The human fetal retinal pigment epithelium: A target tissue for thyroid hormones

Thyroid hormone (T-3) has previously been shown to regulate visual function in experimental animals and humans. To determine if T-3 exerts direct effe cts on retinal function, cultured human fetal retinal pigment epithelial (R PE) cells were tested for the presence of thyroid hormone receptors (TRs) a nd T-3 responses. Using TR-isoform-specific reverse-transcriptase polymeras e chain reaction techniques, mRNA was detected for alpha 1, alpha 2 and bet a 1 TR isoforms. Immunohistochemistry using a polyclonal antibody that simu ltaneously recognizes alpha 1, alpha 2 and beta 1 TRs showed nuclear staini ng of the fetal RPE. Specific binding of I-125-T-3 to RPE cell nuclear extr acts was detected, and Scatchard analysis revealed a K-d of 110 pM. To dete rmine if RPE cells can respond to TBI hyaluronic acid (HA) levels in cell c ulture media were measured after 2, 4 or 6 days of growth in medium contain ing 10(-7) MT3. T-3 inhibited accumulation of HA in the cell culture medium of RPE cells. This effect was not evident at 2 days, but at 4 days there w as 42.8% less HA in cell culture medium of RPE cells grown in 10(-7) M T-3 (p < 0.01, t test). The effect persisted through 6 days, when there was 46. 3% less HA in cell culture medium of RPE cells grown in 10-7 MT3(p < 0.001, t test). The data indicate that human fetal RPE cells are a direct target f or thyroid hormones.