Current Drug Targets - Volume 22, Issue 14, 2021

In the last few years, a massive increase in research has been observed that focuses on investigating the role of mitochondria in the pathogenesis of several neurodegenerative disorders. Mitochondria are vital cell organelles having important roles in different cellular processes, including energy production, calcium signaling, Reactive Oxygen Species (ROS) generation, apoptosis, etc. Therefore, healthy mitochondria are necessary for cell survival and functioning. It would seem feasible that mitochondrial dysfunction will have implications in various pathological conditions. A large body of evidence indicates the role of the mitochondrion as a potential key player in the loss or dysfunction of neurons in various neurodegenerative disorders. In this review, we provide an insight into mitochondrial dysfunction and its involvement in the pathology of several neurological diseases such as Alzheimer’s disease, Parkinson’s disease, Amyotrophic Lateral Sclerosis, Hypoxic- Ischemic Brain Injury, and many more.

Pathophysiologic conditions of neurodegenerative diseases are unquestionably related to protein misfolding. The accumulation of misfolded proteins into relatively ordered structures such as fibrillar intracellular and extracellular amyloids results in tissue lesions that lead to neuronal loss and brain damage. In these pathologies, the occurrence of protein aggregates suggests certain inefficient or insufficient cellular responses of those molecular chaperones that should properly assist the folding of the client proteins. In this regard, most experimental models for neurodegenerative diseases have demonstrated that the overexpression of molecular chaperones provides effective neuroprotection. A subset of these molecular chaperones corresponds to a group of proteins that exhibit peptidylprolyl isomerase enzymatic activity, the immunophilins. Most of the family members of the latter group were first described as being responsible for the immunosuppressive response or they were reported as members of the chaperone complex associated with HSP90 in steroid receptor oligomers. In this article, we review some aspects of the liaison between molecular chaperones and neurodegenerative diseases, in particular heat-shock proteins and immunophilins with demonstrated influence on the proper function of mitochondria. This article is intended to address a field that represents a yet critical unmet clinical need for the development of neuroprotective molecules focused on potentially novel molecular targets.

Flavonoids are chromene analogues abundantly found in plants. It has always been of interest to discover natural flavonoid structures, since living things, including humans, are routinely exposed to these compounds through many dietaries. So far, numerous studies have been conducted on flavonoids with diverse biological actions. The activity results obtained, particularly regarding the effects of flavonoids on various validated and non-validated targets of Alzheimer’s Disease (AD), make these compounds promising agents either to be directly employed in clinical trials or to be utilized as important scaffolds for flavonoid-based drug design studies. Although there are many review articles on the treatment and protective effects of flavonoids on AD, within this review, the effects of flavonoids on mitochondrial dysfunction developing throughout AD have been presented concomitant to their structural organization.

Sodium-Glucose co-transporter inhibitors are a novel class of drugs widely used in the treatment of type 2 diabetes mellitus medical management. This class of drugs has a simple mechanism of action by which they decrease blood glucose levels. They prevent the uptake or re-absorption of glucose in the blood by inhibiting the SGLT2 co-transport channels located in the renal proximal convoluted tubule. Since SGLT2 is the low affinity, high capacity glucose transporter, it allows the co-transport of sodium and glucose through it. SGLT2s are accountable for around 90% of the renal glucose reuptake. Cerebrovascular complications or accidents (CVAs) are the world's leading cause of mortality, resulting in around 6 million deaths annually. Diabetics are prone to develop mitochondrial dysfunction and neurodegeneration due to hyperglycemia and oxidative stress end products. Due to hyperglycemic condition in diabetes, it is always an elevated risk of cerebrovascular dysfunction due to hyperglycemia as it includes endothelial dysfunction, atherosclerosis, hypercoagulability, oxidative stress, renal reperfusion injury which may lead to neuronal degeneration and cognitive impairment. A diabetic individual is more prone to develop risk factors for transient ischemic attacks than a non-diabetic patient. These inhibitors reduce hyperglycemia by blocking renal glucose reabsorption, therefore promoting an increase in renal glucose excretion. This review discusses the potential role of SGLT2 inhibitors in treating CVAs associated with T2DM.

Huntington’s disease (HD) is a prototypical neurodegenerative disease, preferentially disrupting the neurons of the striatum and cortex. Progressive motor dysfunctions, psychiatric disturbances, behavioral impairments, and cognitive decline are the clinical symptoms of HD progression. The disease occurs due to expanded CAG repeats in exon 1 of huntingtin protein (mHtt), causing its aggregation. Multiple cellular and molecular pathways are involved in HD pathology. Mitochondria, as vital organelles have an important role in most neurodegenerative diseases like HD. Over the years, the role of mitochondria in neurons has highly diverged; they not only contribute as a cell power source, but also as dynamic organelles that fragment and then fuse to attain a maximal bioenergetics performance, regulating intracellular calcium homeostasis, reactive oxygen species (ROS) generation, antioxidant activity and involved in apoptotic pathways. Indeed, these events are observed to be affected in HD, resulting in neuronal dysfunction in pre-symptomatic stages. MHtt causes critical transcriptional abnormality by altering the expression of a master co-regulator, peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α), leading to increased susceptibility to oxidative stress and neuronal degeneration. Moreover, mHtt influences multiple cellular signaling events, which end with mitochondrial biogenesis. Here, we resume recent findings that pose mitochondria as an important regulatory organelle in HD and how mHtt affects mitochondrial function, trafficking and homeostasis and makes neurons prone to degeneration. Besides, we also uncover the mitochondrial-based potential targets and therapeutic approaches with imminent or currently ongoing clinical trials.

Advancing age presents a major challenge for the elderly population in terms of quality of life. The risk of cognitive impairment, motor in-coordination, and behavioral inconsistency due to neuronal damage is relatively higher in aging individuals of society. The brain, through its structural and functional integrity, regulates vital physiological events; however, the susceptibility of the brain to aging-related disturbances signals the onset of neurodegenerative diseases. Mitochondrial dysfunctions impair bioenergetic mechanism, synaptic plasticity, and calcium homeostasis in the brain, thus sufficiently implying mitochondria as a prime causal factor in accelerating aging-related neurodegeneration. We have reviewed the fundamental functions of mitochondria in a healthy brain and aimed to address the key issues in aging-related diseases by asking: 1) What goes wrong with mitochondria in the aging brain? 2) What are the implications of mitochondrial damage on motor functions and psychiatric symptoms? 3) How environmental chemicals and metabolic morbidities affect mitochondrial functions? Further, we share insights on opportunities and pitfalls in drug discovery approaches targeting mitochondria to slow down the progression of aging and related neurodegenerative diseases.

The neuron is high-energy utilizing tissue. The rate of neuronal cell respiration is higher than in other cells. Cellular respiration occurs with mitochondria. The healthy production and functions of mitochondria play a key role in the maintenance of healthy neurons. In pathological conditions such as neurodegenerative diseases, healthy mitochondria help to alleviate pathological events in neuronal cells. Conversely, mitochondrial dysfunction promotes the acceleration of the neurodegenerative process. Furthermore, glial-derived mitochondria contribute to multiple roles in the regulation of healthy neuron functions. It also supports releasing of the neurotransmitters; generation of the impulses, regulation of the membrane potential and molecular dynamics; controlling of the axonal transport; controlling of the mitochondrial fission and fusion functions in the peripheral as well as the central nervous system. Moreover, it plays a key role in the regeneration process of neuronal cells. Therefore, healthy mitochondria can provide a healthy environment for neuronal cell function and can treat neurodegenerative disorders. In this review, we explore the current view of healthy mitochondria and their role in healthy neuronal functions.