Abstract 4276: Characterization of Mechanotransduction Pathways Leading to Thoracic Aortic Aneurysms and Dissections
Thoracic aortic aneurysms and dissections (TAAD) are autosomal dominantly inherited in 19% of patients. Mapping studies determined that the disease is genetically heterogeneous with 3 loci and mutations in 4 genes accounting for familial TAAD. However, the resulting pathology is consistently medial degeneration, characterized by increased proteoglycans and loss of elastic fibers. To test the hypothesis that genetic mutations leading to familial TAAD alter common pathways in aortic smooth muscle cells (SMCs), expression profiling using Illumina’s Sentrix HumanRef 8 Expression Beadchip array was done on RNA isolated from SMCs explanted from 6 patients with inherited TAAD with no identified mutation and 3 healthy controls obtained from Life Gift. Significant increases in expression of proteoglycan genes in patients’ SMCs, specifically lumican, podocan, and decorin were confirmed using Q-PCR and tissue immunofluorescence. NCI’s Ingenuity Pathway Analysis predicted alterations in the ERK1/2, insulin receptor and SAPK/JNK pathways (p<0.001), which SMCs activate in response to cyclic stretch. Immunoblotting indicated increased phosphorylation of ERK and GSK-3β, a protein from the insulin receptor pathway, in explanted patient SMCs, also confirmed by increased immunoreactivity against phosphorylated ERK and GSK-3β in the sub-intimal SMCs from patient tissue compared to controls. To determine if mechanotransduction pathway activation was responsible for the medial degeneration a specific inhibitor of GSK-3β, SB216763 was incubated with control cells and significantly increased the expression levels of proteoglycans. Mechanical strain was also applied to control SMCs confirming pathways stimulation with stretch. Incubation with pathway inhibitors against insulin receptor and ERK pathways identify, for the first time, that stretch induced GSK-3β phosphorylation may increased proteoglycan expression and ERK phosphorylation may regulate the expression of MMP2, a protein known to degrade elastic fibers. Furthermore, specific mutations in SMC-specific beta myosin heavy chain and alpha actin in addition to upregulation of pathways activated by cyclic stretch suggest that SMC response to hemodynamic factors play a role in this disease.