Miro1 R272Q disrupts mitochondrial calcium handling and neurotransmitter uptake in dopaminergic neurons

MIRO1 mutation leads to metabolic maladaptation resulting in Parkinson's disease-associated dopaminergic neuron loss

MIRO1 is a mitochondrial outer membrane protein important for mitochondrial distribution, dynamics and bioenergetics. Over the last decade, evidence has pointed to a link between MIRO1 and Parkinson's disease (PD) pathogenesis. Moreover, a heterozygous MIRO1 mutation (p.R272Q) was identified in a PD patient, from which an iPSC-derived midbrain organoid model was derived, showing MIRO1 mutant-dependent selective loss of dopaminergic neurons. Herein, we use patient-specific iPSC-derived midbrain organoids carrying the MIRO1 p.R272Q mutation to further explore the cellular and molecular mechanisms involved in dopaminergic neuron degeneration. Using single-cell RNA sequencing (scRNAseq) analysis and metabolic modeling we show that the MIRO1 p.R272Q mutation affects the dopaminergic neuron developmental path leading to metabolic deficits and disrupted neuron-astrocyte metabolic crosstalk, which might represent an important pathogenic mechanism leading to their loss.

Miro1- a key player in β-cell function and mitochondrial dynamics under diabetes mellitus

Mitochondrial health is crucial for the survival and function of β-cells, preserving glucose homeostasis and effective insulin production. Miro1, a mitochondrial Rho GTPase1 protein, plays an essential role in maintaining thequality of mitochondria by regulating calcium homeostasis and mitophagy. In this review, we aim to explore the dysfunction of Miro1 in type 2 diabetes mellitus (T2DM) and its contribution to impaired Ca2+ signaling, which increases oxidative stress in β-cells. This dysfunction is the hallmark of T2DM pathogenesis, leading to insufficient insulin production and poor glycemic control. Additionally, we discuss the role of Miro1 in modulating insulin secretion and inflammation, highlighting its effect on modulating key signaling cascades in β-cells. Altogether, enhancing Miro1 function and activity could alleviate mitochondrial dysfunction, reducing oxidative stress-mediated damage, and improving pancreatic β-cell survival. Targeting Miro1 with small molecules or gene-editing approaches could provide effective strategies for restoring cell function and insulin secretion in diabetic individuals. Exploring the deeper knowledge of Miro1 functions and interactions could lead to novel therapeutic advances in T2DM management.

Suppression of SIGMAR1 hinders oral cancer cell growth via modulation of mitochondrial Ca2+ dynamics

BACKGROUND

Oral cancer is the most common malignancy of the oral cavity and facial region, affecting the mucosal and epithelial surfaces in the mouth and lips. Unfortunately, OC is often associated with a high mortality rate and limited treatment options for patients.

METHODS AND RESULTS

Herein, we used in silico analysis and in vitro assays to investigate the impact of the Sigma-1 receptor (SIGMAR1) in OC progression by evaluating mitochondrial function, calcium signaling and clonogenic growth. First, the data from the TCGA pan-cancer analysis revealed that SIGMAR1 was overexpressed in OC versus healthy tissue and related to a worse survival rate. Furthermore, we demonstrated that SIGMAR1 silencing led to an increase in mitochondrial membrane potential, a reduction in cellular ATP levels, inhibition of Ca²⁺ influx, and a significant decrease in the clonogenic growth of OC cells.

CONCLUSIONS

Based on these findings, we suggest that SIGMAR1 may influence mitochondrial membrane potential and energy production by modulating Ca2+ uptake, which is critically important to cellular survival. In addition, SIGMAR1 knockdown may offer a potential strategy to be further explored as treatment for OC.

Proteome Dynamics in iPSC-Derived Human Dopaminergic Neurons

Dopaminergic neurons participate in fundamental physiological processes and are the cell type primarily affected in Parkinson's disease. Their analysis is challenging due to the intricate nature of their function, involvement in diverse neurological processes, and heterogeneity and localization in deep brain regions. Consequently, most of the research on the protein dynamics of dopaminergic neurons has been performed in animal cells ex vivo. Here we use iPSC-derived human mid-brain-specific dopaminergic neurons to study general features of their proteome biology and provide datasets for protein turnover and dynamics, including a human axonal translatome. We cover the proteome to a depth of 9409 proteins and use dynamic SILAC to measure the half-life of more than 4300 proteins. We report uniform turnover rates of conserved cytosolic protein complexes such as the proteasome and map the variable rates of turnover of the respiratory chain complexes in these cells. We use differential dynamic SILAC labeling in combination with microfluidic devices to analyze local protein synthesis and transport between axons and soma. We report 105 potentially novel axonal markers and detect translocation of 269 proteins between axons and the soma in the time frame of our analysis (120 h). Importantly, we provide evidence for local synthesis of 154 proteins in the axon and their retrograde transport to the soma, among them several proteins involved in RNA editing such as ADAR1 and the RNA helicase DHX30, involved in the assembly of mitochondrial ribosomes. Our study provides a workflow and resource for the future applications of quantitative proteomics in iPSC-derived human neurons.

MIRO1 controls energy production and proliferation of smooth muscle cells

Background

The outer mitochondrial Rho GTPase 1, MIRO1, mediates mitochondrial motility within cells, but implications for vascular smooth muscle cell (VSMC) physiology and its roles invascular diseases, such as neointima formation following vascular injury are widely unknown.

Methods

An in vivo model of selective Miro1 deletion in VSMCs was generated, and the animals were subjected to carotid artery ligation. The molecular mechanisms relevant to VSMC proliferation were then explored in explanted VSMCs by imaging mitochondrial positioning and cristae structure and assessing the effects on ATP production, metabolic function and interactions with components of the electron transport chain (ETC).

Results

MIRO1 was robustly expressed in VSMCs within human atherosclerotic plaques and promoted VSMC proliferation and neointima formation in mice by blocking cell-cycle progression at G1/S, mitochondrial positioning, and PDGF-induced ATP production and respiration; overexpression of a MIRO1 mutant lacking the EF hands that are required for mitochondrial mobility did not fully rescue these effects. At the ultrastructural level, Miro1 deletion distorted the mitochondrial cristae and reduced the formation of super complexes and the activity of ETC complex I.

Conclusions

Mitochondrial motility is essential for VSMC proliferation and relies on MIRO1. The EF-hands of MIRO1 regulate the intracellular positioning of mitochondria. Additionally, the absence of MIRO1 leads to distorted mitochondrial cristae and reduced ATP generation. Our findings demonstrate that motility is linked to mitochondrial ATP production. We elucidated two unrecognized mechanisms through which MIRO1 influences cell proliferation by modulating mitochondria: first, by managing mitochondrial placement via Ca2+-dependent EF hands, and second, by affecting cristae structure and ATP synthesis.

Modulating mitochondrial calcium channels (TRPM2/MCU/NCX) as a therapeutic strategy for neurodegenerative disorders

Efficient cellular communication is essential for the brain to regulate diverse functions like muscle contractions, memory formation and recall, decision-making, and task execution. This communication is facilitated by rapid signaling through electrical and chemical messengers, including voltage-gated ion channels and neurotransmitters. These messengers elicit broad responses by propagating action potentials and mediating synaptic transmission. Calcium influx and efflux are essential for releasing neurotransmitters and regulating synaptic transmission. Mitochondria, which are involved in oxidative phosphorylation, and the energy generation process, also interact with the endoplasmic reticulum to store and regulate cytoplasmic calcium levels. The number, morphology, and distribution of mitochondria in different cell types vary based on energy demands. Mitochondrial damage can cause excess reactive oxygen species (ROS) generation. Mitophagy is a selective process that targets and degrades damaged mitochondria via autophagosome-lysosome fusion. Defects in mitophagy can lead to a buildup of ROS and cell death. Numerous studies have attempted to characterize the relationship between mitochondrial dysfunction and calcium dysregulation in neurodegenerative diseases such as Alzheimer's Disease, Parkinson's Disease, Huntington's Disease, Amyotrophic lateral sclerosis, spinocerebellar ataxia, and aging. Interventional strategies to reduce mitochondrial damage and accumulation could serve as a therapeutic target, but further research is needed to unravel this potential. This review offers an overview of calcium signaling related to mitochondria in various neuronal cells. It critically examines recent findings, exploring the potential roles that mitochondrial dysfunction might play in multiple neurodegenerative diseases and aging. Furthermore, the review identifies existing gaps in knowledge to guide the direction of future research.

Highly Specialized Mechanisms for Mitochondrial Transport in Neurons: From Intracellular Mobility to Intercellular Transfer of Mitochondria

The highly specialized structure and function of neurons depend on a sophisticated organization of the cytoskeleton, which supports a similarly sophisticated system to traffic organelles and cargo vesicles. Mitochondria sustain crucial functions by providing energy and buffering calcium where it is needed. Accordingly, the distribution of mitochondria is not even in neurons and is regulated by a dynamic balance between active transport and stable docking events. This system is finely tuned to respond to changes in environmental conditions and neuronal activity. In this review, we summarize the mechanisms by which mitochondria are selectively transported in different compartments, taking into account the structure of the cytoskeleton, the molecular motors and the metabolism of neurons. Remarkably, the motor proteins driving the mitochondrial transport in axons have been shown to also mediate their transfer between cells. This so-named intercellular transport of mitochondria is opening new exciting perspectives in the treatment of multiple diseases.