1. ¹Department of Nephrology, Monash Medical Centre, Clayton, Vic, Australia
2. ²Department of Medicine, Monash University, Monash Medical Centre, Clayton, Vic, Australia
3. ³JDRF Albert Einstein Centre for Diabetes Complications, Diabetes and Metabolism Division, Baker Medical Research Institute, Melbourne, Vic, Australia
4. ⁴Section of Immunobiology, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT, USA
5. ⁵Howard Hughes Medical Institute, Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA, USA

Correspondence: Dr DJ Nikolic-Paterson, PhD, Department of Nephrology, Monash Medical Centre, 246 Clayton Road, Clayton, Victoria 3168, Australia. E-mail: david.nikolic-paterson@med.monash.edu.au

Received 14 June 2007; Revised 15 December 2007; Accepted 23 December 2007; Published online 18 February 2008.

Abstract

In vitro studies have implicated activation of the p38 mitogen-activated protein kinase (MAPK) signalling pathway in cytokine-mediated pancreatic -cell injury. Activation of the p38 MAPK occurs through two different upstream kinases, mitogen-activated protein kinase kinase 3 (MKK3) and MKK6. This study examined the role of MKK3 signalling in an in vivo model of cytokine-dependent pancreatic injury induced by multiple low doses of streptozotocin (MLD-STZ). Groups of wild-type (WT) or Mkk3-/- C57BL/6J mice received 5 daily injections of STZ (40 mg/kg) and were killed on day 5, week 2 or week 4. MLD-STZ in WT mice exhibited two distinct phases of pancreatic damage: islet cell apoptosis (immunostaining for cleaved caspase-3) on day 5 in the absence of leukocyte infiltration, and this was followed by islet inflammation (leukocyte infiltration and cytokine production) and further islet cell apoptosis on day 14 resulting in a loss of insulin-producing -cells and an 80% incidence of hyperglycaemia. Mkk3-/- mice were not protected from the initial phase of STZ-induced islet cell apoptosis day 5. However, Mkk3-/- mice were completely protected from the induction of hyperglycaemia. This was attributed to inhibition of leukocyte infiltration, production of pro-inflammatory cytokines and islet cell apoptosis at day 14 of MLD-STZ. In vitro studies showed that cultured islets from Mkk3-/- and WT mice are equally susceptible to STZ and cytokine-induced apoptosis. In conclusion, MKK3 signalling plays an essential role in the development of islet inflammation leading to destruction of -cells and hyperglycaemia in MLD-STZ-induced pancreatic injury.