Human trabecular meshwork cells as a thyroid hormone target tissue: presence of functional thyroid hormone receptors.
OBJECTIVE
To determine whether human trabecular meshwork cells (HTM) are a potential target tissue for thyroid hormone (3,3',5-triiodothyronine, T3).


METHODS
Cultured HTM were assayed for the presence of thyroid hormone receptors (TRs) and retinoid X receptors (RXRs) by reverse-transcriptase polymerase chain reaction (RT-PCR) to detected TR and RXR mRNA, and by immunohistochemistry to detect nuclear TR and RXR proteins. Functionality of the TR was determined by analysis of 125I-T3 binding affinity and capacity in HTM nuclear extracts. Effects of T3 on modulation of hyaluronic acid (HA) levels in HTM were measured as a function of dose and duration of T3 administration.


RESULTS
Analysis of RT-PCR and immunohistochemistry demonstrated that cultured HTM expressed TRalpha1, TRalpha2, and TRbeta1 but not TRbeta2; and RXRalpha but not RXRbeta and RXRgamma isoforms. Saturation binding and analysis of 125I-T3 to HTM nuclear extracts revealed Kd of 57 pM. The number of T3 binding sites extrapolated from a Scatchard plot was 7.3 x 10(10)/microg of HTM nuclear protein extract. T3 supplementation reduced the concentration of HA in the cell medium by 32-43% compared to cells grown in the absence of T3.


CONCLUSIONS
Cultured HTM express three TR isoforms and one RXR isoform, bind T3 with an affinity similar to that of TR in responsive cells, and modulate their HA production in response to T3. These findings indicate that the human trabecular meshwork tissue has the capacity to respond to thyroid hormones.
Duncan
K G
KG
Department of Ophthalmology, University of California, San Francisco 94143, USA.
Jumper
M D
MD
Ribeiro
R C
RC
Bailey
K R
KR
Yen
P M
PM
Sugawara
A
A
Patel
A
A
Stern
R
R
Chin
W W
WW
Baxter
J D
JD
Schwartz
D M
DM
D000328:Adult; D002452:Cell Count / Q000187:drug effects; D002478:Cells, Cultured / Q000187:drug effects; D017931:DNA Primers / Q000737:chemistry; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D009687:Nuclear Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D018168:Receptors, Retinoic Acid / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011988:Receptors, Thyroid Hormone / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D047488:Retinoid X Receptors; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014129:Trabecular Meshwork / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D014284:Triiodothyronine / Q000494:pharmacology
D017931:DNA Primers; D009687:Nuclear Proteins; D012333:RNA, Messenger; D018168:Receptors, Retinoic Acid; D011988:Receptors, Thyroid Hormone; D047488:Retinoid X Receptors; D014157:Transcription Factors; D014284:Triiodothyronine