Philipp. Sci. Lett. 2017 10 (1) 8-13
available online: March 14, 2017
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Received: July 15, 2016
Revised: September 5, 2016
Accepted: September 15, 2016
Intensive genetic selection of animals for their lean growth has dramatically reduced intramuscular fat (marbling) impairing meat palatability. In recent years, extensive efforts have been made to enhance intramuscular fat only to yield limited success. The majority of available studies on intramuscular fat focus on the conversion of preadipocytes to adipocytes, adipocyte lipid metabolism, and hypertrophy through nutritional management. We studied the effect of lowering the extracellular calcium and retinoic acid concentration on adipocyte differentiation. Preadipocytes exposed to continuous lower calcium (lower than 3 mmol/l) and lower retinoic acid (lower than 2 umol/l) accumulated more cytoplasmic lipid compared with the other treatments. Differentiation was monitored by Oil Red O staining of cytoplasmic lipid and triglyceride assay. RT-PCR and Western blot analysis showed that low levels of calcium and retinoic acid upregulated the expressions of adipogenic markers PPARÎ³, C/EBPÎ±, aP2, SREBP-1c and RXR. However, calreticulin, a major calcium buffering protein in the ER, was downregulated. Retinoic acid at low levels induced the expression of PPARÎ³ and reduced the expression of calreticulin. Decreased expression of calreticulin promoted adipogenesis through its effects on calcium homeostasis, causing the indirect regulation of crucial pathways affecting adipogenesis such as the calcineurin and CaMKII pathways. These results suggest that continuous exposure to low calcium and retinoic acid concentration promotes adipogenesis. Modifications on the levels of calcium and retinoic acid can be further studied to positively affect adipogenesis and to apply this knowledge in enhancing intramuscular fat accumulation in beef cattle.