CONNEXIN43 GENE-EXPRESSION IN THE RABBIT ARTERIAL-WALL - EFFECTS OF HYPERCHOLESTEROLEMIA, BALLOON INJURY AND THEIR COMBINATION

The specialized functions of endothelium require intercellular communi cation between endothelial cells within the monolayer, and between end othelium and other cells present in the vessel wall. This is accomplis hed by a combination of paracrine soluble mediators and direct gap-jun ctional intercellular communication (GJIC) mediated by a family of con nexin proteins. A prominent connexin expressed by vascular cells in vi vo and in vitro is connexin 43 (Cx43). We have investigated the in viv o gene regulation of Cx43 in the context of vascular pathology, as a r esult of mechanical injury, hypercholesterolemia or both. The aortoili ac bifurcation in the rabbit was examined following three types of ins ult: (1) diet-induced hypercholesterolemia resulting in macrophage-ric h fatty streak lesions, (2) mechanical, stretch-denudation injury resu lting in intimal smooth muscle cell (SMC) proliferation and (3) mechan ical injury superimposed on hypercholesterolemia resulting in a comple x vascular lesion having characteristics of both interventions. The no rmal rabbit iliac artery expressed approximately equal levels of Cx43 mRNA in the medial SMC layers and in the endothelium. In hypercholeste rolemia-induced atherosclerosis, Cx43 expression was most prominent in macrophage foam cells even though normocholesterolemic precursor mono cytes did not express Cx43 mRNA. Antibodies directed specifically to C x43 protein confirmed the expression of macrophage gap junction protei n in these cells. Medial SMC in hypercholesterolemia exhibited less Cx 43 than their normal counterparts in control animals. Mechanical injur y in the absence of hypercholesterolemia resulted in intimal thickenin g in which Cx43 expression in the intimal SMC was equivalent to that i n the subjacent medial SMC, both being approximately equivalent to nor mal uninjured rabbit medial SMC expression. Cell-specific expression o f Cx43 in combined mechanical injury/hypercholesterolemia was similar to that observed in hypercholesterolemia alone: Cx43 upregulation in m acrophages, while medial SMC were downregulated. Normo- and hyperchole sterolemic alveolar macrophages of the lung and Kupffer cells of the l iver did not exhibit induction of Cx43 mRNA, nor did macrophages isola ted from peritoneal or bronchial lavage fluid of the same animals. Thi s work extends our previous finding of Cx43 upregulation in human athe rectomy tissue and demonstrates that atherosclerotic lesions in situ, in a controlled animal model of atherosclerosis, exhibit cell-specific changes in Cx43 gene expression. Changes in medial SMC migration, pro liferation and phenotype, as well as enhanced interactions between adh erent/infiltrating monocytes and endothelium may be related tu modifie d GJIC pathways in the vessel wall.