Inflammation and Mechanical Stretch Promote Aortic Stiffening in Hypertension Through Activation of p38 MAP Kinase
Rationale: Aortic stiffening commonly occurs in hypertension and further elevates systolic pressure. Hypertension is also associated with vascular inflammation and increased mechanical stretch. The interplay between inflammation, mechanical stretch and aortic stiffening in hypertension remains undefined.
Objective: To determine the role of inflammation and mechanical stretch in aortic stiffening.
Methods and Results: Chronic angiotensin II infusion caused marked aortic adventitial collagen deposition, as quantified by Masson's Trichrome Blue staining and biochemically by hydroxyproline content, in wild-type (WT) but not in Recombination Activation Gene-1 deficient (RAG-1-/-) mice. Aortic compliance, defined by ex-vivo measurements of stress-strain curves, was reduced by chronic angiotensin II infusion in WT mice (p<0.01) but not in RAG-1-/- mice (p<0.05). Adoptive transfer of T cells to RAG-1-/- mice restored aortic collagen deposition and stiffness to values observed in WT mice. Mice lacking the T cell derived cytokine IL-17a were also protected against aortic stiffening. In additional studies, we found that blood pressure normalization by treatment with hydralazine and hydrochlorothiazide prevented angiotensin II-induced vascular T cell infiltration, aortic stiffening and collagen deposition. Finally, we found that mechanical stretch induces expression of collagen 1α1, 3α1 and 5a1 in cultured aortic fibroblasts in a p38 MAP kinase-dependent fashion, and that inhibition of p38 prevented angiotensin II-induced aortic stiffening in vivo. IL-17a also induced collagen 3a1 expression via activation of p38 MAP kinase.
Conclusions: Our data define a pathway in which inflammation and mechanical stretch lead to vascular inflammation that promotes collagen deposition. The resultant increase in aortic stiffness likely further worsens systolic hypertension and its attendant end-organ damage.
- Received July 8, 2013.
- Revision received December 16, 2013.
- Accepted December 17, 2013.