Abstract
Astrocytes influence neighboring neurons through the release of a variety of signals, including exosomes, micro-vesicles that contain a vast heterogeneity of molecules such as cytokines, growth factors, RNAs and micro-RNAs (mi-RNAs) that modify target cells. We hypothesized that hypothalamic astrocytes communicate the metabolic status via exosomes to neighboring POMC neurons to modify their functions in the promotion of satiety and energy expenditure. To this end, primary hypothalamic astrocyte cultures were treated with palmitic acid (PA; 0.5 mM), oleic acid (OA; 0.5 mM) or vehicle for 24 hours and exosomes were isolated from the media and applied (1.25 or 2.50 µg/mL) to a POMC neuronal cell line for 24 hours. Exosomes released in response to PA (E-PA) or OA (E-OA) increased POMC expression (p < 0. 05) with no effect on the expression of markers of ER stress (CHOP) and inflammation [interleukin (IL)-6] compared to exosomes released from vehicle treated astrocytes (E-V) or with no exosomes (control). Seahorse Cell Mito Stress test was performed to determinate modifications in metabolism in the POMC neurons in response to these treatments. The mitochondrial spare respiratory capacity of neurons was increased (p < 0. 0001) in response to both doses of E-PA and E-OA, with the maximal respiration (p < 0. 0001) increasing with E-PA (both doses) or 2.50 µg/mL of E-OA compared to E-V or control. Next-generation miRNA sequencing analysis established the modifications of miRNAs contained in exosomes released by hypothalamic astrocytes in response to PA, with miR-199a-3p and miR-145-5p content being higher in E-PA compared to E-V. Transfection of POMC neurons with a mimetic of miR-199a-3p (1.5 pmol) increased POMC expression and insulin-like growth factor 1 receptor (IGF1r) protein levels (p<0. 05). Moreover, levels of mTOR as well as p70S6k, reported targets of miR-199a-3p, were decreased (both p<0. 05). Mimetic overexpression of miR-145-5p reduced POMC expression (p < 0. 001) and protein levels of insulin receptor substrate 1 (IRS1; p < 0. 001), which is a known target of this miRNA. These results suggest that astrocytes communicate with neurons via exosomes, with the exosomes content being modulated in response to the nutritional environment. The messages contained in astrocytic exosomes can directly alter the neuropeptide expression in targeted neurons as well as of the levels of receptors and factors involved in cell protection, metabolism, and nutrient sensing, with specific miRNAs participating in this process. Furthermore, cellular respiration of POMC neurons treated with fatty acid-modified astrocytic exosomes is modified in a manner that suggests they are preparing for a possible respiratory stress by increasing their spare respiratory capacity and maximal respiration. Presentation: No date and time listed