Intestinal adaptation occurs independently of parenteral long-chain triacylglycerol and with no change in intestinal eicosanoids after mid-small bowel resection in rats

Mechanisms of enteral nutrient-enhanced intestinal adaptation

The role of enteral nutrients in maintaining small intestinal structure and function is well established. Evidence that enteral nutrients induce intestinal adaptation include the structural and functional gradient along the length of the healthy intestine, the atrophy and functional compromise induced by fasting and parenteral nutrition, and the enhanced adaptive capacity of the distal intestine following partial enterectomy. Key mechanisms contributing to enteral nutrient-induced intestinal adaptation include nonspecific luminal stimulation and that provided by specific nutrients, "functional workload" induced by polymeric nutrients, potential stimulation of pancreaticobiliary secretions, secretion of humoral mediators, and induction of intestinal hyperemia.

Suppressor of cytokine signaling-2: a growth hormone-inducible inhibitor of intestinal epithelial cell proliferation

BACKGROUND & AIMS

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) increase intestinal growth. GH is thought to act indirectly via IGF-I. In several models, including rats given total parenteral nutrition (TPN), IGF-I more potently stimulates mucosal growth than GH, even when GH induces similar circulating IGF-I levels. These studies test the hypothesis that GH induces a suppressor of cytokine signaling (SOCS), which inhibits intestinal epithelial cell (IEC) proliferation.

METHODS

Rats on TPN received vehicle, GH, or IGF-I. Jejunal SOCS (SOCS-1, -2, -3, and cytokine-inducible SH2-domain-containing protein [CIS]) and IGF-I messenger RNA (mRNA) were quantified. Caco-2, IEC-6 cells, and SOCS-2 null and wild-type (WT) mice were used to examine the expression and functional role of SOCS-2.

RESULTS

As reported previously, IGF-I, but not GH, prevented mucosal atrophy during TPN, although GH elevated plasma IGF-I and increased body weight. GH, but not IGF-I, induced jejunal SOCS-2 mRNA. SOCS-2 mRNA levels in GH and IGF-I-treated rats inversely correlated with mucosal weight. SOCS-2 is expressed in Caco-2 cells, and elevated SOCS-2 expression in postconfluent cells is associated with reduced proliferative rates. SOCS-2 overexpression in Caco-2 cells inhibited cell proliferation and promoted differentiation. In IEC-6 cells, GH induced SOCS-2 and reduced basal or IGF-I-induced proliferation. GH also reduced proliferative activity in isolated crypts from WT but not SOCS-2 null mice, and SOCS-2 null crypts showed enhanced proliferative responses to GH and IGF-I. SOCS-2 null mice have increased intestinal weight and length.

CONCLUSIONS

SOCS-2 is a GH-inducible, novel inhibitor of intestinal epithelial cell proliferation and intestinal growth.