Palmitate alters miR‐2137 and miR‐503‐5p to induce orexigenic Npy in hypothalamic neuronal cell models: Rescue by oleate and docosahexaenoic acid

Abstract

MicroRNAs (miRNAs) are short noncoding RNA implicated in the pathogenesis of obesity. One cause of obesity is excess exposure to the saturated fatty acid palmitate that can alter miRNA levels in the periphery. Palmitate also promotes obesity by acting on the hypothalamus, the central coordinator of energy homeostasis, to dysregulate hypothalamic feeding neuropeptides and induce ER stress and inflammatory signaling. We hypothesized that palmitate would alter hypothalamic miRNAs that control genes involved in energy homeostasis thereby contributing to the obesity‐promoting effects of palmitate. We found that palmitate upregulated 20 miRNAs and downregulated six miRNAs in the orexigenic NPY/AgRP‐expressing mHypoE‐46 cell line. We focused on delineating the roles of miR‐2137 and miR‐503‐5p, as they were strongly up‐ and downregulated by palmitate, respectively. Overexpression of miR‐2137 increased Npy mRNA levels and downregulated Esr1 levels, while increasing C/ebpβ and Atf3 mRNA. Inhibiting miR‐2137 had the opposite effect, except on Npy, which was unchanged. The most downregulated miRNA by palmitate, miR‐503‐5p, negatively regulated Npy mRNA levels. Exposure to the unsaturated fatty acids oleate or docosahexaenoic acid completely or partially blocked the effects of palmitate on miR‐2137 and miR‐503‐5p as well as Npy, Agrp, Esr1, C/ebpβ and Atf3. MicroRNAs may therefore contribute to palmitate actions in dysregulating NPY/AgRP neurons. Effectively combating the deleterious effects of palmitate is crucial to help prevent or reduce the impact of obesity.

The Involvement of the microRNAs miR-466c and miR-340 in the Palmitate-Mediated Dysregulation of Gonadotropin-Releasing Hormone Gene Expression

“…Since palmitate is known to induce ER stress, miR-503 and miR-351 downregulation may be a stress response instead of a Gnrh-related response. Additionally, we found a significant downregulation of miR-503 following palmitate treatment, which was blunted with oleate co-treatment in the Npy/Agrp-expressing mHypoE-46 cell line [26]. This finding strengthens the idea that the palmitate-mediated suppression of miR-503 is common across different neuronal cell lines.…”

“…Next, to investigate the contribution of miRNAs to the effect of palmitate on Gnrh mRNA expression, we curated a list of candidate miRNAs using a set of selection parameters [24,25]. Murine microRNA candidates were selected based on (i) predicted binding to Gnrh 3 ′ UTR by TargetScanMouse 7.1 and TargetScanHuman 7.1, (ii) predicted fold changes with palmitate treatment based on a microarray in the mHypoE-46 cell line (p < 0.05) [26], and (iii) basal expression levels in the whole hypothalamus and other hypothalamic cells lines (mHypoA-59 and mHypoE-46 cells) as detected by a microRNA microarray (Table 4). microRNA basal expression levels identified by the microarray were validated by qRT-PCR.…”

Bisphenol A Alters the Levels of miRNAs That Directly and/or Indirectly Target Neuropeptide Y in Murine Hypothalamic Neurons

“…This suggests that Npy may be an indirect target of miR-140-5p, miR-29b-1-5p, and let-7b-3p such that these miRNAs could act on other genes that would influence the expression of Npy . Regardless of the mode of miRNA-mediated regulation of target genes, changes to the hypothalamic milieu could alter miRNA-feeding neuropeptide interaction as hypothalamic miRNAs are responsive to hormones, chemicals, and nutrients [ 24 , 25 , 51 , 52 ].…”

“…Previous work in our laboratory has identified three miRNAs that indirectly alter Npy expression [ 24 , 25 ]. Using the obesogenic compound BPA and the saturated fatty acid palmitate, which are potent inducers of Npy , McIlwraith et al sought to identify miRNAs that were concurrently altered with Npy expression [ 24 , 25 ]. Of interest, miR-708-5p, one of the miRNAs increased by BPA, modulates Npy expression as miR-708-5p overexpression increases Npy mRNA [ 25 ].…”

“…Of interest, miR-708-5p, one of the miRNAs increased by BPA, modulates Npy expression as miR-708-5p overexpression increases Npy mRNA [ 25 ]. Furthermore, palmitate increased miR-2137 and decreased miR-503-5p levels in hypothalamic cell models, and the overexpression of miR-2137 and miR-503-5p upregulated and downregulated Npy mRNA levels, respectively [ 24 ]. Since miRNAs primarily act as repressors of gene expression, miR-708-5p and miR-2137 likely increase Npy through an indirect mechanism that does not involve direct binding to the Npy 3′ UTR.…”