title: Heat shock protein 27 overexpression mitigates cytokine-induced islet apoptosis and streptozotocin-induced diabetes.
abstract: Beta-cell apoptosis occurs in diabetes mellitus (DM). Heat shock protein (HSP) 27 (human homolog of rodent HSP25) mitigates stress-induced apoptosis but has not been studied in beta-cells. We tested whether HSP27 overexpression attenuates streptozotocin (SZ)-induced DM in vivo and cytokine-induced islet apoptosis in vitro. DM was ascertained by ip glucose tolerance testing, and fasting serum insulin/glucose was measured. Pancreas was stained for insulin, HSP27, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling, and insulin content was measured. HSP25/27 was measured by immunoblotting, isoelectric focusing, and RT-PCR. Islet HSP25/27 oligomerization and inhibitory kappaB protein kinase gamma (nuclear factor kappaB essential modulator) binding were assessed by coimmunoprecipitation. HSP27 transgene (TG) in pancreas localized predominantly in beta-cells. Baseline pancreatic insulin levels in wild-type (WT) and HSP27TG mice were similar, but lower in WT than HSP27TG after SZ (P < 0.01). Intraperitoneal glucose tolerance testing confirmed protection from SZ-DM in HSP27TG. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and inducible nitric oxide synthase staining were increased in WT vs. HSP27TG islets (P < 0.05) after SZ. Caspase-3 activity was lower in islets from HSP27TG vs. WT mice after cytokine stress in vitro (P < 0.05). There was more HSP25 plus 27 protein from HSP27TG islets than HSP25 from WT (P < 0.01). HSP25 protein but not mRNA was increased in HSP27TG mice. Isoelectric focusing showed similar relative HSP phosphorylation in HSP27TG and WT (P > 0.05). HSP27 bound native HSP25 in TG islets; both bound to inhibitory kappaB protein kinase gamma (nuclear factor kappaB essential modulator). These data show islet protection by HSP27 by mitigation of apoptosis, possibly through nuclear factor kappaB regulation.
authors.affiliation: Harbor-UCLA Los Angeles Biomedical Research Institute, Torrance, California 90502, USA.
authors.forename: Tiane
authors.initials: T
authors.lastname: Dai
authors.forename: Mina
authors.initials: M
authors.lastname: Patel-Chamberlin
authors.forename: Rama
authors.initials: R
authors.lastname: Natarajan
authors.forename: Ivan
authors.initials: I
authors.lastname: Todorov
authors.forename: Jun
authors.initials: J
authors.lastname: Ma
authors.forename: Janine
authors.initials: J
authors.lastname: LaPage
authors.forename: Lynetta
authors.initials: L
authors.lastname: Phillips
authors.forename: Cynthia C
authors.initials: CC
authors.lastname: Nast
authors.forename: Diana
authors.initials: D
authors.lastname: Becerra
authors.forename: Peter
authors.initials: P
authors.lastname: Chuang
authors.forename: Lili
authors.initials: L
authors.lastname: Tong
authors.forename: Jacqueline
authors.initials: J
authors.lastname: de Belleroche
authors.forename: Dominic J
authors.initials: DJ
authors.lastname: Wells
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.forename: Sharon G
authors.initials: SG
authors.lastname: Adler