Pericyte mitogenic activity is reduced in the blood of type 1 diabetic patients with and without retinopathy

Selective loss of capillary pericytes occurs early and specifically in diabetic retinopathy. We have investigated whether blood derivatives from patients with longterm type 1 (insulin-dependent) diabetes and no retinopathy differ from those with retinopathy and/or non-diabetic controls in their ability to stimulate DNA synthesis in cultured bovine retinal pericytes and endothelial cells. As a general trend, whole blood serum, platelet-rich plasma and platelet-free plasma from patients without and with retinopathy stimulated thymidine incorporation in both cell types less than derivatives from controls. Serum, 0.1% v/v final concentration in culture medium, from patients without retinopathy was less active (114.5±24.5% of a standard stimulus produced by 0.1% fetal calf serum) than that from patients with the complication (132.6±20.8%,P=0.003) and both were less potent than control sera (143.6±28.0%,P<0.001 andP=0.013, respectively). Lack of support from circulating factor(s) may contribute to the disappearance of pericytes from the capillary wall in diabetes but further investigations are necessary to clarify the mechanisms that prevent the development of microangiopathy in some patients.