Differential Expression Of Transforming Growth Factor Beta Receptor 2 (TGFβR2) In Circulating Diabetic CD34+ Cells: Implications For Diabetic Retinopathy (DR)

Abstract

Purpose: : We reported that the reparative ability of diabetic CD34⁺ cells can be restored by transient inhibition of endogenous TGF-β1. This ligand mediates its action by binding to TGF-β-R2 receptor homodimers, which then form heterotetrameric complexes with two TGF-β-R1 molecules. We asked whether subpopulations of CD34⁺ cells from diabetics differentially express TGFβR2 and whether endogenous inhibition of TGF-β1 in CD34⁺ cells would modulate surface expression of its receptor, TGF-βR2

Methods: : Progenitors from healthy (n=8) and diabetic (n=8) individuals were lin- enriched and analysed by FACS for expression of CD34, CD45, and CD38, and then analysed for TGF-βR2 expression. Endogenous inhibition of TGF-β1 in CD34⁺ was studied for its effect on TGFβR2-mRNA expression using RT-PCR. Lin^- cells were treated with antisense PMO to TGF-β1 (TGF-β1-PMO) and analysed at T=0,1, 2,3,4,5 days in culture. Bone marrow (BM) lin^- cells from TGF-β1^-/- mice were compared to wild type (WT) BM lin^- cells.

Results: : TGF-β-R2 expression was essentially absent on primitive diabetic CD34⁺CD45⁺CD38 ^LOW cells, with only ~10 % of diabetic cells (CD34⁺ CD45⁺ CD38 ^LOW ) expressed cell surface TGF-βR2 as compared to 85 % healthy CD34⁺CD45⁺CD38^LOW cells (p = 0.001). Comparison of TGF-β-R2 expression between mature progenitors (lin- CD34⁺CD45⁺ CD38⁺) from diabetic and healthy revealed that TGF-βR2 expression did not differ between groups. Treatment of healthy enriched CD34⁺ cells caused an 8 fold (p<0.01) reduction in TGF-β-R2 mRNA while TGF β-1-PMO treatment abolished TGFβR2 in diabetic CD34⁺ cells. Using BM lin- cells from TGF-β1^-/- mice compared to WT BM lin- cells, we found that in the absence of TGF-β1, little to no TGFβR2 was expressed.

Conclusions: : Healthy and diabetic CD34⁺ cells differentially regulate TGF-β-R2 expression which may be due to elevated plasma TGF-β1 among diabetic individuals. Reduction in TGF-βR2 expression in diabetic CD34⁺ cells may relieve TGF-β1 inhibition and enhance proliferation of CD34⁺ cells in the primitive cellular compartment, an outcome that may be necessary for diabetics to maintain the increased demand for these reparative cells and reduce the risk of vasodegeneration and DR.

Keywords: diabetic retinopathy • neovascularization