Enhancing mitophagy as a therapeutic approach for neurodegenerative diseases

Mitophagy in Brain Injuries: Mechanisms, Roles, and Therapeutic Potential

Mitophagy is an intracellular degradation pathway crucial for clearing damaged or dysfunctional mitochondria, thereby maintaining cellular homeostasis and responding to various brain injuries. By promptly removing damaged mitochondria, mitophagy protects cells from further harm and support cellular repair and recovery after injury. In different types of brain injury, mitophagy plays complex and critical roles, from regulating the balance between cell death and survival to influencing neurological recovery. This review aims to deeply explore the role and mechanism of mitophagy in the context of brain injuries and uncover how mitophagy regulates the brain response to injury and its potential therapeutic significance. It emphasizes mitophagy's potential in treating brain injuries, including reducing cell damage, promoting cell recovery, and improving neurological function, thus opening new perspectives and directions for future research and clinical applications.

Impact of diet and exercise on mitochondrial quality and mitophagy in Alzheimer's disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder that affects millions of people worldwide. It is characterized by the accumulation of beta-amyloid and phosphorylated tau, synaptic damage, and mitochondrial abnormalities in the brain, leading to the progressive loss of cognitive function and memory. In AD, emerging research suggests that lifestyle factors such as a healthy diet and regular exercise may play a significant role in delaying the onset and progression of the disease. Mitochondria are often referred to as the powerhouse of the cell, as they are responsible for producing the energy to cells, including neurons to maintain cognitive function. Our article elaborates on how mitochondrial quality and function decline with age and AD, leading to an increase in oxidative stress and a decrease in ATP production. Decline in mitochondrial quality can impair cellular functions contributing to the development and progression of disease with the loss of neuronal functions in AD. This article also covered mitophagy, the process by which damaged or dysfunctional mitochondria are selectively removed from the cell to maintain cellular homeostasis. Impaired mitophagy has been implicated in the progression and pathogenesis of AD. We also discussed the impact of impaired mitophagy implicated in AD, as the accumulation of damaged mitochondria can lead to increased oxidative stress. We expounded how dietary interventions and exercise can help to improve mitochondrial quality, and mitochondrial function and enhance mitophagy in AD. A diet rich in antioxidants, polyphenols, and mitochondria-targeted small molecules has been shown to enhance mitochondrial function and protect against oxidative stress, particularly in neurons with aged and mild cognitively impaired subjects and AD patients. Promoting a healthy lifestyle, mainly balanced diet and regular exercise that support mitochondrial health, in an individual can potentially delay the onset and progression of AD. In conclusion, a healthy diet and regular exercise play a crucial role in maintaining mitochondrial quality and mitochondrial function, in turn, enhancing mitophagy and synaptic activities that delay AD in the elderly populations.

Pharmacological approaches to enhance mitochondrial biogenesis: focus on PGC-1Α, AMPK, and SIRT1 in cellular health

BACKGROUND

Mitochondrial biogenesis is essential for cellular energy balance and metabolic stability. Its dysregulation is linked to various metabolic and neurodegenerative diseases, making it a significant therapeutic target. Pharmacological approaches aimed at enhancing mitochondrial function have gained attention for their potential to restore cellular metabolism.

OBJECTIVES

This review examines recent advancements in pharmacological strategies targeting mitochondrial biogenesis, focusing on the roles of PGC-1α, AMPK, and SIRT1, alongside novel therapeutic agents and drug delivery systems.

METHODS

A systematic review of studies published between 2018 and 2023 was conducted using databases such as PubMed, Web of Science, and Elsevier. Keywords related to mitochondrial biogenesis and pharmacological modulation were used to identify relevant literature.

RESULTS

Various pharmacological agents, including resveratrol, curcumin, and metformin, activate mitochondrial biogenesis through different pathways. SIRT1 activators and AMPK agonists have shown promise in improving mitochondrial function. Advances in mitochondria-targeted drug delivery systems enhance therapeutic efficacy, yet challenges remain in clinical translation due to the complexity of mitochondrial regulation.

CONCLUSION

Pharmacological modulation of mitochondrial biogenesis holds therapeutic potential for metabolic and neurodegenerative diseases. While preclinical studies are promising, further research is needed to optimize drug efficacy, delivery methods, and personalized treatment strategies.

Causal relationship between mitochondrial function and delirium: a bidirectional two-sample Mendelian randomisation analysis

BACKGROUND

Previous studies have suggested a potential link between delirium and mitochondrial function. Consequently, this Mendelian randomisation (MR) study aimed to further investigate their causal relationship.

METHODS

In this bidirectional MR study, the relationship between 73 proteins related to mitochondrial function and delirium, including delirium not induced by alcohol or other psychoactive substances (DEL) and delirium associated with alcohol withdrawal (AL-DEL). The random-effects inverse variance weighting (RE-IVW) method was used as the primary analytical method. Furthermore, multivariable MR (MVMR) analysis was performed to assess the impact of positive exposures and known risk factors for delirium. To ensure the reliability of our findings, heterogeneity and pleiotropy tests were conducted.

RESULTS

The results of the RE-IVW method of MR analysis revealed that two proteins were positively associated with DEL (P < 0.05, odds ratio (OR) >1), whereas one protein was negatively associated with AL-DEL (P < 0.05, OR <1). In MVMR, ATP synthase subunit beta (ATP5F1B) was positively associated with DEL (P < 0.05, OR >1). Moreover, reverse MR analysis demonstrated that DEL was positively associated with three proteins (P < 0.05, OR >1) and negatively associated with two proteins (P < 0.05, OR <1). Finally, none of these associations displayed heterogeneity and horizontal pleiotropy (P > 0.05) or reverse causality.

CONCLUSIONS

This bidirectional, multivariable two-sample MR analysis identified a causal relationship between eight proteins related to mitochondrial function and delirium. These findings offer novel insights that could potentially influence early diagnosis, expand our understanding of the underlying mechanisms, and inform treatment strategies for delirium. Nevertheless, given the possibility of bias, these results should be interpreted with caution.

Opposing roles for AMPK in regulating distinct mitophagy pathways

Mitophagy degrades damaged mitochondria, but we show here that it can also target functional mitochondria. This latter scenario occurs during programmed mitophagy and involves the mitophagy receptors NIX and BNIP3. Although AMP-activated protein kinase (AMPK), the energy-sensing protein kinase, can influence damaged-induced mitophagy, its role in programmed mitophagy is unclear. We found that AMPK directly inhibits NIX-dependent mitophagy by triggering 14-3-3-mediated sequestration of ULK1, via ULK1 phosphorylation at two sites: Ser556 and an additional identified site, Ser694. By contrast, AMPK activation increases Parkin phosphorylation and enhances the rate of depolarization-induced mitophagy, independently of ULK1. We show that this happens both in cultured cells and tissues in vivo, using the mito-QC mouse model. Our work unveils a mechanism whereby AMPK activation downregulates mitophagy of functional mitochondria but enhances that of dysfunctional/damaged ones.

Mitophagy Unveiled: Exploring the Nexus of Mitochondrial Health and Neuroendocrinopathy

Mitochondria play a pivotal role in cellular metabolism, energy production, and apoptotic signaling, making mitophagy, the selective degradation of damaged mitochondria, crucial for mitochondrial health. Dysregulation of mitophagy has been implicated in various neuroendocrinopathies, yet the mechanisms linking these processes remain poorly understood. This review aims to explore the intersection between mitophagy and neuroendocrinopathy, addressing the critical gaps in knowledge regarding how mitochondrial dysfunction may contribute to the pathophysiology of neuroendocrine disorders. We conducted a comprehensive literature review of studies published on mitophagy and neuroendocrinopathies, focusing on data that elucidate the pathways involved and the clinical implications of mitochondrial health in neuroendocrine contexts. Our findings indicate that altered mitophagy may lead to the accumulation of dysfunctional mitochondria, contributing to neuroendocrine dysregulation. We present evidence linking impaired mitochondrial clearance to disease models of conditions such as metabolic syndrome, depression, and stress-related disorders, highlighting the potential for therapeutic interventions targeting mitophagy. While significant advances have been made in understanding mitochondrial biology, the direct interplay between mitophagy and neuroendocrinopathies remains underexplored. This review underscores the necessity for further research to elucidate these connections, which may offer novel insights into disease mechanisms and therapeutic strategies for treating maladaptive neuroendocrine responses.

Mitochondrial Dysfunction in Parkinson's Disease: A Contribution to Cognitive Impairment?

Among the non-motor symptoms associated with Parkinson's disease (PD), cognitive impairment is one of the most common and disabling. It can occur either early or late during the disease, and it is heterogeneous in terms of its clinical manifestations, such as Subjective Cognitive Dysfunction (SCD), Mild Cognitive Impairment (MCI), and Parkinson's Disease Dementia (PDD). The aim of the present review is to delve deeper into the molecular mechanisms underlying cognitive decline in PD. This is extremely important to delineate the guidelines for the differential diagnosis and prognosis of the dysfunction, to identify the molecular and neuronal mechanisms involved, and to plan therapeutic strategies that can halt cognitive impairment progression. Specifically, the present review will discuss the pathogenetic mechanisms involved in the progression of cognitive impairment in PD, with attention to mitochondria and their contribution to synaptic dysfunction and neuronal deterioration in the brain regions responsible for non-motor manifestations of the disease.

Mitochondrial Dysfunction: A Roadmap for Understanding and Tackling Cardiovascular Aging

Cardiovascular aging is a progressive remodeling process constituting a variety of cellular and molecular alterations that are closely linked to mitochondrial dysfunction. Therefore, gaining a deeper understanding of the changes in mitochondrial function during cardiovascular aging is crucial for preventing cardiovascular diseases. Cardiac aging is accompanied by fibrosis, cardiomyocyte hypertrophy, metabolic changes, and infiltration of immune cells, collectively contributing to the overall remodeling of the heart. Similarly, during vascular aging, there is a profound remodeling of blood vessel structure. These remodeling present damage to endothelial cells, increased vascular stiffness, impaired formation of new blood vessels (angiogenesis), the development of arteriosclerosis, and chronic vascular inflammation. This review underscores the role of mitochondrial dysfunction in cardiac aging, exploring its impact on fibrosis and myocardial alterations, metabolic remodeling, immune response remodeling, as well as in vascular aging in the heart. Additionally, we emphasize the significance of mitochondria-targeted therapies in preventing cardiovascular diseases in the elderly.

Mitophagy in neurodegenerative disease pathogenesis

Mitochondria are critical cellular energy resources and are central to the life of the neuron. Mitophagy selectively clears damaged or dysfunctional mitochondria through autophagic machinery to maintain mitochondrial quality control and homeostasis. Mature neurons are postmitotic and consume substantial energy, thus require highly efficient mitophagy pathways to turn over damaged or dysfunctional mitochondria. Recent evidence indicates that mitophagy is pivotal to the pathogenesis of neurological diseases. However, more work is needed to study mitophagy pathway components as potential therapeutic targets. In this review, we briefly discuss the characteristics of nonselective autophagy and selective autophagy, including ERphagy, aggrephagy, and mitophagy. We then introduce the mechanisms of Parkin-dependent and Parkin-independent mitophagy pathways under physiological conditions. Next, we summarize the diverse repertoire of mitochondrial membrane receptors and phospholipids that mediate mitophagy. Importantly, we review the critical role of mitophagy in the pathogenesis of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Last, we discuss recent studies considering mitophagy as a potential therapeutic target for treating neurodegenerative diseases. Together, our review may provide novel views to better understand the roles of mitophagy in neurodegenerative disease pathogenesis.

Mitochondrial DNA Leakage and cGas/STING Pathway in Microglia: Crosstalk Between Neuroinflammation and Neurodegeneration

Neurodegenerative diseases, characterized by abnormal deposition of misfolded proteins, often present with progressive loss of neurons. Chronic neuroinflammation is a striking hallmark of neurodegeneration. Microglia, as the primary immune cells in the brain, is the main type of cells that participate in the formation of inflammatory microenvironment. Cytoplasmic free mitochondrial DNA (mtDNA), a common component of damage-associated molecular patterns (DAMPs), can activate the cGas/stimulator of interferon genes (STING) signalling, which subsequently produces type I interferon and proinflammatory cytokines. There are various sources of free mtDNA in microglial cytoplasm, but mitochondrial oxidative stress accumulation plays the vital role. The upregulation of cGas/STING pathway in microglia contributes to the abnormal and persistent microglial activation, accompanied by excessive secretion of neurotoxic inflammatory mediators such as interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), which exacerbates the damage of neurons and promotes the development of neurodegeneration. Currently, novel therapeutic approaches need to be found to delay the progression of neurodegenerative disorders, and regulation of the cGas/STING signaling in microglia may be a potential target.

Understanding the mechanisms of disease modifying effects of aerobic exercise in people with Alzheimer's disease

Alzheimer's disease (AD) is a very disabling disease. Pathologically, it is characterized by the presence of amyloid plaques and neurofibrillary tangles in the brain that results in neurodegeneration. Its clinical manifestations include progressive memory impairment, language decline and difficulty in carrying out activities of daily living (ADL). The disease is managed using interventions such as pharmacological interventions and aerobic exercise. Use of aerobic exercise has shown some promises in reducing the risk of developing AD, and improving cognitive function and the ability to carry out both basic and instrumental ADL. Although, the mechanisms through which aerobic exercise improves AD are poorly understood, improvement in vascular function, brain glucose metabolism and cardiorespiratory fitness, increase in antioxidant capacity and haemoglobin level, amelioration of immune-related and inflammatory responses, modulation of concentration of circulating Neurotrophins and peptides and decrease in concentration of tau protein and cortisol level among others seem to be the possible mechanisms. Therefore, understanding these mechanisms is important to help characterize the dose and the nature of the aerobic exercise to be given. In addition, they may also help in finding ways to optimize other interventions such as the pharmacological interventions. However, more quality studies are needed to verify the mechanisms.

Targeting Mitochondria as a Therapeutic Approach for Parkinson's Disease

Neurodegeneration is among the most critical challenges that involve modern societies and annually influences millions of patients worldwide. While the pathophysiology of Parkinson's disease (PD) is complicated, the role of mitochondrial is demonstrated. The in vitro and in vivo models and genome-wide association studies in human cases proved that specific genes, including PINK1, Parkin, DJ-1, SNCA, and LRRK2, linked mitochondrial dysfunction with PD. Also, mitochondrial DNA (mtDNA) plays an essential role in the pathophysiology of PD. Targeting mitochondria as a therapeutic approach to inhibit or slow down PD formation and progression seems to be an exciting issue. The current review summarized known mutations associated with both mitochondrial dysfunction and PD. The significance of mtDNA in Parkinson's disease pathogenesis and potential PD therapeutic approaches targeting mitochondrial dysfunction was then discussed.

Mitochondrial defects in pancreatic beta-cell dysfunction and neurodegenerative diseases: Pathogenesis and therapeutic applications

Mitochondria malfunction is linked to the development of β-cell failure and a variety of neurodegenerative disorders. Pancreatic β-cells are normally configured to detect glucose and other food secretagogues in order to adjust insulin exocytosis and maintain glucose homeostasis. As a result of the increased glucose level, mitochondria metabolites and nucleotides are produced, which operate in concert with cytosolic Ca2+ to stimulate insulin secretion. Furthermore, mitochondria are the primary generators of adenosine triphosphate (ATP), reactive oxygen species (ROS), and apoptosis regulation. Mitochondria are concentrated in synapses, and any substantial changes in synaptic mitochondria location, shape, quantity, or function might cause oxidative stress, resulting in faulty synaptic transmission, a symptom of various degenerative disorders at an early stage. However, a greater understanding of the role of mitochondria in the etiology of β-cell dysfunction and neurodegenerative disorder should pave the way for a more effective approach to addressing these health issues. This review looks at the widespread occurrence of mitochondria depletion in humans, and its significance to mitochondria biogenesis in signaling and mitophagy. Proper understanding of the processes might be extremely beneficial in ameliorating the rising worries about mitochondria biogenesis and triggering mitophagy to remove depleted mitochondria, therefore reducing disease pathogenesis.

Critical appraisal on mitochondrial dysfunction in Alzheimer's disease

It is widely recognized that Alzheimer's disease (AD) is a common type of progressive neurodegenerative disorder that results in cognitive impairment over time. Approximately 152 million cases of AD are predicted to be reported by 2050. Amyloid plaques and tau proteins are two major hallmarks of AD which can be seen under electron microscope. Mitochondria plays a vital role in the pathogenesis of AD and mitochondria disruption leads to mitochondrial DNA (mtDNA) dysfunction, alteration of mitochondria dependent Ca2+ homeostasis, copper dysfunction, immune cell dysfunction, etc. In this review, we try to cover all the mechanisms related with mitochondrial dysfunction and mitochondrial pathogenesis that may help us to better understand AD as well as open a new era for therapeutic target of AD and treat this progressive disease.

MCU knockdown in hippocampal neurons improves memory performance of an Alzheimer's disease mouse model

Alzheimer's disease (AD) is a progressive and degenerative disorder accompanied by cognitive decline, which could be promoted by mitochondrial dysfunction induced by mitochondrial Ca ²⁺ (mCa ²⁺) homeostasis Mitochondrial calcium uniporter (MCU), a key channel of mCa ²⁺ uptake, may be a target for AD treatment. In the present study, we reveal for the first time that MCU knockdown in hippocampal neurons improves the memory performance of APP/PS1/tau mice through radial arm maze task. Western blot analysis, transmission electron microscopy (TEM), Golgi staining, immunohistochemistry (IHC) and ELISA results demonstrate that MCU knockdown in hippocampal neurons upregulates the levels of postsynaptic density protein 95 (PSD95) and synaptophysin (SYP), and increases the numbers of synapses and dendritic spines. Meanwhile, MCU knockdown in hippocampal neurons decreases the neuroinflammatory response induced by astrogliosis and high levels of IL-1β and TNF-α, and improves the PINK1-Parkin mitophagy signaling pathway and increases the level of Beclin-1 but decreases the level of P62. In addition, MCU knockdown in hippocampal neurons recovers the average volume and number of mitochondria. These data confirm that MCU knockdown in hippocampal neurons improves the memory performance of APP/PS1/tau mice through ameliorating the synapse structure and function, relieving the inflammation response and recovering mitophagy, indicating that MCU inhibition has the potential to be developed as a novel therapy for AD.

Implications of intracellular protein degradation pathways in Parkinson's disease and therapeutics

Parkinson's disease (PD) pathology is the most common motor neurodegenerative disease that occurs due to the progressive degeneration of dopaminergic neurons of the nigrostriatal pathway of the brain. The histopathological hallmark of the disease is fibrillary aggregate called Lewy bodies which majorly contain α-synuclein, suggesting the critical implication of diminished protein degradation mechanisms in disease pathogenesis. This α-synuclein-containing Lewy bodies are evident in both experimental models as well as in postmortem PD brain and are speculated to be pathogenic but still, the lineal association between these aggregates and the complexity of disease pathology is not yet well established and needs further attention. However, it has been reported that α-synuclein aggregates have consorted with the declined proteasome and lysosome activities. Therefore, in this review, we reappraise intracellular protein degradation mechanisms during PD pathology. This article focused on the findings of the last two decades suggesting the implications of protein degradation mechanisms in disease pathogenesis and based on shreds of evidence, some of the approaches are also suggested which may be adopted to find out the novel therapeutic targets for the management of PD patients.

Mitochondrial Dysfunction in Parkinson’s Disease: From Mechanistic Insights to Therapy

Parkinson’s disease (PD) is one of the most common neurodegenerative movement disorders worldwide. There are currently no cures or preventative treatments for PD. Emerging evidence indicates that mitochondrial dysfunction is closely associated with pathogenesis of sporadic and familial PD. Because dopaminergic neurons have high energy demand, cells affected by PD exhibit mitochondrial dysfunction that promotes the disease-defining the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The mitochondrion has a particularly important role as the cellular “powerhouse” of dopaminergic neurons. Therefore, mitochondria have become a promising therapeutic target for PD treatments. This review aims to describe mitochondrial dysfunction in the pathology of PD, outline the genes associated with familial PD and the factors related to sporadic PD, summarize current knowledge on mitochondrial quality control in PD, and give an overview of therapeutic strategies for targeting mitochondria in neuroprotective interventions in PD.

Are mitophagy enhancers therapeutic targets for Alzheimer's disease?

Healthy mitochondria are essential for functional bioenergetics, calcium signaling, and balanced redox homeostasis. Dysfunctional mitochondria are a central aspect of aging and neurodegenerative diseases such as Alzheimer's disease (AD). The formation and accumulation of amyloid beta (Aβ) and hyperphosphorylated tau (P-tau) play large roles in the cellular changes seen in AD, including mitochondrial dysfunction, synaptic damage, neuronal loss, and defective mitophagy. Mitophagy is the cellular process whereby damaged mitochondria are selectively removed, and it plays an important role in mitochondrial quality control. Dysfunctional mitochondria are associated with increased reactive oxygen species and increased levels of Aβ, P-tau and Drp1, which together trigger mitophagy and autophagy. Impaired mitophagy causes the progressive accumulation of defective organelles and damaged mitochondria, and it has been hypothesized that the restoration of mitophagy may offer therapeutic benefits to AD patients. This review highlights the challenges of pharmacologically inducing mitophagy through two different signaling cascades: 1) The PINK1/parkin-dependent pathway and 2) the PINK1/parkin-independent pathway, with an emphasis on abnormal mitochondrial interactions with Aβ and P-Tau, which alter mitophagy in an age-dependent manner. This article also summarizes recent studies on the effects of mitophagy enhancers, including urolithin A, NAD+, actinonin, and tomatidine, on mutant APP/Aβ and mutant Tau. Findings from our lab have revealed that mitophagy enhancers can suppress APP/Aβ-induced and mutant Tau-induced mitochondrial and synaptic dysfunctions in mouse and cell line models of AD. Finally, we discuss the mechanisms underlying the beneficial health effects of mitophagy enhancers like urolithin A, NAD+, resveratrol and spermidine in AD.

Protective effects of mitophagy enhancers against amyloid beta-induced mitochondrial and synaptic toxicities in Alzheimer disease

The purpose of our study is to determine the protective effects of mitophagy enhancers against mutant APP and amyloid beta (Aβ)-induced mitochondrial and synaptic toxicities in Alzheimer's disease (ad). Over two decades of research from our lab and others revealed that mitochondrial abnormalities are largely involved in the pathogenesis of both early-onset and late-onset ad. Emerging studies from our lab and others revealed that impaired clearance of dead or dying mitochondria is an early event in the disease process. Based on these changes, it has been proposed that mitophagy enhancers are potential therapeutic candidates to treat patients with ad. In the current study, we optimized doses of mitophagy enhancers urolithin A, actinonin, tomatidine, nicotinamide riboside in immortalized mouse primary hippocampal (HT22) neurons. We transfected HT22 cells with mutant APP cDNA and treated with mitophagy enhancers and assessed mRNA and protein levels of mitochondrial dynamics, biogenesis, mitophagy and synaptic genes, cell survival; assessed mitochondrial respiration in mAPP-HT22 cells treated and untreated with mitophagy enhancers. We also assessed mitochondrial morphology in mAPP-HT22 cells treated and untreated with mitophagy enhancers. Mutant APP-HT22 cells showed increased fission, decreased fusion, synaptic & mitophagy genes, reduced cell survival and defective mitochondrial respiration, and excessively fragmented and reduced length of mitochondria. However, these events were reversed in mitophagy-enhancers-treated mutant mAPP-HT22 cells. Cell survival was significantly increased, mRNA and protein levels of mitochondrial fusion, synaptic and mitophagy genes were increased, mitochondrial number is reduced, and mitochondrial length is increased, and mitochondrial fragmentation is reduced in mitophagy-enhancers-treated mutant APP-HT22 cells. Further, urolithin A showed strongest protective effects against mutant APP and Aβ-induced mitochondrial and synaptic toxicities in ad. Based on these findings, we cautiously propose that mitophagy enhancers are promising therapeutic drugs to treat mitophagy in patients with ad.

Phenotypic Assay Leads to Discovery of Mitophagy Inducers with Therapeutic Potential for Parkinson's Disease

Mitophagy, the selective degradation of mitochondria by autophagy, involved in important physiological processes and defects in pathways has been reported in pathological conditions, such as neurodegeneration. Thus, mitophagy is an interesting target for drug discovery programs. In this investigation, we used robust phenotypic assay to screen a set of 50 small heterocyclic compounds to identify inducers of mitophagy. We identified two compounds, VP07 and JAR1.39, that induce Parkin-dependent mitophagy. Based on structure-activity relationship studies, we proposed the ability of the compounds to act as light chain 3 (LC3) interactors, similar to cardiolipin or ceramide, triggering mitophagy via Pink1/Parkin. Finally, we show promising therapeutic applicability in a cellular model of Parkinson's disease.

Mitochondrial Quality Control Strategies: Potential Therapeutic Targets for Neurodegenerative Diseases?

Many lines of evidence have indicated the therapeutic potential of rescuing mitochondrial integrity by targeting specific mitochondrial quality control pathways in neurodegenerative diseases, such as Parkinson's disease, Huntington's disease, and Alzheimer's disease. In addition to ATP synthesis, mitochondria are critical regulators of ROS production, lipid metabolism, calcium buffering, and cell death. The mitochondrial unfolded protein response, mitochondrial dynamics, and mitophagy are the three main quality control mechanisms responsible for maintaining mitochondrial proteostasis and bioenergetics. The proper functioning of these complex processes is necessary to surveil and restore mitochondrial homeostasis and the healthy pool of mitochondria in cells. Mitochondrial dysfunction occurs early and causally in disease pathogenesis. A significant accumulation of mitochondrial damage resulting from compromised quality control pathways leads to the development of neuropathology. Moreover, genetic or pharmaceutical manipulation targeting the mitochondrial quality control mechanisms can sufficiently rescue mitochondrial integrity and ameliorate disease progression. Thus, therapies that can improve mitochondrial quality control have great promise for the treatment of neurodegenerative diseases. In this review, we summarize recent progress in the field that underscores the essential role of impaired mitochondrial quality control pathways in the pathogenesis of neurodegenerative diseases. We also discuss the translational approaches targeting mitochondrial function, with a focus on the restoration of mitochondrial integrity, including mitochondrial dynamics, mitophagy, and mitochondrial proteostasis.

Genotype-driven therapeutic developments in Parkinson's disease

BACKGROUND

Remarkable advances have been reached in the understanding of the genetic basis of Parkinson's disease (PD), with the identification of monogenic causes (mPD) and a plethora of gene loci leading to an increased risk for idiopathic PD. The expanding knowledge and subsequent identification of genetic contributions fosters the understanding of molecular mechanisms leading to disease development and progression. Distinct pathways involved in mitochondrial dysfunction, oxidative stress, and lysosomal function have been identified and open a unique window of opportunity for individualized treatment approaches. These genetic findings have led to an imminent progress towards pathophysiology-targeted clinical trials and potentially disease-modifying treatments in the future.

MAIN BODY OF THE MANUSCRIPT

In this review article we will summarize known genetic contributors to the pathophysiology of Parkinson's disease, the molecular mechanisms leading to disease development, and discuss challenges and opportunities in clinical trial designs.

CONCLUSIONS

The future success of clinical trials in PD is mainly dependent on reliable biomarker development and extensive genetic testing to identify genetic cases. Whether genotype-dependent stratification of study participants will extend the potential application of new drugs will be one major challenge in conceptualizing clinical trials. However, the latest developments in genotype-driven treatments will pave the road to individualized pathophysiology-based therapies in the future.

Targeting Mitochondrial Impairment in Parkinson's Disease: Challenges and Opportunities

The underlying pathophysiology of Parkinson's disease is complex, but mitochondrial dysfunction has an established and prominent role. This is supported by an already large and rapidly growing body of evidence showing that the role of mitochondrial (dys)function is central and multifaceted. However, there are clear gaps in knowledge, including the dilemma of explaining why inherited mitochondriopathies do not usually present with parkinsonian symptoms. Many aspects of mitochondrial function are potential therapeutic targets, including reactive oxygen species production, mitophagy, mitochondrial biogenesis, mitochondrial dynamics and trafficking, mitochondrial metal ion homeostasis, sirtuins, and endoplasmic reticulum links with mitochondria. Potential therapeutic strategies may also incorporate exercise, microRNAs, mitochondrial transplantation, stem cell therapies, and photobiomodulation. Despite multiple studies adopting numerous treatment strategies, clinical trials to date have generally failed to show benefit. To overcome this hurdle, more accurate biomarkers of mitochondrial dysfunction are required to detect subtle beneficial effects. Furthermore, selecting study participants early in the disease course, studying them for suitable durations, and stratifying them according to genetic and neuroimaging findings may increase the likelihood of successful clinical trials. Moreover, treatments involving combined approaches will likely better address the complexity of mitochondrial dysfunction in Parkinson's disease. Therefore, selecting the right patients, at the right time, and using targeted combination treatments, may offer the best chance for development of an effective novel therapy targeting mitochondrial dysfunction in Parkinson's disease.

Lanostane Triterpenoid Metabolites from a Penares sp. Marine Sponge Protect Neuro-2a Cells against Paraquat Neurotoxicity

The results of an investigation of the protective effects of five lanostane triterpenoids: 3β-acetoxy-7β,8β-epoxy-5α-lanost-24-en-30,9α-olide (1), 3β-hydroxy-7β,8β-epoxy-5α-lanost-24-en- 30,9α-olide (2), 29-nor-penasterone (3), penasterone (4), and acetylpenasterol (5), from a marine sponge, Penares sp., against paraquat-induced neuroblastoma Neuro-2a cell damage, are described. The influence of all compounds on viability of the Neuro-2a cells treated with paraquat (PQ) was studied with MTT and fluorescein diacetate assays as well as propidium iodide straining. 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of the compounds as well as their influence on reactive oxygen species (ROS) level and mitochondrial membrane potential in PQ-treated neuronal cells were analyzed. Finally, the effect of the compounds on intracellular level of heat shock protein 70 kDa (Hsp70) and neurite outgrowth in PQ-treated Neuro-2a cells were studied. Studied triterpenoids demonstrated protective effects against PQ-induced neurotoxicity associated with the ability to reduce ROS intracellular level and diminish mitochondrial dysfunction. Acetylpenasterol (5), as a more promising neuroprotective compound, significantly increased the viability of Neuro-2a cells incubated with PQ as well as decreased intracellular ROS level in these cells. Moreover, acetylpenasterol induced Hsp70 expression in PQ-treated cells. It was also shown to inhibit PQ-induced neurite loss and recovered the number of neurite-bearing cells. The relationship between neuroprotective activity of the investigated compounds 1–5 and their chemical structure was also discussed.

Merging the Multi-Target Effects of Phytochemicals in Neurodegeneration: From Oxidative Stress to Protein Aggregation and Inflammation

Wide experimental evidence has been provided in the last decade concerning the neuroprotective effects of phytochemicals in a variety of neurodegenerative disorders. Generally, the neuroprotective effects of bioactive compounds belonging to different phytochemical classes are attributed to antioxidant, anti-aggregation, and anti-inflammatory activity along with the restoration of mitochondrial homeostasis and targeting alterations of cell-clearing systems. Far from being independent, these multi-target effects represent interconnected events that are commonly implicated in the pathogenesis of most neurodegenerative diseases, independently of etiology, nosography, and the specific misfolded proteins being involved. Nonetheless, the increasing amount of data applying to a variety of neurodegenerative disorders joined with the multiple effects exerted by the wide variety of plant-derived neuroprotective agents may rather confound the reader. The present review is an attempt to provide a general guideline about the most relevant mechanisms through which naturally occurring agents may counteract neurodegeneration. With such an aim, we focus on some popular phytochemical classes and bioactive compounds as representative examples to design a sort of main highway aimed at deciphering the most relevant protective mechanisms which make phytochemicals potentially useful in counteracting neurodegeneration. In this frame, we emphasize the potential role of the cell-clearing machinery as a kernel in the antioxidant, anti-aggregation, anti-inflammatory, and mitochondrial protecting effects of phytochemicals.

The NLRP3 inflammasome as a bridge between neuro-inflammation in metabolic and neurodegenerative diseases

Evidence increasingly suggests that type 2 diabetes mellitus (T2DM) is a risk factor for neurodegenerative diseases (NDDs), such as Alzheimer's disease (AD) and Parkinson's disease (PD). These diseases share many pathological processes, including oxidative stress, local inflammation/neuroinflammation and chronic, low-grade (systemic) inflammation, which are exacerbated by aging, a common risk factor for T2DM and NDDs. Here, we focus on the link between chronic inflammation driven by peripheral metabolic disease and how this may impact neurodegeneration in AD and PD. We review the relationship between these common pathological processes in AD and PD from the perspective of the "pro-inflammatory" signaling of the nucleotide-binding oligomerization domain (NOD)-, leucine-rich repeat- (LRR)-, and pyrin domain-containing protein 3 (NLRP3) inflammasome complex. Since the need for effective disease-modifying therapies in T2DM, AD and PD is significant, the relationship between these diseases is important as a positive clinical impact on one may benefit the others. We briefly consider how novel strategies may target neuro-inflammation and provide potential therapies for AD and PD.