Membrane-bound delta-like 1 homolog (Dlk1) promotes while soluble Dlk1 inhibits myogenesis in C2C12 cells

AbstractDelta-like 1 homolog (Dlk1) is important in myogenesis. However, the roles of different Dlk1 isoforms have not been investigated. In C2C12 cell lines producing different Dlk1 isoforms, membrane-bound Dlk1 promoted the hypertrophic phenotype and a higher fusion rate, whereas soluble Dlk1 inhibited myotube formation. Inversed expression patterns of genes related to myogenic differentiation further support these phenotypic changes. In addition, temporal expression and balance between the Dlk1 isoforms have a regulatory role in myogenesis in vivo. Collectively, Dlk1 isoforms have distinctive effects on myogenesis, and its regulation during myogenesis is critical for normal muscle development

Chordin-like 1, a Novel Adipokine, Markedly Promotes Adipogenesis and Lipid Accumulation

White adipose tissue serves as a metabolically dynamic organ that can synthesize and secrete biologically active compounds such as adipokines as well as a caloric reservoir for maintaining energy homeostasis. Adipokines are involved in diverse biological and physiological processes and there have been extensive attempts to characterize the effects of over two dozen adipokines. However, many of these adipokines are produced by not only adipose tissue, but also other tissues. Therefore, investigations into the effects of adipokines on physiological functions have been challenged. In this regard, we aimed to identify a new secreted protein that is encoded by genes specifically expressed in white adipose tissue through analysis of multi-tissue transcriptome and protein expression. As a result, we report a novel adipokine that is encoded by the adipose-specific gene, chordin-like 1 (Chrdl1), which is specifically expressed in white adipose tissue in mice; this expression pattern was conserved in the human orthologous CHRDL1 gene. The expression of Chrdl1 was enriched in fat cells and developmentally regulated in vitro and in vivo, and moreover, its retrovirus-mediated overexpression and recombinant protein treatment led to markedly increased adipogenesis. Further pathway enrichment analysis revealed enriched pathways related to lipogenesis and adipogenic signaling. Our findings support a pro-adipogenic role of CHRDL1 as a new adipokine and pave the way toward animal studies and future research on its clinical implications and development of anti-obesity therapy

Skeletal muscle characterization of Japanese quail line selectively bred for lower body weight as an avian model of delayed muscle growth with hypoplasia.

This study was designed to extensively characterize the skeletal muscle development in the low weight (LW) quail selected from random bred control (RBC) Japanese quail in order to provide a new avian model of impaired and delayed growth in physically normal animals. The LW line had smaller embryo and body weights than the RBC line in all age groups (P<0.05). During 3 to 42 d post-hatch, the LW line exhibited approximately 60% smaller weight of pectoralis major muscle (PM), mainly resulting from lower fiber numbers compared to the RBC line (P<0.05). During early post-hatch period when myotubes are still actively forming, the LW line showed impaired PM growth with prolonged expression of Pax7 and lower expression levels of MyoD, Myf-5, and myogenin (P<0.05), likely leading to impairment of myogenic differentiation and consequently, reduced muscle fiber formation. Additionally, the LW line had delayed transition of neonatal to adult myosin heavy chain isoform, suggesting delayed muscle maturation. This is further supported by the finding that the LW line continued to grow unlike the RBC line; difference in the percentages of PMW to body weights between both quail lines diminished with increasing age from 42 to 75 d post-hatch. This delayed muscle growth in the LW line is accompanied by higher levels of myogenin expression at 42 d (P<0.05), higher percentage of centered nuclei at 42 d (P<0.01), and greater rate of increase in fiber size between 42 and 75 d post-hatch (P<0.001) compared to the RBC line. Analysis of physiological, morphological, and developmental parameters during muscle development of the LW quail line provided a well-characterized avian model for future identification of the responsible genes and for studying mechanisms of hypoplasia and delayed muscle growth

Expression of the different myosin heavy chain (MHC) isoforms and myogenic factors in the low weight (LW) and random bred control (RBC) quail lines.

<p>Time point comparison of the neonatal MHC isoform using 2E9 monoclonal antibody (A), adult MHC isoform using AB8 monoclonal antibody (B), Pax7 (E), MyoD (F), and Myf-5 (I) between the LW and RBC quail lines (1 quail per each time point). Quail line comparison of neonatal MHC isoforms at 3 and 75 d post-hatch (C), adult MHC isoform at 28, 42, and 75 d post-hatch (D), Pax7 at 7 and 14 d post-hatch (G), MyoD at 0, 3, and 7 d post-hatch (H), and Myf-5 at 3 and 7 d post-hatch (J) (3 quail per each time point and each quail line). Expressions of myogenin mRNA in the two quail lines at 0, 3, 7, 14, 28, 42, and 75 d post-hatch (K). Total RNA was isolated from the pectoralis major muscle. Expressions of myogenin were measured by quantitative real-time PCR with avian ribosomal protein 13 (RPS13) as a control for normalization. Protein staining of the different quail lines at each time point (L; 1 quail per each time point) and at 0, 3, 7, 14, 28, 42, and 75 d post-hatch (M; 3 quail per each time point and each quail line). Gels used as a control of protein loading. Bars indicate standard errors. Level of significance: NS, not significant; * <i>P</i><0.05; ** <i>P</i><0.01; *** <i>P</i><0.001.</p

Muscle fiber cross-sectional area (CSA) and density of the pectoralis major muscle on the different quail lines at 42 and 75 d post-hatch.

a–b<p>Different superscripts in the each muscle region represent significant differences (<i>P</i><0.05).</p><p>Abbreviations: LW, low weight; RBC, random bred control.</p

Loss of Fat with Increased Adipose Triglyceride Lipase-Mediated Lipolysis in Adipose Tissue during Laying Stage in Quail

The goal of the current study was to investigate regulation of key genes involved in lipid metabolism in adipose and liver to relate lipolytic and lipogenic capacities with physiological changes at the pre-laying, onset of laying, and actively laying stages of quail. Followed by a 50 % increase from pre-laying to onset of laying, adipose to body weight ratio was significantly reduced by 60 % from the onset of laying to the actively laying stage (P < 0.05), mainly resulting from the significantly increased adipocyte size from the pre-laying stage to the onset of laying and reduction of adipocyte size from the onset of laying to the actively laying stage (P < 0.05). In the adipose tissue of actively laying quail, increased protein expression and phosphorylation of adipose triglyceride lipase (ATGL) together with an elevated mRNA expression of comparative gene identification-58, an activator of ATGL, contributes to increased lipolytic activity, as proved by increased amounts of plasma non-esterified fatty acid (P < 0.05). In addition, decreased mRNA expression of fatty acid transport protein in the actively laying quail could contribute to the adipocyte hypotrophy (P < 0.05). In the liver, relative mRNA expression of apo-very low density lipoprotein (VLDL)-II increased significantly from the pre-laying to actively laying stages (P < 0.05), indicating increased apoVLDL-II actively facilitated VLDL secretion in the actively laying quail. These results suggest that the laying birds undergo active lipolysis in the adipocyte, and increase VLDL secretion from the liver in order to secure a lipid supply for yolk maturation

Muscle fiber cross-sections and centered nuclei in the pectoralis major muscle between the low weight (LW) and random bred control (RBC) quail lines at 42 d post-hatch that were stained for hematoxylin and eosin (A); Comparison of centered nuclei percentage relative to total counted nuclei between LW and RBC quail lines at 42 d post-hatch (B).

<p>Arrows indicate centered nuclei. Bars indicate standard errors. Level of significance: *** <i>P</i><0.001.</p

Comparison of embryo weight (A) and embryo percentage relative to egg weight (B) between the low weight (LW) and random bred control (RBC) quail lines.

<p>Bars indicate standard errors. Level of significance: * <i>P</i><0.05; *** <i>P</i><0.001.</p

Muscle fiber cross-sections in the pectoralis major muscle between the low weight (LW) and random bred control (RBC) quail lines at 42 (A) and 75 (B) d post-hatch that were stained for myosin ATPase activity after acidic preincubation (pH 4.6).

<p>Bar indicates 100 µm. Abbreviations: IIA, fiber type IIA (fast-twitch and oxido-glycolytic); IIB, fiber type IIB (fast-twitch and glycolytic).</p

Muscle fiber type composition of the pectoralis major muscle on the different quail lines at 42 and 75 d post-hatch.

a–b<p>Different superscripts in the each muscle region represent significant differences (<i>P</i><0.05).</p><p>Abbreviations: LW, low weight; RBC, random bred control.</p