Abstract
Goat intramuscular fat (IMF) content is mainly determined by the processes of intramuscular preadipocytes adipogenic differentiation and mature adipocyte lipid accumulation. However, the underlying regulators of these biological processes remain largely unknown. Here, we report that the expression of Liver X receptor alpha (LXRα) reaches a peak at early stage and then gradually decreases during goat intramuscular adipogenesis. Knockdown of LXRα mediated by two independent siRNAs significantly inhibits intramuscular adipocytes lipid accumulation and upregulates preadipocytes marker- preadipocyte factor 1 (pref1) expression. Consistently, siRNA treatments robustly decrease mRNA level of adipogenic related genes, including CCAAT enhancer binding protein alpha (Cebpα), Peroxisome proliferator activated receptor gamma (Pparg), Sterol regulatory element binding protein isoform 1c (Srebp1c), Fatty acids binding protein (aP2) and Lipoprotein lipase (Lpl). Next, adenovirus overexpression of LXRα does not affect intramuscular adipocytes adipogenesis manifested by Oil Red O signal measurement and adipogenic specific genes detection. Mechanically, we found that both CCAAT enhancer binding protein beta (Cebpβ) and Kruppel like factor 8 (Klf8) are potential targets of LXRα, indicated by having putative binding sites of LXRα at the promoter of these genes and similar expression pattern during adipogenesis comparing to LXRα. Importantly, mRNA levels of Cebpβ and Klf8 are downregulated significantly in goat LXRα knockdown intramuscular adipocyte. These results demonstrate that loss function of LXRα inhibits intramuscular adipogenesis possibly through down-regulation of Cebpβ and Klf8. Our research will provide new insights into mechanical regulation of goat IMF deposition.
Highlights
Intramuscular fat (IMF) content provides an indicator for marble score grading system of goat meat and high marbling cuts are consumption pursuits in many countries [1]
The data showed that LXRα had highest mRNA level in lung (Lun), six-fold higher than heart (Hea), whereas its mRNA level was lowest in longissimus dorsi (LD) muscle and middle expression level in kidney (Kid), visceral white adipose tissue (VWAT) and spleen (Spl), three, three- and two-fold higher than heart, respectively (Figure 1A)
Given that the LXRα mRNA level in muscle does not completely represent its expression in IMF because of extremely small population of intramuscular adipocytes in skeletal muscle tissue, intramuscular preadipocytes were isolated from longissimus dorsi (LD) muscle
Summary
Intramuscular fat (IMF) content provides an indicator for marble score grading system of goat meat and high marbling cuts are consumption pursuits in many countries [1]. The molecular regulators involved in process of preadipocyte adipogenesis from subcutaneous or visceral white adipose tissues (SWAT or VWAT) have been well established in recent decades, including key transcriptional factors (CCAAT enhancer binding protein, Cebpβ; Cebpα; Peroxisome proliferator activated receptor gamma, Pparg; sterol regulatory element binding protein isoform 1c, Srebp1c; and Kruppel like factor, Klf8) and triglycerides synthesis genes (Fatty acids binding protein, Fabp or aP2) [5]. RNA-seq or microarray assay explores the global comparison gene expression and miRNAome between subcutaneous and intramuscular adipocytes in pig, bovine or goat [7,8,9,10], the exact function and regulation mechanism of these differential regulators in intramuscular adipogenesis remains largely unknown
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