Vitamin A regulates intramuscular adipose tissue and muscle development:promoting high-quality beef production

During growth in cattle,the development of intramuscular adipose tissue and muscle is dependent upon cell hyperplasia(increased number of adipocytes)and hypertrophy(increased size of adipocytes).Based on the results of previous studies,other adipose tissue depots(e.g.,perirenal and subcutaneous)develop from the fetal stage primarily as brown adipose tissue.The hyperplastic stage of intramuscular adipose is considered to develop from late pregnancy,but there is no evidence indicating that intramuscular adipose tissue develops initially as brown adipose tissue.Hyperplastic growth of intramuscular adipose continues well into postweaning and is dependent on the timing of the transition to grain-based diets;thereafter,the late-stage development of intramuscular adipose tissue is dominated by hypertrophy.For muscle development,hyperplasia of myoblasts lasts from early(following development of somites in the embryo)to middle pregnancy,after which growth of muscle is the result of hypertrophy of myofibers.Vitamin A is a fat-soluble compound that is required for the normal immunologic function,vision,cellular proliferation,and differentiation.Here we review the roles of vitamin A in intramuscular adipose tissue and muscle development in cattle.Vitamin A regulates both hyperplasia and hypertrophy in in vitro experiments.Vitamin A supplementation at the early stage and restriction at fattening stage generate opposite effects in the beef cattle.Appropriate vitamin A supplementation and restriction strategy increase intramuscular adipose tissue development(i.e.,marbling or intramuscular fat)in some in vivo trials.Besides,hyperplasia and hypertrophy of myoblasts/myotubes were affected by vitamin A treatment in in vitro trials.Additionally,some studies reported an interaction between the alcohol dehydrogenase-1C(ADH1C)genotype and vitamin A feed restriction for the development of marbling and/or intramuscular adipose tissue,which was dependent on the timing and level of vitamin A restriction.Therefore,the feed strategy of vitamin A has the visible impact on the marbling and muscle development in the cattle,which will be helpful to promote the quality of the beef.

Quantification of intermuscular and intramuscular adipose tissue using magnetic resonance imaging after neurodegenerative disorders

Ectopic adiposity has gained considerable attention because of its tight association with metabolic and cardiovascular health in persons with spinal cord injury（SCI）. Ectopic adiposity is characterized by the storage of adipose tissue in non-subcutaneous sites. Magnetic resonance imaging（MRI） has proven to be an effective tool in quantifying ectopic adiposity and provides the opportunity to measure different adipose depots including intermuscular adipose tissue（IMAT） and intramuscular adipose tissue（Intra MAT） or intramuscular fat（IMF）. It is highly important to distinguish and clearly define these compartments, because controversy still exists on how to accurately quantify these adipose depots. Investigators have relied on separating muscle from fat pixels based on their characteristic signal intensities. A common technique is plotting a threshold histogram that clearly separates between muscle and fat peaks. The cut-offs to separate between muscle and fat peaks are still not clearly defined and different cut-offs have been identified. This review will outline and compare the Midpoint and Otsu techniques, two methods used to determine the threshold between muscle and fat pixels on T1 weighted MRI. The process of water/fat segmentation using the Dixon method will also be outlined. We are hopeful that this review will trigger more research towards accurately quantifying ectopic adiposity due to its high relevance to cardiometabolic health after SCI.

Oleic acid Stimulates the Formation of Adipocyte-Like Cells from Bovine Satellite Cells via <i>G-Protein Coupled Receptor 43</i>and <i>CCAAT/Enhancer-Binding Protein Beta</i>

Numerous physiological and pathological processes are controlled by free fatty acids, which act as signaling molecules in mammals. We hypothesized that oleic acid (Ole) might stimulate the formation of satellite-cell-derived intramuscular adipose tissue. The role of Ole as a ligand of G-protein-coupled receptor 43 (GPR43) was previously identified. Thus, the objective of the current study was to determine the effect of Ole on GPR43 and factors related to the adipogenic differentiation of bovine satellite cells (BSC). Treatments of 100 μM and 500 μM Ole tended to induce greater (P < 0.10) mRNA expression of CCAAT/enhancer-binding protein β (C/EBPβ) compared to all other doses. The mRNA abundance of peroxisome proliferator-activated receptor γ (PPARγ) was not altered (P > 0.10) by treatment. The addition of 100 μM and 500 μM of Ole upregulated (P < 0.05) GPR43 mRNA expression. Protein level of GPR43 was increased (P < 0.05) by 100 μM of Ole treatments. Addition of Ole to BSC cultures induced transformation of myogenic cells into adipocyte-like cells that formed cytoplasmic lipid droplets. Increased expression of C/EBPβ in response to Ole might suppress myogenic differentiation. After the treatment of cells with Ole, increased expression of GPR43 could lead to phosphorylation of 5’ AMP-activated protein kinase α (AMPKα). Altogether, the results indicated that increased Ole might stimulate adipose tissue accumulation within the skeletal muscle of cattle by promoting adipogenic differentiation and activation of GPR43 in satellite cells.