COL4A2 Mutations Impair COL4A1 and COL4A2 Secretion and Cause Hemorrhagic Stroke

Abstract

Collagen, type IV, alpha 1 (COL4A1) and alpha 2 (COL4A2) form heterotrimers and are abundant components of basement membranes, including those of the cerebral vasculature. COL4A1 mutations are an increasingly recognized cause of multisystem disorders, including highly penetrant cerebrovascular disease and intracerebral hemorrhage (ICH). Because COL4A1 and COL4A2 are structurally and functionally associated, we hypothesized that variants in COL4A2 would also cause ICH. We sequence COL4A2 in 96 patients with ICH and identify three rare, nonsynonymous coding variants in four patients that are not present in a cohort of 144 ICH-free individuals. All three variants change evolutionarily conserved amino acids. Using a cellular assay, we show that these putative mutations cause intracellular accumulation of COL4A1 and COL4A2 at the expense of their secretion, which supports their pathogenecity. Furthermore, we show that Col4a2 mutant mice also have completely penetrant ICH and that mutations in mouse and human lead to retention of COL4A1 and COL4A2 within the endoplasmic reticulum (ER). Importantly, two of the three putative mutations found in patients trigger ER stress and activate the unfolded protein response. The identification of putative COL4A2 mutations that might contribute to ICH in human patients provides insight into the pathogenic mechanisms of this disease. Our data suggest that COL4A2 mutations impair COL4A1 and COL4A2 secretion and can also result in cytotoxicity. Finally, our findings suggest that, collectively, mutations in COL4A1 and COL4A2 contribute to sporadic cases of ICH.

The expanding phenotype of COL4A1 and COL4A2 mutations: clinical data on 13 newly identified families and a review of the literature

“…Of the mutations in Supplementary Figure S1 online, only the COL4A2 mutation in family L was previously reported in a sporadic adult patient with intracerebral hemorrhage. 26 It introduces a glycine at the triple helical domain of the protein and was shown to be pathogenic using functional studies. 26 All but one of the COL4A1 mutation missense changes led to substitution of glycine in the triple helical domain of the protein (families A, B, C, G, H, I, K, and M).…”

“…26 It introduces a glycine at the triple helical domain of the protein and was shown to be pathogenic using functional studies. 26 All but one of the COL4A1 mutation missense changes led to substitution of glycine in the triple helical domain of the protein (families A, B, C, G, H, I, K, and M). The changes in families A, C, G, and M have an official status of "variant of unknown clinical significance, " although they are likely pathogenic in view of their predicted effect on the protein.…”

“…For this, a PubMed search was performed, identifying 27 articles with clinical and mutation data on COL4A1 7,8,[10][11][12][13][14][15][16][17][18][19][20][21][22][29][30][31][32][33][34][35][36][37][38][39][40] and 3 articles with data on COL4A2 mutations. [26][27][28] A total of 137 individuals with a COL4A1 mutation from 60 families and 15 individuals with a COL4A2 mutation from 7 families have been reported. Several clinical phenotypes were identified and described in more detail.…”

“…The same COL4A2 mutation was previously reported in two adult patients with intraparenchymal hemorrhage; the mutation was proven to be pathogenic in in vitro functional studies. 26 …”

“…In 2012 several parallel genetic, epidemiologic, and functional studies revealed COL4A2 mutations in both familial and sporadic porencephaly. [26][27][28] The disease resulting from both COL4A1 and COL4A2 mutations is extremely variable, with broad intra-and interfamilial variation and evidence for reduced penetrance. Sporadic individuals with severe presentation may harbor a de novo mutation.…”