NEW YORK – Researchers have uncovered a cluster of mutations in the CELA2A gene that are associated with metabolic syndrome and early-onset atherosclerosis.
Metabolic syndrome is a constellation of inherited risk factors for coronary artery disease, such as increased blood pressure, diabetes, and abnormal cholesterol levels, and affects more than a third of adults in the US, according to the Centers for Disease Control and Prevention.
In a new study, researchers from Yale School of Medicine focused on individuals and families with early-onset coronary artery disease and metabolic syndrome, cases in whom the condition arose before 30 years of age. By sequencing the exomes of these individuals and their family members, the researchers uncovered multiple independent mutations affecting the CELA2A gene, which encodes chymotrypsin-like elastase family member 2A, that appear to be associated with early-onset disease. Through additional analyses, they found that the CELA2A protein is a circulating enzyme that reduces platelet hyperactivation as well as affects insulin secretion, degradation, and sensitivity.
"Our analyses show that impaired regulation of plasma insulin is a major consequence of disease-inducing CELA2A mutations. The potential to exploit disease pathways makes CELA2A an appealing target for treating diabetes and its complications," Yale's Arya Mani and colleagues wrote in their paper, which appeared today in Nature Genetics.
Through an index case of a 28-year-old American woman of European ancestry with early-onset CAD, the researchers identified a multiplex kindred with 25 affected individuals. Of 53 of her extended family members, 25 were diagnosed with early-onset CAD. Clinical data on 11 living family members with the condition found that they all had similar risk factors, such as high triglyceride levels, low high-density lipoprotein levels, and type 2 diabetes. Meanwhile, the 12 unaffected family members had normal triglyceride and near-normal HDL levels and none had diabetes.
The researchers sequenced the exomes of the index case as well as those of 29 other index cases. At the same time, they conducted a gene-burden analysis based on the family pedigree of the first index case, for which they used DNA samples from 35 family members, both affected and unaffected. From this, they tied a region of chromosome 1 to CAD. This linked region, they noted, harbored a single missense mutation within an intron of the CELA2A gene that segregated with disease.
By two measures — both PolyPhen-2 and SIFT — the 885G>A mutation the researchers uncovered is predicted to be damaging, and the researchers' linkage analysis strongly indicated a link between this locus and CAD.
Additionally, among the other index cases, the researchers also found likely deleterious mutations affecting the CELA2A gene, including two missense mutations and one splice site mutation.
Because of the apparent systemic effects of mutated CELA2, the researchers examined where the protein is expressed. Through combination of western blotting and ELISA testing, they found that, in mice and human cadavers, CELA2 is expressed in a range of tissues — though especially in the pancreas — and is a circulating plasma protein. Mutation carriers, though, had reduced plasma elastase activity compared to non-carriers, they noted.
As individuals with mutated CELA2 commonly also had type 2 diabetes, the researchers assessed the effect of the wild-type version on insulin levels following a meal. In humans, they found that CELA2 levels rise after eating in parallel to the rise in insulin. Further, in mice, they found that CELA2 encourages insulin secretion.
Mutated CELA2, meanwhile, was linked to a decreased ability to break down insulin.
The researchers also noted that CELA2 binds integrin A2B — a protein needed for platelet aggregation — which leads to its cleavage and reduced platelet activation. Mutated CELA2, though, promotes hyperactivation and aggregation of platelets, they reported.
"Loss of these functions by the mutant proteins provides insight into disease mechanisms and suggests that CELA2A could be an attractive therapeutic target," the researchers wrote.