Adipose tissue is conventionally recognized as a metabolic organ responsible for storing energy. However, a proportion of adipose tissue also functions as a thermogenic organ, contributing to the inhibition of weight gain and prevention of metabolic diseases. In recent years, there has been significant progress in the study of thermogenic fats, particularly brown adipose tissue (BAT). Despite this progress, the mechanism underlying thermogenesis in beige adipose tissue remains highly controversial. It is widely acknowledged that beige adipose tissue has three additional thermogenic mechanisms in addition to the conventional UCP1-dependent thermogenesis: Ca²⁺ cycling thermogenesis, creatine substrate cycling thermogenesis, and triacylglycerol/fatty acid cycling thermogenesis. This paper delves into these three mechanisms and reviews the latest advancements in the molecular regulation of thermogenesis from the molecular genetic perspective. The objective of this review is to provide readers with a foundation of knowledge regarding the beige fats and a foundation for future research into the mechanisms of this process, which may lead to the development of new strategies for maintaining human health.

MicroRNAs play essential roles in biological processes by regulating gene expression at the post-transcriptional level. Our previous studies suggested the role of miR-26a in porcine fat accumulation. Here, through gain- and loss-of-function analyses, we first showed that miR-26a increased the proliferation of porcine preadipocytes by promoting cell division and that miR-26a inhibited the preadipocyte differentiation. Next, acyl-CoA dehydrogenase, medium chain (ACADM) was revealed to promote the proliferation and differentiation of preadipocytes for the first time. Then, it was revealed that miR-26a regulates adipogenesis by directly binding to the 3′ untranslated region of ACADM and the long-chain acyl-Co A synthetase 1 (ACSL1) gene, a previously known regulator of adipogenesis. Finally, RNA-sequencing, performed on preadipocytes overexpressing miR-26a, identified 337 differentially expressed genes in the early stage of adipogenesis; among them, nine genes were characterized as potential targets of miR-26a. The 337 genes were mainly involved in Gene Ontology terms related to cell division, indicating that cell cycle progression was also a major event regulated by miR-26a during adipogenesis. We provide novel data for understanding the molecular mechanisms underlying adipogenesis, which will contribute to controlling fat accumulation in animals.

Many efforts have been made to reveal the mechanisms underlying skeletal muscle development because of its importance in animals. However, knowledge on chromatin accessibility, a prerequisite for gene expression, remains limited. Here, dynamic changes in chromatin accessibility were analyzed in the skeletal muscles of Min pigs at the ages of 30, 90, and 210 d using an assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq). A total of 16,301 differentially accessible regions (DARs) associated with 7455 genes were identified among three developmental stages. Seven out of eight DARs selected for a functional analysis were found to regulate reporter gene expression significantly (p < 0.05), indicating that DARs are active in gene expression. A total of 2219 differentially expressed genes (DEGs) were identified with RNA sequencing (RNA-seq). Through integrated analyses of ATAC-seq and RNA-seq data, 54 DEG_DAR_genes and 61 transcription factors (TFs) were characterized as critical for muscle development. Among them, Kruppel-like factor 5 (KLF5), targeted to 36 DEG_DAR_genes, was the most important TF. The effects of KLF5 on DEG_DAR_gene expression were then analyzed with molecular biology techniques. KLF5 was found to regulate SLPI (secretory leukocyte proteinase inhibitor) expression by directly binding to the promoter; KLF5 was also involved in APOA1 (apolipoprotein A-I) expression through affecting the regulatory role of DAR located in the intron. These results indicate that the TFs identified were functional. Altogether, the chromatin accessibility region, TFs, and genes important for muscle development in Min pigs were identified. The results provide novel data for further revealing the mechanisms underlying the epigenetic regulation of muscle development.

Objective: This study was conducted to reveal the role of nuclear poly(A) binding protein 1 (PABPN1) in the proliferation of preadipocytes, and to reveal the relationship between PABPN1 and cAMP response element (CRE)-binding protein (CREB) in the regulation of preadipocyte proliferation.Methods: Vectors overexpressing and siRNAs against PABPN1/CREB were transiently transfected into both porcine preadipocytes and mouse 3T3-L1 cells. Preadipocyte proliferation was measured with cell counting kit-8, 5-ethynyl-2′-deoxyuridine, real-time quantitative polymerase chain reaction, Western blotting, and flow cytometry analyses. Additionally, the transcriptional regulation of CREB on PABPN1 were analyzed with dual-luciferase reporter gene and electrophoretic mobility shift assay.Results: Overexpression of PABPN1 inhibits, and knockdown of PABPN1 promotes, the proliferation of both porcine preadipocytes and 3T3-L1 cell lines. PABPN1 overexpression increased, while knockdown decreased, the cell population in the G0/G1 phase. These indicates that PABPN1 repressed preadipocyte proliferation by inhibiting cell cycle progress. Additionally, it was revealed that CREB regulated the expression of PABPN1 through binding to the promoter and that CREB inhibited preadipocyte proliferation by repressed cell cycle progress. Furthermore, we showed that PABPN1 functions as a downstream gene of CREB to regulate the proliferation of preadipocytes.Conclusion: PABPN1 inhibits preadipocyte proliferation by suppressing the cell cycle. We also found that CREB could promote PABPN1 expression by binding to a motif in the promoter. Further analysis confirmed that PABPN1 functions as a downstream gene of CREB to regulate the proliferation of preadipocytes. These results suggest that the CREB/PABPN1 axis plays a role in the regulation of preadipocyte proliferation, which will contribute to further revealing the mechanism of fat accumulation.

Circular RNA (CircRNA) can regulate gene expression through acting as a competitive endogenous RNA (ceRNA), thus becoming involved in various biological processes. However, little was known about the role of circRNA in the formation of meat quality in pigs. Here, circRNAs were first characterized in muscles with differential meat quality and myofiber composition, longissimus thoracis, and semitendinosus muscles, with RNA-sequencing (RNA-seq). A total of 1126 differentially expressed circRNAs were identified. Among them, Circ-06958 is highly expressed in both muscles. Circ-06958 originated from Long-chain acyl-CoA synthetase 1 (ACSL1), a gene involved in muscle development. Circ-06958 was then characterized experimentally for the first time. Next, it was revealed that Circ-06958 increased proliferation of muscle cells, including porcine skeletal muscle satellite cells (PMSCs) and C2C12 myoblasts, by promoting cell cycle progression. Circ-06958 was mainly localized in cytoplasm, indicating it can function as a ceRNA. A regulatory axis Circ-06958/miR-31-5p/Adenylate Kinase 4 (AK4) axis was constructed with molecular biology techniques. Afterward, it was shown that miR-31-5p inhibited cell proliferation by affecting cell cycle progression in the two cells, while AK4 increased it. We made it clear that Circ-06958 promoted muscle cell proliferation via the miR-31-5p/AK4 axis. The results will contribute to further revealing the mechanisms through which meat quality generates.