BONE MORPHOGENETIC PROTEIN 4 INDUCES ID1 AND ID3 TRANSCRIPTION FACTORS IN TRABECULAR MESHWORK CELLS.

Purpose: Bone morphogenetic protein4 (BMP4) attenuates transforming growth factor β2 (TGFβ2) mediated responses in trabecular meshwork (TM) cells. However, the overall regulatory mechanisms of this inhibition remain unclear. BMP4 regulates various cellular processes by induction of transcription factor known as inhibitors of DNA binding protein (ID1, ID3) which bind and suppress other transcription factors. The purpose of the current study is to determine whether BMP4 will induce ID1 and ID3 expression in cultured human TM cells. This study will aid in understanding whether BMP4 transcriptionally suppress TGFβ-2 responses in TM cells via induction of IDs. Methods: Transformed (GTM-3) and primary TM cells were treated with different doses of recombinant BMP-4 for various time points (0-48 hrs.) to study ID1/ID3 induction. Quantitative RT- PCR and western immunoblotting were used to study ID1 and ID3 mRNA and protein expression. Results: BMP-4 significantly induced IDl and ID3 m RNA levels in TM cells (p<0.05). Maximum IDl and ID3 induction was observed at a BMP4 dose of l0ng/ml. ID1 and ID3 mRNA induction in GTM3 cells significantly (p<0.05) peaked at 6 hr after BMP4 treatment. Maximum induction of IDl and ID3 proteins was observed at 12 hrs. after BMP-4 treatment. Similar induction of ID1 and ID3 mRNA was observed in primary TM cells. Conclusions: BMP4 induces ID1 and ID3 in cultured human trabecular meshwork cells. BMP4 induction of ID1 and/or ID3 may be responsible for the BMP4 suppression of TGFb2 activity in TM cells