The PERK Eukaryotic Initiation Factor 2α Kinase Is Required for the Development of the Skeletal System, Postnatal Growth, and the Function and Viability of the Pancreas

Abstract

Phosphorylation of eukaryotic initiation factor 2α (eIF-2α) is typically associated with stress responses and causes a reduction in protein synthesis. However, we found high phosphorylated eIF-2α (eIF-2α[P]) levels in nonstressed pancreata of mice. Administration of glucose stimulated a rapid dephosphorylation of eIF-2α. Among the four eIF-2α kinases present in mammals, PERK is most highly expressed in the pancreas, suggesting that it may be responsible for the high eIF-2α[P] levels found therein. We describe a Perk knockout mutation in mice. Pancreata of Perk^−/− mice are morphologically and functionally normal at birth, but the islets of Langerhans progressively degenerate, resulting in loss of insulin-secreting beta cells and development of diabetes mellitus, followed later by loss of glucagon-secreting alpha cells. The exocrine pancreas exhibits a reduction in the synthesis of several major digestive enzymes and succumbs to massive apoptosis after the fourth postnatal week. Perk^−/− mice also exhibit skeletal dysplasias at birth and postnatal growth retardation. Skeletal defects include deficient mineralization, osteoporosis, and abnormal compact bone development. The skeletal and pancreatic defects are associated with defects in the rough endoplasmic reticulum of the major secretory cells that comprise the skeletal system and pancreas. The skeletal, pancreatic, and growth defects are similar to those seen in human Wolcott-Rallison syndrome.

We thank Lillian B. Nanney and Kelly Parman of the Mouse Pathology and Immunohistochemistry Core Lab at Vanderbilt University Medical Center for their help with the processing and immunostaining of mouse tissues. We gratefully acknowledge Mark Magnuson of the Transgenic Mouse/Embryonic Stem Cell Shared Resource at Vanderbilt University Medical Center for his assistance with the design of the targeted Perk knockout, and we thank Cathleen Pettepher for her help in generating the Perk knockout mice. Our thanks also go to the staff of the Electron Microscopy Facility at the Pennsylvania State University for their technical assistance with transmission electron microscopy and immunohistochemistry, to Jeffery O'Neil for his help with monitoring mouse growth and blood glucose levels, and to Donna Brantlinger Black for her help with preparation of the manuscript. Finally, we thank Ronald Wek for providing PERK cDNA clones, DNA sequence information, anti-PERK (hPEK) antisera, and valuable discussions throughout this work.

This work was supported by the Culpeper Foundation, the Vanderbilt Clinical Nutrition Research Unit, The Pennsylvania State University, and National Institutes of Health grant GM56957 (to D.R.C.).