The overall goal of this research is to establish whether maintenance of connexin 43 (Cx43)-mediated gap junction intercellular communication (GJIC) and Cx43 hemichannel (HC) activity in the retinal capillaries of diabetic patients plays a protective role against the development of retinal vascular cell loss and vascular permeability associated with diabetic retinopathy (DR). Substantial evidence suggests that reduced GJIC activity in retinal vascular cells may contribute to the breakdown of homeostatic balance in DR (1-4). We have shown that the expression of Cx43, the principal gap junction protein, is downregulated in retinal vascular cells in high glucose (HG) condition with concomitant reduction in GJIC activity (3, 4) that contributes to loss of retinal vascular cells and capillary leakage. Preliminary data indicate HG reduces Cx43 HC activity and trigger apoptotic cell death (5). Recently, we observed that maintenance of cell-cell coupling inhibits HG-induced apoptosis and excess cell monolayer permeability in vitro (6). Based on these findings, we hypothesize that preventing hyperglycemia-induced Cx43 downregulation and GJIC activity would promote vascular homeostasis, restore Cx43 HC activity and Cx43 phosphorylation, ultimately preventing loss of retinal vascular cells and capillary leakage in DR. The hypothesis is supported by findings from previous funding period that showed (i) HG-induced downregulation of Cx43 expression contributes to the breakdown of endothelial barrier tight junctions by reducing ZO-1 and occludin expression (7, 8) and that restoration of Cx43 expression (7) and gap junction coupling prevents HG-induced apoptosis and cell monolayer permeability in retinal endothelial cells (6); (ii) Cx43 expression is downregulated in human retinas, and that the severity of retinal vascular cell loss is linked to the extent to which Cx43 downregulation develops (9). The hypothesis is also supported by key preliminary data that Cx43 phosphorylation is altered at s368 and s373 negatively impacting Cx43 functionality in GJIC and HC activity. Additionally, reports indicate that ZO-1, a component of the tight junction, interacts directly with Cx43 (10), and regulates Cx43-mediated GJIC activity (11, 12). Having observed ZO-1 to be reduced in retinal vascular cells by HG/diabetes (13), we propose to examine whether Cx43 downregulation, compromised GJIC, altered HC activity, and altered Cx43 phosphorylation promotes retinal vascular cell loss and tight junction dysfunction in vascular permeability. Findings are expected to provide valuable insight into a novel mechanism underlying retinal vascular cell loss and capillary leakage, and a potential strategy to prevent retinal vascular lesions in DR.
Diabetic retinopathy is characterized by retinal vascular lesions that ultimately lead to vision loss and blindness. Currently, there is no cure for diabetic retinopathy, the leading cause of blindness in the working age Americans. It is expected that findings from this project would provide valuable insight towards testing a novel mechanism underlying retinal vascular cell loss and capillary leakage, the two prominent retinal vascular lesions associated with the pathogenesis of diabetic retinopathy.
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