The differential expression of lipocalin-2 in pig tissues and its molecular mechanism of regulating cell viability, differentiation, adipogenesis, and glycometabolism in porcine intramuscular preadipocytes.

Abstract

Lipocalin-2 (LCN-2) is an adipocytokine secreted mainly by adipose tissue. Increasing evidences suggest that LCN-2 is an inflammatory factor associated with insulin resistance, obesity, and its complications. The precise mechanism of the development of obesity-related disorders induced by LCN-2 is not very clear. This study evaluated the expression of LCN-2 in pig tissues and its molecular mechanism of regulating preadipocyte differentiation in porcine intramuscular preadipocytes. LCN-2 expression in tissues of Tongcheng pigs, intramuscular adipose tissue of Tongcheng pigs (fat type) and Landrace pigs (lean type) in embryonic stage and growth stage, and adipocyte differentiation-induced porcine intramuscular preadipocytes was detected using reverse transcription polymerase chain reaction (qRT-PCR). After LCN-2 treatment, cell viability was measured by the methyl thiazolyl tetrazolium (MTT) method, mRNA expression of CCAAT/enhancer binding protein-ɑ (C/EBPɑ), adipocyte determination and differentiation factor-1 (ADD1), fatty acid desaturase (FAD), fatty acid synthase (FAS), and glucose transporter (GLUT) 1,4 was determined by qRT-PCR, protein expression of LCN-2 and peroxisome proliferator-activated receptor-γ (PPARγ) was analyzed by Western blot. Results of qRT-PCR indicated that LCN-2 showed significantly higher expression in high-intramuscular fat (IMF) pigs compared to low-IMF pigs (P < 0.05). LCN-2 expression in porcine intramuscular preadipocytes was significantly upregulated after adipocytic differentiation induction (P < 0.05). Silencing of LCN-2 with LCN-2 siRNA (siLCN-2) inhibited cell viability, lipid droplets, protein expression of PPARγ, and mRNA expression of C/EBPa, ADD1, FAD, FAS, and GLUT 1,4. siLCN-2 treated cells also showed a lower content of triglyceride and release of glucose. Moreover, LCN-2-induced downregulation of cell viability, adipocytic differentiation, adipogenesis, and glycometabolism of porcine intramuscular preadipocytes was partially blocked by the PPARγ inhibitor (GW9662). It is indicated that LCN-2 silencing suppresses cell viability, adipocytic differentiation and adipogenesis, glycometabolism, and fat deposition of porcine intramuscular preadipocytes through suppression of the PPARγ signaling pathway.