Retinoblastoma protein: a molecular regulator of chronic venous insufficiency

Chronic venous insufficiency (CVI) and varicose vein (VV) formation is characterized histologically by the transformation of smooth muscle cells (SMC) from a contractile to a secretory phenotype and by intense collagen deposition. The subcellular regulation point for these processes may be the retinoblastoma protein (pRb), a known inhibitor of cellular proliferation and regulator of differentiation. We hypothesize that pRb phosphorylation is associated with VV formation and functions as a possible subcellular regulator.

Patients were separated into two groups. Group 1 (n = 6) consisted of vein specimens obtained from patients undergoing coronary artery bypass grafting. Group 2 (n = 6) consisted of patients with symptomatic CVI and duplex confirmed refluxing greater saphenous veins (GSVs) who required GSV stripping. Western blots of GSV protein extracts were performed with anti-human pRb monoclonal antibodies and the degree of nonphosphorylated and phosphorylated pRb was determined. Results were quantified using image analysis of band intensities (computer calibrated intensity units). The ultrastructural appearance of SMCs and the vein wall architecture were qualitatively analyzed with electron microscopy in both groups.

Phosphorylated pRb from varicose GSVs exhibited intensities of 523 +/- 188 units, while phosphorylated pRb from normal GSVs demonstrated intensities of 153 +/- 41 units (P < 0.05). SMCs in varicosed GSVs were surrounded by disorganized collagen deposits and displayed a secretory phenotype with spherical vacuolated cells. SMCs from normal GSVs appeared spindle shaped with a purported contractile phenotype and a well-structured extracellular matrix.

Our data demonstrate that VV formation, in patients with CVI, is associated with phosphorylated pRb and the transformation of SMCs from a contractile to a secretory ultrastructural morphology. The data suggest that SMC dedifferentiation is regulated by pRb and the disinhibition of this protein (phosphorylation) may be an significant factor in the development of lower extremity varicosities.