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

Immortalization and Characterization of GFAP-expressing Glial Cells from the Adult Mouse Hypothalamus, Cortex, and Brain Stem

The generation of astrocyte cell lines from the hypothalamus is key to study glial involvement in hypothalamic physiology, including energy homeostasis. As such, we immortalized astrocytes from the hypothalamus of an adult male CD-1 mouse using SV40 T-antigen to generate the mHypoA-Ast1 cell line. A comparative approach was taken with two other murine GFAP-expressing cell lines that were also generated in this study: a mixed glial cell line from the cortex (mCortA-G1) and an oligodendrocyte cell line from the brainstem (mBstA-Olig1), as well as an established microglial cell line (IMG). mHypoA-Ast1 cells express GFAP, alongside other astrocytic markers such as Aldh1l1, Aqp4, Glt1 and S100b, and express low levels of microglial, ependymal and oligodendrocyte markers. 100 ng/mL lipopolysaccharide (LPS) elevated mRNA levels of Il6, Il1b, Tnfα and Cxcl5 in mHypoA-Ast1 cells after 4 h, while 50 μM palmitate increased Il6 and Chop mRNA, demonstrating the ability of these cells to respond to inflammatory and nutrient signals. Interestingly, co-culture of mHypoA-Ast1 cells with mHypoE-N46 hypothalamic neuronal cells prevented the palmitate-mediated increase in orexigenic neuropeptide Agrp mRNA in mHypoE-N46 cells, suggesting that this cell line can alter neuronal responses to nutrients. In conclusion, we report mHypoA-Ast1 cells representing a functional astrocyte cell line from the adult mouse brain that can be used to study the complex interactions of hypothalamic cells, as well as dysregulation that may occur in disease states, providing a key tool for neuroendocrine research.

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

Diets high in saturated fatty acids are associated with obesity and infertility. Palmitate, the most prevalent circulating saturated fatty acid, is sensed by hypothalamic neurons, contributing to homeostatic dysregulation. Notably, palmitate elevates the mRNA levels of gonadotropin-releasing hormone (Gnrh) mRNA and its activating transcription factor, GATA binding protein 4 (Gata4). GATA4 is essential for basal Gnrh expression by binding to its enhancer region, with Oct-1 (Oct1) and CEBP-β (Cebpb) playing regulatory roles. The pre- and post-transcriptional control of Gnrh by palmitate have not been investigated. Given the ability of palmitate to alter microRNAs (miRNAs), we hypothesized that palmitate-mediated dysregulation of Gnrh mRNA involves specific miRNAs. In the mHypoA-GnRH/GFP neurons, palmitate significantly downregulated six miRNAs (miR-125a, miR-181b, miR-340, miR-351, miR-466c and miR-503), and the repression was attenuated by co-treatment with 100 μM of oleate. Subsequent mimic transfections revealed that miR-466c significantly downregulates Gnrh, Gata4, and Chop mRNA and increases Per2, whereas miR-340 upregulates Gnrh, Gata4, Oct1, Cebpb, and Per2 mRNA. Our findings suggest that palmitate may indirectly regulate Gnrh at both the pre- and post-transcriptional levels by altering miR-466c and miR-340, which in turn regulate transcription factor expression levels. In summary, palmitate-mediated dysregulation of Gnrh and, consequently, reproductive function involves parallel transcriptional mechanisms.

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

The hypothalamus is a vital regulator of energy homeostasis. Orexigenic neuropeptide Y (NPY) neurons within the hypothalamus can stimulate feeding and suppress energy expenditure, and dysregulation of these neurons may contribute to obesity. We previously reported that bisphenol A (BPA), an endocrine disruptor with obesogenic properties, alters Npy transcription in hypothalamic neurons by inducing oxidative stress. We hypothesized that hypothalamic microRNAs (miRNAs), a class of small non-coding RNAs, could directly regulate Npy gene expression by binding the 3' untranslated region (UTR). Five predicted Npy-targeting miRNA candidates were uncovered through TargetScan and were detected in Npy-expressing hypothalamic neuronal cell models and hypothalamic neuronal primary cultures. BPA dysregulated the expression of a number of these hypothalamic miRNAs. We examined the effects of putative Npy-targeting miRNAs using miRNA mimics, and we found that miR-143-3p, miR-140-5p, miR-29b-1-5p, and let-7b-3p altered Npy expression in the murine hypothalamic cell lines. Importantly, miR-143-3p targets the mouse Npy 3' UTR, as detected using a luciferase construct containing the potential 3' UTR binding sites. Overall, this study established the first hypothalamic miRNA that directly targets the 3' UTR of mouse Npy, emphasizing the involvement of miRNAs in the NPY system and providing an alternative target for control of NPY levels.

Promise and Perils of MicroRNA Discovery Research: Working Toward Quality Over Quantity

Since the first microRNA (miRNA) was described in 1993 in the humble worm Caenorhabditis elegans, the miRNA field has boomed, with more than 100 000 related patents filed and miRNAs now in ongoing clinical trials. Despite an advanced understanding of the biogenesis and action of miRNAs, applied miRNA research faces challenges and irreproducibility due to a lack of standardization. This review provides guidelines regarding miRNA investigation, while focusing on the pitfalls and considerations that are often overlooked in prevailing applied miRNA research. These include miRNA annotation and quantification, to modulation, target prediction, validation, and the study of circulating miRNAs.

Palmitate alters miRNA content of small extracellular vesicles secreted from NPY/AgRP-expressing hypothalamic neurons

Exosomes (sEVs) are extracellular vesicles involved in the pathogenesis of obesity. Notably, exosomal microRNAs (miRNAs) have emerged as crucial mediators of communication between cells and are involved in the development of obesity. One region of the brain known to be dysregulated in obesity is the hypothalamus. It coordinates whole-body energy homeostasis through stimulation and inhibition of the orexigenic neuropeptide (NPY)/agouti-related peptide (AgRP) neurons and anorexigenic proopiomelanocortin (POMC) neurons. A role for hypothalamic astrocytic exosomes in communication with POMC neurons was previously elucidated. Yet, it was unknown whether NPY/AgRP neurons secreted exosomes. We previously established that the saturated fat palmitate alters the intracellular levels of miRNAs and we now questioned whether palmitate would also alter the miRNA content of exosomal miRNAs. We found that the mHypoE-46 cell line secreted particles consistent with the size of exosomes and that palmitate altered levels of a spectrum of miRNAs associated with exosomes. The predicted KEGG pathways of the collective miRNA predicted targets included fatty acid metabolism and insulin signaling. Of note, one of these altered secreted miRNAs was miR-2137, which was also altered within the cells. We also found that while sEVs collected from the mHypoE-46 neurons increased Pomc mRNA in the mHypoA-POMC/GFP-2 cells after 48 hours, the effect was absent with sEVs isolated following palmitate treatment, indicating another potential route by which palmitate promotes obesity. Hypothalamic neuronal exosomes may therefore play a role in the control of energy homeostasis that may be disrupted in obese conditions.