Cell Death and Autophagy in Chronic Pancreatitis

点击翻译按钮获取中文摘要

Chronic pancreatitis (CP) is a disease of the exocrine pancreas common among Veterans patient population, the pathogenesis of which remains obscure and for which there are no specific or effective treatments. The disease is burdened with poor quality of life of the patients and excess mortality, considerable health care costs, and is a major risk factor for the deadly pancreatic cancer. Among a few known genetic factors predisposing to pancreatitis are mutations in a protein called SPINK1, which increase the risk of chronic pancreatitis 20- to 40-fold. The function of this protein is not clear; mice with genetic deletion of Spink3, the mouse ortholog of SPINK1, die shortly after birth, thus preventing investigation of long-term effects of SPINK deficiency. To overcome this obstacle, we developed transgenic mice in which one of the two Spink3 alleles ablated in Spink3-/- mice is replaced by human SPINK1. In these mice (termed SPINK1- in) the expression of SPINK is partially restored under control of its endogenous promoter. We found that such restoration rescues Spink3-/- mice from lethality; and further, that SPINK1-in mice develop spontaneous pancreatitis, thus representing a new genetic model of CP. We propose to use this new genetic model, as well as the commonly used repetitive-cerulein experimental model to elucidate the pathogenic mechanism of CP, in particular, the death pathways of acinar cells, the main cell type of the exocrine pancreas. Acinar cell death is a major complication of CP, leading to parenchymal loss, pancreas atrophy, and exocrine insufficiency. Maintaining acinar cell survival to prevent or reduce parenchymal loss in CP is of paramount importance as a therapeutic approach. However, essentially nothing is known on the modalities and mechanisms of acinar cell death in CP. Our preliminary results indicate that a distinct type of programmed necrosis, termed necroptosis, is the major modality of acinar cell death in CP. The data further indicate that upregulation of kinase RIP3 underlies necroptosis in CP models. Autophagy is the principal cellular degradative, lysosome-driven mechanism; it mediates cell adaptation to stresses by removing damaged organelles and protein aggregates toxic for the cell. SPINK1-in mice very early develop massive accumulation of autophagic vacuoles in acinar cells, an indication of impaired autophagic flux. Our preliminary results further suggest that underlying mechanisms involve lysosomal dysfunction caused by loss of LAMP2, a major lysosomal membrane protein. Autophagy is a key cell survival mechanism; in particular, it eliminates a multiprotein complex termed necrosome, which mediates necroptosis. However, whether autophagy is impaired in CP, and whether it plays a role in acinar cell death in CP, has not been studied. We propose to use the genetic and experimental models of CP to elucidate the mechanisms of autophagic/lysosomal dysfunction and acinar cell death, and the link between these pathologies in CP. The central hypothesis of this proposal is that the major pathway of acinar cell death in CP is necroptosis, mediated by autophagic/lysosomal dysfunction. Pharmacologic and genetic approaches to inhibit necroptosis and to restore efficient autophagy will prevent acinar cell death and ameliorate CP. We propose the following Specific Aims: 1) Determine the mechanisms of acinar cell death in the genetic and experimental models of CP; 2) Determine the mechanisms of autophagic/lysosomal dysfunction in CP models; 3) Determine the role of impaired autophagy in acinar cell death in CP models.