Trophic factor deprivation (TFD) activates c-Jun N-terminal kinases (JNKs), culminating in coordinate AP1-dependent transactivation of the BH3-only BCL-2 proteins BIM(EL) and HRK, which in turn are critical for BAX-dependent cytochrome c release, caspase activation, and apoptosis. Here, we report that TFD caused not only induction but also phosphorylation of BIM(EL). Mitochondrially localized JNKs but not upstream activators, like mixed-lineage kinases (MLKs) or mitogen-activated protein kinase kinases (MKKs), specifically phosphorylated BIM(EL) at Ser65, potentiating its proapoptotic activity. Inhibition of the JNK pathway attenuated BIM(EL) expression, prevented BIM(EL) phosphorylation, and abrogated TFD-induced apoptosis. Conversely, activation of this pathway promoted BIM(EL) expression and phosphorylation, causing BIM- and BAX-dependent cell death. Thus, JNKs regulate the proapoptotic activity of BIM(EL) during TFD, both transcriptionally and posttranslationally.

Photoreceptor death is the root cause of vision loss in many retinal disorders, and there is an unmet need for neuroprotective modalities to improve photoreceptor survival. The biosynthetic requirement of photoreceptors is among the highest in the body, and to meet this demand, photoreceptors maintain their ability to perform aerobic glycolysis. This highly regulated form of glycolysis allows cells to efficiently budget their metabolic needs and may be a critical link between photoreceptor function and survival. Pyruvate kinase muscle isozyme 2 (PKM2) is a key regulator of aerobic glycolysis. In the present study, we characterized the effect of PKM2 deletion on baseline functioning and survival of photoreceptors over time by utilizing a photoreceptor-specific, PKM2 knockout mouse model. We found that upon PKM2 deletion, PKM1 is upregulated in the outer retina and there is increased expression of genes involved in glucose metabolism, which led to chronic degenerative changes in the outer retina of these mice. We also discovered that this metabolic reprogramming provided a survival advantage to photoreceptors in an experimental model of retinal detachment. This study strongly supports the hypothesis that reprogramming metabolism may be a novel therapeutic strategy for photoreceptor neuroprotection during acute stress.The retina has two circulations-retinal, for the inner retinal neurons, and choroidal, which through the retinal pigment epithelium (RPE), feeds the outer retina. Inner retinal neurons are exquisitely sensitive to ischemia, and irreversible inner retinal injury occurs after 2-4 hours of central retinal artery occlusion 1 . On the other hand, the choroidal circulation supplies the outer retina where the photoreceptors are located. Photoreceptors are therefore deprived of oxygen and glucose when they separate from the underlying retinal pigment epithelium, which occurs in retinal detachment. Unlike inner retinal neurons, photoreceptors are able to withstand prolonged periods of oxygen and nutrient deprivation, as demonstrated by numerous clinical studies that show visual gain when the retina is re-apposed to RPE surgically within days to weeks after initial retinal detachment symptoms 2-4 . It is hypothesized that this survival may be largely secondary to the specific metabolic demands and metabolic machinery present in the photoreceptors.Warburg and colleagues first demonstrated that neoplastic cells convert glucose to lactate despite the presence of oxygen, which is known as aerobic glycolysis or the Warburg effect 5 . In these cells, aerobic glycolysis functions to meet the high demand for metabolic energy and biosynthetic intermediates. Interestingly, Warburg noted that the retina was the only non-proliferative tissue that was capable of aerobic glycolysis and further studies showed that this effect is limited to the photoreceptors [5][6][7][8] . It has been hypothesized that the constant turnover of photoreceptor outer segments, with its extremely high metabolic requirements, drives aerobic glycoly...

The activation of the c-Jun N-terminal kinase (JNK) pathway is critical for naturally occurring neuronal cell death during development and may be important for the pathological neuronal cell death of neurodegenerative diseases. The small molecule inhibitor of the mixed-lineage kinase (MLK) family of kinases, CEP-1347, inhibits the activation of the JNK pathway and, consequently, the cell death in many cell culture and animal models of neuronal death. CEP-1347 has the ability not only to inhibit cell death but also to maintain the trophic status of neurons in culture. The possible importance of the JNK pathway in neurodegenerative diseases such as Alzheimer's and Parkinson's diseases provides a rationale for the use of CEP-1347 for the treatment of these diseases. CEP-1347 has the potential of not only retarding disease progression but also reversing the severity of symptoms by improving the function of surviving neurons.

Genentech, Bayer, Novartis, and Allergan. He receives research support from Genentech/Roche C. A. Curcio receives research support from Heidelberg Engineering and owns stock of MacRegen. C.G. Besirli is a consultant for iRenix Medical, Janssen, receiveds equity (iRenix Medical) and royalty (iRenix Medical, ONL Therapeutics), clinical trial support (MeiraGTx, Spark Therapeutics, 4DMT, Regeneron, Novartis), and research support