Fibronectin overexpression in retinal microvessels of patients with diabetes.
OBJECTIVE
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.
Roy
S
S
Schepens Eye Research Institute, Boston, MA 02114, USA.
Cagliero
E
E
Lorenzi
M
M
D000368:Aged; D001483:Base Sequence; D017931:DNA Primers / Q000737:chemistry; D048909:Diabetes Complications; D003930:Diabetic Retinopathy / Q000378:metabolism*; D005260:Female; D005353:Fibronectins / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D007124:Immunoenzyme Techniques; D017403:In Situ Hybridization; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis; D012194:RNA-Directed DNA Polymerase; D012160:Retina / Q000378:metabolism; D012171:Retinal Vessels / Q000378:metabolism*
D017931:DNA Primers; D005353:Fibronectins; D012333:RNA, Messenger; D012194:RNA-Directed DNA Polymerase