Calcineurin Inhibition at the Clinical Phase of Prion Disease Reduces Neurodegeneration, Improves Behavioral Alterations and Increases Animal Survival

Abstract

Prion diseases are fatal neurodegenerative disorders characterized by a long pre-symptomatic phase followed by rapid and progressive clinical phase. Although rare in humans, the unconventional infectious nature of the disease raises the potential for an epidemic. Unfortunately, no treatment is currently available. The hallmark event in prion diseases is the accumulation of a misfolded and infectious form of the prion protein (PrPSc). Previous reports have shown that PrPSc induces endoplasmic reticulum stress and changes in calcium homeostasis in the brain of affected individuals. In this study we show that the calcium-dependent phosphatase Calcineurin (CaN) is hyperactivated both in vitro and in vivo as a result of PrPSc formation. CaN activation mediates prion-induced neurodegeneration, suggesting that inhibition of this phosphatase could be a target for therapy. To test this hypothesis, prion infected wild type mice were treated intra-peritoneally with the CaN inhibitor FK506 at the clinical phase of the disease. Treated animals exhibited reduced severity of the clinical abnormalities and increased survival time compared to vehicle treated controls. Treatment also led to a significant increase in the brain levels of the CaN downstream targets pCREB and pBAD, which paralleled the decrease of CaN activity. Importantly, we observed a lower degree of neurodegeneration in animals treated with the drug as revealed by a higher number of neurons and a lower quantity of degenerating nerve cells. These changes were not dependent on PrPSc formation, since the protein accumulated in the brain to the same levels as in the untreated mice. Our findings contribute to an understanding of the mechanism of neurodegeneration in prion diseases and more importantly may provide a novel strategy for therapy that is beneficial at the clinical phase of the disease.

FK506 reduces abnormal prion protein through the activation of autolysosomal degradation and prolongs survival in prion-infected mice

“…17,18 Rapamycin did extend survival to a moderate extent only under certain experimental conditions. 19,25 In our study, the early administration at 20 d.p.i of FK506 prolonged the survival of Fukuoka-1-infected mice. In contrast, the late administration (60 d.p.i.)…”

“…Mukherjee et al have recently reported that FK506 suppressed the function of calcineurin leading to the reduction of prion-induced neurodegeneration, 25 and concluded that FK506 treatment does not alter the extent of accumulation of PRNP Sc , astrocytosis or microglial activation at the terminal stage of the disease. These findings are consistent with our observation that no significant difference was observed between the brains of FK506-treated mice and those of control animals at the terminal stage.…”

“…21 Recent studies reveal neuroprotective effects in cerebral ischemia 22 and several neurodegenerative disorders, 23,24 including TSE. 25 On the other hand, FKBP39 has recently been reported to suppress autophagy in drosophila. 26 This result raises the possibility that FK506 could also influence the autophagy-lysosomal system in mammalian cells.…”

ER stress in neurodegenerative disease: from disease mechanisms to therapeutic interventions

“…Remarkably, targeting of the anti-apoptotic protein BCL-2 to the ER membrane could decrease PrP Sc toxicity and cells infected with prions were more susceptible to ER stress-induced apoptosis [148,155,156]. At the molecular level PrP Sc conversion may affect ER calcium homeostasis [157,155], triggering ER stress [154], which may culminate in cellular death [159].…”

Insights from Therapeutic Studies for PrP Prion Disease

“…Moreover, conditional knockout of Prnp expression halted disease progression and recovered certain brain functions even after disease onset (Mallucci et al 2002(Mallucci et al , 2003 (Karapetyan et al 2013). For example, the compound tacrolimus has been shown to reduce both membrane and intracellular PrP C levels by a nontranscriptional mechanism (Karapetyan et al 2013), to suppress neurodegenerative processes in prioninfected animals by acting as a calcineurin inhibitor (Mukherjee et al 2010), and to activate autophagy in both prion-infected cells and animals (Nakagaki et al 2013).…”