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Z. Zhang, P. Zhang, J. Makita, J. Randazzo, P. Kador; Signaling Differences Between Rat Retinal Capillary Pericyte and Endothelial Cells Cultured Under Hyperglycemic Conditions. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5103.
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© ARVO (1962-2015); The Authors (2016-present)
Selective pericyte retinal capillary destruction has been reported to be the hallmark of diabetic retinopathy. In dog, both in vitro and in vivo studies link this selective destruction to pericyte destruction to the aldose reductase (AR) catalyzed accumulation of polyols which subsequently initiates apoptosis. In contrast, studies with rat retinal capillaries and pericyte and endothelial cell lines report that that AR activity is present in both cell types. Nevertheless, sorbitol accumulates only in pericytes and they undergo apoptosis. The purpose of this study was to extend these observations by investigating the relationship between AR, sugar alcohol accumulation and cellular signaling changes in rat retinal capillary pericyte (TR-rPCT) and endothelial (TR-iBRB) cells.
Rat TR-rPCT and TR-iBRB cells were cultured for up to 48 hours in media containing up to 50 mM glucose with/without the aldose reductase inhibitors (ARIs) Al1576 or tolrestat. Sugar Alcohol levels were measured by HPLC. Cell viability and apoptosis were determined by commercial DAPI and TUNEL staining. Western Blots using commercially available antibodies were used to measure growth factor and signaling expression.
Pericytes grown in 25 or 50 mM glucose accumulated sorbitol and this accumulation was decreased by the presence of ARIs. However, the accumulation of sorbitol did not initiate ER stress. In these pericytes Western blot analysis indicated increases in of bFGF, IGF-1, TGF-β, p-Akt, p-c-Raf, p-ERK1/2, and p-SAPK/JNK expression compared to similar cells grown in 5 mM glucose containing media and these increases were reduced by the presence of ARIs. In contrast endothelial cells which do not accumulate sorbitol showed only slight increases in b-FGF, P-AKT, and P-c-RAF with little or no effect of ARIs on these increases. None of the other parameters were altered after 48 hr of culture.
Since activation p-ERK 1/2 and p-c-Raf, which is upstream of p-ERK 1/2, is associated with apoptosis, their activation in pericytes but not endothelial cells supports the observation that apoptosis predominantly occurs in the rat pericyte cells. Moreover, the observation that their activation is reduced by ARIs and ARIs reduce apoptosis in cultured pericytes support the premise that sorbitol accumulation is associated with the initiation of apoptosis through p-ERK 1/2 and p-c-Raf signaling.
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