Altered expression of growth factors and cytokines in keratoconus, bullous keratopathy and diabetic human corneas

The purpose of this study was to identify the growth factors and cytokines present in normal and diseased corneas. Total RNA was isolated from normal and diseased corneas. cDNA was synthesized from individual corneas and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was performed with primers to IL-1alpha, 1IL-8, PDGF-B, BMP-2, BMP-4, IGF-I, TGF-beta2, FGF-2, and VEGF. After normalization to beta2-microglobulin, several factors were identified that were significantly different from normal. Antibodies to IGF-I, BMP-2, VEGF and TGF-beta2 were used for immunohistochemistry. A total of 93 corneas were used for this study including 31 normal, 20 keratoconus, 19 bullous keratopathy (pseudophakic and aphakic, PBK/ABK), and 23 diabetic corneas. The VEGF RNA levels were significantly decreased in the keratoconus and PBK/ABK corneas but increased in the diabetic corneas. BMP-2 gene expression was lower than normal in the PBK/ABK and diabetic corneas. IGF-I and BMP-4 RNA levels were increased in PBK/ABK. In the immunohistochemical studies, the protein patterns paralleled those found at the mRNA level. The only exception was IGF-I in diabetic corneas that showed increased staining in the epithelium and its basement membrane without a significant increase in mRNA levels. TGF-beta2 mRNA and protein levels were similar to normal in all diseased corneas. Thus, no alterations in the tested growth factors/cytokines were unique to keratoconus corneas. In contrast, PBK/ABK corneas had specific significant elevations of BMP-4 and IGF-I. Diabetic corneas were unique in their increased VEGF mRNA levels. These data suggest that while some growth factor/cytokine alterations are non-specific and can be found in multiple corneal diseases, there are others that are unique to that disease.

Effects of cholesterol and apolipoprotein E on retinal abnormalities in ApoE-deficient mice

PURPOSE

To examine the pathologic changes in the retina of apolipoprotein E (apoE)-deficient mice fed a high-cholesterol diet.

METHODS

ApoE-deficient mice (ApoE) were maintained on either regular mouse chow (ApoE-R) or a high-cholesterol diet (ApoE-C) for 25 weeks. Age-matched control C57BL/6J mice (C57) were also maintained on either regular mouse chow (C57-R) or a cholesterol-containing diet (C57-C). Retinal function was assessed by dark-adapted electroretinography (ERG). The eyes were embedded, sectioned, and analyzed by histologic and immunohistochemical methods, as well as by light and transmission electron microscopy.

RESULTS

After the 25-week feeding period, ERG tracings of ApoE-C mice revealed significant increases of a- and b-wave implicit times when compared with the C57-R group of mice. In addition, there were reductions in oscillatory potential (OP) amplitudes in the ApoE-C group. However, a- and b-wave amplitudes appeared to be unchanged among the four groups of mice. Light microscopic examination of the retinas showed that compared with control C57-R mice, ApoE-C mice had significantly lower cell numbers in the inner and outer nuclear layers (85.1% +/- 4.6%, P < 0.05 and 81.4% +/- 3.7%, P < 0.01 of C57-R controls, respectively). Transmission electron microscopy of apoE-deficient mice revealed cells of the inner nuclear layer with condensation of nuclear chromatin and perinuclear vacuolization in focal areas. Bruch's membrane was also found to be thicker, and its elastic lamina appeared disorganized and discontinuous. Immunohistochemistry demonstrated diminished or no immunoreactivity for carbonic anhydrase II and calretinin in the retinal layers of apoE-deficient mice.

CONCLUSIONS

Overall, there were increasing abnormalities of retinal function and cellular morphology among the four groups of mice in the order of C57-R < C57-C < ApoE-R < ApoE-C. These findings suggest that apoE and/or cholesterol play an important role in retinal function.