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Somatostatin protects photoreceptor cells against high glucose-induced apoptosis
Ana I Arroba1, Aurora Mazzeo, Daniele Cazzoni2
1Alberto Sols Biomedical Research Institute (IIBm) (CSIC/UAM), 28029 Madrid, Spain; Spanish Biomedical Research Centre in Diabetes and Associated Metabolic Disorders (CIBERdem), ISCIII, Madrid, Spain.
Purpose:
Many cellular and molecular studies in experimental animals and early retinal function tests in patients with diabetic retinopathy (DR) have shown that retinal neurodegeneration is an early event in the pathogenesis of the disease. Somatostatin (SST) is one of the most important neuroprotective factors synthesized by the retina: SST levels are decreased in parallel to retinal neurodegeneration in early stages of DR. In this study, we characterized the induction of apoptosis (programmed cell death) in a 661W photoreceptor-like cell line cultured under high glucose (HG) conditions and the effect of SST.
Methods:
A 661W photoreceptor-like cell line and retinal explants from 10-week-old male C57BL/6 mice were cultured under HG conditions and treated with SST.
Results:
Hyperglycemia significantly reduced the cellular viability by increasing the percentage of apoptotic cells, and this effect was ameliorated by SST (p˂0.05). Activation of caspase-8 by hyperglycemia was found in the 661W cells and retinal explants and decreased in the presence of SST (p˂0.05). Moreover, we detected activation of calpain-2 associated with hyperglycemia-induced cell death, as well as increased protein tyrosine phosphatase 1B (PTP1B) protein levels; both had a pattern of cleavage that was absent in the presence of SST (p˂0.05). Treatment of the 661W cells and retinal explants with SST for 24 h increased the phosphorylation of type 1 insulin-like growth factor receptor (IGF-IR; tyrosine 1165/1166) and protein kinase B (Akt; serine 473), suggesting this survival signaling is activated in the neuroretina by SST (p˂0.05).
Conclusions:
This study has provided new mechanistic insights first into the involvement of calpain-2 and PTP1B in the loss of cell survival and increased caspase-8-dependent apoptosis induced by hyperglycemia in photoreceptor cells and second, on the protective effect of SST against apoptosis by the enhancement of IGF-IR-mediated Akt phosphorylation.
Insights
Diabetic retinopathy (DR) causes photoreceptor cell death. Somatostatin (SST) protects against high glucose-induced apoptosis by enhancing IGF-IR/Akt signaling, offering a potential therapeutic avenue for DR.
Area of Science:
- Ophthalmology
- Neuroscience
- Cell Biology
Background:
- Diabetic retinopathy (DR) is characterized by early retinal neurodegeneration.
- Somatostatin (SST) is a neuroprotective factor with decreased levels in early DR.
- Understanding DR pathogenesis and identifying neuroprotective agents are critical.
Purpose of the Study:
- To investigate the role of high glucose (HG) in inducing apoptosis in photoreceptor-like cells.
- To characterize the effect of Somatostatin (SST) on HG-induced apoptosis.
- To elucidate the molecular mechanisms underlying SST's neuroprotective effects in DR.
Main Methods:
- Utilized a 661W photoreceptor-like cell line and mouse retinal explants.
- Exposed cells and explants to high glucose (HG) conditions.
- Treated cultures with Somatostatin (SST) and analyzed apoptosis, caspase-8, calpain-2, PTP1B, and IGF-IR/Akt signaling.
Main Results:
- High glucose (HG) significantly increased apoptosis in photoreceptor cells, an effect reduced by SST.
- HG activated caspase-8, calpain-2, and increased PTP1B levels; SST treatment ameliorated these changes.
- SST enhanced IGF-IR and Akt phosphorylation, indicating activation of a pro-survival pathway.
Conclusions:
- Hyperglycemia induces photoreceptor apoptosis via calpain-2 and PTP1B activation.
- Somatostatin (SST) protects photoreceptor cells from hyperglycemia-induced apoptosis.
- SST's protective mechanism involves enhancing IGF-IR-mediated Akt phosphorylation.
