CNS mitochondria in neurodegenerative disorders

FDA-approved 5-HT1F receptor agonist lasmiditan induces mitochondrial biogenesis and enhances locomotor and blood-spinal cord barrier recovery after spinal cord injury

Vascular and mitochondrial dysfunction are well-established consequences of spinal cord injury (SCI). Evidence suggests mitigating these dysfunctions may be an effective approach in treating SCI. The goal of this study was to elucidate if mitochondrial biogenesis (MB) induction with a new, selective and FDA-approved 5-hydroxytryptamine receptor 1F (5-HT_1F) receptor agonist, lasmiditan, can stimulate locomotor recovery and restoration of the blood-spinal cord barrier (BSCB) after SCI. Female C57BL/6 J mice were subjected to moderate SCI using a force-controlled impactor-induced contusion model followed by daily administration of lasmiditan (0.1 mg/kg, i.p.) beginning 1 h after injury. In the naïve spinal cord, electron microscopy revealed increased mitochondrial density and mitochondrial area, as well as enhanced mitochondrial DNA content. FCCP-uncoupled oxygen consumption rate (OCR), a functional marker of MB, was also increased in the naïve spinal cord following lasmiditan treatment. We observed disrupted mitochondrial DNA content, PGC-1α levels and FCCP-OCR in the injury site 3d after SCI. Lasmiditan treatment attenuated, and in some cases restored these deficits. Lasmiditan treatment also resulted in increased locomotor capability as early as 7d post-SCI, with treated mice reaching a Basso-Mouse Scale score of 3.3 by 21d, while vehicle-treated mice exhibited a score of 2.0. Integrity of the BSCB was assessed using Evans Blue dye extravasation. While SCI increased dye extravasation at 3d and 7d, dye accumulation in the spinal cord of lasmiditan-treated mice was attenuated 7d post-SCI, suggesting accelerated BSCB recovery. Finally, lasmiditan treatment resulted in decreased lesion volume and spared myelinated tissue 7d post-SCI. Collectively, these data reveal that 5-HT_1F receptor agonist-induced MB using the FDA-approved drug lasmiditan may be an effective therapeutic strategy for the treatment of SCI.

Mitochondrial biogenesis as a therapeutic target for traumatic and neurodegenerative CNS diseases

Central nervous system (CNS) diseases, both traumatic and neurodegenerative, are characterized by impaired mitochondrial bioenergetics and often disturbed mitochondrial dynamics. The dysregulation observed in these pathologies leads to defective respiratory chain function and reduced ATP production, thereby promoting neuronal death. As such, attenuation of mitochondrial dysfunction through induction of mitochondrial biogenesis (MB) is a promising, though still underexplored, therapeutic strategy. MB is a multifaceted process involving the integration of highly regulated transcriptional events, lipid membrane and protein synthesis/assembly and replication of mtDNA. Several nuclear transcription factors promote the expression of genes involved in oxidative phosphorylation, mitochondrial import and export systems, antioxidant defense and mitochondrial gene transcription. Of these, the nuclear-encoded peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) is the most commonly studied and is widely accepted as the 'master regulator' of MB. Several recent preclinical studies document that reestablishment of mitochondrial homeostasis through increased MB results in inhibited injury progression and increased functional recovery. This perspective will briefly review the role of mitochondrial dysfunction in the propagation of CNS diseases, while also describing current research strategies that mediate mitochondrial dysfunction and compounds that induce MB for the treatment of acute and chronic neuropathologies.

Combination therapy with astaxanthin and epidermal neural crest stem cells improves motor impairments and activates mitochondrial biogenesis in a rat model of spinal cord injury

Spinal cord injury (SCI), a multifactorial disease, can lead to irreversible motor and sensory disabilities. Cell therapy in combination with pharmacological agents can be a promising approach to attenuate SCI damages. Epidermal neural crest stem cells (EPI-NCSCs) extracted from bulge hair follicle in adults are attractive candidates due to the possibility of autologous transplantation. This study evaluated the effect of EPI-NCSCs combined with astaxanthin (Ast), a potent antioxidant, on damages induced by SCI. Male rats were treated with Ast (0.2 mM) and EPI-NCSCs (10⁶/10 μl PBS) alone and combined together after SCI contusion. Motor function was assessed by Basso, Beattie and Bresnahan (BBB) test on days 1, 3, 7, 14, 21, 28, 35 and 42 post-injury. Motor neurons number and myelin level were evaluated on days 14 and 42 using Nissl and Luxol Fast Blue staining. The gene expression of mitochondrial biogenesis involved factors (PGC1α, NRF1 and TFAM) was measured by qPCR. All treatments improved motor function, with the highest BBB score in Ast + Cell compared to Ast and Cell. Decreased motor neurons number and myelin level following SCI, were increased by Ast, Cell and Ast + Cell, but combination therapy significantly had a better effect. We observed reduction in PGC1α, NRF1, and TFAM expression in spinal tissue after SCI, and treatment with Cell and Ast + Cell significantly restored NRF1 and TFAM mRNA levels. These results suggested that Ast in combination with EPI-NCSCs has better effects on behavioral dysfunction, motor neuron loss and demyelination after SCI. These protective effects may be attributed to mitochondrial biogenesis activation.

5-hydroxytryptamine 1F Receptor Agonist Induces Mitochondrial Biogenesis and Promotes Recovery from Spinal Cord Injury

Spinal cord injury (SCI) is characterized by vascular disruption leading to ischemia, decreased oxygen delivery, and loss of mitochondrial homeostasis. This mitochondrial dysfunction results in loss of cellular functions, calcium overload, and oxidative stress. Pharmacological induction of mitochondrial biogenesis (MB) may be an effective approach to treat SCI. LY344864, a 5-hydroxytryptamine 1F (5-HT1F) receptor agonist, is a potent inducer of MB in multiple organ systems. To assess the efficacy of LY344864-induced MB on recovery post-SCI, female mice were subjected to moderate force-controlled impactor-induced contusion SCI followed by daily LY344864 administration for 21 days. Decreased mitochondrial DNA and protein content was present in the injury site 3 days post-SCI. LY344864 treatment beginning 1 h after injury attenuated these decreases, indicating MB. Additionally, injured mice treated with LY344864 displayed decreased Evan's Blue dye accumulation in the spinal cord compared with vehicle-treated mice 7 days after injury, suggesting restoration of vascular integrity. LY344864 also increased locomotor capability, with treated mice reaching a Basso-Mouse Scale score of 3.4 by 21 days, whereas vehicle-treated mice exhibited a score of 1.9. Importantly, knockout of the 5-HT1F receptor blocked LY344864-induced recovery. Remarkably, a similar degree of locomotor restoration was observed when treatment initiation was delayed until 8 h after injury. Furthermore, cross-sectional analysis of the spinal cord 21 days after injury revealed decreased lesion volume with delayed LY344864 treatment initiation, emphasizing the potential clinical applicability of this therapeutic approach. These data provide evidence that induction of MB via 5-HT1F receptor agonism may be a promising strategy for the treatment of SCI. SIGNIFICANCE STATEMENT: Treatment with LY344864 induces mitochondrial biogenesis in both the naive and injured mouse spinal cord. In addition, treatment with LY344864 beginning after impactor-induced contusion spinal cord injury improves mitochondrial homeostasis, blood-spinal cord barrier integrity, and locomotor function within 7 days. Importantly, similar locomotor results are observed whether treatment is initiated at 1 h after injury or 8 h after injury. These data indicate the potential for pharmacological induction of mitochondrial biogenesis through a 5-hydroxytryptamine 1F agonist as a novel therapeutic approach for spinal cord injury.

Molecular Regulation Mechanisms and Interactions Between Reactive Oxygen Species and Mitophagy

The generation of reactive oxygen species (ROS) in response to oxidative stress has important effects on cell development, normal function, and survival. It may cause oxidative damage to intracellular macromolecular substances and mitochondria through several signaling pathways. However, the damaged mitochondria promote further ROS generation, creating a vicious cycle that can cause cellular injury. In addition, excessive ROS produced by damaged mitochondria can trigger mitophagy, a process that can scavenge impaired mitochondria and reduce ROS level to maintain stable mitochondrial function in cells. Therefore, mitophagy heaps maintain cellular homeostasis under oxidative stress. In this article, we review recent advances in cellular damage caused by excessive ROS, the mechanism of mitophagy, and the close relationship between ROS and mitophagy. This review provides a new perspective on therapeutic strategies for related diseases.

Pharmacological Stimulation of Mitochondrial Biogenesis Using the Food and Drug Administration-Approved β2-Adrenoreceptor Agonist Formoterol for the Treatment of Spinal Cord Injury

A hallmark of the progressive cascade of damage referred to as secondary spinal cord injury (SCI) is vascular disruption resulting in decreased oxygen delivery and loss of mitochondria homeostasis. While therapeutics targeting restoration of single facets of mitochondrial function have proven largely ineffective clinically post-SCI, comprehensively addressing mitochondrial function via pharmacological stimulation of mitochondrial biogenesis (MB) is an underexplored strategy. This study examined the effects of formoterol, a mitochondrial biogenic Food and Drug Administration-approved selective and potent β₂-adrenoreceptor (ADRB2) agonist, on recovery from SCI in mice. Female C57BL/6 mice underwent moderate SCI using a force-controlled impactor-induced contusion model, followed by daily formoterol intraperitoneal administration (0.1 mg/kg) beginning 1 h post-SCI. The SCI resulted in decreased mitochondrial protein expression, including PGC-1α, in the injury and peri-injury sites as early as 3 days post-injury. Formoterol treatment attenuated this decrease in PGC-1α, indicating enhanced MB, and restored downstream mitochondrial protein expression to that of controls by 15 days. Formoterol-treated mice also exhibited less histological damage than vehicle-treated mice 3 days after injury-namely, decreased lesion volume and increased white and gray matter sparing in regions rostral and caudal to the injury epicenter. Importantly, locomotor capability of formoterol-treated mice was greater than vehicle-treated mice by 7 days, reaching a Basso Mouse Scale score two points greater than that of vehicle-treated SCI mice by 15 days. Interestingly, similar locomotor restoration was observed when initiation of treatment was delayed until 8 h post-injury. These data provide evidence of ADRB2-mediated MB as a therapeutic approach for the management of SCI.

5-HT1F receptor-mediated mitochondrial biogenesis for the treatment of Parkinson's disease

BACKGROUND AND PURPOSE

Parkinson's disease is characterized by progressive decline in motor function due to degeneration of nigrostriatal dopaminergic neurons, as well as other deficits including cognitive impairment and behavioural abnormalities. Mitochondrial dysfunction, leading to loss of ATP-dependent cellular functions, calcium overload, excitotoxicity and oxidative stress, is implicated in the pathophysiology of Parkinson's disease. Using the 5-HT1F receptor agonist LY344864, a known inducer of mitochondrial biogenesis (MB), we investigated the therapeutic efficacy of stimulating MB on dopaminergic neuron loss in a mouse model of Parkinson's disease.

EXPERIMENTAL APPROACH

Male C57BL/6 mice underwent bilateral intrastriatal 6-hydroxydopamine or saline injections and daily treatment with 2 mg·kg-1 LY344864 or vehicle for 14 days beginning 7 days post-lesion. Tyrosine hydroxylase immunoreactivity (TH-ir) and MB were assessed in the brains of all groups following treatment, and locomotor activity was evaluated prior to lesioning, 7 days post-lesion and after treatment.

KEY RESULTS

Increased mitochondrial DNA content and nuclear- and mitochondrial-encoded mRNA and protein expression was observed in specific brain regions of LY344864-treated naïve and lesioned mice, indicating augmented MB. LY344864 attenuated TH-ir loss in the striatum and substantia nigra compared to vehicle-treated lesioned animals. LY344864 treatment also increased locomotor activity in 6-hydroxydopamine lesioned mice, while vehicle treatment had no effect.

CONCLUSIONS AND IMPLICATIONS

These data revealed that LY344864-induced MB attenuates dopaminergic neuron loss and improves behavioural endpoints in this model. We suggest that stimulating MB may be beneficial for the treatment of Parkinson's disease and that the 5-HT1F receptor may be an effective therapeutic target.

Mitochondrial-Based Therapeutics for the Treatment of Spinal Cord Injury: Mitochondrial Biogenesis as a Potential Pharmacological Target

Spinal cord injury (SCI) is characterized by an initial trauma followed by a progressive cascade of damage referred to as secondary injury. A hallmark of secondary injury is vascular disruption leading to vasoconstriction and decreased oxygen delivery, which directly reduces the ability of mitochondria to maintain homeostasis and leads to loss of ATP-dependent cellular functions, calcium overload, excitotoxicity, and oxidative stress, further exacerbating injury. Restoration of mitochondria dysfunction during the acute phases of secondary injury after SCI represents a potentially effective therapeutic strategy. This review discusses the past and present pharmacological options for the treatment of SCI as well as current research on mitochondria-targeted approaches. Increased antioxidant activity, inhibition of the mitochondrial permeability transition, alternate energy sources, and manipulation of mitochondrial morphology are among the strategies under investigation. Unfortunately, many of these tactics address single aspects of mitochondrial dysfunction, ultimately proving largely ineffective. Therefore, this review also examines the unexplored therapeutic efficacy of pharmacological enhancement of mitochondrial biogenesis, which has the potential to more comprehensively improve mitochondrial function after SCI.

Hypoxia activation of mitophagy and its role in disease pathogenesis

SIGNIFICANCE

Mitochondria utilize most of the oxygen to produce adenosine triphosphate via electron transfer coupled with oxidative phosphorylation. Hypoxia undoubtedly induces reduced energy production via decreased mitochondrial metabolic activity or altered hypoxia-inducible factor-1- and peroxisome proliferator-activated receptor gamma coactivator 1-dependent mitochondrial biogenesis. Hypoxia may also activate mitophagy to selectively remove damaged or unwanted mitochondria for both mitochondrial quantity and quality control. Increasing evidence has shown that the accumulation of damaged mitochondria is a characteristic of aging and aging-related diseases, such as metabolic disorder, cancer, and neurodegenerative disease.

RECENT ADVANCES

Both receptor-dependent and PTEN-induced putative kinase 1-PARKIN-dependent mitophagy have been described. Mitophagy receptors include Atg32 in yeast, as well as NIX/BNIP3L, B-cell lymphoma 2/adenovirus E1B 19-kDa-interacting protein 3 and FUN14 domain containing 1 in mammals. In response to hypoxia or mitochondrial oxidative stress, receptor-mediated mitophagy was found to be activated via both transcriptional and post-translational modification.

CRITICAL ISSUES

To date, the molecular mechanisms by which hypoxia triggers mitophagy and by which mitophagy contributes to the pathogenesis of aging-related diseases remain to be explored.

FUTURE DIRECTIONS

An improved understanding of the regulation of mitochondrial quality may provide a strategy for treating aging-related diseases by targeting mitochondria and mitophagy pathways.