High fat feeding affects the number of GPR120 cells and enteroendocrine cells in the mouse stomach

Abstract

Long-term intake of dietary fat is supposed to be associated with adaptive reactions of the organism and it is assumptive that this is particularly true for fat responsive epithelial cells in the mucosa of the gastrointestinal tract. Recent studies suggest that epithelial cells expressing the receptor for medium and long chain fatty acids, GPR120 (FFAR4), may operate as fat sensors. Changes in expression level and/or cell density are supposed to be accompanied with a consumption of high fat (HF) diet. To assess whether feeding a HF diet might impact on the expression of fatty acid receptors or the number of lipid sensing cells as well as enteroendocrine cell populations, gastric tissue samples of non-obese and obese mice were compared using a real time PCR and immunohistochemical approach. In this study, we have identified GPR120 cells in the corpus region of the mouse stomach which appeared to be brush cells. Monitoring the effect of HF diet on the expression of GPR120 revealed that after 3 weeks and 6 months the level of mRNA for GPR120 in the tissue was significantly increased which coincided with and probably reflected a significant increase in the number of GPR120 positive cells in the corpus region; in contrast, within the antrum region, the number of GPR120 cells decreased. Furthermore, dietary fat intake also led to changes in the number of enteroendocrine cells producing either ghrelin or gastrin. After 3 weeks and even more pronounced after 6 months the number of ghrelin cells and gastrin cells was significantly increased. These results imply that a HF diet leads to significant changes in the cellular repertoire of the stomach mucosa. Whether these changes are a consequence of the direct exposure to HF in the luminal content or a physiological response to the high level of fat in the body remains elusive.

Keywords: FFAR; diet induced obesity; fatty acid receptor; lipid sensing cells; stomach.

Figure 1

Body weights after standard and HF diet feeding for different time periods. (A) After 3 weeks fed with the HF diet, body weight of CF, and HF mice was almost comparable (n = 5, each). (B) HF diet feeding for 6 months resulted in excess body weight of DIO mice relative to CF controls (n = 5, each). P-values were calculated using the unpaired t-test. Data presented as mean ± S.D. Statistically significant results are indicated by ^*P < 0.05, ^**P < 0.005, ^***P < 0.0001 and n.s., not significant.

Figure 2

Impact of HF feeding and feeding duration on relative mRNA amounts for the LCFA receptor GPR120 and numbers of GPR120 and ghrelin cells in the corpus of CF and HF mice. (A) Relative expression levels for GPR120 were measured using real time PCR (n = 5, each group). Feeding a HF diet for 3 weeks already increased GPR120 mRNA levels 1.5 fold in HF mice (dotted) relative to controls (hatched). After 6 months mRNA amounts increased 1.8 times. Data are expressed in relative arbitrary units (RAU) as mean ± S.D and generated in triplicate. Statistically significant results determined by the unpaired t-test are indicated by ^*P < 0.05, ^**P < 0.005, ^***P < 0.0001, and n.s., not significant. (B) In longitudinal sections through the oxyntic mucosa GPR120 immunoreactive cells were restricted to the upper half. (C) CgA positive cells were located in the lower portion of the gastric epithelium. Hatched lines separate the gastric apical and basal halves and arrowheads mark the basement membrane of the gastric mucosa. Sections were counterstained with DAPI. Scale bar (B,C), 20 μm. (D–F) Double immunolabeling analyses demonstrate the colocalization of GPR120 (D) and the brush cell marker acTub (E), as shown in the merged image (F) scale bar (D–F), 5 μm (G) Quantification of GPR120 positive cells upon a HF diet for 3 weeks and 6 months. In the apical half of the corpus mucosa immunoreactive cells for GPR120 were counted in a unit area of 320 × 260 μm on four to five consecutive longitudinal sections. Mean numbers (± S.D.) of immunopositive cells in CF (hatched) and HF (dotted) mice (n = 5, each). Cell densities are expressed as labeled cell numbers per unit area. (H) Both short- and long-term feeding a HF diet increased the frequency of ghrelin cells in the corpus.

Figure 3

Effect of HF feeding on relative mRNA amounts of fatty acid receptors and numbers of GPR120 and gastrin cells in the antrum of CF and HF mice. (A) Feeding a HF diet for 3 weeks did not change mRNA levels for GPR120 and GPR43. HF mice (dotted), controls (hatched). Real time PCR data are expressed in relative arbitrary units (RAU) as mean ± S.D and generated in triplicate (n = 5, each). (B) Frequency of GPR120 immunoreactive cells decreased in the antrum of HF fed mice after 3 weeks and 6 months, respectively. (C) After 3 weeks and 6 months density of gastrin cells is elevated upon a HF diet in the antrum. Mean numbers (± S.D.) of immunopositive cells in CF (hatched) and HF (dotted) mice (n = 5, each). Cell densities are expressed as labeled cell numbers per unit area. ^*P < 0.05, ^**P < 0.005, and ^***P < 0.0001, n.s., not significant.