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

Mutations in the m-AAA proteases AFG3L2 and SPG7 are causing isolated dominant optic atrophy

Objective To improve the genetic diagnosis of dominant optic atrophy (DOA), the most frequently inherited optic nerve disease, and infer genotype-phenotype correlations.MethodsExonic sequences of 22 genes were screened by new-generation sequencing in patients with DOA who were investigated for ophthalmology, neurology, and brain MRI.ResultsWe identified 7 and 8 new heterozygous pathogenic variants in SPG7 and AFG3L2. Both genes encode for mitochondrial matricial AAA (m-AAA) proteases, initially involved in recessive hereditary spastic paraplegia type 7 (HSP7) and dominant spinocerebellar ataxia 28 (SCA28), respectively. Notably, variants in AFG3L2 that result in DOA are located in different domains to those reported in SCA28, which likely explains the lack of clinical overlap between these 2 phenotypic manifestations. In comparison, the SPG7 variants identified in DOA are interspersed among those responsible for HSP7 in which optic neuropathy has previously been reported.ConclusionsOur results position SPG7 and AFG3L2 as candidate genes to be screened in DOA and indicate that regulation of mitochondrial protein homeostasis and maturation by m-AAA proteases are crucial for the maintenance of optic nerve physiology

Ancestral gene acquisition as the key to virulence potential in environmental Vibrio populations

Diseases of marine animals caused by bacteria of the genus Vibrio are on the rise worldwide. Understanding the eco-evolutionary dynamics of these infectious agents is important for predicting and managing these diseases. Yet, compared to Vibrio infecting humans, knowledge of their role as animal pathogens is scarce. Here we ask how widespread is virulence among ecologically differentiated Vibrio populations, and what is the nature and frequency of virulence genes within these populations? We use a combination of population genomics and molecular genetics to assay hundreds of Vibrio strains for their virulence in the oyster Crassostrea gigas, a unique animal model that allows high-throughput infection assays. We show that within the diverse Splendidus clade, virulence represents an ancestral trait but has been lost from several populations. Two loci are necessary for virulence, the first being widely distributed across the Splendidus clade and consisting of an exported conserved protein (R5.7). The second is a MARTX toxin cluster, which only occurs within V. splendidus and is for the first time associated with virulence in marine invertebrates. Varying frequencies of both loci among populations indicate different selective pressures and alternative ecological roles, based on which we suggest strategies for epidemiological surveys

Transcription Factor Rational Design Improves Directed Differentiation of Human Mesenchymal Stem Cells Into Skeletal Myocytes

There is great interest in transdifferentiating cells from one lineage into those of another and in dedifferentiating mature cells back into a stem/progenitor cell state by deploying naturally occurring transcription factors (TFs). Often, however, steering cellular differentiation pathways in a predictable and efficient manner remains challenging. Here, we investigated the principle of combining domains from different lineage-specific TFs to improve directed cellular differentiation. As proof-of-concept, we engineered the whole-human TF MyoDCD, which has the NH2-terminal transcription activation domain (TAD) and adjacent DNA-binding motif of MyoD COOH-terminally fused to the TAD of myocardin (MyoCD). We found via reporter gene and marker protein assays as well as by a cell fusion readout system that, targeting the TAD of MyoCD to genes normally responsive to the skeletal muscle-specific TF MyoD enforces more robust myogenic reprogramming of nonmuscle cells than that achieved by the parental, prototypic master TF, MyoD. Human mesenchymal stem cells (hMSCs) transduced with a codon-optimized microdystrophin gene linked to a synthetic striated muscle-specific promoter and/or with MyoD or MyoDCD were evaluated for complementing the genetic defect in Duchenne muscular dystrophy (DMD) myocytes through heterotypic cell fusion. Cotransduction of hMSCs with MyoDCD and microdystrophin led to chimeric myotubes containing the highest dystrophin levels