Increased adipocyte differentiation may be mediated by extracellular calcium levels through effects on calreticulin and peroxisome proliferator activated receptor gamma expression in intramuscular stromal vascular cells isolated from Hanwoo beef cattle

Abstract

Marbling is the intramuscular deposition of adipose tissue and is said to be directly associated with beef quality. Nutritional manipulations are a common practice among beef cattle producers in order to achieve better quality meat. The objective of the current study was to investigate the effects of increasing extracellular calcium on the differentiation of intramuscular stromal vascular cells (IM SVCs) isolated from Hanwoo beef cattle. Primary cell isolates of SVCs were differentiated for 14 days while exposed to increasing concentrations (1.8, 3.6, 7.2, 10.8 mM) of calcium in the media. The correlation between adipogenesis and calcium concentrations was determined through SVC differentiation monitored by RT-PCR, Western blot analysis for PPARγ, C/EBPα, calreticulin, FABP4 and GLUT4 expression. In addition, expression of both phospholipase C gamma (PLC-γ) and protein kinase C (PKC) were investigated since both have possible links to intracellular calcium increase and the expression of several adipogenic genes including FABP4 and GLUT4. Results of the current study provide evidence that stromal vascular cells exposed to the lower concentrations of extracellular calcium have higher rates of adipogenesis possibly due to a decrease in the expression of calreticulin, a known inhibitor of PPARγ expression, and PKC activation followed by PLC-γ activation, leading to the expression of adipogenic genes. Data derived from this study shows that in vitro, decreasing calcium levels present in the microenvironment of fat precursor cells lead to a higher percentage of adipogenesis.