Mitochondrial transport in neurons and evidence for its involvement in acute neurological disorders

Mitochondrial dysfunction in Alzheimer's disease: Guiding the path to targeted therapies

Alzheimer's disease (AD) is characterized by progressive neurodegeneration, marked by the accumulation of amyloid-β (Aβ) plaques and tau tangles. Emerging evidence suggests that mitochondrial dysfunction plays a pivotal role in AD pathogenesis, driven by impairments in mitochondrial quality control (MQC) mechanisms. MQC is crucial for maintaining mitochondrial integrity through processes such as proteostasis, mitochondrial dynamics, mitophagy, and precise communication with other subcellular organelles. In AD, disruptions in these processes lead to bioenergetic failure, gene dysregulation, the accumulation of damaged mitochondria, neuroinflammation, and lipid homeostasis impairment, further exacerbating neurodegeneration. This review elucidates the molecular pathways involved in MQC and their pathological relevance in AD, highlighting recent discoveries related to mitochondrial mechanisms underlying neurodegeneration. Furthermore, we explore potential therapeutic strategies targeting mitochondrial dysfunction, including gene therapy and pharmacological interventions, offering new avenues for slowing AD progression. The complex interplay between mitochondrial health and neurodegeneration underscores the need for innovative approaches to restore mitochondrial function and mitigate the onset and progression of AD.

The inter-organelle cross-talk finely orchestrated in the amyloidogenic processing of amyloid precursor protein in dendritic arborization neurons of Drosophila

Background: Organelles in neuronal dendrites facilitate local metabolic processes and energy supply, crucial for dendrite development and neurodegenerative diseases. The distinct functions of dendritic organelles have been well studied, however, their crosstalk under physiological and pathological contexts remains elusive. We aimed to establish an in vivo model system of contacts between multi-organelles for investigating the modulation of inter-organelle crosstalk in Alzheimer's disease (AD). Methods: A dendrite model of organelle contacts was developed in Drosophila neurons using a set of proximity-driven probes and four-color Airyscan super-resolution imaging. The systematic modulations among multiple contact sites (CSs) between organelles were examined by manipulating CS tethers and vesicular transporters. Finally, perturbations of these CSs and the dendrite structure in the amyloidogenic processing of amyloid precursor protein (APP) were evaluated by introducing three stages of the processing in this model system. Results: A dynamic network, interconnected via CSs and organized with multi-organelle contacts, was presented among Golgi outposts, the endoplasmic reticulum, lysosomes, and mitochondria (GELM). The CS modulations were found to encompass both their density and motility. Notably, multi-CSs participated in complementary modulations spanning across different cellular pathways. Furthermore, the CS network was revealed to be progressively disturbed in APP amyloidogenic processing, with upregulations in density and motility extending from single- to multi-CSs. These CS perturbations, along with defects in dendrite structural plasticity, could be partially rescued by knocking down Miro. Conclusion: The elucidation of CS modulation modes in the GELM network model reveals a cascaded dysregulation of organelle crosstalk during APP amyloidogenic processing. It expands the mechanisms of inter-organelle communication and provides novel insights into neurodegeneration in AD pathology.

Beyond static snapshots: Mitochondria in action

Mitochondria are dynamic organelles essential for cellular homeostasis, undergoing continuous fission and fusion processes that regulate their morphology, distribution, and function. Disruptions in these dynamics are linked to numerous diseases, including neurodegenerative disorders and cancer. Understanding these processes is vital for developing therapeutic strategies aimed at mitigating mitochondrial dysfunction. This review provides an overview of recent perspectives on mitochondrial dynamics, focusing on the need for live video microscopy imaging in order to fully understand mitochondrial phenotypes and pathology. Advanced imaging tools, such as machine learning-based segmentation and label-free microscopy approaches, have the potential to transform our ability to study mitochondrial dynamics in live cells.

Synaptic mitochondria: A crucial factor in the aged hippocampus

Aging is a multifaceted biological process characterized by progressive molecular and cellular damage accumulation. The brain hippocampus undergoes functional deterioration with age, caused by cellular deficits, decreased synaptic communication, and neuronal death, ultimately leading to memory impairment. One of the factors contributing to this dysfunction is the loss of mitochondrial function. In neurons, mitochondria are categorized into synaptic and non-synaptic pools based on their location. Synaptic mitochondria, situated at the synapses, play a crucial role in maintaining neuronal function and synaptic plasticity, whereas non-synaptic mitochondria are distributed throughout other neuronal compartments, supporting overall cellular metabolism and energy supply. The proper function of synaptic mitochondria is essential for synaptic transmission as they provide the energy required and regulate calcium homeostasis at the communication sites between neurons. Maintaining the structure and functionality of synaptic mitochondria involves intricate processes, including mitochondrial dynamics such as fission, fusion, transport, and quality control mechanisms. These processes ensure that mitochondria remain functional, replace damaged organelles, and sustain cellular homeostasis at synapses. Notably, deficiencies in these mechanisms have been increasingly associated with aging and the onset of age-related neurodegenerative diseases. Synaptic mitochondria from the hippocampus are particularly vulnerable to age-related changes, including alterations in morphology and a decline in functionality, which significantly contribute to decreased synaptic activity during aging. This review comprehensively explores the critical roles that mitochondrial dynamics and quality control mechanisms play in preserving synaptic activity and neuronal function. It emphasizes the emerging evidence linking the deterioration of synaptic mitochondria to the aging process and the development of neurodegenerative diseases, highlighting the importance of these organelles from hippocampal neurons as potential therapeutic targets for mitigating cognitive decline and synaptic degeneration associated with aging. The novelty of this review lies in its focus on the unique vulnerability of hippocampal synaptic mitochondria to aging, underscoring their importance in maintaining brain function across the lifespan.

The bioenergetics of traumatic brain injury and its long-term impact for brain plasticity and function

Mitochondria provide the energy to keep cells alive and functioning and they have the capacity to influence highly complex molecular events. Mitochondria are essential to maintain cellular energy homeostasis that determines the course of neurological disorders, including traumatic brain injury (TBI). Various aspects of mitochondria metabolism such as autophagy can have long-term consequences for brain function and plasticity. In turn, mitochondria bioenergetics can impinge on molecular events associated with epigenetic modifications of DNA, which can extend cellular memory for a long time. Mitochondrial dysfunction leads to pathological manifestations such as oxidative stress, inflammation, and calcium imbalance that threaten brain plasticity and function. Hence, targeting mitochondrial function may have great potential to lessen the outcomes of TBI.

An in vitro multi-organ microphysiological system (MPS) to investigate the gut-to-brain translocation of neurotoxins

The death of dopamine-producing neurons in the substantia nigra in the base of the brain is a defining pathological feature in the development of Parkinson's disease (PD). PD is, however, a multi-systemic disease, also affecting the peripheral nervous system and gastrointestinal tract (GIT) that interact via the gut-brain axis (GBA). Our dual-flow GIT-brain microphysiological system (MPS) was modified to investigate the gut-to-brain translocation of the neurotoxin trigger of PD, 1-methyl-4-phenylpyridinium (MPP+), and its impact on key GIT and brain cells that contribute to the GBA. The modular GIT-brain MPS in combination with quantitative and morphometric image analysis methods reproduces cell specific neurotoxin-induced dopaminergic cytotoxicity and mitochondria-toxicity with the drug having no detrimental impact on the viability or integrity of cellular membranes of GIT-derived colonic epithelial cells. Our findings demonstrate the utility and capability of the GIT-brain MPS for measuring neuronal responses and its suitability for identifying compounds or molecules produced in the GIT that can exacerbate or protect against neuronal inflammation and cell death.

Proposal for Manual Osteopathic Treatment of the Phrenic Nerve

The article reviews the anatomical path of the phrenic nerve and its anastomoses, with the most up-to-date knowledge reported in the literature. We have briefly reviewed the possible phrenic dysfunctions, with the final aim of presenting an osteopathic manual approach for the treatment of the most superficial portion of the nerve, using a gentle technique. The approach we propose is, therefore, a theory based on clinical experience and the rationale that we can extrapolate from the literature. We hope that the article will be a stimulus for further experimental investigations using the technique illustrated in the article. To the authors' knowledge, this is the first article that takes into consideration the hypothesis of an osteopathic treatment with gentle techniques for the phrenic nerve.

[Optineurin and mitochondrial dysfunction in neurodegeneration]

Optineurin (OPTN) is a multifunctional protein playing a crucial role as a receptor in selective autophagy. OPTN gene mutations are linked to diseases such as normal-tension glaucoma and amyotrophic lateral sclerosis. Recognized as a critical receptor for mitophagy, OPTN is pivotal in selectively degrading damaged mitochondria. This process is essential to prevent their accumulation, the generation of reactive oxygen species, and the release of pro-apoptotic factors. Mitophagy's quality control is governed by the PINK1 kinase and the cytosolic ubiquitin ligase Parkin, whose mutations are associated with Parkinson's disease. This review highlights recent insights emphasizing OPTN's role in mitophagy and its potential involvement in neurodegenerative diseases.