Purpose: To examine whether fibronectin is synthesized in the adult human retina and whether diabetes alters its amount, level of expression, and pattern of splicing.
Methods: Retinas were obtained after death from 24 patients (age, 64 +/- 6 years) with 8 +/- 5 years of diabetes and 24 age-matched control subjects. Retinal localization of fibronectin and its amount in retinal vessels were examined with the immunoperoxidase technique. Fibronectin mRNA in the total retina was studied with reverse transcriptase-polymerase chain reaction using primers encompassing the alternatively spliced exon ED-A. The levels of fibronectin mRNA were measured relative to an internal standard (beta-actin mRNA). To detect and measure fibronectin expression in microvessels, retinal trypsin digests were studied by in situ hybridization.
Results: In the adult human retina, fibronectin is present exclusively in the walls of the vessels, including capillaries, and in the internal limiting membrane. In diabetic vessels, immunoreactive fibronectin was increased 1.4-fold over levels in control vessels (P = 0.05). Fibronectin is synthesized locally, and the predominant mRNA species excludes the ED-A region. The splicing pattern was not altered by diabetes. However, in the retinas of patients with diabetes, the levels of fibronectin mRNA were increased 1.3-fold over levels in control retinas (P = 0.028), whereas actin mRNA levels were similar in the two groups. Levels of fibronectin mRNA showed a substantial increase in the microvessels of patients with diabetes (0.49 +/- 0.18 grains/cell versus 0.15 +/- 0.12 grains/cell in control microvessels; P = 0.009.
Conclusions: Fibronectin is synthesized in the adult human retina. Diabetes increases the amount of fibronectin in retinal vessels and upregulates its expression without changing the splicing pattern of the ED-A segment. Increased synthesis and deposition of fibronectin by microvascular cells may modify the interactions of cells and matrix with functional consequences relevant to the lesions of retinopathy.