Human trabecular meshwork cells secrete neurotrophins and express neurotrophin receptors (Trk)

The purpose of this study was to compare the mRNA expression of neurotrophins (NTs) and NT receptors (Trk) in cultured human trabecular meshwork (HTM) cells and ex vivo HTM tissues, to immunolocalize both NT and Trk receptors in cultured HTM cells, and to demonstrate secretion of NTs by HTM cells.

Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the expression of NT and Trk receptor mRNAs in early-passaged, cultured HTM cells from donors of several ages. RT-PCR was used on ex vivo HTM tissues from donors to compare and contrast mRNA expression with cell culture results. In addition, immunohistochemistry was used to localize the translated NT and low- (p75) and high- (Trk) affinity NT receptor proteins within cultured HTM cells and trabecular meshwork tissues. Last, enzyme-linked immunoassay (ELISA) was used to demonstrate secretion of NTs by HTM cells.

Amplification products of the expected size for NTs were detected in both cultured HTM cells and ex vivo HTM tissues. Specifically identified were amplification products for the following NTs: NGF, BDNF, NT-3, and NT-4. Amplification products for the full-length Trk A and Trk C high-affinity receptor were observed, as well as truncated isoforms for Trk B and Trk C. No amplification products were produced for the full-length Trk B receptor nor for the low-affinity p75 receptor. Immunohistochemistry indicated that proteins for the various NTs and full-length and truncated Trk receptors were translated by cultured HTM cells and tissues. Immunoassays (ELISA) detected BDNF, NT-4, NGF, and NT-3 in the culture media from HTM cells.

The results demonstrate, for the first time, mRNA expression for NT and Trk receptors by both cultured HTM cells and ex vivo HTM tissues. NTs were immunolocalized in HTM tissues and cultured HTM cells are capable of secreting NTs. Specific NTs acting through high-affinity Trk receptors within the HTM may be involved in maintaining the normal function of this complex tissue.