The receptor subunit Tom20 is dynamically associated with the TOM complex in mitochondria of human cells

SIRT5 modulates mitochondria function via mitophagy and antioxidant mechanisms to facilitate oocyte maturation in mice

Mitochondrial homeostasis, closely associated with mitophagy and antioxidant mechanisms, is essential for proper meiotic spindle assembly and chromosome segregation during oocyte maturation. SIRT5, known to modulate mitochondrial function under various conditions, has been shown to impact oocyte quality when inhibited, however, the precise mechanisms linking SIRT5 to mitochondrial homeostasis during meiotic progression remain unclear. In this study, we demonstrate that SIRT5 localizes predominantly at the periphery of the meiotic spindle and is enriched on chromosomes during oocyte maturation. Inhibition of SIRT5 led to significant meiotic defects, including disrupted spindle organization and chromosome misalignment. These defects were associated with increased histone acetylation, which impaired kinetochore-microtubule attachments. Moreover, SIRT5 inhibition resulted in mitochondrial dysfunction, subsequently elevating ROS levels and triggering oxidative stress, which further exacerbated meiotic abnormalities. Mechanistically, SIRT5 inhibition disrupted the balance of Parkin-dependent mitophagy by inducing ULK phosphorylation. Additionally, it activated the PI3K/Akt signaling pathway, which increased NADPH consumption and reduced GSH levels. Collectively, these findings reveal that SIRT5 plays dual roles in maintaining mitochondrial homeostasis during oocyte maturation: (1) by regulating Parkin-dependent mitophagy to prevent excessive mitochondrial clearance, and (2) by preserving the NADPH/GSH antioxidant system to ensure redox balance. These insights provide potential targets for improving oocyte quality and addressing mitochondrial dysfunction-related reproductive disorders in females.

MitoStores: stress-induced aggregation of mitochondrial proteins

Most mitochondrial proteins are synthesized in the cytosol and post-translationally imported into mitochondria. If the rate of protein synthesis exceeds the capacity of the mitochondrial import machinery, precursor proteins can transiently accumulate in the cytosol. The cytosolic accumulation of mitochondrial precursors jeopardizes cellular protein homeostasis (proteostasis) and can be the cause of diseases. In order to prevent these toxic effects, most non-imported precursors are rapidly degraded by the ubiquitin-proteasome system. However, cells employ a second layer of defense which is the facilitated sequestration of mitochondrial precursor proteins in transient protein aggregates. The formation of such structures is triggered by nucleation factors such as small heat shock proteins. Disaggregases and chaperones can liberate precursors from cytosolic aggregates to pass them on to the mitochondrial import machinery or, under persistent stress conditions, to the proteasome for degradation. Owing to their role as transient buffering systems, these aggregates were referred to as MitoStores. This review articles provides a general overview about the MitoStore concept and the early stages in mitochondrial protein biogenesis in yeast and, in cases where aspects differ, in mammalian cells.

Reactive oxygen species control protein degradation at the mitochondrial import gate

While reactive oxygen species (ROS) have long been known to drive aging and neurodegeneration, their persistent depletion below basal levels also disrupts organismal function. Cells counteract loss of basal ROS via the reductive stress response, but the identity and biochemical activity of ROS sensed by this pathway remain unknown. Here, we show that the central enzyme of the reductive stress response, the E3 ligase Cullin 2-FEM1 homolog B (CUL2FEM1B), specifically acts at mitochondrial TOM complexes, where it senses ROS produced by complex III of the electron transport chain (ETC). ROS depletion during times of low ETC activity triggers the localized degradation of CUL2FEM1B substrates, which sustains mitochondrial import and ensures the biogenesis of the rate-limiting ETC complex IV. As complex III yields most ROS when the ETC outpaces metabolic demands or oxygen availability, basal ROS are sentinels of mitochondrial activity that help cells adjust their ETC to changing environments, as required for cell differentiation and survival.

NEK10 kinase ablation affects mitochondrial morphology, function and protein phosphorylation status

BACKGROUND

NEK10, a serine/threonine/tyrosine kinase belonging to the NEK (NIMA-related kinases) family, has been associated with diverse cellular processes. However, no specific target pathways have been identified. Our previous work knocking down NEK10 in HeLa cells suggested a functional association with mitochondria, as we observed altered mitochondrial morphology, mitochondrial oxygen consumption, mtDNA integrity, and reactive oxygen species levels.

METHODS

To better understand this association, we studied human HAP1 cells fully knockout for NEK10 and confirmed that NEK10 has an important role in mitochondrial homeostasis. We performed the study of mitochondrial respiration, mitochondrial morphology, mitochondrial mass, and mtDNA analysis. Additionally, we showed proteome and phosphoproteome data of crude mitochondrial fraction of Parental and NEK10 KO cells using liquid chromatography-mass spectrometry (LC-MS/MS).

RESULTS

In the absence of NEK10 several mitochondrial functions were disturbed. Moreover, proteome and phosphoproteome analyses of mitochondrial fractions showed that NEK10 alters the threonine phosphorylation status of several mitochondrial/endoplasmic reticulum components, including HSP60, NDUFB4, and TOM20. These changes impacted the steady-state levels of a larger group of proteins, preferentially involving respiratory complexes and autophagy pathways.

CONCLUSION

We concluded that NEK10 plays a key role in mitochondrial function, possibly by modulating the phosphorylation status of mitochondrial proteins.

DYRK1A signalling synchronizes the mitochondrial import pathways for metabolic rewiring

Mitochondria require an extensive proteome to maintain a variety of metabolic reactions, and changes in cellular demand depend on rapid adaptation of the mitochondrial protein composition. The TOM complex, the organellar entry gate for mitochondrial precursors in the outer membrane, is a target for cytosolic kinases to modulate protein influx. DYRK1A phosphorylation of the carrier import receptor TOM70 at Ser91 enables its efficient docking and thus transfer of precursor proteins to the TOM complex. Here, we probe TOM70 phosphorylation in molecular detail and find that TOM70 is not a CK2 target nor import receptor for MIC19 as previously suggested. Instead, we identify TOM20 as a MIC19 import receptor and show off-target inhibition of the DYRK1A-TOM70 axis with the clinically used CK2 inhibitor CX4945 which activates TOM20-dependent import pathways. Taken together, modulation of DYRK1A signalling adapts the central mitochondrial protein entry gate via synchronization of TOM70- and TOM20-dependent import pathways for metabolic rewiring. Thus, DYRK1A emerges as a cytosolic surveillance kinase to regulate and fine-tune mitochondrial protein biogenesis.

Super-resolution microscopies, technological breakthrough to decipher mitochondrial structure and dynamic

Mitochondria are complex organelles with an outer membrane enveloping a second inner membrane that creates a vast matrix space partitioned by pockets or cristae that join the peripheral inner membrane with several thin junctions. Several micrometres long, mitochondria are generally close to 300 nm in diameter, with membrane layers separated by a few tens of nanometres. Ultrastructural data from electron microscopy revealed the structure of these mitochondria, while conventional optical microscopy revealed their extraordinary dynamics through fusion, fission, and migration processes but its limited resolution power restricted the possibility to go further. By overcoming the limits of light diffraction, Super-Resolution Microscopy (SRM) now offers the potential to establish the links between the ultrastructure and remodelling of mitochondrial membranes, leading to major advances in our understanding of mitochondria's structure-function. Here we review the contributions of SRM imaging to our understanding of the relationship between mitochondrial structure and function. What are the hopes for these new imaging approaches which are particularly important for mitochondrial pathologies?

GUCY2C signaling limits dopaminergic neuron vulnerability to toxic insults

Mitochondrial dysfunction and reactive oxygen species (ROS) accumulation within the substantia nigra pars compacta (SNpc) are central drivers of dopaminergic (DA) neuron death in Parkinson's disease (PD). Guanylyl cyclases and their second messenger cyclic (c)GMP support mitochondrial function, protecting against ROS and promoting cell survival in several tissues. However, the role of the guanylyl cyclase-cGMP axis in defining the vulnerability of DA neurons in the SNpc in PD remains unclear, in part due to the challenge of manipulating cGMP levels selectively in midbrain DA neurons. In that context, guanylyl cyclase C (GUCY2C), a receptor primarily expressed by intestinal epithelial cells, was discovered recently in midbrain DA neurons. Here, we demonstrate that GUCY2C promotes mitochondrial function, reducing oxidative stress and protecting DA neurons from degeneration in the 1-methyl-4-phenyl- 1,2,3,6-tetrahydropyridine (MPTP) mouse model. GUCY2C is overexpressed in the SNpc in PD patients and in mice treated with MPTP, possibly reflecting a protective response to oxidative stress. Moreover, cGMP signaling protects against oxidative stress, mitochondrial impairment, and cell death in cultured DA neurons. These observations reveal a previously unexpected role for the GUCY2C-cGMP signaling axis in controlling mitochondrial dysfunction and toxicity in SNpc DA neurons, highlighting the therapeutic potential of targeting DA neuron GUCY2C to prevent neurodegeneration in PD.

Mitochondrial Outer Membrane Translocase MoTom20 Modulates Mitochondrial Morphology and Is Important for Infectious Growth of the Rice Blast Fungus Magnaporthe oryzae

Mitochondria are highly dynamic organelles that constantly change their morphology to adapt to the cellular environment through fission and fusion, which is critical for a cell to maintain normal cellular functions. Despite the significance of this process in the development and pathogenicity of the rice blast fungus Magnaporthe oryzae, the underlying mechanism remains largely elusive. Here, we identified and characterized a mitochondrial outer membrane translocase, MoTom20, in M. oryzae. Targeted gene deletion revealed that MoTom20 plays an important role in vegetative growth, conidiogenesis, penetration, and infectious growth of M. oryzae. The growth rate, conidial production, appressorium turgor, and pathogenicity are decreased in the ΔMotom20 mutant compared with the wild-type and complemented strains. Further analysis revealed that MoTom20 localizes in mitochondrion and plays a key role in regulating mitochondrial fission and fusion balance, which is critical for infectious growth. Finally, we found that MoTom20 is involved in fatty-acid utilization, and its yeast homolog ScTom20 is able to rescue the defects of ΔMotom20 in mitochondrial morphology and pathogenicity. Overall, our data demonstrate that MoTom20 is a key regulator for mitochondrial morphology maintenance, which is important for infectious growth of the rice blast fungus M. oryzae. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Tom20 gates PINK1 activity and mediates its tethering of the TOM and TIM23 translocases upon mitochondrial stress

Mutations in PTEN-induced putative kinase 1 (PINK1) cause autosomal recessive early-onset Parkinson's disease (PD). PINK1 is a Ser/Thr kinase that regulates mitochondrial quality control by triggering mitophagy mediated by the ubiquitin (Ub) ligase Parkin. Upon mitochondrial damage, PINK1 accumulates on the outer mitochondrial membrane forming a high-molecular-weight complex with the translocase of the outer membrane (TOM). PINK1 then phosphorylates Ub, which enables recruitment and activation of Parkin followed by autophagic clearance of the damaged mitochondrion. Thus, Parkin-dependent mitophagy hinges on the stable accumulation of PINK1 on the TOM complex. Yet, the mechanism linking mitochondrial stressors to PINK1 accumulation and whether the translocases of the inner membrane (TIMs) are also involved remain unclear. Herein, we demonstrate that mitochondrial stress induces the formation of a PINK1-TOM-TIM23 supercomplex in human cultured cell lines, dopamine neurons, and midbrain organoids. Moreover, we show that PINK1 is required to stably tether the TOM to TIM23 complexes in response to stress such that the supercomplex fails to accumulate in cells lacking PINK1. This tethering is dependent on an interaction between the PINK1 N-terminal-C-terminal extension module and the cytosolic domain of the Tom20 subunit of the TOM complex, the disruption of which, by either designer or PD-associated PINK1 mutations, inhibits downstream mitophagy. Together, the findings provide key insight into how PINK1 interfaces with the mitochondrial import machinery, with important implications for the mechanisms of mitochondrial quality control and PD pathogenesis.

Progress in pH-Sensitive sensors: essential tools for organelle pH detection, spotlighting mitochondrion and diverse applications

pH-sensitive fluorescent proteins have revolutionized the field of cellular imaging and physiology, offering insight into the dynamic pH changes that underlie fundamental cellular processes. This comprehensive review explores the diverse applications and recent advances in the use of pH-sensitive fluorescent proteins. These remarkable tools enable researchers to visualize and monitor pH variations within subcellular compartments, especially mitochondria, shedding light on organelle-specific pH regulation. They play pivotal roles in visualizing exocytosis and endocytosis events in synaptic transmission, monitoring cell death and apoptosis, and understanding drug effects and disease progression. Recent advancements have led to improved photostability, pH specificity, and subcellular targeting, enhancing their utility. Techniques for multiplexed imaging, three-dimensional visualization, and super-resolution microscopy are expanding the horizon of pH-sensitive protein applications. The future holds promise for their integration into optogenetics and drug discovery. With their ever-evolving capabilities, pH-sensitive fluorescent proteins remain indispensable tools for unravelling cellular dynamics and driving breakthroughs in biological research. This review serves as a comprehensive resource for researchers seeking to harness the potential of pH-sensitive fluorescent proteins.

Interactions of amyloidogenic proteins with mitochondrial protein import machinery in aging-related neurodegenerative diseases

Most mitochondrial proteins are targeted to the organelle by N-terminal mitochondrial targeting sequences (MTSs, or "presequences") that are recognized by the import machinery and subsequently cleaved to yield the mature protein. MTSs do not have conserved amino acid compositions, but share common physicochemical properties, including the ability to form amphipathic α-helical structures enriched with basic and hydrophobic residues on alternating faces. The lack of strict sequence conservation implies that some polypeptides can be mistargeted to mitochondria, especially under cellular stress. The pathogenic accumulation of proteins within mitochondria is implicated in many aging-related neurodegenerative diseases, including Alzheimer's, Parkinson's, and Huntington's diseases. Mechanistically, these diseases may originate in part from mitochondrial interactions with amyloid-β precursor protein (APP) or its cleavage product amyloid-β (Aβ), α-synuclein (α-syn), and mutant forms of huntingtin (mHtt), respectively, that are mediated in part through their associations with the mitochondrial protein import machinery. Emerging evidence suggests that these amyloidogenic proteins may present cryptic targeting signals that act as MTS mimetics and can be recognized by mitochondrial import receptors and transported into different mitochondrial compartments. Accumulation of these mistargeted proteins could overwhelm the import machinery and its associated quality control mechanisms, thereby contributing to neurological disease progression. Alternatively, the uptake of amyloidogenic proteins into mitochondria may be part of a protein quality control mechanism for clearance of cytotoxic proteins. Here we review the pathomechanisms of these diseases as they relate to mitochondrial protein import and effects on mitochondrial function, what features of APP/Aβ, α-syn and mHtt make them suitable substrates for the import machinery, and how this information can be leveraged for the development of therapeutic interventions.

GUCY2C signaling limits dopaminergic neuron vulnerability to toxic insults

Mitochondrial dysfunction and reactive oxygen species (ROS) accumulation within the substantia nigra pars compacta (SNpc) are central drivers of dopaminergic (DA) neuron death in Parkinson's disease (PD). Guanylyl cyclases, and their second messengers cyclic (c)GMP, support mitochondrial function, protecting against ROS and promoting cell survival in a number of tissues. However, the role of the guanylyl cyclase-cGMP axis in defining the vulnerability of DA neurons in the SNpc in PD remains unclear, in part due to the challenge of manipulating cGMP levels selectively in midbrain DA neurons. In that context, guanylyl cyclase C (GUCY2C), a receptor primarily expressed by intestinal epithelial cells, was discovered recently in midbrain DA neurons. Here, we demonstrate that GUCY2C promotes mitochondrial function, reducing oxidative stress and protecting DA neurons from degeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of neurodegeneration. GUCY2C is overexpressed in the SNpc in PD patients and in mice treated with MPTP, possibly reflecting a protective response to oxidative stress. Moreover, cGMP signaling protects against oxidative stress, mitochondrial impairment, and cell death in cultured DA neurons. These observations reveal a previously unexpected role for the GUCY2C-cGMP signaling axis in controlling mitochondrial dysfunction and toxicity in nigral DA neurons, highlighting the therapeutic potential of targeting DA neuron GUCY2C to prevent neurodegeneration in PD.

Mitochondrial microproteins: critical regulators of protein import, energy production, stress response pathways, and programmed cell death

Mitochondria rely upon the coordination of protein import, protein translation, and proper functioning of oxidative phosphorylation (OXPHOS) complexes I-V to sustain the activities of life for an organism. Each process is dependent upon the function of profoundly large protein complexes found in the mitochondria [translocase of the outer mitochondrial membrane (TOMM) complex, translocase of the inner mitochondrial membrane (TIMM) complex, OXPHOS complexes, mitoribosomes]. These massive protein complexes, in some instances more than one megadalton, are built up from numerous protein subunits of varying sizes, including many proteins that are ≤100-150 amino acids. However, these small proteins, termed microproteins, not only act as cogs in large molecular machines but also have important steps in inhibiting or promoting the intrinsic pathway of apoptosis, coordinate responses to cellular stress, and even act as hormones. This review focuses on microproteins that occupy the mitochondria and are critical for its function. Although the microprotein field is relatively new, researchers have long recognized the existence of these mitochondrial proteins as critical components of virtually all aspects of mitochondrial biology. Thus, recent studies estimating that hundreds of new microproteins of unknown function exist and are missing from current genome annotations suggests that the mitochondrial "microproteome" is a rich area for future biological investigation.

Multiple tethers of organelle contact sites are involved in α-synuclein toxicity in yeast

The protein α-synuclein (α-syn) is one of the major factors linked to Parkinson's disease, yet how its misfolding and deposition contribute to the pathology remains largely elusive. Recently, contact sites among organelles were implicated in the development of this disease. Here, we used the budding yeast Saccharomyces cerevisiae, in which organelle contact sites have been characterized extensively, as a model to investigate their role in α-syn cytotoxicity. We observed that lack of specific tethers that anchor the endoplasmic reticulum to the plasma membrane resulted in cells with increased resistance to α-syn expression. Additionally, we found that strains lacking two dual-function proteins involved in contact sites, Mdm10 and Vps39, were resistant to the expression of α-syn. In the case of Mdm10, we found that this is related to its function in mitochondrial protein biogenesis and not to its role as a contact site tether. In contrast, both functions of Vps39, in vesicular transport and as a tether of the vacuole-mitochondria contact site, were required to support α-syn toxicity. Overall, our findings support that interorganelle communication through membrane contact sites is highly relevant for α-syn-mediated toxicity.

Spatial subcellular organelle networks in single cells

Organelles play important roles in human health and disease, such as maintaining homeostasis, regulating growth and aging, and generating energy. Organelle diversity in cells not only exists between cell types but also between individual cells. Therefore, studying the distribution of organelles at the single-cell level is important to understand cellular function. Mesenchymal stem cells are multipotent cells that have been explored as a therapeutic method for treating a variety of diseases. Studying how organelles are structured in these cells can answer questions about their characteristics and potential. Herein, rapid multiplexed immunofluorescence (RapMIF) was performed to understand the spatial organization of 10 organelle proteins and the interactions between them in the bone marrow (BM) and umbilical cord (UC) mesenchymal stem cells (MSCs). Spatial correlations, colocalization, clustering, statistical tests, texture, and morphological analyses were conducted at the single cell level, shedding light onto the interrelations between the organelles and comparisons of the two MSC subtypes. Such analytics toolsets indicated that UC MSCs exhibited higher organelle expression and spatially spread distribution of mitochondria accompanied by several other organelles compared to BM MSCs. This data-driven single-cell approach provided by rapid subcellular proteomic imaging enables personalized stem cell therapeutics.

Mitochondrial protein transport: Versatility of translocases and mechanisms

Biogenesis of mitochondria requires the import of approximately 1,000 different precursor proteins into and across the mitochondrial membranes. Mitochondria exhibit a wide variety of mechanisms and machineries for the translocation and sorting of precursor proteins. Five major import pathways that transport proteins to their functional intramitochondrial destination have been elucidated; these pathways range from the classical amino-terminal presequence-directed pathway to pathways using internal or even carboxy-terminal targeting signals in the precursors. Recent studies have provided important insights into the structural organization of membrane-embedded preprotein translocases of mitochondria. A comparison of the different translocases reveals the existence of at least three fundamentally different mechanisms: two-pore-translocase, β-barrel switching, and transport cavities open to the lipid bilayer. In addition, translocases are physically engaged in dynamic interactions with respiratory chain complexes, metabolite transporters, quality control factors, and machineries controlling membrane morphology. Thus, mitochondrial preprotein translocases are integrated into multi-functional networks of mitochondrial and cellular machineries.

Melatonin promoted osteogenesis of human periodontal ligament cells by regulating mitochondrial functions through the translocase of the outer mitochondrial membrane 20

BACKGROUND AND OBJECTIVE

Melatonin plays an important role in various beneficial functions, including promoting differentiation. However, effects on osteogenic differentiation, especially in human periodontal cells (hPDLCs), still remain inconclusive. Mitochondria are highly dynamic organelles that play an important role in various biological processes in cells, including energy metabolism and oxidative stress reaction. Furthermore, the translocase of the outer mitochondrial membrane 20 (TOM20) is responsible for recognizing and transporting precursor proteins. Thus, the objective of this study was to evaluate the functionality of melatonin on osteogenesis in human periodontal cells and to explore the involved mechanism of mitochondria.

METHODS

The hPDLCs were extracted and identified by flow cytometry and multilineage differentiation. We divided hPDLCs into control group, osteogenic induction group, and osteogenesis with melatonin treatment group (100, 10, and 1 μM). Then we used a specific siRNA to achieve interference of TOM20. Alizarin red and Alkaline phosphatase staining and activity assays were performed to evaluate osteogenic differentiation. Osteogenesis-related genes and proteins were measured by qPCR and western blot. Mitochondrial functions were tested using ATP, NAD+/NADH, JC-1, and Seahorse Mito Stress Test kits. Finally, TOM20 and mitochondrial dynamics-related molecules expression were also assessed by qPCR and western blot.

RESULTS

Our results showed that melatonin-treated hPDLCs had higher calcification and ALP activity as well as upregulated OCN and Runx2 expression at mRNA and protein levels, which was the most obvious in 1 μM melatonin-treated group. Meanwhile, melatonin supplement elevated intracellular ATP production and mitochondrial membrane potential by increasing mitochondrial oxidative metabolism, hence causing a lower NAD⁺ /NADH ratio. In addition, we also found that melatonin treatment raised TOM20 level and osteogenesis and mitochondrial functions were both suppressed after knocking down TOM20.

CONCLUSION

We found that melatonin promoted osteogenesis of hPDLCs and 1 μM melatonin had the most remarkable effect. Melatonin treatment can reinforce mitochondrial functions by upregulating TOM20.

Golgi damage caused by dysfunction of PiT-2 in primary familial brain calcification

The Golgi apparatus is vital for protein modification and molecular trafficking. It is essential for nerve development and activity, and damage thereof is implicated in many neurological diseases. Primary familial brain calcification (PFBC) is a rare inherited neurodegenerative disease characterized by multiple brain calcifications. SLC20A2, which encodes the inorganic phosphate transporter 2 (PiT-2) protein, is the main pathogenic gene in PFBC. The PiT-2 protein is a sodium-dependent phosphate type III transporter, and dysfunction leads to a deficit in the cellular intake of inorganic phosphate (Pi) and calcium deposits. Whether the impaired Golgi apparatus is involved in the PFBC procession requires elucidation. In this study, we constructed induced pluripotent stem cells (iPSCs) derived from two PFBC patients with different SLC20A2 gene mutations (c.613G > A or del exon10) and two healthy volunteers as dependable cell models for research on pathogenic mechanism. To study the mechanism, we differentiated iPSCs into neurons and astrocytes in vitro. Our study found disruptive Golgi structure and damaged autophagy in PFBC neurons with increased activity of mTOR. We also found damaged mitochondria and increased apoptosis in the PFBC dopaminergic neurons and astrocytes. In this study, we prove that dysfunctional PiT-2 leads to an imbalance of cellular Pi, which may disrupt the Golgi apparatus with impaired autophagy, mitochondria and apoptosis in PFBC. Our study provides a new avenue for understanding nerve damage and pathogenic mechanism in brain calcifications.

Activation of autophagy triggers mitochondrial loss and changes acetylation profile relevant for mechanotransduction in bladder cancer cells

Bladder cells are constantly exposed to multiple xenobiotics and bioactive metabolites. In addition to this challenging chemical environment, they are also exposed to shear stress originating from urine and interstitial fluids. Hence, physiological function of bladder cells relies on a high biochemical and biomechanical adaptive competence, which, in turn, is largely supported via autophagy-related mechanisms. As a negative side of this plasticity, bladder cancer cells are known to adapt readily to chemotherapeutic programs. At the molecular level, autophagy was described to support resistance against pharmacological treatments and to contribute to the maintenance of cell structure and metabolic competence. In this study, we enhanced autophagy with rapamycin (1-100 nM) and assessed its effects on the motility of bladder cells, as well as the capability to respond to shear stress. We observed that rapamycin reduced cell migration and the mechanical-induced translocation potential of Krüppel-like transcription factor 2 (KLF2). These effects were accompanied by a rearrangement of cytoskeletal elements and mitochondrial loss. In parallel, intracellular acetylation levels were decreased. Mechanistically, inhibition of the NAD + -dependent deacetylase sirtuin-1 (SIRT1) with nicotinamide (NAM; 0.1-5 mM) restored acetylation levels hampered by rapamycin and cell motility. Taken together, we described the effects of rapamycin on cytoskeletal elements crucial for mechanotransduction and the dependency of these changes on the mitochondrial turnover caused by autophagy activation. Additionally, we could show that targeted metabolic intervention could revert the outcome of autophagy activation, reinforcing the idea that bladder cells can easily adapt to multiple xenobiotics and circumvent in this way the effects of single chemicals.

The Adhesion GPCR VLGR1/ADGRV1 Regulates the Ca2+ Homeostasis at Mitochondria-Associated ER Membranes

The very large G protein-coupled receptor (VLGR1, ADGRV1) is the largest member of the adhesion GPCR family. Mutations in VLGR1 have been associated with the human Usher syndrome (USH), the most common form of inherited deaf-blindness as well as childhood absence epilepsy. VLGR1 was previously found as membrane–membrane adhesion complexes and focal adhesions. Affinity proteomics revealed that in the interactome of VLGR1, molecules are enriched that are associated with both the ER and mitochondria, as well as mitochondria-associated ER membranes (MAMs), a compartment at the contact sites of both organelles. We confirmed the interaction of VLGR1 with key proteins of MAMs by pull-down assays in vitro complemented by in situ proximity ligation assays in cells. Immunocytochemistry by light and electron microscopy demonstrated the localization of VLGR1 in MAMs. The absence of VLGR1 in tissues and cells derived from VLGR1-deficient mouse models resulted in alterations in the MAM architecture and in the dysregulation of the Ca²⁺ transient from ER to mitochondria. Our data demonstrate the molecular and functional interaction of VLGR1 with components in MAMs and point to an essential role of VLGR1 in the regulation of Ca²⁺ homeostasis, one of the key functions of MAMs.

Cannabidiol Enhances Microglial Beta-Amyloid Peptide Phagocytosis and Clearance via Vanilloid Family Type 2 Channel Activation

Alzheimer’s disease (AD) is associated with the accumulation and aggregation of amyloid in the brain. The cation channel TRPV2 may mediate the pathological changes in mild cognitive impairment. A high-affinity agonist of TRPV2 named cannabidiol is one of the candidate drugs for AD. However, the molecular mechanism of cannabidiol via TRPV2 in AD remains unknown. The present study investigated whether cannabidiol enhances the phagocytosis and clearance of microglial Aβ via the TRPV2 channel. We used a human dataset, mouse primary neuron and microglia cultures, and AD model mice to evaluate TRPV2 expression and the ability of microglial amyloid-β phagocytosis in vivo and in vitro. The results revealed that TRPV2 expression was reduced in the cortex and hippocampus of AD model mice and AD patients. Cannabidiol enhanced microglial amyloid-β phagocytosis through TRPV2 activation, which increased the mRNA expression of the phagocytosis-related receptors, but knockdown of TRPV2 or Trem2 rescued the expression. TRPV2-mediated effects were also dependent on PDK1/Akt signaling, a pathway in which autophagy was indispensable. Furthermore, cannabidiol treatment successfully attenuated neuroinflammation while simultaneously improving mitochondrial function and ATP production via TRPV2 activation. Therefore, TRPV2 is proposed as a potential therapeutic target in AD, while CBD is a promising drug candidate for AD.