Obesity is a major driver of metabolic diseases such as nonalcoholic fatty liver disease, certain cancers, and insulin resistance. However, there are no effective drugs to treat obesity. Betaine is a nontoxic, chemically stable and naturally occurring molecule. This study shows that dietary betaine supplementation significantly inhibits the white fat production in a high-fat diet (HFD)-induced obese mice. This might be due to betaine preventing the formation of new white fat (WAT), and guiding the original WAT to burn through stimulated mitochondrial biogenesis and promoting browning of WAT. Furthermore, dietary betaine supplementation decreases intramyocellular lipid accumulation in HFD-induced obese mice. Further analysis shows that betaine supplementation reduced intramyocellular lipid accumulation might be associated with increasing polyunsaturated fatty acids (PUFA), fatty acid oxidation, and the inhibition of fatty acid synthesis in muscle. Notably, by performing insulin-tolerance tests (ITTs) and glucose-tolerance tests (GTTs), dietary betaine supplementation could be observed for improvement of obesity and non-obesity induced insulin resistance. Together, these findings could suggest that inhibiting WAT production, intramyocellular lipid accumulation and inflammation, betaine supplementation limits HFD-induced obesity and improves insulin resistance.

Intramuscular fat (IMF) content and composition are considered crucial indicators of porcine meat quality. However, the molecular mechanism of porcine IMF development is still mostly unclear. Recently, new evidence suggested that microRNA (miRNAs) play important roles in porcine intramuscular adipogenesis. Previously, microRNA-125a-5p (miR-125a-5p) was identified as an important regulator of adipogenesis. In the present study, we found that the expression of miR-125a-5p is dynamically regulated during porcine intramuscular preadipocytes differentiation and that its expression levels in different porcine muscle tissues were negatively involved with IMF content. To investigate the potential function role of miR-125a-5p in IMF development, porcine intramuscular preadipocytes were collected and transfected with miR-125a-5p mimics, inhibitors, or a negative control (NC), respectively. The results showed that overexpression of miR-125a-5p promoted proliferation and inhibited differentiation of porcine intramuscular preadipocytes while inhibition of miR-125a-5p had the opposite effects. Furthermore, a luciferase reporter assay demonstrated that porcine kruppel like factor 3 (KLF13) is a target gene of miR-125a-5p during porcine intramuscular preadipocytes differentiation. Interestingly, porcine ELOVL fatty acid elongase 6 (ELOVL6), a regulator of fatty acid composition, was also identified as a target gene of miR-125a-5p during porcine intramuscular adipogenesis. Further studies show that miR-125a-5p overexpression reduced total saturated fatty acids (SFA) content and monounsaturated fatty acids (MUFA)/SFA ratios while having no significant impact on polyunsaturated fatty acids (PUFA)/SFA and n-6/n-3 ratios. Taken together, our results identified that miR-125a-5p may be a novel regulator of porcine intramuscular adipogenesis and the fatty acid composition of porcine IMF.

Excessive accumulation of adipose tissue is a main cause of obesity or overweight, which is significantly involved in increasing the risk of diseases. Recently, numerous studies have proved that microRNAs (miRNAs) play important roles in adipogenesis by negatively regulating gene expression at posttranscriptional levels. In this study, we showed that miR-125a-5p was expressed at lower levels in the adipose tissues of high-fat diet (HFD)-fed mice than the normal chow (NCW)-fed mice. MiR-125a-5p expression were strongly up-regulated by nearly five-fold, when 3T3-L1 preadipocyte were induced and differentiated into mature adipocytes. Functional analysis indicated that overexpression of miR-125a-5p promoted 3T3-L1 preadipocyte proliferation and inhibited its differentiation. By contrast, inhibition of miR-125a-5p repressed 3T3-L1 preadipocyte proliferation and accelerated its differentiation. Furthermore, a dual-luciferase reporter assay demonstrated that signal transducer and activator of transcription 3 (STAT3) is a direct target gene of miR-125a-5p during 3T3-L1 preadipocyte differentiation. Further analysis confirmed that the process of miR-125a-5p inhibiting 3T3-L1 preadipocyte differentiation might be associated with the regulation of fatty acid metabolism related genes. Taken together, our results indicated that miR-125a-5p might promote 3T3-L1 preadipocyte proliferation, whereas inhibiting 3T3-L1 preadipocyte differentiation by negatively regulating STAT3.