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Heat Shock Protein 27 Overexpression Mitigates Cytokine-Induced Islet Apoptosis and Streptozotocin-Induced Diabetes

Harbor-UCLA Los Angeles Biomedical Research Institute (T.D., M.P.-C., J.M., J.L., L.P., D.B., P.C., L.T., Y.W., S.G.A.), Torrance, California 90502; Beckman Research Institute of City of Hope (R.N., I.T.), Duarte, California 91010; Cedars-Sinai Medical Center (C.C.N.), Los Angeles, California 90048; and Imperial College (J.d.B., D.J.W.), London SW7 2AZ, United Kingdom

Address all correspondence and requests for reprints to: Sharon G. Adler, M.D., Harbor-UCLA, Los Angeles Biomedical Research Institute, Division of Nephrology and Hypertension, 1124 West Carson Street, Torrance, California 90502. E-mail: sadler{at}labiomed.org.

β-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 β-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 B protein kinase (nuclear factor B essential modulator) binding were assessed by coimmunoprecipitation. HSP27 transgene (TG) in pancreas localized predominantly in β-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 B protein kinase (nuclear factor B essential modulator). These data show islet protection by HSP27 by mitigation of apoptosis, possibly through nuclear factor B regulation.