Master of Science
Physiology and Biophysics
S. Murthy Karnam
Recent deorphanization of several G-protein-coupled receptors (GPRs) as endogenous receptors for free fatty acids (FFAs) has increased our understanding of these nutrients as signaling molecules and the integral role of gut microbiota in the regulation of host defense mechanisms, energy metabolism, gastrointestinal motility and secretion. There are five distinct FFA receptors (FFRAs: FFAR1, FFAR2, FFAR3, FFAR4 and GPR84) that differ in molecular structure, ligand specificity, expression pattern, and functional properties. FFARs are grouped according to the chain length of FFAs that activate each FFAR.
Enteric glial cells and enteroendocrine cells play a pivotal role in the secretion of gliotransmitters and peptide hormones, respectively, in response to specific stimuli. Neurotrophins such as brain-derived neurotrophic factor (BDNF) are essential for the development and integrity of enteric nervous system in the gut and play an important role in the regulation of gastrointestinal functions including motility and secretion.
The aim of this study was to identify the expression of FFARs in enteric glial cells and endocrine cells and determine the effects of fatty acids in the regulation of BDNF levels. Expression studies of FFARs by quantitative PCR, western blot and Immunohistochemistry from glial cells and enteroendocrine cells (STC-1 cells) demonstrated predominant expression of FFAR4 in STC-1 cells and predominant expression of FFAR1 in glial cells. Both FFAR1 and FFAR4 are activated by long-chain fatty acid.
Activation of specific G protein(s) coupled to FFAR1 and FFAR4 and signaling pathways downstream of G proteins in response to the endogenous long chain fatty acid, linolenic acid (100 µM), demonstrated both FFAR1 and FFAR4 are coupled to Gαq and stimulation of PLC-β/IP3/ Ca2+ pathway. In enteroendocrine cells (STC-1) long chain fatty acids preferentially activate FFAR4, whereas in glial cells long chain fatty acids preferentially activate FFAR1. Furthermore, measurement of changes in BDNF levels in response to linolenic acid by immunocytochemistry and enzyme-linked immunosorbent assay (ELISA) demonstrated that in STC-1 cells, long chain fatty acids increased BDNF content via FFAR4, whereas in glial cells they increased BDNF content via FFAR1. The present study shed light on the expression and physiological role of long chain fatty acids and FFARs in the regulation of BDNF levels, and thus, gastrointestinal functions.
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Available for download on Saturday, May 08, 2021