TRAUMATIC BRAIN INJURY: CYCLOPHILIN D AS A THERAPEUTIC TARGET AND THE NEUROPATHOLOGY CAUSED BY BLAST

With an estimated incidence of 1.5 million each year, traumatic brain injury (TBI) is a major cause of mortality and morbidity in the United States. Opening of the mitochondrial permeability transition pore (mPTP) is a key event contributing to TBI pathology. Cyclophilin D (CypD), a matrix peptidyl-prolyl cis-trans isomerase, is believed to be the regulating component of the mPTP. Cyclosporin A, an immunosuppressant drug, inhibits CypD and blocks mPTP formation and has been shown to be neuroprotective following TBI. However, it is unclear if CsA’s neuroprotective mechanism is due to inhibition of CypD and/or immuno-suppression. Therefore to directly assess the contribution of CypD to TBI pathology, CypD knockout mice were subjected to a controlled cortical impact model of TBI. CypD ablation resulted in increased tissue sparing, hippocampal protection, and improved mitochondrial complex I driven respiration. Next a dose-response study of the Cyclophilin D inhibitor, NIM811, was performed. NIM811 administration following TBI resulted in improved cognition, increased tissue sparing, and improved mitochondrial function. These results suggest a major role for CypD in TBI pathology and validate CypD as a potential therapeutic target for TBI. TBI has been proposed to be the signature injury of the current Middle Eastern conflicts with an estimated prevalence of 15-60 % among combat soldiers. Although the brain does appear to be vulnerable to blast, the exact mechanisms underlying the injury remain unclear. Adult male Sprague-Dawley rats were exposed to a moderate level of blast overpressure. Following blast, blood brain barrier disruption was evident at 3 and 24 h post-exposure, oxidative damage increased at 3 h post-exposure, and microglia were activated in the hippocampus at 5 and 10 days post-exposure. This may widen future neuroprotective avenues for blast since blast brain injury appears to share similar mechanisms of injury with other TBI models

Mitochondria, Amyloid β, and Alzheimer's Disease

Hypometabolism is a hallmark of Alzheimer's disease (AD) and implicates a mitochondrial role in the neuropathology associated with AD. Mitochondrial amyloid-beta (Aβ) accumulation precedes extracellular Aβ deposition. In addition to increasing oxidative stress, Aβ has been shown to directly inhibit mitochondrial enzymes. Inhibition of mitochondrial enzymes as a result of oxidative damage or Aβ interaction perpetuates oxidative stress and leads to a hypometabolic state. Additionally, Aβ has also been shown to interact with cyclophilin D, a component of the mitochondrial permeability transition pore, which may promote cell death. Therefore, ample evidence exists indicating that the mitochondrion plays a vital role in the pathophysiology observed in AD

Mitochondria, Amyloid β, and Alzheimer\u27s Disease

Hypometabolism is a hallmark of Alzheimer\u27s disease (AD) and implicates a mitochondrial role in the neuropathology associated with AD. Mitochondrial amyloid-beta (Aβ) accumulation precedes extracellular Aβ deposition. In addition to increasing oxidative stress, Aβ has been shown to directly inhibit mitochondrial enzymes. Inhibition of mitochondrial enzymes as a result of oxidative damage or Aβ interaction perpetuates oxidative stress and leads to a hypometabolic state. Additionally, Aβ has also been shown to interact with cyclophilin D, a component of the mitochondrial permeability transition pore, which may promote cell death. Therefore, ample evidence exists indicating that the mitochondrion plays a vital role in the pathophysiology observed in AD

Genetic Approach to Elucidate the Role of Cyclophilin D in Traumatic Brain Injury Pathology

Cyclophilin D (CypD) has been shown to play a critical role in mitochondrial permeability transition pore (mPTP) opening and the subsequent cell death cascade. Studies consistently demonstrate that mitochondrial dysfunction, including mitochondrial calcium overload and mPTP opening, is essential to the pathobiology of cell death after a traumatic brain injury (TBI). CypD inhibitors, such as cyclosporin A (CsA) or NIM811, administered following TBI, are neuroprotective and quell neurological deficits. However, some pharmacological inhibitors of CypD have multiple biological targets and, as such, do not directly implicate a role for CypD in arbitrating cell death after TBI. Here, we reviewed the current understanding of the role CypD plays in TBI pathobiology. Further, we directly assessed the role of CypD in mediating cell death following TBI by utilizing mice lacking the CypD encoding gene Ppif. Following controlled cortical impact (CCI), the genetic knockout of CypD protected acute mitochondrial bioenergetics at 6 h post-injury and reduced subacute cortical tissue and hippocampal cell loss at 18 d post-injury. The administration of CsA following experimental TBI in Ppif-/- mice improved cortical tissue sparing, highlighting the multiple cellular targets of CsA in the mitigation of TBI pathology. The loss of CypD appeared to desensitize the mitochondrial response to calcium burden induced by TBI; this maintenance of mitochondrial function underlies the observed neuroprotective effect of the CypD knockout. These studies highlight the importance of maintaining mitochondrial homeostasis after injury and validate CypD as a therapeutic target for TBI. Further, these results solidify the beneficial effects of CsA treatment following TBI

Neurodegeneration progresses despite complete elimination of clinical relapses in a mouse model of multiple sclerosis.

BACKGROUND: [corrected] Multiple Sclerosis has two clinical phases reflecting distinct but inter-related pathological processes: focal inflammation drives the relapse-remitting stage and neurodegeneration represents the principal substrate of secondary progression. In contrast to the increasing number of effective anti-inflammatory disease modifying treatments for relapse-remitting disease, the absence of therapies for progressive disease represents a major unmet clinical need. This raises the unanswered question of whether elimination of clinical relapses will prevent subsequent progression and if so how early in the disease course should treatment be initiated. Experimental autoimmune encephalomyelitis in the Biozzi ABH mouse recapitulates the clinical and pathological features of multiple sclerosis including relapse-remitting episodes with inflammatory mediated demyelination and progressive disability with neurodegeneration. To address the relationship between inflammation and neurodegeneration we used an auto-immune tolerance strategy to eliminate clinical relapses in EAE in a manner analogous to the clinical effect of disease modifying treatments. RESULTS: By arresting clinical relapses in EAE at two distinct stages, early and late disease, we demonstrate that halting immune driven demyelination even after the first major clinical event is insufficient to prevent long-term neurodegeneration and associated gliosis. Nonetheless, early intervention is partially neuroprotective, whereas later interventions are not. Furthermore early tolerisation is also associated with increased remyelination. CONCLUSIONS: These findings are consistent with both a partial uncoupling of inflammation and neurodegeneration and that the regenerative response of remyelination is negatively correlated with inflammation. These findings strongly support the need for early combinatorial treatment of immunomodulatory therapies and neuroprotective treatments to prevent long-term neurodegeneration in multiple sclerosis

Selective Inhibition of the Mitochondrial Permeability Transition Pore Protects against Neurodegeneration in Experimental Multiple Sclerosis

The mitochondrial permeability transition pore is a recognized drug target for neurodegenerative conditions such as multiple sclerosis and for ischemia-reperfusion injury in the brain and heart. The peptidylprolyl isomerase, cyclophilin D (CypD, PPIF), is a positive regulator of the pore, and genetic downregulation or knock-out improves outcomes in disease models. Current inhibitors of peptidylprolyl isomerases show no selectivity between the tightly conserved cyclophilin paralogs and exhibit significant off-target effects, immunosuppression, and toxicity. We therefore designed and synthesized a new mitochondrially targeted CypD inhibitor, JW47, using a quinolinium cation tethered to cyclosporine. X-ray analysis was used to validate the design concept, and biological evaluation revealed selective cellular inhibition of CypD and the permeability transition pore with reduced cellular toxicity compared with cyclosporine. In an experimental autoimmune encephalomyelitis disease model of neurodegeneration in multiple sclerosis, JW47 demonstrated significant protection of axons and improved motor assessments with minimal immunosuppression. These findings suggest that selective CypD inhibition may represent a viable therapeutic strategy for MS and identify quinolinium as a mitochondrial targeting group for <i>in vivo</i> use

Cognition based bTBI mechanistic criteria; a tool for preventive and therapeutic innovations

Blast-induced traumatic brain injury has been associated with neurodegenerative and neuropsychiatric disorders. To date, although damage due to oxidative stress appears to be important, the specific mechanistic causes of such disorders remain elusive. Here, to determine the mechanical variables governing the tissue damage eventually cascading into cognitive deficits, we performed a study on the mechanics of rat brain under blast conditions. To this end, experiments were carried out to analyse and correlate post-injury oxidative stress distribution with cognitive deficits on a live rat exposed to blast. A computational model of the rat head was developed from imaging data and validated against in vivo brain displacement measurements. The blast event was reconstructed in silico to provide mechanistic thresholds that best correlate with cognitive damage at the regional neuronal tissue level, irrespectively of the shape or size of the brain tissue types. This approach was leveraged on a human head model where the prediction of cognitive deficits was shown to correlate with literature findings. The mechanistic insights from this work were finally used to propose a novel helmet design roadmap and potential avenues for therapeutic innovations against blast traumatic brain injury