Colonic dysmotility associated with high‐fat diet‐induced obesity: Role of enteric glia

Abstract

The present study was designed to examine the role of enteric glial cells (EGCs) in colonic neuromuscular dysfunctions in a mouse model of high‐fat diet (HFD)‐induced obesity. C57BL/6J mice were fed with HFD or standard diet (SD) for 1, 2, or 8 weeks. Colonic interleukin (IL)‐1β, IL‐6, and malondialdehyde (MDA) levels were measured. Expression of occludin in colonic tissues was examined by western blot. Substance P (SP), S100β, GFAP, and phosphorylated mitogen‐activated protein kinase 1 (pERK) were assessed in whole mount specimens of colonic plexus by immunohistochemistry. Colonic tachykininergic contractions, elicited by electrical stimulation or exogenous SP, were recorded in the presence or absence of fluorocitrate (FC). To mimic exposure to HFD, cultured EGCs were incubated with palmitate (PA) and/or lipopolysaccharide (LPS). SP and IL‐1β levels were assayed in the culture medium by ELISA. HFD mice displayed an increase in colonic IL‐1β and MDA, and a reduction of occludin at week 2. These changes occurred to a greater extent at week 8. In vitro electrically evoked tachykininergic contractions were enhanced in HFD mice after 2 or 8 weeks, and they were blunted by FC. Colonic IL‐6 levels as well as substance P and S100β density in myenteric ganglia of HFD mice were increased at week 8, but not at week 1 or 2. In cultured EGCs, co‐incubation with palmitate plus LPS led to a significant increase in both SP and IL‐1β release. HFD‐induced obesity is characterized by a hyperactivation of EGCs and is involved in the development of enteric motor disorders through an increase in tachykininergic activity and release of pro‐inflammatory mediators.

Glial A2B Adenosine Receptors Modulate Abnormal Tachykininergic Responses and Prevent Enteric Inflammation Associated with High Fat Diet-Induced Obesity

“…Increasing evidence points to an active involvement of EGCs in controlling several homeostatic gut functions, including mucosal sensation, secretion, motility, and immune responses, as well as a pivotal role in the pathophysiology of enteric motor dysfunctions associated with inflammatory conditions [9,35]. In line with this view, our previous study highlighted the contribution of enteric glia in the onset of colonic motor alterations associated with HFD-induced obesity, through an increase in tachykininergic activity and release of pro-inflammatory mediators (i.e., IL-1β) [9].…”

“…Electrically evoked contractions were recorded from colonic preparations maintained in Krebs solution containing 100 µM L-NAME, 10 µM guanethidine, 1 µM atropine, 1 µM GR159897, 1 µM SB218795, and 1 µM BAY60-6583 or 10 nM MRS1754, either in the absence or presence of 50 µM FC. Concentrations were selected in accordance with previous studies [9,21].…”

“…Fresh isolated distal colonic 3 cm segments from SD and HFD mice were gently flushed with warm (37 • C) Krebs solution to remove any luminal content, and incubated with or without 50 µM FC for 1 h in organ baths containing Krebs solution at 37 • C, bubbled with 95% O 2 + 5% CO 2 [9,24]. The colonic segments were then fixed with 4% paraformaldehyde in phosphate buffered saline (PBS) for 2 h at room temperature.…”

“…A stock solution of palmitate (PA, Sigma-Aldrich) was prepared as previously described by Antonioli et al [9]. Briefly, to obtain 200 mM of stock solution, PA was dissolved in pre-heated water and the mixture was incubated at 70 • C overnight with constant vortexing.…”

“…The mechanisms underlying the onset and development of such disorders in the setting of obesity are still scarcely investigated. However, a recent paper from our group showed that EGCs are involved in the development of enteric motor disorders associated with a high fat diet (HFD), through an increase in the release of pro-inflammatory mediators and tachykininergic neurotransmission [9].…”