Endoplasmic reticulum-mitochondria coupling increases during doxycycline-induced mitochondrial stress in HeLa cells

Enhancing healthy aging with small molecules: A mitochondrial perspective

The pursuit of enhanced health during aging has prompted the exploration of various strategies focused on reducing the decline associated with the aging process. A key area of this exploration is the management of mitochondrial dysfunction, a notable characteristic of aging. This review sheds light on the crucial role that small molecules play in augmenting healthy aging, particularly through influencing mitochondrial functions. Mitochondrial oxidative damage, a significant aspect of aging, can potentially be lessened through interventions such as coenzyme Q10, alpha-lipoic acid, and a variety of antioxidants. Additionally, this review discusses approaches for enhancing mitochondrial proteostasis, emphasizing the importance of mitochondrial unfolded protein response inducers like doxycycline, and agents that affect mitophagy, such as urolithin A, spermidine, trehalose, and taurine, which are vital for sustaining protein quality control. Of equal importance are methods for modulating mitochondrial energy production, which involve nicotinamide adenine dinucleotide boosters, adenosine 5'-monophosphate-activated protein kinase activators, and compounds like metformin and mitochondria-targeted tamoxifen that enhance metabolic function. Furthermore, the review delves into emerging strategies that encourage mitochondrial biogenesis. Together, these interventions present a promising avenue for addressing age-related mitochondrial degradation, thereby setting the stage for the development of innovative treatment approaches to meet this extensive challenge.

Cypermethrin induces Sertoli cell apoptosis through endoplasmic reticulum-mitochondrial coupling involving IP3R1-GRP75-VDAC1

A widely used type II pyrethroid pesticide cypermethrin (CYP) is one of endocrine disrupting chemicals (EDCs) with anti-androgenic activity to induce male reproductive toxicology. However, the mechanisms have not been fully elucidated. This study was to explore the effects of CYP on apoptosis of mouse Sertoli cells (TM4) and the roles of endoplasmic reticulum (ER)-mitochondria coupling involving 1,4,5-trisphosphate receptor type1-glucose-regulated protein 75-voltage-dependent anion channel 1 (IP3R1-GRP75-VDAC1). TM4 were cultured with different concentrations of CYP. Flow cytometry, calcium (Ca2+) fluorescent probe, transmission electron microscopy and confocal microscopy, and western blot were to examine apoptosis of TM4, mitochondrial Ca2+, ER-mitochondria coupling, and expressions of related proteins. CYP was found to increase apoptotic rates of TM4 significantly. CYP was shown to significantly increase expressions of cleaved caspase-3, cleaved poly ADP-ribose polymerase (PARP). Concentration of mitochondrial Ca2+ was increased by CYP treatment significantly. CYP significantly enhanced ER-mitochondria coupling. CYP was shown to increase expressions of IP3R, Grp75 and VDAC1 significantly. We suggest that CYP induces apoptosis in TM4 cells by facilitating mitochondrial Ca2+ overload regulated by ER-mitochondria coupling involving IP3R1-GRP75-VDAC1. This study identifies a novel mechanism of CYP-induced apoptosis in Sertoli cells.

Cristae shaping and dynamics in mitochondrial function

Mitochondria are multifunctional organelles of key importance for cell homeostasis. The outer mitochondrial membrane (OMM) envelops the organelle, and the inner mitochondrial membrane (IMM) is folded into invaginations called cristae. As cristae composition and functions depend on the cell type and stress conditions, they recently started to be considered as a dynamic compartment. A number of proteins are known to play a role in cristae architecture, such as OPA1, MIC60, LETM1, the prohibitin (PHB) complex and the F1FO ATP synthase. Furthermore, phospholipids are involved in the maintenance of cristae ultrastructure and dynamics. The use of new technologies, including super-resolution microscopy to visualize cristae dynamics with superior spatiotemporal resolution, as well as high-content techniques and datasets have not only allowed the identification of new cristae proteins but also helped to explore cristae plasticity. However, a number of open questions remain in the field, such as whether cristae-resident proteins are capable of changing localization within mitochondria, or whether mitochondrial proteins can exit mitochondria through export. In this Review, we present the current view on cristae morphology, stability and composition, and address important outstanding issues that might pave the way to future discoveries.

Mitoribosomal synthetic lethality overcomes multidrug resistance in MYC-driven neuroblastoma

Mitochondria are central for cancer responses to therapy-induced stress signals. Refractory tumors often show attenuated sensitivity to apoptotic signaling, yet clinically relevant molecular actors to target mitochondria-mediated resistance remain elusive. Here, we show that MYC-driven neuroblastoma cells rely on intact mitochondrial ribosome (mitoribosome) processivity and undergo cell death following pharmacological inhibition of mitochondrial translation, regardless of their multidrug/mitochondrial resistance and stem-like phenotypes. Mechanistically, inhibiting mitoribosomes induced the mitochondrial stress-activated integrated stress response (ISR), leading to downregulation of c-MYC/N-MYC proteins prior to neuroblastoma cell death, which could be both rescued by the ISR inhibitor ISRIB. The ISR blocks global protein synthesis and shifted the c-MYC/N-MYC turnover toward proteasomal degradation. Comparing models of various neuroectodermal tumors and normal fibroblasts revealed overexpression of MYC proteins phosphorylated at the degradation-promoting site T58 as a factor that predetermines vulnerability of MYC-driven neuroblastoma to mitoribosome inhibition. Reducing N-MYC levels in a neuroblastoma model with tunable MYCN expression mitigated cell death induction upon inhibition of mitochondrial translation and functionally validated the propensity of neuroblastoma cells for MYC-dependent cell death in response to the mitochondrial ISR. Notably, neuroblastoma cells failed to develop significant resistance to the mitoribosomal inhibitor doxycycline over a long-term repeated (pulsed) selection. Collectively, we identify mitochondrial translation machinery as a novel synthetic lethality target for multidrug-resistant MYC-driven tumors.

Role of Mitochondria-ER Contact Sites in Mitophagy

Mitochondria are often referred to as the "powerhouse" of the cell. However, this organelle has many more functions than simply satisfying the cells' metabolic needs. Mitochondria are involved in calcium homeostasis and lipid metabolism, and they also regulate apoptotic processes. Many of these functions require contact with the ER, which is mediated by several tether proteins located on the respective organellar surfaces, enabling the formation of mitochondria-ER contact sites (MERCS). Upon damage, mitochondria produce reactive oxygen species (ROS) that can harm the surrounding cell. To circumvent toxicity and to maintain a functional pool of healthy organelles, damaged and excess mitochondria can be targeted for degradation via mitophagy, a form of selective autophagy. Defects in mitochondria-ER tethers and the accumulation of damaged mitochondria are found in several neurodegenerative diseases, including Parkinson's disease and amyotrophic lateral sclerosis, which argues that the interplay between the two organelles is vital for neuronal health. This review provides an overview of the different mechanisms of mitochondrial quality control that are implicated with the different mitochondria-ER tether proteins, and also provides a novel perspective on how MERCS are involved in mediating mitophagy upon mitochondrial damage.

Methods for assessing change in brain plasticity at night and psychological resilience during daytime between repeated long-duration space missions

This study was designed to examine the feasibility of analyzing heart rate variability (HRV) data from repeat-flier astronauts at matching days on two separate missions to assess any effect of repeated missions on brain plasticity and psychological resilience, as conjectured by Demertzi. As an example, on the second mission of a healthy astronaut studied about 20 days after launch, sleep duration lengthened, sleep quality improved, and spectral power (ms²) co-varying with activity of the salience network (SN) increased at night. HF-component (0.15-0.50 Hz) increased by 61.55%, and HF-band (0.30-0.40 Hz) by 92.60%. Spectral power of HRV indices during daytime, which correlate negatively with psychological resilience, decreased, HF-component by 22.18% and HF-band by 37.26%. LF-component and LF-band, reflecting activity of the default mode network, did not change significantly. During the second mission, 24-h acrophases of HRV endpoints did not change but the 12-h acrophase of TF-HRV did (P < 0.0001), perhaps consolidating the circadian system to help adapt to space by taking advantage of brain plasticity at night and psychological resilience during daytime. While this N-of-1 study prevents drawing definitive conclusions, the methodology used herein to monitor markers of brain plasticity could pave the way for further studies that could add to the present results.

The key role of proteostasis at mitochondria-associated endoplasmic reticulum membrane in vanadium-induced nephrotoxicity using a proteomic strategy

Excessive vanadium (V) contamination is an attracting growing concern, which can negatively affect the health of human and ecosystems. But how V causes nephrotoxicity and the role of mitochondria-associated endoplasmic reticulum membrane (MAM) in V-induced nephrotoxicity have remained elusive. To explore the detailed mechanism and screen of potential effective drugs for V-evoked nephrotoxicity, a total of 72 ducks were divided into two groups, control group and V group (30 mg/kg V). Results showed that excessive V damaged kidney function of ducks including causing histopathological abnormality, biochemical makers derangement and oxidative stress. Then MAM of duck kidneys was extracted to investigate differentially expressed proteins (DEPs) under V exposure using proteomics analysis. Around 4240 MAM-localized proteins were identified, of which 412 DEPs showed dramatic changes, including 335 upregulated and 77 downregulated DEPs. On the basis of gene ontology (GO), string and KEGG database analysis, excessive V led to nephrotoxicity primarily by affecting MAM-mediated metabolic pathways, especially elevating the endoplasmic Reticulum (ER) proteostasis related pathway. Further validation analysis of the detected genes and proteins of ER proteostasis related pathway under V poisoning revealed a consistent relationship with proteome analysis, indicating that V disrupted MAM-mediated ER proteostasis. Accordingly, our data proved the critical role for MAM in V-evoked nephrotoxicity, particularly with MAM-mediated ER proteostasis, providing promising insights into the toxicological exploration mechanisms of V.

A tale of two pathways: Regulation of proteostasis by UPRmt and MDPs

Mitochondrial fitness is critical to organismal health and its impairment is associated with aging and age-related diseases. As such, numerous quality control mechanisms exist to preserve mitochondrial stability, including the unfolded protein response of the mitochondria (UPRmt). The UPRmt is a conserved mechanism that drives the transcriptional activation of mitochondrial chaperones, proteases, autophagy (mitophagy), and metabolism to promote restoration of mitochondrial function under stress conditions. UPRmt has direct ramifications in aging, and its activation is often ascribed to improve health whereas its dysfunction tends to correlate with disease. This review pairs a description of the most recent findings within the field of UPRmt with a more poorly understood field: mitochondria-derived peptides (MDPs). Similar to UPRmt, MDPs are microproteins derived from the mitochondria that can impact organismal health and longevity. We then highlight a tantalizing interconnection between UPRmt and MDPs wherein both mechanisms may be efficiently coordinated to maintain organismal health.

IP3R at ER-Mitochondrial Contact Sites: Beyond the IP3R-GRP75-VDAC1 Ca2+ Funnel

Membrane contact sites (MCS) circumvent the topological constraints of functional coupling between different membrane-bound organelles by providing a means of communication and exchange of materials. One of the most characterised contact sites in the cell is that between the endoplasmic reticulum and the mitochondrial (ERMCS) whose function is to couple cellular Ca2+ homeostasis and mitochondrial function. Inositol 1,4,5-trisphosphate receptors (IP3Rs) on the ER, glucose-regulated protein 75 (GRP 75) and voltage-dependent anion channel 1 (VDAC1) on the outer mitochondrial membrane are the canonical component of the Ca2+ transfer unit at ERMCS. These are often reported to form a Ca2+ funnel that fuels the mitochondrial low-affinity Ca2+ uptake system. We assess the available evidence on the IP3R subtype selectivity at the ERMCS and consider if IP3Rs have other roles at the ERMCS beyond providing Ca2+. Growing evidence suggests that all three IP3R subtypes can localise and regulate Ca2+ signalling at ERMCS. Furthermore, IP3Rs may be structurally important for assembly of the ERMCS in addition to their role in providing Ca2+ at these sites. Evidence that various binding partners regulate the assembly and Ca2+ transfer at ERMCS populated by IP3R-GRP75-VDAC1, suggesting that cells have evolved mechanisms that stabilise these junctions forming a Ca2+ microdomain that is required to fuel mitochondrial Ca2+ uptake.

Mitochondrial unfolded protein response in ischemia-reperfusion injury

Mitochondrial unfolded protein response (UPRmt) is a mitochondrial stress response that activates the transcriptional program of mitochondrial chaperone proteins and proteases to keep protein homeostasis in mitochondria. Ischemia-reperfusion injury results in multiple severe clinical issues linked to high morbidity and mortality in various disorders. The pathophysiology and pathogenesis of ischemia-reperfusion injury are complex and multifactorial. Emerging evidence showed the roles of UPRmt signaling in ischemia-reperfusion injury. Herein, we discuss the regulatory mechanisms underlying UPRmt signaling in C. elegans and mammals. Furthermore, we review the recent studies into the roles and mechanisms of UPRmt signaling in ischemia-reperfusion injury of the heart, brain, kidney, and liver. Further research of UPRmt signaling will potentially develop novel therapeutic strategies against ischemia-reperfusion injury.

The aging of ER-mitochondria communication: A journey from undifferentiated to aged cells

The complex physiology of eukaryotic cells requires that a variety of subcellular organelles perform unique tasks, even though they form highly dynamic communication networks. In the case of the endoplasmic reticulum (ER) and mitochondria, their functional coupling relies on the physical interaction between their membranes, mediated by domains known as mitochondria-ER contacts (MERCs). MERCs act as shuttles for calcium and lipid transfer between organelles, and for the nucleation of other subcellular processes. Of note, mounting evidence shows that they are heterogeneous structures, which display divergent behaviors depending on the cell type. Furthermore, MERCs are plastic structures that remodel according to intra- and extracellular cues, thereby adjusting the function of both organelles to the cellular needs. In consonance with this notion, the malfunction of MERCs reportedly contributes to the development of several age-related disorders. Here, we integrate current literature to describe how MERCs change, starting from undifferentiated cells, and their transit through specialization, malignant transformation (i.e., dedifferentiation), and aging/senescence. Along this journey, we will review the function of MERCs and their relevance for pivotal cell types, such as stem and cancer cells, cardiac, skeletal, and smooth myocytes, neurons, leukocytes, and hepatocytes, which intervene in the progression of chronic diseases related to age.

Stable Integration of Inducible SPLICS Reporters Enables Spatio-Temporal Analysis of Multiple Organelle Contact Sites upon Modulation of Cholesterol Traffic

The study of organelle contact sites has received a great impulse due to increased interest in the understanding of their involvement in many disease conditions. Split-GFP-based contact sites (SPLICS) reporters emerged as essential tools to easily detect changes in a wide range of organelle contact sites in cultured cells and in vivo, e.g., in zebrafish larvae. We report here on the generation of a new vector library of SPLICS cloned into a piggyBac system for stable and inducible expression of the reporters in a cell line of interest to overcome any potential weakness due to variable protein expression in transient transfection studies. Stable HeLa cell lines expressing SPLICS between the endoplasmic reticulum (ER) and mitochondria (MT), the ER and plasma membrane (PM), peroxisomes (PO) and ER, and PO and MT, were generated and tested for their ability to express the reporters upon treatment with doxycycline. Moreover, to take advantage of these cellular models, we decided to follow the behavior of different membrane contact sites upon modulating cholesterol traffic. Interestingly, we found that the acute pharmacological inhibition of the intracellular cholesterol transporter 1 (NPC1) differently affects membrane contact sites, highlighting the importance of different interfaces for cholesterol sensing and distribution within the cell.

Hijacking Cellular Stress Responses to Promote Lifespan

Organisms are constantly exposed to stress both from the external environment and internally within the cell. To maintain cellular homeostasis under different environmental and physiological conditions, cell have adapted various stress response signaling pathways, such as the heat shock response (HSR), unfolded protein responses of the mitochondria (UPR^MT), and the unfolded protein response of the endoplasmic reticulum (UPR^ER). As cells grow older, all cellular stress responses have been shown to deteriorate, which is a major cause for the physiological consequences of aging and the development of numerous age-associated diseases. In contrast, elevated stress responses are often associated with lifespan extension and amelioration of degenerative diseases in different model organisms, including C. elegans. Activating cellular stress response pathways could be considered as an effective intervention to alleviate the burden of aging by restoring function of essential damage-clearing machinery, including the ubiquitin-proteosome system, chaperones, and autophagy. Here, we provide an overview of newly emerging concepts of these stress response pathways in healthy aging and longevity with a focus on the model organism, C. elegans.

TRAP1 in Oxidative Stress and Neurodegeneration

Tumor necrosis factor receptor-associated protein 1 (TRAP1), also known as heat shock protein 75 (HSP75), is a member of the heat shock protein 90 (HSP90) chaperone family that resides mainly in the mitochondria. As a mitochondrial molecular chaperone, TRAP1 supports protein folding and contributes to the maintenance of mitochondrial integrity even under cellular stress. TRAP1 is a cellular regulator of mitochondrial bioenergetics, redox homeostasis, oxidative stress-induced cell death, apoptosis, and unfolded protein response (UPR) in the endoplasmic reticulum (ER). TRAP1 has attracted increasing interest as a therapeutical target, with a special focus on the design of TRAP1 specific inhibitors. Although TRAP1 was extensively studied in the oncology field, its role in central nervous system cells, under physiological and pathological conditions, remains largely unknown. In this review, we will start by summarizing the biology of TRAP1, including its structure and related pathways. Thereafter, we will continue by debating the role of TRAP1 in the maintenance of redox homeostasis and protection against oxidative stress and apoptosis. The role of TRAP1 in neurodegenerative disorders will also be discussed. Finally, we will review the potential of TRAP1 inhibitors as neuroprotective drugs.

Quantification of organelle contact sites by split-GFP-based contact site sensors (SPLICS) in living cells

Membrane contact sites between organelles are essential for maintaining cellular homeostasis, which requires the continuous exchange of signaling molecules, ions, nutrients and lipids. Alterations of different contact sites are associated with a wide spectrum of human diseases. However, visualizing and quantifying these contact sites remains a challenge. This protocol describes the use of split-GFP-based contact site sensors (SPLICS) in microscopy applications for mapping organelle contact sites both in fixed and living cells. SPLICS sensors are engineered to express equimolar amounts of the organelle-targeted nonfluorescent β11 and GFP1-10 portions of the split-GFP protein in a single vector, and are capable of reconstituting fluorescence when two opposing membranes come into proximity. Reconstitution will occur only over the cell volume at defined contact sites resulting in a bright signal that can be detected easily and quantified automatically with specific custom-made plugins. The use of minimal targeting sequences facilitates targeting specificity and membrane coverage, avoiding artifacts due to full-length fusion protein overexpression and, thus, possible perturbations of the cell's physiology. SPLICS sensors engineered to simultaneously detect multiple contact sites within the same cell have been generated by exploiting the ability of the β11 GFP fragment to reconstitute different color-shifted variants of the GFP1-10 fragment. Here, we describe a detailed protocol to set up SPLICS expression in living cells (2-3 d), detection and acquisition (1 d), and automated quantification with custom plugins (1-2 d). We also advise on construct design and characterization for novel organelle contacts.