T. Shan

Comparisons of different muscle metabolic enzymes and muscle fiber types in Jinhua and Landrace pigs.

Western and indigenous Chinese pig breeds show obvious differences in muscle growth and meat quality, however, the underlying molecular mechanism remains unclear. The main objective of this study was to evaluate the breed-specific mechanisms controlling meat quality and postmortem muscle metabolism. The specific purpose was to investigate the variations in meat quality, muscle fiber type, and enzyme activity between local Jinhua and exotic Landrace pigs at the same age (180 d of age), as well as the same BW of 64 kg, respectively. We compared differentially expressed muscle fiber types such as types I and IIa (oxidative), type IIb (glycolytic), as well as type IIx (intermediate) fibers in LM and soleus muscles of Jinhua and Landrace pigs using real-time reverse-transcription PCR. Furthermore, the metabolic enzyme activities of lactate dehydrogenase, as well as succinic dehydrogenase and malate dehydrogenase, were used as markers of glycolytic and oxidative capacities, respectively. Results showed that Jinhua pigs exhibited greater intramuscular fat content and less drip loss compared with the Landrace (P < 0.01). Meanwhile, the mRNA abundance of oxidative and intermediate fibers was increased in Jinhua pigs, whereas the glycolytic fibers were more highly expressed in the Landrace (P < 0.01). In addition, Jinhua pigs possessed greater oxidative capacity than that of the Landrace (P < 0.05). These results suggested that the increased expression of the oxidative and intermediate fibers and greater activities of oxidative enzymes in Jinhua pigs were related to meat quality as indicated by a greater intramuscular fat and reduced drip loss. Based on these results, we conclude that muscle fiber composition and postmortem muscle metabolism can explain, in part, the variation of meat quality in Jinhua and Landrace pigs. These results may provide valuable information for understanding the molecular mechanism responsible for breed specific differences in growth performance and meat quality.

Porcine adipose triglyceride lipase complementary deoxyribonucleic acid clone, expression pattern, and regulation by resveratrol

Adipose triglyceride lipase (ATGL) was recently identified and described as a major novel triglyceride lipase in animals. In this study, we aimed to study the tissue-specific and developmental expression pattern of porcine ATGL (pATGL) and the effect of resveratrol (RES) on expression of pATGL in vitro. The full-length cDNA sequence of pATGL was 1,958 bp (accession no. EF583921), with a 1,458-bp open reading frame encoding a 486-AA protein (the predicted molecular mass of 53.2 kDa, accession no. ABS58651). Comparison of the deduced AA sequence with the bovine, mouse, rat, dog, and human adipose triglyceride lipase showed 87, 84, 83, 81, and 80% similarity, respectively. Furthermore, the pATGL was highly expressed in porcine adipose tissue, to a lesser degree in kidney, heart, and muscle, and least but detectable in brain. In s.c. adipose tissue, pATGL mRNA was low at birth (1 kg of BW) and then increased, reaching a maximal value at 20 kg of BW (approximately 8 wk old; P < 0.01). In peritoneal and omental adipose tissue, the greatest expression of pATGL was observed at 40 kg of BW (approximately 12 wk old). In vitro, exposure of cultured adipocytes to 40 and 80 muM RES for 24 h increased the mRNA levels of pATGL by 95.3% (P < 0.05) and 146.8% (P < 0.01), respectively. Accordingly, lipid accumulation was decreased by 25.7% (P < 0.05) and 60.8% (P < 0.01), respectively. When treated with RES for 48 h, the mRNA levels of pATGL were increased by 104.1% (P < 0.05) and 163.1% (P < 0.01), respectively. As expected, lipid accumulation was decreased by 9.7% (P > 0.05) and 29.0% (P < 0.05), respectively. These results add to our understanding of the role of pATGL in adipose tissue development and as a potential target for regulating fat deposition and meat quality.

Breed difference and regulation of the porcine adipose triglyceride lipase and hormone sensitive lipase by TNFα

Adipose triglyceride lipase (ATGL) and hormone sensitive lipase (HSL) are major novel triglyceride lipases in animals. The aim of this study was to determine if there are differences in the porcine ATGL (pATGL) and HSL genes between Jinhua pigs (a fatty breed) and Landrace pigs (a leaner breed). In addition, the effect of TNFalpha and pATGL-specific siRNA (pATGL-siRNA) on the expression of pATGL and HSL in porcine adipocytes was also examined. Compared with Landrace pigs, the body weight (BW) of Jinhua pigs was lower (P < 0.01), while intramuscular fat content (in the longissimus dorsi muscle), as well as the back fat thickness and body fat content were higher (P < 0.01). The expression of pATGL and HSL mRNA in Jinhua pigs was lower (P < 0.01) in subcutaneous adipose tissue, and greater (P < 0.01) in longissimus dorsi muscle compared with Landrace pigs. In vitro treatment of porcine adipocytes with TNFalpha decreased (P < 0.01) the glycerol release and the gene expression of pATGL, HSL and PPARgamma in porcine adipocytes. Furthermore, transfection with pATGL-siRNA significantly decreased (P < 0.01) the expression of pATGL, while it had no effect on the expression of HSL. Treatment with 25 ng/ml TNFalpha in conjunction with pATGL-siRNA significantly decreased (P < 0.01) the expression of pATGL and HSL in cultured porcine adipocytes. These results provide useful information to further the understanding of the function of pATGL and HSL in porcine lipid metabolism, which should be applicable to the regulation of fat deposition and improvement of meat quality.

Porcine sirtuin 1 gene clone, expression pattern, and regulation by resveratrol.

Sirtuin1 (Sirt1) is a NAD-dependent deacetylase that plays important roles in a variety of biological processes. In the current study, we examined tissue-specific and different expression pattern of porcine Sirt1 and the effect of resveratrol (RES) on expression of Sirt1 in porcine adipocytes. The full-length complementary DNA sequence of porcine Sirt1 was 4,024 bp (GenBank accession no: EU030283), with a 2,226-bp open reading frame encoding a 742-AA protein (a predicted molecular mass of 80.9 kDa; GenBank accession no. ABS29571). Comparison of the deduced AA sequence with the corresponding sequences of human, dog, cattle, and mouse Sirt1 showed 82 to 92% similarity. Furthermore, the porcine Sirt1 was highly expressed in porcine brain, to a lesser degree in spleen and white adipose tissue, and had low but detectable expression in liver. In subcutaneous adipose tissue and omental adipose tissue, expression of the porcine Sirt1 mRNA was greater in adult pigs than in young pigs (P < 0.01). In vitro, exposure of cultured adipocytes to 40 and 80 micro M RES for 24 h increased mRNA levels of porcine Sirt1 by 47.86% (P < 0.01) and 91.04% (P < 0.01), respectively. Accordingly, lipid accumulation and NEFA release were decreased (P < 0.05), respectively. After cultures were treated with RES for 48 h, the mRNA level of porcine Sirt1 was increased by 103.84% (P < 0.01) and 148.79% (P < 0.01), respectively. Lipid accumulation was decreased and NEFA release was increased (P < 0.05), respectively. These results provide information needed for manipulating Sirt1 expression in regulating fat deposition in pigs.

Breed difference and regulation of the porcine Sirtuin 1 by insulin.

Sirtuin 1 (Sirt1) plays an important role in fat metabolism. In the current study, we examined the breed differences in Sirt1 between Jinhua pigs (a fatty breed of China) and Landrace pigs (a leaner breed). In addition, the effect of insulin on the gene expression of Sirt1 and the major lipase, adipose triglyceride lipase (ATGL), and hormone-sensitive lipase (HSL) in fat metabolism was also studied in vitro. Compared with the Landrace pigs, the BW of Jinhua pigs was less (P < 0.01), whereas the body fat content were greater (P < 0.01). The protein content and the mRNA abundance of Sirt1 in Jinhua pigs were less (P < 0.01) in subcutaneous adipose tissues compared with the Landrace pigs. Likewise, the mRNA abundance of ATGL and HSL were also less (P < 0.01) in Jinhua pigs. In vitro, treatment with a different dose of insulin (10, 50 and 100 nM) decreased (P < 0.01) glycerol release and the mRNA abundance of Sirt1, ATGL, and HSL in porcine adipocytes. Likewise, treatment with 50 nM insulin for 24 and 48 h also decreased (P < 0.05) glycerol release and the expression of Sirt1, ATGL, and HSL in porcine adipocytes. Furthermore, insulin and Sirt1-specific small interfering RNA treatment decreased (P < 0.01) the expression of Sirt1, ATGL, and HSL compared with the control or insulin treatment. These results indicate that insulin may regulate transcription of Sirt1, ATGL, and HSL in porcine adipocytes and provide information for manipulating these gene expressions in regulating fat metabolism in pigs.

Sirtuin 1 affects the transcriptional expression of adipose triglyceride lipase in porcine adipocytes1

To investigate whether sirtuin 1 (Sirt1) could affect the transcriptional expression of the adipose triglyceride lipase (ATGL) gene, we treated porcine adipocytes with the general Sirt1 activator resveratrol (RES) with the Sirt1 inhibitor nicotinamide (NAM) or a knockdown of Sirt1 by Sirt1-specific small interfering RNA (siRNA). The RES (50 μM) activated Sirt1 gene expression and increased ATGL gene expression and glycerol release (P < 0.01). The Sirt1 inhibitor NAM or knockdown with Sirt1 siRNA further proved that the ATGL mRNA abundances were decreased (P < 0.05) after inhibition with Sirt1 in adipocytes. Furthermore, we found the opposite Sirt1 regulation pattern for PPARγ to that of ATGL in adipocytes. In summary, Sirt1 regulates the transcriptional expression of ATGL in adipocytes, and PPARγ appears to have an important role in this process. These results add to our understanding of the role of Sirt1 in adipose mobilization.

Roles of Notch Signaling in Adipocyte Progenitor Cells and Mature Adipocytes

Adipose tissues, composed with mature adipocytes and preadipocytic stromal/stem cells, play crucial roles in whole body energy metabolism and regenerative medicine. Mature adipocytes are derived and differentiated from mesenchymal stem cells (MSCs) or preadipocytes. This differentiation process, also called adipogenesis, is regulated by several signaling pathways and transcription factors. Notch1 signaling is a highly conserved pathway that is indispensable for stem cell hemostasis and tissue development. In adipocyte progenitor cells, Notch1 signaling regulates the adipogenesis process including proliferation and differentiation of the adipocyte progenitor cells in vitro. Notably, the roles of Notch1 signaling in beige adipocytes formation, adipose development, and function, and the whole body energy metabolism have been recently reported. Here, we mainly review and discuss the roles of Notch1 signaling in adipogenesis in vitro as well as in beige adipocytes formation, adipocytes dedifferentiation, and function in vivo. J. Cell. Physiol. 232: 1258–1261, 2017.

Regulation role of CRTC3 in skeletal muscle and adipose tissue

The cyclic adenosine monophosphate (cAMP)—protein kinase A (PKA) signaling pathway plays important role in regulating energy homeostasis. Many of the effects of the cAMP‐PKA signaling is mediated through the cAMP responsive element binding protein (CREB) and its coactivator CREB‐regulated transcription coactivators (CRTCs). CRTC3 is a member of CRTCs family proteins and plays important roles in glucose and energy metabolism. Previous studies show that global knockout of CRTC3 enhances oxygen consumption and energy expenditure and subsequently protects the knockout animal against obesity. In skeletal muscle, CRTC3 affects lipid and glycogen metabolism and mitochondrial biogenesis. In white adipocytes, CRTC3 regulates GLUT4 expression and glucose uptake. More recently, the localization and function of CRTC3 in brown fat have been reported. In this review, we mainly discuss the regulatory role of CRTC3 in skeletal muscle and adipose tissues.

New Roles of Lkb1 in Regulating Adipose Tissue Development and Thermogenesis

Adipose tissues regulate energy metabolism and reproduction. There are three types of adipocytes (brown, white, and beige adipocytes) in mammals. White adipocytes store energy and are closely associated with obesity and other metabolic diseases. The beige and brown adipocytes have numerous mitochondria and high levels of UCP1 that dissipates lipid to generate heat and defend against obesity. The global epidemic of obesity and its associated metabolic diseases urge an imperative need for understating the regulation of adipogenesis. Liver kinase B1 (Lkb1), also called STK11, is a master kinase of the AMPK subfamily and plays crucial roles in regulating glucose and energy homeostasis in various metabolic tissues. In this review, we focus on the regulatory roles of Lkb1 in regulating preadipocyte differentiation, adipose tissue development, and thermogenesis. J. Cell. Physiol. 232: 2296–2298, 2017.

Lkb1 regulation of skeletal muscle development, metabolism and muscle progenitor cell homeostasis

Liver kinase B1 (Lkb1), also named as Serine/Threonine protein kinase 11 (STK11), is a serine/threonine kinase that plays crucial roles in various cellular processes including cell survival, cell division, cellular polarity, cell growth, cell differentiation, and cell metabolism. In metabolic tissues, Lkb1 regulates glucose homeostasis and energy metabolism through phosphorylating and activating the AMPK subfamily proteins. In skeletal muscle, Lkb1 affects muscle development and postnatal growth, lipid and fatty acid oxidation, glucose metabolism, and insulin sensitivity. Recently, the regulatory roles of Lkb1 in regulating division, self‐renew, proliferation, and differentiation of skeletal muscle progenitor cells have been reported. In this review, we discuss the roles of Lkb1 in regulating skeletal muscle progenitor cell homeostasis and skeletal muscle development and metabolism.