Carboxyl-ester lipase is a digestive pancreatic enzyme encoded by the highly polymorphic CEL gene1. Mutations in CEL cause maturity-onset diabetes of the young (MODY) with pancreatic exocrine dysfunction2. Here we identified a hybrid allele (CEL-HYB), originating from a crossover between CEL and its neighboring pseudogene CELP. In a discovery cohort of familial chronic pancreatitis cases, the carrier frequency of CEL-HYB was 14.1% (10/71) compared with 1.0% (5/478) in controls (odds ratio [OR] = 15.5, 95% confidence interval [CI] = 5.1-46.9, P = 1.3 × 10−6). Three replication studies in non-alcoholic chronic pancreatitis cohorts identified CEL-HYB in a total of 3.7% (42/1,122) cases and 0.7% (30/4,152) controls (OR = 5.2, 95% CI = 3.2-8.5, P = 1.2 × 10−11; formal meta-analysis). The allele was also enriched in alcoholic chronic pancreatitis. Expression of CEL-HYB in cellular models revealed reduced lipolytic activity, impaired secretion, prominent intracellular accumulation and induced autophagy. The hybrid variant of CEL is the first chronic pancreatitis gene identified outside the protease/antiprotease system of pancreatic acinar cells.

Mitochondrial dysfunction and altered proteostasis are central features of neurodegenerative diseases. The pitrilysin metallopeptidase 1 (PITRM1) is a mitochondrial matrix enzyme, which digests oligopeptides, including the mitochondrial targeting sequences that are cleaved from proteins imported across the inner mitochondrial membrane and the mitochondrial fraction of amyloid beta (Ab). We identified two siblings carrying a homozygous PITRM1 missense mutation (c.548G>A, p.Arg183Gln) associated with an autosomal recessive, slowly progressive syndrome characterised by mental retardation, spinocerebellar ataxia, cognitive decline and psychosis. The pathogenicity of the mutation was tested in vitro, in mutant fibroblasts and skeletal muscle, and in a yeast model. A Pitrm1 +/À heterozygous mouse showed progressive ataxia associated with brain degenerative lesions, including accumulation of Ab-positive amyloid deposits. Our results show that PITRM1 is responsible for significant Ab degradation and that impairment of its activity results in Ab accumulation, thus providing a mechanistic demonstration of the mitochondrial involvement in amyloidotic neurodegeneration.

CEL-maturity onset diabetes of the young (MODY), diabetes with pancreatic lipomatosis and exocrine dysfunction, is due to dominant frameshift mutations in the acinar cell carboxyl ester lipase gene (CEL). As Cel knock-out mice do not express the phenotype and the mutant protein has an altered and intrinsically disordered tandem repeat domain, we hypothesized that the disease mechanism might involve a negative effect of the mutant protein. In silico analysis showed that the pI of the tandem repeat was markedly increased from pH 3.3 in wild-type (WT) to 11.8 in mutant (MUT) human CEL. By stably overexpressing CEL-WT and CEL-MUT in HEK293 cells, we found similar glycosylation, ubiquitination, constitutive secretion, and quality control of the two proteins. The CEL-MUT protein demonstrated, however, a high propensity to form aggregates found intracellularly and extracellularly. Different physicochemical properties of the intrinsically disordered tandem repeat domains of WT and MUT proteins may contribute to different short and long range interactions with the globular core domain and other macromolecules, including cell membranes. Thus, we propose that CEL-MODY is a protein misfolding disease caused by a negative gain-of-function effect of the mutant proteins in pancreatic tissues.Most monogenic forms of diabetes are due to mutations in genes expressed in the pancreatic beta cell. Previously, Raeder et al.(1) reported a novel monogenic syndrome caused by mutations in the carboxyl ester lipase gene (CEL) (OMIM 609812; CEL-MODY 2 or MODY8), characterized by dominantly inherited childhood-onset pancreatic exocrine dysfunction and diabetes mellitus from adulthood. Notably, this gene is not transcribed in beta cells but is mainly expressed in pancreatic acinar tissue (2, 3) and lactating mammary glands (4, 5). The CEL enzyme (EC 3.1.1.13), also known as bile salt-stimulated/dependent lipase, is secreted into the intestine and activated by bile salts, playing a role in the hydrolysis and absorption of cholesterol-and lipid-soluble vitamins (6).The human CEL gene is ϳ10 kb in size and consists of 11 exons. In the last exon, there is a variable number of tandem repeats (VNTR) where the 33-bp nearly identical segments are repeated usually between 7 and 23 times (1, 7-9). The VNTR of the most common CEL allele has 16 repeats, thereby encoding a protein consisting of 745 amino acids with a predicted molecular mass of ϳ79 kDa. The rat Cel is secreted from the acinar cells and is thought to follow the classical pathway of secretory proteins (for review see Ref.3). In the endoplasmic reticulum (ER), the protein is co-translationally N-glycosylated at a conserved Asn residue (Asn-210), serving as a client protein for the molecular chaperone GRP94 and being associated with ER membranes (10, 11). The VNTR-encoded protein C terminus is heavily O-glycosylated in the mature protein, probably on Thr residues before or after PVPP motifs in the first 10 repeats (12). The O-glycosylation sites are present in a region enriched in the amino ...