Basic Research Work Plan

Mitochondria are membrane bound organelles whose principal function is to provide energy for the cell in the form of adenosine triphosphate (ATP) through the oxidative phosphorylation complexes located on the inner mitochondrial membrane.

Neurons need large amounts of ATP to control the intracellular ionic homeostasis required to regulate neurotransmission. Moreover, many proteins and processes critical for brain plasticity require ATP. These include cytoskeletal components involved in axoplasmic transport (microtubules, actin filament, kinesins, myosins, etc.), ion-motive ATPases and a myriad of protein phosphorylation reactions.

Since most of the ATP produced in neurons comes from oxidative phosphorylation, neurons are critically dependant on mitochondrial function and oxygen supply. In addition to ATP synthesis, mitochondria are key regulators of calcium homeostasis, free radical production, steroid synthesis and apoptosis. Each of these factors could also be associated with essential mechanisms involved in neurodegenerative diseases along with mechanisms regulating neuronal and synaptic plasticity.

Considering the importance of mitochondrial functions in neurons, it is hypothesized that dysfunction of mitochondria causes loss of brain plasticity, synaptic impairment, axonal injury and neuronal loss, all of which are major hallmarks of neurodegenerative diseases.

One of the aims of the MitoTarget research is to further understand how each of those elements are ordered and linked to each other and how a loss of regulation of the balance between each of these mechanisms leads to neuronal degeneration and cell death.

Basic research work plan is divided into 5 work packages:

WP-1: Mitochondrial dynamics in neurodegenerative diseases and assessment of the effects of new small molecules

Defects in morphology and axonal transport of mitochondria are one of the earliest pathological features reported to date in ALS models. Aims of this work plan are to extend these observations to the non-SOD1 related ALS disease and to other neurodegenerative diseases (AD, HD, and HSP), and define whether they could be targeted by a novel class of neuroprotective compounds identified by Trophos.

WP-2: Mitochondrial membrane properties in the process of neurodegeneration and assessment of the effects of new small molecules

Recent studies reveal the unexpected presence of lipid microdomains in mitochondrial membranes thereby possibly modulating mitochondrial morphology, opening of the mitochondrial permeability transition pore and recruitment of pro-apoptotic factors.

The aim of this work plan is to find evidence for changes in mitochondrial membrane properties and gain an understanding of the impact of mitochondrial lipid rafts in the context of brain disease and repair. A second aim is to characterize the mechanism of action of mitochondrial targeted compounds. These compounds share chemical structure homology with cholesterol and so could impact mitochondrial membrane fluidity and lipid raft composition and function.

WP-3: Mitochondrial metabolic function and oxidative stress in neurodegenerative diseases and assessment of the effects of new small molecules

While oxidative stress is widely described in neurodegenerative diseases, whether it is a primary cause of pathogenesis or is merely a consequence of the disease is still debated.

Aims of this work plan are to provide answers to this key question by precisely characterizing oxidative damage and defects in mitochondrial respiratory chain function in cellular disease models, and to identify surrogate markers that could be used in future clinical trials.

Finally, efficacy of mitochondrial targeted compounds to reduce oxidative damage in cellular models of neurodegenerative diseases will be tested using previously characterized surrogate markers.

WP-4: Mitochondrial apoptotic pathways in neurodegenerative diseases and assessment of the effects of new small molecules

While control of mitochondrial membrane permeabilization (MMP) is thought to be of significant therapeutic benefit for neuroprotection, whether the mitochondrial permeability transition pore (mPTP) is the leading cause for MMP is still controversial.

The main objective of this work plan is to obtain further evidence of mPTP disturbances in neurodegeneration and to dissect upstream and downstream events. Trophos has identified a series of compounds that target constitutive proteins of the mPTP and delay neuronal death. Further dissection of their proposed mechanism of action will be performed.

WP-5: In vivo evidence of mitochondrial-targeted therapeutics

The mitochondrial targeted compound, TRO19622 (olesoxime), has already shown efficacy in delaying disease onset and improving survival of mutant SOD1G93A mice. Aims of this work plan are to further characterize its activity in other animal models of neurodegenerative diseases, based upon their in vitro activities demonstrated in WP1 to WP4. Phenotype and survival will be used as primary endpoints while potential surrogate markers of mitochondrial dysfunction, identified and validated in WP1 to WP4, will be used as secondary endpoints. Showing efficacy of Trophos’ compounds on one of these markers would validate their presumed mechanism of action in vivo.