Expression of neurotrophic factors and their receptors in keratoconic cornea

Purpose: To measure the expression level and pattern of neurotrophic factors and their receptors in keratoconus (KC) cornea using quantitative RT-PCR (qPCR) and immunostaining. Materials and Methods: Twenty-one recipient corneal buttons after keratoplasty from KC cornea and four age-matched normal corneas were obtained. The 25 corneal tissues were divided into two pieces; one fragment of each sample was used for immunostaining whereas the other fragment was used for qPCR. Using primary antibodies and specific qPCR primer, immunostaining and qPCR were performed to analyze the expression level of the neurotrophic factors and receptors. Results: Nerve growth factor and its receptors (TrkA and p75NTR) were not expressed in the center of normal cornea. However, TrkA and the p75NTR were clearly expressed in a membrane bound staining pattern and the mRNA levels were significantly higher in KC (p < 0.001). The mRNA expression of brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF) and neurotrophin (NT)-4 mRNA was also elevated in KC (p < 0.001). BDNF was expressed in epithelium of normal cornea. However, in KC, its expression was found to be extending into the anterior stromal layer. CNTF was hardly expressed in normal cornea. In KC, the entire epithelium expressed CNTF, especially in perinuclear area. NT-4 was expressed throughout the epithelium and stroma in KC. Conclusion: The change in expression of neurotrophic factors in KC may suggest that these factors play an important role in the pathogenesis of KC and serve as new markers for the progression of KC.