Suppressors of cytokine-signaling proteins induce insulin resistance in the retina and promote survival of retinal cells.
OBJECTIVE
Suppressors of cytokine signaling (SOCS) are implicated in the etiology of diabetes, obesity, and metabolic syndrome. Here, we show that some SOCS members are induced, while others are constitutively expressed, in retina and examine whether persistent elevation of SOCS levels in retina by chronic inflammation or cellular stress predisposes to developing insulin resistance in retina, a condition implicated in diabetic retinopathy.


METHODS
SOCS-mediated insulin resistance and neuroprotection in retina were investigated in 1) an experimental uveitis model, 2) SOCS1 transgenic rats, 3) insulin-deficient diabetic rats, 4) retinal cells depleted of SOCS6 or overexpressing SOCS1/SOCS3, and 5) oxidative stress and light-induced retinal degeneration models.


RESULTS
We show that constitutive expression of SOCS6 protein in retinal neurons may improve glucose metabolism, while elevated SOCS1/SOCS3 expression during uveitis induces insulin resistance in neuroretina. SOCS-mediated insulin resistance, as indicated by its inhibition of basally active phosphoinositide 3-kinase/AKT signaling in retina, is validated in retina-specific SOCS1 transgenic rats and retinal cells overexpressing SOCS1/SOCS3. We further show that the SOCS3 level is elevated in retina by oxidative stress, metabolic stress of insulin-deficient diabetes, or light-induced retinal damage and protects ganglion cells from apoptosis, suggesting that upregulation of SOCS3 may be a common physiologic response of neuroretinal cells to cellular stress.


CONCLUSIONS
Our data suggest two-sided roles of SOCS proteins in retina. Whereas SOCS proteins may improve glucose metabolism, mitigate deleterious effects of inflammation, and promote neuroprotection, persistent SOCS3 expression caused by chronic inflammation or cellular stress can induce insulin resistance and inhibit neurotrophic factors, such as ciliary neurotrophic factor, leukemia inhibitory factor, and insulin, that are essential for retinal cell survival.
Liu
Xuebin
X
Molecular Immunology Section, Laboratory of Immunology, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-1857, USA.
Mameza
Marie G
MG
Lee
Yun Sang
YS
Eseonu
Chikezie I
CI
Yu
Cheng-Rong
CR
Kang Derwent
Jennifer J
JJ
Egwuagu
Charles E
CE
D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000502:physiology*; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D007333:Insulin Resistance / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009924:Organ Culture Techniques; D010857:Pigment Epithelium of Eye / Q000502:physiology; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D012160:Retina / Q000166:cytology* / Q000502:physiology* / Q000503:physiopathology; D012165:Retinal Ganglion Cells / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D014162:Transfection
D034741:RNA, Small Interfering; C571066:SOCS6 protein, rat; C491411:Socs3 protein, mouse; C473086:Socs6 protein, mouse; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins