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Partial restoration of protein synthesis rates by the small molecule ISRIB prevents neurodegeneration without pancreatic toxicity.

Halliday M, Radford H, Sekine Y, Moreno J, Verity N, le Quesne J, Ortori CA, Barrett DA, Fromont C, Fischer PM, Harding HP, Ron D, Mallucci GR - Cell Death Dis (2015)

Bottom Line: Activation of the PERK branch of the unfolded protein response (UPR) in response to protein misfolding within the endoplasmic reticulum (ER) results in the transient repression of protein synthesis, mediated by the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2α).Critically, ISRIB treatment resulted in only partial restoration of global translation rates, as compared with the complete restoration of protein synthesis seen with GSK2606414.Thus, fine-tuning the extent of UPR inhibition and subsequent translational de-repression uncouples neuroprotective effects from pancreatic toxicity.

View Article: PubMed Central - PubMed

Affiliation: Medical Research Council Toxicology Unit, Hodgkin Building, University of Leicester, Leicester, UK.

ABSTRACT
Activation of the PERK branch of the unfolded protein response (UPR) in response to protein misfolding within the endoplasmic reticulum (ER) results in the transient repression of protein synthesis, mediated by the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2α). This is part of a wider integrated physiological response to maintain proteostasis in the face of ER stress, the dysregulation of which is increasingly associated with a wide range of diseases, particularly neurodegenerative disorders. In prion-diseased mice, persistently high levels of eIF2α cause sustained translational repression leading to catastrophic reduction of critical proteins, resulting in synaptic failure and neuronal loss. We previously showed that restoration of global protein synthesis using the PERK inhibitor GSK2606414 was profoundly neuroprotective, preventing clinical disease in prion-infected mice. However, this occured at the cost of toxicity to secretory tissue, where UPR activation is essential to healthy functioning. Here we show that pharmacological modulation of eIF2α-P-mediated translational inhibition can be achieved to produce neuroprotection without pancreatic toxicity. We found that treatment with the small molecule ISRIB, which restores translation downstream of eIF2α, conferred neuroprotection in prion-diseased mice without adverse effects on the pancreas. Critically, ISRIB treatment resulted in only partial restoration of global translation rates, as compared with the complete restoration of protein synthesis seen with GSK2606414. ISRIB likely provides sufficient rates of protein synthesis for neuronal survival, while allowing some residual protective UPR function in secretory tissue. Thus, fine-tuning the extent of UPR inhibition and subsequent translational de-repression uncouples neuroprotective effects from pancreatic toxicity. The data support the pursuit of this approach to develop new treatments for a range of neurodegenerative disorders that are currently incurable.

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ISRIB is not toxic to the pancreas, unlike GSK2606414. (a) GSK2606414 treatment (green bar) mildly raises blood glucose levels compared with control (black bar), vehicle-treated (gray bar) and ISRIB-treated (blue bar) mice (n=6–9 for each group). (b) GSK2606414 treatment leads to a significant reduction in pancreas weight, while ISRIB treatment has no effect (n=3–6 for each group). (c) Representative images of hematoxylin and eosin-stained pancreas sections. GSK2606414 treatment leads to extensive destruction of exocrine acinar pancreatic tissue, while ISRIB-treated tissue is histologically normal. Scale bar=200 μm. *P<0.05, ***P<0.001, Student's t-test, two-tailed. Bar graphs show mean values±S.E.M.
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fig5: ISRIB is not toxic to the pancreas, unlike GSK2606414. (a) GSK2606414 treatment (green bar) mildly raises blood glucose levels compared with control (black bar), vehicle-treated (gray bar) and ISRIB-treated (blue bar) mice (n=6–9 for each group). (b) GSK2606414 treatment leads to a significant reduction in pancreas weight, while ISRIB treatment has no effect (n=3–6 for each group). (c) Representative images of hematoxylin and eosin-stained pancreas sections. GSK2606414 treatment leads to extensive destruction of exocrine acinar pancreatic tissue, while ISRIB-treated tissue is histologically normal. Scale bar=200 μm. *P<0.05, ***P<0.001, Student's t-test, two-tailed. Bar graphs show mean values±S.E.M.

Mentions: To understand the systemic effects of both compounds in causing weight loss, we treated another group of prion-infected mice for 5 weeks with either GSK2606414 or ISRIB and examined the pancreas and measured blood glucose levels. The latter were unaffected by ISRIB treatment but were mildly but significantly elevated by GSK2606414 (Figure 5a), consistent with previous findings.10 However, morphological examination of the pancreas showed that chronic GSK2606414 treatment was toxic, causing ~50% reduction in pancreatic weight (Figure 5b) and extensive destruction of exocrine acinar pancreatic tissue (Figure 5c). Critically, ISRIB treatment produced no detectable pancreatic toxicity; pancreatic weights were normal (Figure 5b) and structure and integrity of exocrine and endocrine pancreatic tissues was preserved (Figure 5c). Thus, while reversal of translational inhibition by both GSK2606414 and ISRIB is neuroprotective, the two compounds have very different adverse effect profiles on the pancreas.


Partial restoration of protein synthesis rates by the small molecule ISRIB prevents neurodegeneration without pancreatic toxicity.

Halliday M, Radford H, Sekine Y, Moreno J, Verity N, le Quesne J, Ortori CA, Barrett DA, Fromont C, Fischer PM, Harding HP, Ron D, Mallucci GR - Cell Death Dis (2015)

ISRIB is not toxic to the pancreas, unlike GSK2606414. (a) GSK2606414 treatment (green bar) mildly raises blood glucose levels compared with control (black bar), vehicle-treated (gray bar) and ISRIB-treated (blue bar) mice (n=6–9 for each group). (b) GSK2606414 treatment leads to a significant reduction in pancreas weight, while ISRIB treatment has no effect (n=3–6 for each group). (c) Representative images of hematoxylin and eosin-stained pancreas sections. GSK2606414 treatment leads to extensive destruction of exocrine acinar pancreatic tissue, while ISRIB-treated tissue is histologically normal. Scale bar=200 μm. *P<0.05, ***P<0.001, Student's t-test, two-tailed. Bar graphs show mean values±S.E.M.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4385927&req=5

fig5: ISRIB is not toxic to the pancreas, unlike GSK2606414. (a) GSK2606414 treatment (green bar) mildly raises blood glucose levels compared with control (black bar), vehicle-treated (gray bar) and ISRIB-treated (blue bar) mice (n=6–9 for each group). (b) GSK2606414 treatment leads to a significant reduction in pancreas weight, while ISRIB treatment has no effect (n=3–6 for each group). (c) Representative images of hematoxylin and eosin-stained pancreas sections. GSK2606414 treatment leads to extensive destruction of exocrine acinar pancreatic tissue, while ISRIB-treated tissue is histologically normal. Scale bar=200 μm. *P<0.05, ***P<0.001, Student's t-test, two-tailed. Bar graphs show mean values±S.E.M.
Mentions: To understand the systemic effects of both compounds in causing weight loss, we treated another group of prion-infected mice for 5 weeks with either GSK2606414 or ISRIB and examined the pancreas and measured blood glucose levels. The latter were unaffected by ISRIB treatment but were mildly but significantly elevated by GSK2606414 (Figure 5a), consistent with previous findings.10 However, morphological examination of the pancreas showed that chronic GSK2606414 treatment was toxic, causing ~50% reduction in pancreatic weight (Figure 5b) and extensive destruction of exocrine acinar pancreatic tissue (Figure 5c). Critically, ISRIB treatment produced no detectable pancreatic toxicity; pancreatic weights were normal (Figure 5b) and structure and integrity of exocrine and endocrine pancreatic tissues was preserved (Figure 5c). Thus, while reversal of translational inhibition by both GSK2606414 and ISRIB is neuroprotective, the two compounds have very different adverse effect profiles on the pancreas.

Bottom Line: Activation of the PERK branch of the unfolded protein response (UPR) in response to protein misfolding within the endoplasmic reticulum (ER) results in the transient repression of protein synthesis, mediated by the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2α).Critically, ISRIB treatment resulted in only partial restoration of global translation rates, as compared with the complete restoration of protein synthesis seen with GSK2606414.Thus, fine-tuning the extent of UPR inhibition and subsequent translational de-repression uncouples neuroprotective effects from pancreatic toxicity.

View Article: PubMed Central - PubMed

Affiliation: Medical Research Council Toxicology Unit, Hodgkin Building, University of Leicester, Leicester, UK.

ABSTRACT
Activation of the PERK branch of the unfolded protein response (UPR) in response to protein misfolding within the endoplasmic reticulum (ER) results in the transient repression of protein synthesis, mediated by the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2α). This is part of a wider integrated physiological response to maintain proteostasis in the face of ER stress, the dysregulation of which is increasingly associated with a wide range of diseases, particularly neurodegenerative disorders. In prion-diseased mice, persistently high levels of eIF2α cause sustained translational repression leading to catastrophic reduction of critical proteins, resulting in synaptic failure and neuronal loss. We previously showed that restoration of global protein synthesis using the PERK inhibitor GSK2606414 was profoundly neuroprotective, preventing clinical disease in prion-infected mice. However, this occured at the cost of toxicity to secretory tissue, where UPR activation is essential to healthy functioning. Here we show that pharmacological modulation of eIF2α-P-mediated translational inhibition can be achieved to produce neuroprotection without pancreatic toxicity. We found that treatment with the small molecule ISRIB, which restores translation downstream of eIF2α, conferred neuroprotection in prion-diseased mice without adverse effects on the pancreas. Critically, ISRIB treatment resulted in only partial restoration of global translation rates, as compared with the complete restoration of protein synthesis seen with GSK2606414. ISRIB likely provides sufficient rates of protein synthesis for neuronal survival, while allowing some residual protective UPR function in secretory tissue. Thus, fine-tuning the extent of UPR inhibition and subsequent translational de-repression uncouples neuroprotective effects from pancreatic toxicity. The data support the pursuit of this approach to develop new treatments for a range of neurodegenerative disorders that are currently incurable.

Show MeSH
Related in: MedlinePlus