Chunmei Shi

The role of microRNA-26b in human adipocyte differentiation and proliferation

Recent findings indicate that microRNAs (miRNAs) are involved in the regulatory network of adipogenesis and obesity. Thus far, only a few human miRNAs are known to function as adipogenic regulators, fanning interest in studies on the functional role of miRNAs during adipogenesis in humans. In a previous study, we used a microarray to assess miRNA expression during human preadipocyte differentiation. We found that expression of the miR-26b was increased in mature adipocytes. MiR-26b is an intronic miRNA located in the intron of CTDSP1 (carboxy terminal domain, RNA polymerase II, polypeptide A, small phosphatase 1). Target prediction and Renilla luciferase analyses revealed the phosphatase and tensin homolog gene (PTEN) as a putative target gene. In this study, we found that miR-26b was gradually upregulated during adipocyte differentiation. To understand the roles of miR-26b in adipogenesis, we adopted a loss-of-function approach to silence miR-26b stably in human preadipocytes. We found that miR-26b inhibition effectively suppressed adipocyte differentiation, as evidenced by decreased lipid droplets and the ability of miR-26b to decrease mRNA levels of adipocyte-specific molecular markers and triglyceride accumulation. Furthermore, the cell growth assay revealed that miR-26b inhibition promoted proliferation. Nevertheless, it had no effect on apoptosis. Taken together, these data indicate that miR-26b may be involved in adipogenesis and could be targeted for therapeutic intervention in obesity.

miR-148a is Associated with Obesity and Modulates Adipocyte Differentiation of Mesenchymal Stem Cells through Wnt Signaling

Obesity results from numerous, interacting genetic, behavioral, and physiological factors. Adipogenesis is partially regulated by several adipocyte-selective microRNAs (miRNAs) and transcription factors that regulate proliferation and differentiation of human adipose-derived mesenchymal stem cells (hMSCs-Ad). In this study, we examined the roles of adipocyte-selective miRNAs in the differentiation of hMSCs-Ad to adipocytes. Results showed that the levels of miR-148a, miR-26b, miR-30, and miR-199a increased in differentiating hMSCs-Ad. Among these miRNAs, miR-148a exhibited significant effects on increasing PPRE luciferase activity (it represents PPAR-dependent transcription, a major factor in adipogenesis) than others. Furthermore, miR-148a expression levels increased in adipose tissues from obese people and mice fed high-fat diet. miR-148a acted by suppressing its target gene, Wnt1, an endogenous inhibitor of adipogenesis. Ectopic expression of miR-148a accelerated differentiation and partially rescued Wnt1-mediated inhibition of adipogenesis. Knockdown of miR-148a also inhibited adipogenesis. Analysis of the upstream region of miR-148a locus identified a 3 kb region containing a functional cAMP-response element-binding protein (CREB) required for miR-148a expression in hMSCs-Ad. The results suggest that miR-148a is a biomarker of obesity in human subjects and mouse model, which represents a CREB-modulated miRNA that acts to repress Wnt1, thereby promoting adipocyte differentiation.

MiR-146b is a regulator of human visceral preadipocyte proliferation and differentiation and its expression is altered in human obesity.

Visceral obesity is an independent risk factor for metabolic syndrome, and abnormal fat accumulation is linked to increases in the number and size of adipocytes. MiR-146b was a miRNA highly expressed in mature adipocytes while very lowly expressed in human mesenchymal stem cells (hMSCs) and human visceral preadipocytes (vHPA). In this paper, we mainly focused on the roles of miR-146b in adipogenesis. We found miR-146b could inhibit the proliferation of visceral preadipocytes and promote their differentiation. MiR-146b in human visceral adipocytes inhibited the expression of KLF7, a member of the Kruppel-like transcription factors, as demonstrated by a firefly luciferase reporter assay, indicating that KLF7 is a direct target of the endogenous miR-146b. MiR-146b expression was significantly altered in visceral and subcutaneous adipose tissues in human overweight and obese subjects, and in the epididymal fat tissues and brown fat tissues of diet-induced obese mice. Our data indicates that miR-146b may be a new therapeutic target against human visceral obesity and metabolic dysfunction.

MiR-335, an Adipogenesis-Related MicroRNA, is Involved in Adipose Tissue Inflammation

During the development of obesity, adipose tissue releases a host of different adipokines and inflammatory cytokines, such as leptin, resistin, tumor necrosis factor α (TNF-α), Interleukin-6 (IL-6), and adiponectin, which mediate insulin resistance. Recently, some microRNAs (miRNAs) regulated by adiponectin were identified as novel targets for controlling adipose tissue inflammation. Therefore, the relationship between adipokines and miRNA is worth studying. MiR-335 is an adipogenesis-related miRNA and implicated in both fatty acid metabolism and lipogenesis. In this study, we focused on the association of miR-335 and adipokines, and examined the expression trend of miR-335 during human adipocyte differentiation. Our results showed that miR-335 is significantly upregulated with treatment of leptin, resistin, TNF-α, and IL-6 in human mature adipocytes, and its expression elevated in the process of adipocyte differentiation. Interestingly, the transcriptional regulation of miR-335 by these adipokines seems independent of its host gene (mesoderm-specific transcript homolog, MEST). Thus, we cloned and identified potential promoter of miR-335 within the intron of MEST. As a result, a fragment about 600-bp length upstream sequences of miR-335 had apparent transcription activity. These findings indicated a novel role for miR-335 in adipose tissue inflammation, and miR-335 might play an important role in the process of obesity complications via its own transcription mechanism.

Differential DNA Methylation Status Between Human Preadipocytes and Mature Adipocytes

Obesity is a multifactorial disease resulting from interactions between susceptibility genes, psychosocial, and environmental factors. However, it is becoming evident that interindividual differences in obesity susceptibility depend also on epigenetic factors, although the mechanisms have not been fully elucidated. We have undertaken a genome-wide analysis of DNA methylation of human preadipocytes and mature adipocytes to examine the differences in methylation between them. We found hypomethylation occurring in 2,701 genes and hypermethylation in 1,070 genes after differentiation. Meanwhile, Gene Ontology analysis and Ingenuity Pathway Analysis showed many significant gene functions and pathways with altered methylation status after adipocyte differentiation. In addition, Signal-Net analysis showed that tumor necrosis factor-α, mitogen-activated protein kinase, and interleukin-8 were important to the formation of this network. Our results suggest that DNA methylation mechanisms may be involved in regulating the differentiation process of human preadipocytes.

Adipogenic miRNA and meta-signature miRNAs involved in human adipocyte differentiation and obesity

MicroRNAs (miRNAs) have been identified as a new class of regulatory molecules that influence many biological functions, including metabolism, adipocyte differentiation. To determine the role of adipogenic miRNAs in the adipocyte differentiation process, we used microarray technology to monitor miRNA levels in human adipose-derived mesenchymal stem cells (hMSCs-Ad), human stromal vascular cells (SVCs) and differentiated adipocytes. 79 miRNAs were found to be differentially expressed, most of which are located in obesity related chromosomal regions but have not been previously linked to adipocyte differentiation process. A systematic search was made for relevant studies in academic data bases, involving the Gene Expression Omnibus (GEO) ArrayExpress, Pubmed and Embase database. Eight studies on human adipocyte differentiation or obesity were included in the final analysis. After combining our microarray data with meta-analysis of published microarray data, we detected 42 differently expressed miRNAs (meta-signature miRNAs) in mature adipocytes compared to SVCs or hMSCs-Ad. Our study shows meta-signature miRNAs specific for adipogenesis, several of which are correlated with key gene targets demonstrating functional relationships to pathways in BMP signaling pathway, Cell differentiation, Wnt signaling, insulin receptor signaling pathway, MAPK signaling, Cell cycle and lipid metabolic process. Our study shows that the first evidence of hsa-let-7 family, hsa-miR-15a-5p, hsa-miR-27a-3p, hsa-miR-106b-5p, hsa-miR-148a-3p and hsa-miR-26b-5p got a great weight in adipogenesis. We concluded that meta-signature miRNAs involved in adipocyte differentiation and provided pathophysiological roles and novel insight into obesity and its related metabolic diseases.

TNF-α, IL-6, and leptin increase the expression of miR-378, an adipogenesis-related microRNA in human adipocytes.

Obesity has become a global public health problem associated with complications including type 2 diabetes, cardiovascular disease, and several cancers. Adipocyte differentiation (adipogenesis) plays an important role in obesity and energy homeostasis. Adipose tissue secretes multiple cytokines and adipokines which can cause the complications of obesity, especially insulin resistance. TNF-α, IL-6, leptin, and resistin have been identified as the main regulators of obesity and insulin activity. miR-378 is highly induced during adipogenesis and has been reported to be positively regulated in adipogenesis. In the current study, matured human adipocytes were treated with TNF-α, IL-6, leptin, or resistin on the 15th day after the induction of human pre-adipocyte differentiation. We demonstrated that TNF-α, IL-6, and leptin upregulated miR-378 expression indicating that miR-378 probably is a novel mediator in the development of insulin resistance related to obesity.

Differential lncRNA expression profiles in brown and white adipose tissues

Long non-coding RNAs (lncRNAs) are an important class of pervasive genes involved in a variety of biological functions. It can serve as key co-activators of proteins involved in transcriptional regulation. Studies have found that white and brown adipocytes both originate from the mesoderm. However, it remains unclear whether lncRNAs function during adipogenesis or in energy metabolism in brown adipose tissue (BAT) and white adipose tissue (WAT). In this study, we used lncRNA microarray technology to evaluate differences in the lncRNA expression profiles of WAT and BAT. We observed 735 up-regulated and 877 down-regulated lncRNAs (fold change >4.0). To reveal the potential functions of these lncRNAs, we applied GO and pathway analyses to study the differentially expressed lncRNAs. We found that AK142386 and AK133540 may affect adipogenesis and metabolism. Our data indicate that AK142386 and AK133540 may be involved in BAT and WAT development through their target genes Hoxa3 and Acad10. Together, we have identified numerous lncRNAs and these lncRNAs can potentially serve as a required component for proper adipogenesis.

FFAs and adipokine-mediated regulation of hsa-miR-143 expression in human adipocytes

Accumulating evidence suggests that microRNAs (miRNAs) play an important role in regulating the pathways in adipose tissue that control processes such as adipogenesis, insulin resistance, and inflammation. MiR-143 is a well-characterized miRNA involved in adipogenesis and may be involved in regulating insulin resistance. Free fatty acids (FFAs) and adipokines, such as tumor necrosis factor-α (TNF-α), leptin, resistin, and interleukin-6 (IL-6), have already been identified as main regulators of obesity and insulin sensitivity. Therefore, we studied the effects of these inflammatory cytokines on the expression of miR-143. FFAs, resistin, and leptin downregulated miR-143 expression in human adipocytes, whereas TNF-α and IL-6 had little effect on miR-143 expression. These results suggest that the expression of miR-143 is affected by a variety of factors that are related to insulin sensitivity. Therefore, miR-143 may be an important mediator in the development of obesity-related insulin resistance.

Peptidome analysis of human milk from women delivering macrosomic fetuses reveals multiple means of protection for infants

Breastfeeding is associated with a lower incidence of obesity, diabetes, and cardiovascular disease later in life. While macrosomic infants have a higher risk of developing obesity and other metabolic disorders. Breast milk may contain special nutrients to meet the different growth needs of different infants. Whether mothers make breast milk different to meet the requirement of macrosomic infants is still unknown. Here, we conducted a comparison between mothers delivering macrosomic and non-macrosomic infants in colostrum endogenous peptides. More than 400 peptides, originating from at least 34 protein precursors, were identified by Liquid Chromatography/Mass Spectrometry (LC/MS). Out of these, 29 peptides found to be significant differently expressed (|fold change| ≥ 3, P < 0.01). Blastp analysis revealed 41 peptides may have established biological activities, which exhibit immunomodulating, antibacterial action, antioxidation, opioid agonist and antihypertensive activity. Furthermore, we found that peptide located at β-Casein 24-38 AA has antimicrobial effect against E. coli, Y. enterocolitica and S. aureus. While, κ-Casein 89-109 AA-derived peptide plays as a regulator of preadipocyte proliferation. The profile of endogenous peptides from macrosomic term infants is different from non-macrosomic terms. This different peptide expression potentially has specific physiological function to benefit macrosomic infants. Finally, we believe that our research is a meaningfull finding which may add to the understanding of milk peptide physiological action.