Ganglioside GM3 depletion reverses impaired wound healing in diabetic mice by activating IGF-1 and insulin receptors.

Ganglioside GM3 mediates adipocyte insulin resistance, but the role of GM3 in diabetic wound healing, a major cause of morbidity, is unclear. The purpose of this study was to determine whether GM3 depletion promotes diabetic wound healing and directly activates keratinocyte (KC) insulin pathway signaling. GM3 synthase (GM3S) expression is increased in human diabetic foot skin, ob/ob and diet-induced obese diabetic mouse skin, and in mouse KCs exposed to increased glucose. GM3S knockout in diet-induced obese mice prevents the diabetic wound-healing defect. KC proliferation, migration, and activation of insulin receptor (IR) and insulin growth factor-1 receptor (IGF-1R) are suppressed by excess glucose in wild-type cells, but increased in GM3S (-/-) KCs with supplemental glucose. Co-immunoprecipitation of IR, IR substrate 1 (IRS-1), and IGF-1R, and increased IRS-1 and Akt phosphorylation accompany receptor activation. GM3 supplementation or inhibition of IGF-1R or PI3K reverses the increased migration of GM3S(-/-) KCs, whereas IR knockdown only partially suppresses migration.

Topical delivery of siRNA-based spherical nucleic acid nanoparticle conjugates for gene regulation.

Topical application of nucleic acids offers many potential therapeutic advantages for suppressing genes in the skin, and potentially for systemic gene delivery. However, the epidermal barrier typically precludes entry of gene-suppressing therapy unless the barrier is disrupted. We now show that spherical nucleic acid nanoparticle conjugates (SNA-NCs), gold cores surrounded by a dense shell of highly oriented, covalently immobilized siRNA, freely penetrate almost 100% of keratinocytes in vitro, mouse skin, and human epidermis within hours after application. Significantly, these structures can be delivered in a commercial moisturizer or phosphate-buffered saline, and do not require barrier disruption or transfection agents, such as liposomes, peptides, or viruses. SNA-NCs targeting epidermal growth factor receptor (EGFR), an important gene for epidermal homeostasis, are > 100-fold more potent and suppress longer than siRNA delivered with commercial lipid agents in cultured keratinocytes. Topical delivery of 1.5 uM EGFR siRNA (50 nM SNA-NCs) for 3 wk to hairless mouse skin almost completely abolishes EGFR expression, suppresses downstream ERK phosphorylation, and reduces epidermal thickness by almost 40%. Similarly, EGFR mRNA in human skin equivalents is reduced by 52% after 60 h of treatment with 25 nM EGFR SNA-NCs. Treated skin shows no clinical or histological evidence of toxicity. No cytokine activation in mouse blood or tissue samples is observed, and after 3 wk of topical skin treatment, the SNA structures are virtually undetectable in internal organs. SNA conjugates may be promising agents for personalized, topically delivered gene therapy of cutaneous tumors, skin inflammation, and dominant negative genetic skin disorders.

Epimorphin(-/-) mice have increased intestinal growth, decreased susceptibility to dextran sodium sulfate colitis, and impaired spermatogenesis.

Dynamic and reciprocal epithelial-mesenchymal interactions are critical for the normal morphogenesis and maintenance of epithelia. Epimorphin has been identified as a unique molecule expressed by mesenchymal cells and myofibroblasts and has putative morphogenetic effects in multiple epithelial tissues, including intestine, skin, mammary gland, lung, gallbladder, and liver. To define the in vivo role of epimorphin, we created epimorphin-null mice by targeted inactivation of the epimorphin gene. Male epimorphin-/- mice are sterile due to abnormal testicular development and impaired spermatogenesis. Intestinal growth is increased in epimorphin-/- mice due to augmented crypt cell proliferation and crypt fission during the neonatal (suckling) period, mediated at least in part by changes in bone morphogenetic protein (Bmp) and Wnt/beta-catenin signaling pathways. Colonic mucosal injury and colitis induced by dextran sodium sulfate (DSS) are ameliorated in epimorphin-/- mice, probably due to the increased proliferative capacity of the epimorphin-/- colon. These in vivo findings support the notion that epimorphin is a key stromal regulator of epithelial cell proliferation and growth in the intestine. In addition, our studies demonstrate a novel and critical role for epimorphin in regulating testicular development and growth as well as spermatogenesis.

Targeted intestinal overexpression of the immediate early gene tis7 in transgenic mice increases triglyceride absorption and adiposity.

Following loss of functional small bowel surface area due to surgical resection, the remnant gut undergoes an adaptive response characterized by increased crypt cell proliferation and enhanced villus height and crypt depth, resulting in augmented intestinal nutrient absorptive capacity. Previous studies showed that expression of the immediate early gene tis7 is markedly up-regulated in intestinal enterocytes during the adaptive response. To study its role in the enterocyte, transgenic mice were generated that specifically overexpress TIS7 in the gut. Nucleotides -596 to +21 of the rat liver fatty acid-binding protein promoter were used to direct abundant overexpression of TIS7 into small intestinal upper crypt and villus enterocytes. TIS7 transgenic mice had increased total body adiposity and decreased lean muscle mass compared with normal littermates. Oxygen consumption levels, body weight, surface area, and small bowel weight were decreased. On a high fat diet, transgenic mice exhibited a more rapid and proportionately greater gain in body weight with persistently elevated total body adiposity and increased hepatic fat accumulation. Bolus fat feeding resulted in a greater increase in serum triglyceride levels and an accelerated appearance of enterocytic, lamina propria, and hepatic fat. Changes in fat homeostasis were linked to increased expression of genes involved in enterocytic triglyceride metabolism and changes in growth with decreased insulin-like growth factor-1 expression. Thus, TIS7 overexpression in the intestine altered growth, metabolic rate, adiposity, and intestinal triglyceride absorption. These results suggest that TIS7 is a unique mediator of nutrient absorptive and metabolic adaptation following gut resection.

Growth factor regulation of PC4/TIS7, an immediate early gene expressed during gut adaptation after resection.

BACKGROUND: To define the molecular mechanisms underlying the intestinal adaptive response after partial small bowel resection, we previously identified a cohort of genes regulated in the remnant adaptive ileum. One is PC4/TIS7, an immediate early gene preferentially up-regulated during the first 48 hours after resection. To further the mechanisms that regulate gut adaptation, we sought to identify upstream regulators of PC4/TIS7 expression. METHODS: PC4/TIS7 expression in adaptive versus transection control mouse gut was examined at 48 hours after 50% intestinal resection, and its cellular localization was determined by immunohistochemistry. The effects of intestinotrophic peptides and growth factors on PC4/TIS7 expression were examined in vitro in the crypt epithelial cell line IEC 18 and in vivo in the mouse. RESULTS: PC4/TIS7 was expressed in the cytoplasm of IEC 18 cells and in adaptive mouse ileal crypt and villus enterocytes. Epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) increased PC4/TIS7 mRNA levels in postconfluent, quiescent IEC 18 cells, but insulin-like growth factor 1 (IGF-1) and nerve growth factor (NGF) had no effect. A stable derivative of glucagon-like peptide 2 (GLP-2), r(gly2)GLP-2, was most potent in increasing PC4/TIS7 expression; however, stimulation of proliferation and differentiation were not observed. To determine the effect of GLP-2 on PC4/TIS7 expression in vivo, r(gly2)GLP-2 was administered intraperitoneally to mice. PC4/TIS7 mRNA expression was increased in small bowel in response to GLP-2 compared with vehicle control. CONCLUSIONS: These results suggest that PC4/TIS7 plays a role in intracellular signaling in the intestinal epithelium during the adaptive response, possibly as a common downstream effector for several intestinotrophic growth factors.

Epimorphin expression in intestinal myofibroblasts induces epithelial morphogenesis.

The formation of the crypt-villus axis during gut ontogeny requires continued reciprocal interactions between the endoderm and mesenchyme. Epimorphin/syntaxin 2 (epimorphin) is a mesenchymal protein expressed in the fetal gastrointestinal tract during villus morphogenesis. To elucidate its role in gut ontogeny, the epimorphin cDNA was transfected, in sense and antisense orientations, into a rat intestinal myofibroblast cell line, MIC 216. To determine the effects of epimorphin on the epithelium, myofibroblasts were cocultured with the Caco2 cell line. Caco2 cells spread in a simple monolayer over antisense-transfected cells lacking epimorphin. In contrast, sense-transfected myofibroblasts induced Caco2 cells to form compact, round clusters with small lumens. These morphologic differences were preserved in Transwell cocultures in which cell-cell contact was prevented, suggesting that epimorphin's effects were mediated by secreted factor(s). To determine the effects of epimorphin on crypt-villus axis formation in an in vivo model, rat gut endoderm was combined with epimorphin-transfected myofibroblasts and implanted into the chick intracoelomic cavity. The grafts in which epimorphin was overexpressed revealed multiple well-formed villi with crypt-like units, whereas those in which epimorphin expression was inhibited developed into round cystic structures without crypts or villi. Of several potential secreted morphogens, only the expression of bone morphogenetic protein 4 (Bmp4) was increased in the epimorphin-transfected cells. Incubation with noggin partially blocked the transfected myofibroblasts' effects on Caco2 colony morphology. These results indicate that mesenchymal epimorphin has profound effects on crypt-villus morphogenesis, mediated in part by secreted factor(s) including the Bmp's.