Insulin Rescues Retinal Neurons from Apoptosis by a Phosphatidylinositol 3-Kinase/Akt-mediated Mechanism That Reduces the Activation of Caspase-3

Abstract

The ability of insulin to protect neurons from apoptosis was examined in differentiated R28 cells, a neural cell line derived from the neonatal rat retina. Apoptosis was induced by serum deprivation, and the number of pyknotic cells was counted. p53 and Akt were examined by immunoblotting after serum deprivation and insulin treatment, and caspase-3 activation was examined by immunocytochemistry. Serum deprivation for 24 h caused ϳ20% of R28 cells to undergo apoptosis, detected by both pyknosis and activation of caspase-3. 10 nM insulin maximally reduced the amount of apoptosis with a similar potency as 1.3 nM (10 ng/ml) insulin-like growth factor 1, which acted as a positive control. Insulin induced serine phosphorylation of Akt, through the phosphatidylinositol (PI) 3-kinase pathway. Inhibition of PI 3-kinase with wortmannin or LY294002 blocked the ability of insulin to rescue the cells from apoptosis. SN50, a peptide inhibitor of NF-B nuclear translocation, blocked the rescue effect of insulin, but neither insulin or serum deprivation induced phosphorylation of IB. These results suggest that insulin is a survival factor for retinal neurons by activating the PI 3-kinase/Akt pathway and by reducing caspase-3 activation. The rescue effect of insulin does not appear to be mediated by NF-B or p53. These data suggest that insulin provides trophic support for retinal neurons through a PI 3-kinase/Akt-dependent pathway.

Expression of antiapoptotic and proapoptotic molecules in diabetic retinas

“…[12][13][14] In addition, apoptosis of retinal neurons induced by serum deprivation was reduced by insulin via activating the PI 3-kinase/Akt pathway. 15 Furthermore, retinal PI 3-kinase/Akt signalling pathway was activated by optic nerve clamping and had a neuroprotective effect on injured retinal ganglion cells. 16 In agreement with our results, immunoreactivity for phosphorylated Akt was detected in retinal ganglion cells in the injured retina.…”

“…[11][12][13][14][15][16] Several studies showed that Cox-2 functions as a survival factor by protecting cells from apoptosis. [17][18][19][20][21] Overexpression of Mcl-1, a member of the Bcl-2 family, 22 delays apoptosis by a broad array of agents.…”

In IGF-I receptor-deficient leiomyosarcoma cells autocrine IGF-II induces cell invasion and protection from apoptosis via the insulin receptor isoform A

“…Insulin was a slightly more potent anti-apoptotic agent than IGF-II, an expected consequence of the fact that insulin binds to and activates IR-A with higher affinity than IGF-II . Accordingly, insulin was a more potent stimulator of IR autophosphorylation and of the IRS-1/PI3K/Akt pathway, which plays a major role in apoptosis control (Barber et al, 2001;Hiromura et al, 2002).…”

The Protective Effects of Insulin on Hydrogen Peroxide-Induced Oxidative Stress in C6 Glial Cells

“…Akt mediation of IGF-1 induced survival of cerebellar neurons has been documented (Blair et al, 1999). Insulin acts as a survival factor for retinal neurons through activation of the PI3K/Akt pathway (Barber et al, 2001). Huntington's disease, a neurodegenerative disorder that manifests itself in involuntary movements, personality changes, and dementia in patients is associated with death of neurons in the striatum and alteration in the huntingtin protein.…”