Erk Activation Occurs at the Human Carotid Bifurcation

Cinà CS*, Ingram AJ, Perron L, Krepinsky JC
Division of Vascular Surgery* and Nephrology, McMaster University, Hamilton ON

Background: We have observed extracellular signaling-regulated kinase 1/2 (Erk1/2)-mitogen-activated protein kinase (MAPK) activation in vascular smooth muscle- like cells in response to cyclic mechanical strain, and such activation mediates proliferation and matrix elaboration. Others have observed acute Erk activation in human arteries after mechanical (angioplasty) trauma, and Angiotensin II (AII) infusion activates Erk in rat aortae. Thus, we asked whether chronic Erk activation might occur at a site of ongoing mechanical strain (the carotid bifurcation), whether this was related to AII and if such activation was associated with cellular proliferation at this site.

Methods: Human carotid arteries (n=50 to date) were collected at the time of endarterectomy en bloc from intima to external elastic lamina. Two sections were taken from grossly normal artery above (external) and below (common) the bifurcation and through the lesional area at the bifurcation itself. One was placed in liquid nitrogen for later protein extraction and one into OCT compound for immunostaining. Clinical data were collected anonymously into a database. Twelve samples (6 from subjects taking ACE inhibitors and 6 without ACE inhibitor therapy) form the basis of this report. Protein from each section was extracted analysed by western blotting for Erk activation and proliferating cell nuclear antigen (PCNA) expression. Localization of active (phosphorylated) Erk was assessed by immunostaining.

Results: The strongest Erk activation was observed at the bifurcation, with lesser activation in the common carotid and little activation in external carotid. Expression of PCNA mirrored Erk activation. Immunostaining revealed Erk activation primarily in the medial layer; little activation was observed in atheromatous lesion. Therapy with ACE inhibitors did not affect the levels or location of Erk activation observed.

Conclusion: Chronic Erk activation is seen at the human carotid bifurcation, and is associated with PCNA expression. The role of Erk in the development of lesions at this site in response to mechanical strain merits further study.