Role of catestatin in intestinal epithelial cell turnover and glucose uptake in hyperleptinemic type 2 diabetic mice

Abstract

The small intestine is the major site for nutrient absorption and is critical in maintenance of euglycemia. We previously showed that the intestinal Na+/glucose cotransporter isoform 1 (SGLT1), responsible for the majority of Na+‐dependent glucose uptake, is decreased in hyperleptinemic db/db mice, but not in leptin‐deficient ob/ob mice. Further, we showed that only hyperleptinemic mice exhibit increased intestinal mucosal mass with longer villi and deeper crypts compared to controls. Catestatin (CST), a 21‐amino acid fragment of chromogranin A, has been shown to modulate leptin signaling. Therefore, we hypothesized that CST treatment would affect leptin signaling in db/db mice resulting in normalization of intestinal epithelial cell turnover and better glycemic control. In order to understand the increased mucosal mass in hyperleptinemic mice, we quantified intestinal proliferation and apoptosis in the jejunum of db/db, ob/ob, and control (db/con, ob/con) mice (n=4–5/genotype). Compared to controls, db/db mice had more proliferating cell nuclear antigen‐positive cells in the crypt compartment (2,361±110 vs 1,453±211 cells; P<0.05) indicating an increased proliferative response, while cleaved caspase‐3 staining, a marker for apoptosis, showed reduced apoptosis in the crypts (2.5±0.5 vs 9.5±0.5 cells; P<0.05) and villi tips (5±1 vs 9±1 cells; P<0.05). Proliferation and apoptosis were not different between control and ob/ob mice. In a separate cohort, we treated db/db (n=4) and db/con (n=5) mice for 7 days with CST (5 mg/kg/day i.p.). After 7 days, CST treatment not only restored intestinal SGLT1 expression but also normalized villus length and intestinal proliferation to levels found in controls. To study if there is a functional consequence of elevated leptin levels and consequently reduced SGLT1 abundance for intestinal glucose uptake, we performed oral glucose tolerance tests (OGTT) by administering glucose (2 g/kg, 1% of bw via oral gavage) without or with phlorizin, an SGLT1/2 inhibitor (0.5 g/kg), to db/db and db/con mice (n=4–8/genotype). Blood glucose was measured at 0, 15, 30, 45, 60 and 120 min and the area under the curve (AUC) was calculated. Compared to vehicle, phlorizin significantly improved glycemic control in db/con mice (AUC: 13,857±4,051 vs 36,483±7,747; P<0.05) but was without effect in db/db mice (AUC: 12,794±4,675 vs 13,714±2,648; P=NS). In addition, phlorizin treatment mimicked the glucose profile found in SGLT1 knockout mice subjected to OGTT (AUC: 6,325±2,535). In conclusion, CST may be a novel regulator that interferes with leptin signaling in hyperleptinemic db/db mice and may lead to beneficial consequences on intestinal turnover and restoration of SGLT1 abundance.Support or Funding InformationThis work was supported by a Bastyr University Faculty‐Student Research Grant, O'Brien Center for Acute Kidney Injury Research Grant P30DK079337, Diabetes Endocrinology Research Center P30DK063491, American Heart Association 15BGIA22410018, and Satellite Healthcare (a not‐for‐profit renal care provider).