Cardiovascular diseases including aortic aneurysms are generally considered disease of the older population related to environmental factors and life style choices including smoking, and obesity caused by high fat and salt diets. However, 20 percent of individuals affected by thoracic aortic aneurysm and dissections (TAAD) have a heritable form, commonly attributed to mutations in genes that encode for extracellular matrix (ECM) proteins and growth factors that contribute to vascular wall integrity. While there are a number of genes now identified as containing causal mutations for inherited forms of TAAD, causal genes in 75% of families with this disease have not been discovered. We recently identified a family with TAAD with unknown etiology. Through whole genome sequencing, we identified a missense mutation in the lysyl oxidase (LOX) gene (c.893T>G encoding p. Met298Arg) that segregated with the aneurysm phenotype in the family. LOX is an extracellular enzyme that catalyzes the amine oxidation reaction for critical crosslinking and maturation of elastin and collagen- key ECM proteins in the vessel wall. To understand the mechanism underlying Lox-associated aneurysmal disease, we used the CRISPR/Cas9 genome editing system to introduce the human mutation into mice (M298R in humans, M292R in mice). Characterization of the vascular system in mice carrying the M292R mutation confirmed that the mutation does indeed lead to aortic aneurysm formation. Animals homozygous for the M292R mutation died within a few hours of birth due to ruptured aortic aneurysm. Animals heterozygous for the mutation, however, did not develop aneurysms at 3 months of age, but had fragmented elastic fibers in the aorta wall, suggesting that the mutant animals may be predisposed to develop vascular disease when exposed of injurious stimuli. In this proposal, we will utilize this M292R mouse model to characterize mechanisms leading to changes in the arterial wall and determine whether additional vascular wall stress will induce thoracic aortic aneurysms. Furthermore, we will identify mechanisms underlying altered LOX function caused by the mutation that ultimately leads to aneurysm formation. Identification of Lox as a causal gene for familial TAAD will not only allow us to screen for Lox during clinical genetic testing, but understanding the mechanism behind how the mutation affects Lox enzyme function will provide insight into potential therapeutic development.
Aortic aneurysm rupture is the 13th cause of death in the United States. One-fifth of these cases are hereditary; yet only 25% of the responsible genes are known. We have identified a mutation in a gene called lysyl oxidase, for the first time, which causes aortic aneurysm in a family and generated a mouse model bearing the human mutation to study how the mutation causes disease.
| Halabi, Carmen M; Broekelmann, Thomas J; Lin, Michelle et al. (2017) Fibulin-4 is essential for maintaining arterial wall integrity in conduit but not muscular arteries. Sci Adv 3:e1602532 |
