofibroblasts, and/or modulates the fibrotic phenotype and Smad expression of the cell population. In addition, we investigated the role of follistatin in this process. Incubation of cells with recombinant myostatin protein did not affect the proportion of myofibroblasts in the culture, but significantly upregulated the expression of fibrotic markers such as collagen and the key profibrotic factors transforming growth factor-b1 (TGF-b1) and plasminogen activator inhibitor (PAI-1), as well as Smad3 and 4, and the pSmad2/3. An antifibrotic process evidenced by the upregulation of follistatin, Smad7, and matrix metalloproteinase 8 accompanied these changes. Follistatin inhibited TGF-b1 induction by myostatin. Transfection with a cDNA expressing myostatin upregulated PAI-1, whereas an shRNA against myostatin blocked this effect. In conclusion, myostatin induced a fibrotic phenotype without significantly affecting differentiation into myofibroblasts. The concurrent endogenous antifibrotic reaction confirms the view that phenotypic switches in multipotent and differentiated cells may affect the progress or reversion of fibrosis, and that myostatin pharmacological inactivation may be a novel therapeutic target against fibrosis.

Introduction Muscle derived stem cells (MDSC) and other stem cells implanted into the penile corpora cavernosa ameliorate erectile dysfunction in type 1 diabetic (T1D) rat models by replenishing the lost corporal smooth muscle cells (SMC) and reducing fibrosis. However, no conclusive data on this question in T2/D/obesity models is available. Aim. We studied whether: a) MDSC from T2D Obese Zucker (OZ) rats at an early stage of diabetes (ED-SC), counteract corporal veno-occlusive dysfunction (CVOD) and corporal SMC loss/lipofibrosis when implanted in the OZ rats at a late stage of diabetes; b) MDSC from these late diabetes OZ rats (LD-SC) differ from ED-SC in their gene transcriptional phenotype and repair capacity. Methods and Outcomes ED-SC and LD-SC were compared by DNA microarray assays, and ED-SC were incubated in vitro under high glucose conditions (ED-HG-SC). These three MDSC types were injected into the corpora cavernosa of late diabetes OZ rats (OZ/ED, OZ/LD, and OZ/ED-HG rats respectively). Untreated OZ (OZ/UT) and non-diabetic Lean Zucker (LZ/UT) rats were controls. Two months later, rats were subjected to cavernosometry and the penile shaft and corporal tissues were subjected to histopathology and DNA microarray assays. Results Implanted ED-SC and ED-HG-SC, improved CVOD, counteracted corporal SMC/collagen decrease and fat infiltration in long-term T2D rats, and upregulated nNOS and eNOS. LD-SC acquired an inflammatory/profibrotic/oxidative/dyslipidemic transcriptional phenotype, and failed to repair the corporal tissue. Conclusions MDSC from pre-diabetic rats injected into the corpora cavernosa of long-term diabetic T2D rats improve CVOD and the underlying histopathology. In contrast, MDSC from long-term uncontrolled diabetic T2D rats, are imprinted by the hyperglycemic/dyslipidemic milieu with a noxious phenotype associated with an impaired tissue repair capacity. Diabetes-impacted stem cells may lack tissue repair efficacy as autografts, and should either be reprogrammed in vitro, or substituted by stem cells from allogenic non-diabetic sources.

Myostatin (Mst) is a negative regulator of skeletal muscle in humans and animals. It is moderately expressed in the heart of sheep and cattle, increasing considerably after infarction. Genetic blockade of Mst expression increases cardiomyocyte growth. We determined whether Mst overexpression in the heart of transgenic mice reduces left ventricular size and function, and inhibits in vitro cardiomyocyte proliferation. Young transgenic mice overexpressing Mst in the heart (Mst transgenic mice (TG) under a muscle creatine kinase (MCK) promoter active in cardiac and skeletal muscle, and Mst knockout (Mst (K/K)) mice were used. Xiscan angiography revealed that the left ventricular ejection fraction did not differ between the Mst TG and the Mst (K/K) mice, when compared with their respective wild-type strains, despite the decrease in whole heart and left ventricular size in Mst TG mice, and their increase in Mst (K/K) animals. The expected changes in cardiac Mst were measured by RT-PCR and western blot. Mst and its receptor (ActRIIb) were detected by RT-PCR in rat H9c2 cardiomyocytes. Transfection of H9c2 with plasmids expressing Mst under muscle-specific creatine kinase promoter, or cytomegalovirus promoter, enhanced p21 and reduced cdk2 expression, when assessed by western blot. A decrease in cell number occurred by incubation with recombinant Mst (formazan assay), without affecting apoptosis or cardiomyocyte size. Anti-Mst antibody increased cardiomyocyte replication, whereas transfection with the Mst-expressing plasmids inhibited it. In conclusion, Mst does not affect cardiac systolic function in mice overexpressing or lacking the active protein, but it reduces cardiac mass and cardiomyocyte proliferation.

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