The Notch Pathway Attenuates Interleukin 1β (IL1β)-mediated Induction of Adenylyl Cyclase 8 (AC8) Expression during Vascular Smooth Muscle Cell (VSMC) Trans-differentiation

Abstract Vascular smooth muscle cell (VSMC) trans-differentiation, or their switch from a contractile/quiescent to a secretory/inflammatory/migratory state, is known to play an important role in pathological vascular remodeling including atherosclerosis and post-angioplasty restenosis. Several reports have established the Notch pathway as tightly regulating VSMC response to various stress factors through growth, migration, apoptosis and de-differentiation. More recently, we showed that alterations of the Notch pathway also govern VSMC acquisition of the inflammatory state, one of the major events accelerating atherosclerosis. We also evidenced that the inflammatory context of atherosclerosis triggers a de novo expression of Adenylyl Cyclase isoform 8, associated with the properties developed by trans-differentiated VSMCs. As an initial approach to understanding the regulation of AC8 expression, we examined the role of the Notch pathway. Here we show that inhibiting the Notch pathway enhances IL1β's effect on AC8 expression, amplifies its deleterious effects on VSMC trans-differentiated phenotype and decreases Notch target genes HRT1 and HRT3. Conversely, Notch activation resulted in blocking AC8 expression and up-regulated HRT1 and HRT3 expression. Furthermore, over-expressing HRT1 and HRT3 significantly decreased IL1β-induced AC8 expression. In agreement with these in vitro findings, the in vivo rat carotid balloon-injury model of restenosis evidenced that AC8 de novo expression coincided with the down-regulation of Notch3 pathway. These results, demonstrating that the Notch pathway attenuates IL1β-mediated AC8 up-regulation in trans-differentiated VSMCs, suggest that AC8 expression, besides being induced by the pro-inflammatory cytokine IL1β, is also dependent on the down-regulation of the Notch pathway occurring in an inflammatory context.