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The brain dense vascular network is essential for distributing oxygen and nutrients to neural cells. The network develops during embryogenesis and leads to the formation of the endothelial blood-brain barrier (BBB). This barrier is surrounded by mural cells (pericytes and vascular smooth muscle cells (VSMCs)) and fibroblasts. Here, we compared the molecular and functional properties of brain vascular cells on postnatal day (P)5 vs. P15, via a transcriptomic analysis of purified mouse cortical microvessels (MVs) and the identification of vascular-cell-type-specific or -preferentially expressed transcripts. We found that endothelial cells (ECs), VSMCs and fibroblasts follow specific molecular maturation programs over this time period. In particular, ECs acquire P-glycoprotein (P-gP)-mediated efflux capacities. The arterial VSMC network expands, acquires contractile proteins (such as smooth muscle actin (SMA) and myosin heavy chain 11 (Myh11)) and becomes contractile. We also analyzed samples of human brain cortex from the early prenatal stage through to adulthood: the expression of endothelial P-gP increased at birth and Myh11 in VSMCs acts as a developmental switch (as in the mouse) at birth and up to the age of 2 of 5 years. Thus, in both mice and humans, the early postnatal phase is a critical period during which the essential properties of cerebral blood vessels (i.e. the endothelial efflux of xenobiotics and other molecules, and the VSMC contractility required for vessel tone and brain perfusion) are acquired and mature.

Absence of the astrocyte-specific membrane protein MLC1 is responsible for megalencephalic leukoencephalopathy with subcortical cysts (MLC); this rare type of leukodystrophy is characterized by early-onset macrocephaly and progressive white matter vacuolation that lead to ataxia, spasticity, and cognitive decline. During postnatal development (from P5 to P15 in the mouse), MLC1 forms a membrane complex with GlialCAM (another astrocytic transmembrane protein) at the junctions between perivascular astrocytic processes (PvAPs, which along with blood vessels form the gliovascular unit (GVU)). We analyzed the GVU in the Mlc1 knock-out mouse model of MLC. The absence of MLC1 led to an accumulation of fluid in the brain but did not modify the endothelial organization or the integrity of the blood-brain barrier. From P10 onward, the postnatal acquisition of vascular smooth muscle cell contractility was altered, resulting in a marked reduction in arterial perfusion and neurovascular coupling. These anomalies were correlated with alterations in astrocyte morphology, astrocyte polarity and the structural organization of the PvAP’s perivascular coverage, and poor intraparenchymal circulation of the cerebrospinal fluid (CSF). Hence, MLC1 is required for the postnatal development and organization of PvAPs and controls vessel contractility and intraparenchymal interstitial fluid clearance. Our data suggest that (i) MLC is a developmental disorder of the GVU, and (ii) PvAP and VSMC maturation defects are primary events in the pathogenesis of MLC and therapeutic targets for this disease.

Several studies have emphasized the importance of immune composition of the melanoma microenvironment for clinical outcome. The contribution of IL4I1, a phenylalanine oxidase with immunoregulatory functions, has not been yet explored. Here we studied a primary cutaneous melanoma series from stage I–III patients to investigate the association between in situ IL4I1 expression and clinical parameters or tumor-infiltrating T-cell subsets. IL4I1 was detected in 87% of tumors and was mainly expressed by tumor-associated macrophages and very rare FoxP3+ regulatory T cells. The proportion of IL4I1+ cells was higher in patients with an ulcerated melanoma or with a positive sentinel lymph node and tended to correlate with a rapid relapse and shorter overall survival. This proportion also correlated positively with the presence of regulatory T cells and negatively with the presence of cytotoxic CD8+ T cells. The location of IL4I1+ cells may also be relevant to predict prognosis, because their presence near tumor cells was associated with sentinel lymph node invasion and higher melanoma stage. Collectively, our data show that IL4I1+ cells shape the T-cell compartment and are associated with a higher risk of poor outcome in melanoma, supporting a key role for IL4I1 in immune evasion.

International audience; While the signaling pathways and transcription factors active in adult slow- and fast-type muscles begin to be characterized, genesis of muscle fiber-type diversity during mammalian development remains unexplained. We provide evidence showing that Six homeoproteins are required to activate the fast-type muscle program in the mouse primary myotome. Affymetrix transcriptomal analysis of Six1(-/-)Six4(-/-) E10.5 somites revealed the specific down-regulation of many genes of the fast-type muscle program. This data was confirmed by in situ hybridization performed on Six1(-/-)Six4(-/-) embryos. The first mouse myocytes express both fast-type and slow-type muscle genes. In these fibers, Six1 and Six4 expression is required to specifically activate fast-type muscle genes. Chromatin immunoprecipitation experiments confirm the binding of Six1 and Six4 on the regulatory regions of these muscle genes, and transfection experiments show the ability of these homeoproteins to activate specifically identified fast-type muscle genes. This in vivo wide transcriptomal analysis of the function of the master myogenic determinants, Six, identifies them as novel markers for the differential activation of a specific muscle program during mammalian somitic myogenesis.

Glycogen storage disease type II (GSDII) or Pompe disease is an autosomal recessive disorder caused by acid alpha-glucosidase (GAA) deficiency, leading to lysosomal glycogen accumulation. Affected individuals store glycogen mainly in cardiac and skeletal muscle tissues resulting in fatal hypertrophic cardiomyopathy and respiratory failure in the most severe infantile form. Enzyme replacement therapy has already proved some efficacy, but results remain variable especially in skeletal muscle. Substrate reduction therapy was successfully used to improve the phenotype in several lysosomal storage disorders. We have recently demonstrated that shRNA-mediated reduction of glycogen synthesis led to a significant reduction of glycogen accumulation in skeletal muscle of GSDII mice. In this paper, we analyzed the effect of a complete genetic elimination of glycogen synthesis in the same GSDII model. GAA and glycogen synthase 1 (GYS1) KO mice were inter-crossed to generate a new double-KO model. GAA/GYS1-KO mice exhibited a profound reduction of the amount of glycogen in the heart and skeletal muscles, a significant decrease in lysosomal swelling and autophagic build-up as well as a complete correction of cardiomegaly. In addition, the abnormalities in glucose metabolism and insulin tolerance observed in the GSDII model were corrected in double-KO mice. Muscle atrophy observed in 11-month-old GSDII mice was less pronounced in GAA/GYS1-KO mice, resulting in improved exercise capacity. These data demonstrate that long-term elimination of muscle glycogen synthesis leads to a significant improvement of structural, metabolic and functional defects in GSDII mice and offers a new perspective for the treatment of Pompe disease.

Background Intramyocellular lipid accumulation is strongly related to insulin resistance in humans, and we have shown that high glucose concentration induced de novo lipogenesis and insulin resistance in murin muscle cells. Alterations in Wnt signaling impact the balance between myogenic and adipogenic programs in myoblasts, partly due to the decrease of Wnt10b protein. As recent studies point towards a role for Wnt signaling in the pathogenesis of type 2 diabetes, we hypothesized that activation of Wnt signaling could play a crucial role in muscle insulin sensitivity. Methodology/Principal Findings Here we demonstrate that SREBP-1c and Wnt10b display inverse expression patterns during muscle ontogenesis and regeneration, as well as during satellite cells differentiation. The Wnt/β-catenin pathway was reactivated in contracting myotubes using siRNA mediated SREBP-1 knockdown, Wnt10b over-expression or inhibition of GSK-3β, whereas Wnt signaling was inhibited in myoblasts through silencing of Wnt10b. SREBP-1 knockdown was sufficient to induce Wnt10b protein expression in contracting myotubes and to activate the Wnt/β-catenin pathway. Conversely, silencing Wnt10b in myoblasts induced SREBP-1c protein expression, suggesting a reciprocal regulation. Stimulation of the Wnt/β-catenin pathway i) drastically decreased SREBP-1c protein and intramyocellular lipid deposition in myotubes; ii) increased basal glucose transport in both insulin-sensitive and insulin-resistant myotubes through a differential activation of Akt and AMPK pathways; iii) restored insulin sensitivity in insulin-resistant myotubes. Conclusions/Significance We conclude that activation of Wnt/β-catenin signaling in skeletal muscle cells improved insulin sensitivity by i) decreasing intramyocellular lipid deposition through downregulation of SREBP-1c; ii) increasing insulin effects through a differential activation of the Akt/PKB and AMPK pathways; iii) inhibiting the MAPK pathway. A crosstalk between these pathways and Wnt/β-catenin signaling in skeletal muscle opens the exciting possibility that organ-selective modulation of Wnt signaling might become an attractive therapeutic target in regenerative medicine and to treat obese and diabetic populations.

Adult skeletal muscles in vertebrates are composed of different types of myofibers endowed with distinct metabolic and contraction speed properties. Genesis of this fiber-type heterogeneity during development remains poorly known, at least in mammals. Six1 and Six4 homeoproteins of the Six / sine oculis family are expressed throughout muscle development in mice, and Six1 protein is enriched in the nuclei of adult fast-twitch myofibers. Furthermore, Six1/Six4 proteins are known to control the early activation of fast-type muscle genes in myocytes present in the mouse somitic myotome. Using double Six1 : Six4 mutants ( SixdKO ) to dissect in vivo the genesis of muscle fiber-type heterogeneity, we analyzed here the phenotype of the dorsal/epaxial muscles remaining in SixdKO . We show by electron microscopy analysis that the absence of these homeoproteins precludes normal sarcomeric organization of the myofiber leading to a dystrophic aspect, and by immunohistochemistry experiments a deficiency in synaptogenesis. Affymetrix transcriptome analysis of the muscles remaining in E18.5 SixdKO identifies a major role for these homeoproteins in the control of genes that are specifically activated in the adult fast/glycolytic myofibers, particularly those controlling Ca 2+ homeostasis. Absence of Six1 and Six4 leads to the development of dorsal myofibers lacking expression of fast-type muscle genes, and mainly expressing a slow-type muscle program. The absence of restriction of the slow-type program during the fetal period in SixdKO back muscles is associated with a decreased HDAC4 protein level, and subcellular relocalization of the transcription repressor Sox6. Six genes thus behave as essential global regulators of muscle gene expression, as well as a central switch to drive the skeletal muscle fast phenotype during fetal development.