Association of miR-34a and miR-143 levels with PPARγ gene expression in adipose tissues of non-diabetic adults

MicroRNA-34a and promoter methylation contribute to peroxisome proliferator-activated receptor gamma gene expression in patients with type 2 diabetes

AIMS

This study aimed to investigate the roles of DNA methylation and miR-34a in the regulation of peroxisome proliferator-activated receptor gamma (PPARγ) in patients with type 2 diabetes (T2D).

METHODS

We investigated the methylation status of four regions of the PPARγ promoter and PPARγ expression in a panel of 84 T2D patients using methylation-specific PCR (MSP) and RT-qPCR, respectively. Moreover, we quantified DNA methyltransferases (DNMTs) expression and global DNA methylation levels by RT-qPCR and ELISA, respectively. We measured the expression levels of miR-34a and protein expression of PPARγ by stem-loop RT-qPCR and ELISA, respectively.

RESULTS

We found significant DNA hypermethylation in the R2 and R3 regions of the PPARγ promoter in people with diabetes. Functionally, this was associated with a significant reduction in PPARγ expression. In addition, we observed a significant increase in 5-methylcytosine levels in people with diabetes. A marked increase in circulating miR-34a in the early stages of T2D (up to 10 years) and a significant decrease in circulating miR-34a with increasing diabetes duration from 10 years after the onset of diabetes. Interestingly, upregulation of DNA methyltransferases 1 (DNMT1), DNMT3A, and DNMT3B was observed in people with diabetes, and the average expression of DNMTs was negatively correlated with circulating miR-34a levels. In contrast, the serum protein level of PPARγ, a direct target of miR-34a, increased considerably with diabetes duration and showed a negative correlation with circulating miR-34a, cholesterol, triglyceride, and low-density lipoprotein.

CONCLUSION

PPARγ promoter hypermethylation and miR-34a upregulation are associated with T2D pathogenesis through PPARγ dysregulation.

Molecular and Metabolic Analysis of Arsenic-Exposed Humanized AS3MT Mice

BACKGROUND

Chronic exposure to inorganic arsenic (iAs) has been associated with type 2 diabetes (T2D). However, potential sex divergence and the underlying mechanisms remain understudied. iAs is not metabolized uniformly across species, which is a limitation of typical exposure studies in rodent models. The development of a new "humanized" mouse model overcomes this limitation. In this study, we leveraged this model to study sex differences in the context of iAs exposure.

OBJECTIVES

The aim of this study was to determine if males and females exhibit different liver and adipose molecular profiles and metabolic phenotypes in the context of iAs exposure.

METHODS

Our study was performed on wild-type (WT) 129S6/SvEvTac and humanized arsenic + 3 methyl transferase (human AS3MT) 129S6/SvEvTac mice treated with 400   ppb of iAs via drinking water ad libitum. After 1 month, mice were sacrificed and the liver and gonadal adipose depots were harvested for iAs quantification and sequencing-based microRNA and gene expression analysis. Serum blood was collected for fasting blood glucose, fasting plasma insulin, and homeostatic model assessment for insulin resistance (HOMA-IR).

RESULTS

We detected sex divergence in liver and adipose markers of diabetes (e.g., miR-34a, insulin signaling pathways, fasting blood glucose, fasting plasma insulin, and HOMA-IR) only in humanized (not WT) mice. In humanized female mice, numerous genes that promote insulin sensitivity and glucose tolerance in both the liver and adipose are elevated compared to humanized male mice. We also identified Klf11 as a putative master regulator of the sex divergence in gene expression in humanized mice.

DISCUSSION

Our study underscored the importance of future studies leveraging the humanized mouse model to study iAs-associated metabolic disease. The findings suggested that humanized males are at increased risk for metabolic dysfunction relative to humanized females in the context of iAs exposure. Future investigations should focus on the detailed mechanisms that underlie the sex divergence. https://doi.org/10.1289/EHP12785.

Role of MicroRNAs in Dietary Interventions for Obesity and Obesity-Related Diseases

Obesity and related metabolic syndromes pose a serious threat to human health and quality of life. A proper diet is a safe and effective strategy to prevent and control obesity, thus maintaining overall health. However, no consensus exists on the connotations of proper diet, and it is attributed to various factors, including "nutritional dark matter" and the "matrix effect" of food. Accumulating evidence confirms that obesity is associated with the in vivo levels of miRNAs, which serve as potential markers and regulatory targets for obesity onset and progression; food-derived miRNAs can regulate host obesity by targeting the related genes or gut microbiota across the animal kingdom. Host miRNAs mediate food nutrient-gut microbiota-obesity interactions. Thus, miRNAs are important correlates of diet and obesity onset. This review outlines the recent findings on miRNA-mediated food interventions for obesity, thereby elucidating their potential applications. Overall, we provide new perspectives and views on the evaluation of dietary nutrition, which may bear important implications for dietary control and obesity prevention.

Small Heterodimer Partner Modulates Macrophage Differentiation during Innate Immune Response through the Regulation of Peroxisome Proliferator Activated Receptor Gamma, Mitogen-Activated Protein Kinase, and Nuclear Factor Kappa B Pathways

Hepatic macrophages act as the liver's first line of defense against injury. Their differentiation into proinflammatory or anti-inflammatory subpopulations is a critical event that maintains a delicate balance between liver injury and repair. In our investigation, we explored the influence of the small heterodimer partner (SHP), a nuclear receptor primarily associated with metabolism, on macrophage differentiation during the innate immune response. During macrophage differentiation, we observed significant alterations in Shp mRNA expression. Deletion of Shp promoted M1 differentiation while interfering with M2 polarization. Conversely, overexpression of SHP resulted in increased expression of peroxisome proliferator activated receptor gamma (Pparg), a master regulator of anti-inflammatory macrophage differentiation, thereby inhibiting M1 differentiation. Upon lipopolysaccharide (LPS) injection, there was a notable increase in the proinflammatory M1-like macrophages, accompanied by exacerbated infiltration of monocyte-derived macrophages (MDMs) into the livers of Shp myeloid cell specific knockout (Shp-MKO). Concurrently, we observed significant induction of tumor necrosis factor alpha (Tnfa) and chemokine (C-C motif) ligand 2 (Ccl2) expression in LPS-treated Shp-MKO livers. Additionally, the mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) pathways were activated in LPS-treated Shp-MKO livers. Consistently, both pathways were hindered in SHP overexpression macrophages. Finally, we demonstrated that SHP interacts with p65, thereby influencing macrophage immune repones. In summary, our study uncovered a previously unrecognized role of SHP in promoting anti-inflammatory macrophage differentiation during the innate immune response. This was achieved by SHP acting as a regulator for the Pparg, MAPK, and NF-κB pathways.

miRNAs as cornerstones in adipogenesis and obesity

In recent decades, obesity has extensively emerged to the level of pandemics. It's significantly associated with serious co-morbidities that could decrease life quality and even life expectancy. Obesity has several determinants, such as age, sex, endocrine, and genetic factors. The miRNAs have emerged as genetic factors affecting obesity. The miRNAs are small noncoding nucleic acids that can modify gene expression and hence, control biological processes. The miRNAs can greatly affect many biological processes in obesity, such as adipogenesis, lipid metabolism, and homeostasis. As a result, the entry of miRNAs in obesity therapeutic approaches has been strongly advised as miRNAs mimics, inhibitors, and stimulators. Hence, this review aims to point out a summarized and updated overview of miRNAs and their roles in obesity and its included processes, such as adipogenesis and lipid metabolism. Besides, we also review recent applications of miRNAs as a treatment approach for obesity.

MiR-19 Family Impairs Adipogenesis by the Downregulation of the PPARγ Transcriptional Network

microRNAs (miRNAs) are a class of small endogenous RNA that play pivotal roles in both the differentiation and function of adipocytes during the development of obesity. Despite this, only a few miRNA families have been identified as key players in adipogenesis. Here, we show the relevance of the miR-19 family, miR-19a and miR-19b, in lipid accumulation and the expansion of the adipose tissue in obesity. We observed that miR-19s were upregulated in the abdominal subcutaneous adipose tissue (aSAT) of human patients with morbid obesity, whereas after bariatric surgery, their expression was reduced. In vitro experiments identified miR-19a and b as crucial actors in adipogenesis and lipid accumulation. Overall, our results suggest a novel role of the miR-19 family in the regulatory networks underlying adipogenesis and, therefore, adipose tissue dysfunction.

Elevated miR-143 and miR-34a gene expression in human visceral adipose tissue are associated with insulin resistance in non-diabetic adults: a cross-sectional study

OBJECTIVE

We aimed to evaluate the association of miR-143 and miR-34a expression in human visceral (VAT) and subcutaneous (SAT) adipose tissues with insulin resistance (IR).

METHODS

VAT and SAT were obtained from 176 participants without diabetes. miR-143 and miR-34a expressions in VAT and SAT were measured using qRT-PCR. Fasting serum insulin and glucose concentration, homeostatic model assessment of IR index (HOMA-IR) and β-cell function (HOMA-B), and quantitative insulin-sensitivity check index (QUICKI) were calculated.

RESULTS

After adjustment for age, sex and body mass index (BMI), VAT miR-143 expression was positively associated with fasting plasma glucose (FPG), insulin, and HOMA-IR, and negatively associated with HOMA-B and QUICKI. miR-34a expression in VAT was directly associated with FPG, insulin, and HOMA-IR and negatively associated with QUICKI. In SAT, miR-34a expression was positively associated with insulin and negatively associated with QUICKI. The interaction terms of HOMA-IR and BMI categories were significant for both miR gene expressions in VAT. After stratifying participants based on BMI, the association of miR-143 and miR-34a expressions in VAT with IR indices remained significant only in obese patients.

CONCLUSION

miR-143 and miR-34a expressions in VAT were independent predictors of IR in people without diabetes, and that this association was conditional on the degree of obesity.

LEVEL OF EVIDENCE

Level of evidence III, cross-sectional analytic study.

The Stress-Responsive microRNA-34a Alters Insulin Signaling and Actions in Adipocytes through Induction of the Tyrosine Phosphatase PTP1B

Metabolic stresses alter the signaling and actions of insulin in adipocytes during obesity, but the molecular links remain incompletely understood. Members of the microRNA-34 (miR-34 family play a pivotal role in stress response, and previous studies showed an upregulation of miR-34a in adipose tissue during obesity. Here, we identified miR-34a as a new mediator of adipocyte insulin resistance. We confirmed the upregulation of miR-34a in adipose tissues of obese mice, which was observed in the adipocyte fraction exclusively. Overexpression of miR-34a in 3T3-L1 adipocytes or in fat pads of lean mice markedly reduced Akt activation by insulin and the insulin-induced glucose transport. This was accompanied by a decreased expression of VAMP2, a target of miR-34a, and an increased expression of the tyrosine phosphatase PTP1B. Importantly, PTP1B silencing prevented the inhibitory effect of miR-34a on insulin signaling. Mechanistically, miR-34a decreased the NAD⁺ level through inhibition of Naprt and Nampt, resulting in an inhibition of Sirtuin-1, which promoted an upregulation of PTP1B. Furthermore, the mRNA expression of Nampt and Naprt was decreased in adipose tissue of obese mice. Collectively, our results identify miR-34a as a new inhibitor of insulin signaling in adipocytes, providing a potential pathway to target to fight insulin resistance.

Epigenetic Regulation of Estrogen Receptor Genes' Expressions in Adipose Tissue in the Course of Obesity

Estrogen affects adipose tissue function. Therefore, this study aimed at assessing changes in the transcriptional activity of estrogen receptor (ER) α and β genes (ESR1 and ESR2, respectively) in the adipose tissues of obese individuals before and after weight loss and verifying whether epigenetic mechanisms were involved in this phenomenon. ESR1 and ESR2 mRNA and miRNA levels were evaluated using real-time PCR in visceral (VAT) and subcutaneous adipose tissue (SAT) of 78 obese (BMI > 40 kg/m2) and 31 normal-weight (BMI = 20−24.9 kg/m2) individuals and in 19 SAT samples from post-bariatric patients. ESR1 and ESR2 methylation status was studied using the methylation-sensitive digestion/real-time PCR method. Obesity was associated with a decrease in mRNA levels of both ERs in SAT (p < 0.0001) and ESR2 in VAT (p = 0.0001), while weight loss increased ESR transcription (p < 0.0001). Methylation levels of ESR1 and ESR2 promoters were unaffected. However, ESR1 mRNA in the AT of obese subjects correlated negatively with the expression of hsa-miR-18a-5p (rs = −0.444), hsa-miR-18b-5p (rs = −0.329), hsa-miR-22-3p (rs = −0.413), hsa-miR-100-5p (rs = −0.371), and hsa-miR-143-5p (rs = −0.289), while the expression of ESR2 in VAT correlated negatively with hsa-miR-576-5p (rs = −0.353) and in SAT with hsa-miR-495-3p (rs = −0.308). In conclusion, obesity-associated downregulation of ER mRNA levels in adipose tissue may result from miRNA interference.