Activating mitofusins interrupts mitochondrial degeneration and delays disease progression in SOD1 mutant amyotrophic lateral sclerosis

Mitochondria in aging and age-associated diseases

Mitochondria, essential for cellular energy, are crucial in neurodegenerative disorders (NDDs) and their age-related progression. This review highlights mitochondrial dynamics, mitovesicles, homeostasis, and organelle communication. We examine mitochondrial impacts from aging and NDDs, focusing on protein aggregation and dysfunction. Prospective therapeutic approaches include enhancing mitophagy, improving respiratory chain function, maintaining calcium and lipid balance, using microRNAs, and mitochondrial transfer to protect function. These strategies underscore the crucial role of mitochondrial health in neuronal survival and cognitive functions, offering new therapeutic opportunities.

Therapeutic targeting of the oxidative stress generated by pathological molecular pathways in the neurodegenerative diseases, ALS and Huntington's

Neurodegenerative disorders are characterized by a progressive decline of specific neuronal populations in the brain and spinal cord, typically containing aggregates of one or more proteins. They can result in behavioral alterations, memory loss and a decline in cognitive and motor abilities. Various pathways and mechanisms have been outlined for the potential treatment of these diseases, where redox regulation is considered as one of the most common druggable targets. For example, in amyotrophic lateral sclerosis (ALS) with superoxide dismutase-1 (SOD1) pathology, there is a downregulation of the antioxidant response nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. TDP-43 proteinopathy in ALS is associated with elevated levels of reactive oxygen species and mitochondrial dyshomeostasis. In ALS with mutant FUS, poly ADP ribose polymerase-dependent X ray repair cross complementing 1/DNA-ligase recruitment to the sites of oxidative DNA damage is affected, thereby causing defects in DNA damage repair. Oxidative stress in Huntington's disease (HD) with mutant huntingtin accumulation manifests as protein oxidation, metabolic energetics dysfunction, metal ion dyshomeostasis, DNA damage and mitochondrial dysfunction. The impact of oxidative stress in the progression of these diseases further warrants studies into the role of antioxidants in their treatment. While an antioxidant, edaravone, has been approved for therapeutics of ALS, numerous antioxidant molecules failed to pass the clinical trials despite promising initial studies. In this review, we summarize the oxidative stress pathways and redox modulators that are investigated in ALS and HD using various models.

Sensory-Motor Neuropathy in Mfn2 T105M Knock-in Mice and Its Reversal by a Novel Piperine-Derived Mitofusin Activator

Mitochondrial dysfunction is a hallmark of many genetic neurodegenerative diseases, but therapeutic options to reverse mitochondrial dysfunction are limited. While recent studies support the possibility of improving mitochondrial fusion/fission dynamics and motility to correct mitochondrial dysfunction and resulting neurodegeneration in Charcot-Marie-Tooth disease (CMT) and other neuropathies, the clinical utility of reported compounds and relevance of preclinical models are uncertain. Here, we describe motor and sensory neuron dysfunction characteristic of clinical CMT type 2 A in a CRISPR/Casp-engineered Mfn2 Thr105Met (T105M) mutant knock-in mouse. We further demonstrate that daily oral treatment with a novel mitofusin activator derived from the natural product piperine can reverse these neurologic phenotypes. Piperine derivative 8015 promoted mitochondrial fusion and motility in Mfn2-deficient cells in a mitofusin-dependent manner and reversed mitochondrial dysfunction in cultured fibroblasts and reprogrammed motor neurons from a human CMT2A patient carrying the MFN2 T105M mutation. Like previous mitofusin activators, 8015 exhibited stereospecific functionality, but the more active stereoisomer, 8015-P2, is unique in that it has subnanomolar potency and undergoes entero-hepatic recirculation which extends its in vivo half-life. Daily administration of 8015-P2 to Mfn2 T105M knock-in mice for 6 weeks normalized neuromuscular and sensory dysfunction and corrected histological/ultrastructural neurodegeneration and neurogenic myoatrophy. These studies describe a more clinically relevant mouse model of CMT2A and an improved mitofusin activator derived from piperine. We posit that 8015-P2 and other piperine derivatives may benefit CMT2A or other neurodegenerative conditions wherein mitochondrial dysdynamism plays a contributory role. SIGNIFICANCE STATEMENT: Mitochondrial dysfunction is widespread and broadly contributory in neurodegeneration, but difficult to target therapeutically. Here, we describe 8015-P2, a new small molecule mitofusin activator with ∼10-fold greater potency and improved in vivo pharmacokinetics versus comparators, and demonstrate its rapid reversal of sensory and motor neuron dysfunction in an Mfn2 T105M knock-in mouse model of Charcot-Marie-Tooth disease type 2 A. These findings further support the therapeutic approach of targeting mitochondrial dysdynamism in neurodegeneration.

Current potential pathogenic mechanisms of copper-zinc superoxide dismutase 1 (SOD1) in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rare neurodegenerative disease which damages upper and lower motor neurons (UMN and LMN) innervating the muscles of the trunk, extremities, head, neck and face in cerebrum, brain stem and spinal cord, which results in the progressive weakness, atrophy and fasciculation of muscle innervated by the related UMN and LMN, accompanying with the pathological signs leaded by the cortical spinal lateral tract lesion. The pathogenesis about ALS is not fully understood, and no specific drugs are available to cure and prevent the progression of this disease at present. In this review, we reviewed the structure and associated functions of copper-zinc superoxide dismutase 1 (SOD1), discuss why SOD1 is crucial to the pathogenesis of ALS, and outline the pathogenic mechanisms of SOD1 in ALS that have been identified at recent years, including glutamate-related excitotoxicity, mitochondrial dysfunction, endoplasmic reticulum stress, oxidative stress, axonal transport disruption, prion-like propagation, and the non-cytologic toxicity of glial cells. This review will help us to deeply understand the current progression in this field of SOD1 pathogenic mechanisms in ALS.

Mitigating the Functional Deficit after Neurotoxic Motoneuronal Loss by an Inhibitor of Mitochondrial Fission

Amyotrophic lateral sclerosis (ALS) is an extremely complex neurodegenerative disease involving different cell types, but motoneuronal loss represents its main pathological feature. Moreover, compensatory plastic changes taking place in parallel to neurodegeneration are likely to affect the timing of ALS onset and progression and, interestingly, they might represent a promising target for disease-modifying treatments. Therefore, a simplified animal model mimicking motoneuronal loss without the other pathological aspects of ALS has been established by means of intramuscular injection of cholera toxin-B saporin (CTB-Sap), which is a targeted neurotoxin able to kill motoneurons by retrograde suicide transport. Previous studies employing the mouse CTB-Sap model have proven that spontaneous motor recovery is possible after a subtotal removal of a spinal motoneuronal pool. Although these kinds of plastic changes are not enough to counteract the functional effects of the progressive motoneuron degeneration, it would nevertheless represent a promising target for treatments aiming to postpone ALS onset and/or delay disease progression. Herein, the mouse CTB-Sap model has been used to test the efficacy of mitochondrial division inhibitor 1 (Mdivi-1) as a tool to counteract the CTB-Sap toxicity and/or to promote neuroplasticity. The homeostasis of mitochondrial fission/fusion dynamics is indeed important for cell integrity, and it could be affected during neurodegeneration. Lesioned mice were treated with Mdivi-1 and then examined by a series of behavioral test and histological analyses. The results have shown that the drug may be capable of reducing functional deficits after the lesion and promoting synaptic plasticity and neuroprotection, thus representing a putative translational approach for motoneuron disorders.

Computational screening of damaging nsSNPs in human SOD1 genes associated with amyotrophic lateral sclerosis identifies destabilising effects of G38R and G42D mutations through in silico evaluation

Amyotrophic lateral sclerosis (ALS), a complicated neurodegenerative disorder affected by hereditary and environmental variables, is a condition. In this study, the genetic makeup of ALS is investigated, with a focus on the SOD1 gene's single-nucleotide polymorphisms (SNPs) and their ability to affect disease risk. Eleven high-risk missense variations that may impair the functionality of the SOD1 protein were discovered after a thorough examination of SNPs in the SOD1 gene. These mutations were chosen using a variety of prediction approaches, highlighting their importance in the aetiology of ALS. Notably, it was discovered that the stability of the SOD1 wild-type protein structure was compromised by the G38R and G42D SOD1 variants. Additionally, Edaravone, a possible ALS medication, showed a greater affinity for binding mutant SOD1 structures, pointing to potential personalised treatment possibilities. The high-risk SNPs discovered in this investigation seem to have functional effects, especially on the stability of proteins and their interactions with other molecules. This study clarifies the complex genetics of ALS and offers insights into how these genetic variations may affect the effectiveness of therapeutic interventions, particularly in the context of edaravone. In this study advances our knowledge of the genetic mechanisms causing ALS vulnerability and prospective therapeutic strategies. Future studies are necessary to confirm these results and close the gap between individualised clinical applications and improved ALS care.

Reversing Dysdynamism to Interrupt Mitochondrial Degeneration in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis is one of several chronic neurodegenerative conditions in which mitochondrial abnormalities are posited to contribute to disease progression. Therapeutic options targeting mitochondria include enhancing metabolism, suppressing reactive oxygen production and disrupting mitochondria-mediated programmed cell death pathways. Herein is reviewed mechanistic evidence supporting a meaningful pathophysiological role for the constellation of abnormal mitochondrial fusion, fission and transport, collectively designated mitochondrial dysdynamism, in ALS. Following this is a discussion on preclinical studies in ALS mice that seemingly validate the idea that normalizing mitochondrial dynamism can delay ALS by interrupting a vicious cycle of mitochondrial degeneration, leading to neuronal die-back and death. Finally, the relative benefits of suppressing mitochondrial fusion vs. enhancing mitochondrial fusion in ALS are speculated upon, and the paper concludes with the prediction that the two approaches could be additive or synergistic, although a side-by-side comparative trial may be challenging to perform.

Disturb mitochondrial associated proteostasis: Neurodegeneration and imperfect ageing

The disturbance in mitochondrial functions and homeostasis are the major features of neuron degenerative conditions, like Parkinson’s disease, Amyotrophic Lateral Sclerosis, and Alzheimer’s disease, along with protein misfolding. The aberrantly folded proteins are known to link with impaired mitochondrial pathways, further contributing to disease pathogenesis. Despite their central significance, the implications of mitochondrial homeostasis disruption on other organelles and cellular processes remain insufficiently explored. Here, we have reviewed the dysfunction in mitochondrial physiology, under neuron degenerating conditions. The disease misfolded proteins impact quality control mechanisms of mitochondria, such as fission, fusion, mitophagy, and proteasomal clearance, to the detriment of neuron. The adversely affected mitochondrial functional roles, like oxidative phosphorylation, calcium homeostasis, and biomolecule synthesis as well as its axes and contacts with endoplasmic reticulum and lysosomes are also discussed. Mitochondria sense and respond to multiple cytotoxic stress to make cell adapt and survive, though chronic dysfunction leads to cell death. Mitochondria and their proteins can be candidates for biomarkers and therapeutic targets. Investigation of internetworking between mitochondria and neurodegeneration proteins can enhance our holistic understanding of such conditions and help in designing more targeted therapies.