CRIF1 is essential for the synthesis and insertion of oxidative phosphorylation polypeptides in the mammalian mitochondrial membrane

Mitochondrial Regulator CRIF1 Plays a Critical Role in the Development and Homeostasis of Alveolar Macrophages via Maintaining Metabolic Fitness

The importance of mitochondrial function in macrophages is well established. Alveolar macrophages (AMs), the tissue-resident macrophages (TRMs) of the lung, are particularly dependent on mitochondria-driven oxidative phosphorylation (OXPHOS) to support their functions and maintain homeostasis. However, the specific genes and pathways that regulate OXPHOS in AMs remain unclear. In this study, we investigated the role of CR6-interacting factor 1 (CRIF1), a mitochondrial regulator, as a key factor that specifically modulates the metabolic fitness and maintenance of AMs. Using single-cell RNA sequencing and transcriptomic analyses, we found CRIF1 to be highly expressed in AMs compared to TRMs from other tissues, correlating with enhanced OXPHOS activity. Genetic ablation of Crif1 in macrophages resulted in a marked reduction in AM populations exclusively in the lung, while other TRM populations were unaffected. CRIF1-deficient AMs exhibited an altered metabolic profile, including impaired mitochondrial function, increased glycolysis, and aberrant lipid accumulation. These findings underscore the essential role of CRIF1 in regulating mitochondrial functions and metabolic fitness in AMs, distinguishing it from broader mitochondrial regulators like mitochondrial transcription factor A, which operates across multiple TRM populations. Our study provides critical insights into the tissue-specific regulation of macrophage metabolism and suggests potential therapeutic avenues for lung diseases associated with AM dysfunction.

Unique architectural features of mammalian mitochondrial protein synthesis

Mitochondria rely on coordinated expression of their own mitochondrial DNA (mtDNA) with that of the nuclear genome for their biogenesis. The bacterial ancestry of mitochondria has given rise to unique and idiosyncratic features of the mtDNA and its expression machinery that can be specific to different organisms. In animals, the mitochondrial protein synthesis machinery has acquired many new components and mechanisms over evolution. These include several new ribosomal proteins, new stop codons and ways to recognise them, and new mechanisms to deliver nascent proteins into the mitochondrial inner membrane. Here we describe the mitochondrial protein synthesis machinery in mammals and its unique mechanisms of action elucidated to date and highlight the technologies poised to reveal the next generation of discoveries in mitochondrial translation.

The Downregulation of CRIF1 Exerts Antitumor Effects Partially via TP53-Induced Glycolysis and Apoptosis Regulator Induction in BT549 Breast Cancer Cells

BACKGROUND/OBJECTIVES

Mitochondrial oxidative phosphorylation (OXPHOS) has been exploited as a therapeutic target in cancer treatments because of its crucial role in tumorigenesis. CR6-interacting factor 1 (CRIF1), a mitochondrial ribosomal subunit protein, is essential for the regulation of mitochondrial OXPHOS capacity. However, the mechanism of CRIF1 in triple-negative breast cancer (TNBC) cells remains unclear.

METHODS/RESULTS

We showed that the downregulation of CRIF1 reduced cell proliferation in the TNBC cell lines MDA-MB-468, MDA-MB-231, and, especially, BT549. In addition, wound scratch and Transwell assays showed that CRIF1 deficiency inhibited the migration and invasion of BT549 cells. CRIF1 downregulation resulted in the suppression of mitochondrial bioenergetics in BT549 cells, specifically affecting the inhibition of OXPHOS complexes I and II. This was evidenced by a decrease in the mitochondrial oxygen consumption rate and the depolarization of the mitochondrial membrane potential. Damage to mitochondria resulted in a lower adenosine triphosphate level and an elevated production of mitochondrial reactive oxygen species. In addition, CRIF1 deficiency decreased hypoxia-inducible factor 1α accumulation, NADPH synthesis, and TP53-induced glycolysis and apoptosis regulator (TIGAR) expression in BT549 cells. These events contributed to G0/G1-phase cell cycle inhibition and the upregulation of the cell cycle protein markers p53, p21, and p16. Transfection with a TIGAR overexpression plasmid reversed these effects and prevented CRIF1 downregulation-induced proliferation and migration reduction.

CONCLUSIONS

These results indicate that blocking mitochondrial OXPHOS synthesis via CRIF1 may have a therapeutic antitumor effect in BT549 TNBC cells.

Unraveling the roles and mechanisms of mitochondrial translation in normal and malignant hematopoiesis

Due to spatial and genomic independence, mitochondria possess a translational mechanism distinct from that of cytoplasmic translation. Several regulators participate in the modulation of mitochondrial translation. Mitochondrial translation is coordinated with cytoplasmic translation through stress responses. Importantly, the inhibition of mitochondrial translation leads to the inhibition of cytoplasmic translation and metabolic disruption. Therefore, defects in mitochondrial translation are closely related to the functions of hematopoietic cells and various immune cells. Finally, the inhibition of mitochondrial translation is a potential therapeutic target for treating multiple hematologic malignancies. Collectively, more in-depth insights into mitochondrial translation not only facilitate our understanding of its functions in hematopoiesis, but also provide a basis for the discovery of new treatments for hematological malignancies and the modulation of immune cell function.

Brown fat-specific mitoribosomal function is crucial for preventing cold exposure-induced bone loss

This study examines the interplay between ambient temperature, brown adipose tissue (BAT) function, and bone metabolism, emphasizing the effects of cold exposure and BAT mitochondrial activity on bone health. Utilizing ovariectomized (OVX) mice to model primary osteoporosis and BAT-specific mitochondrial dysfunction (BKO) mice, we evaluated the impact of housing temperature on bone density, immune modulation in bone marrow, and the protective role of BAT against bone loss. Cold exposure was found to universally reduce bone mass, enhance osteoclastogenesis, and alter bone marrow T-cell populations, implicating the immune system in bone remodeling under cold stress. The thermogenic function of BAT, driven by mitochondrial oxidative phosphorylation, was crucial in protecting against bone loss. Impaired BAT function, through surgical removal or mitochondrial dysfunction, exacerbated bone loss in cold environments, highlighting BAT's metabolic role in maintaining bone health. Furthermore, cold-induced changes in BAT function led to systemic metabolic shifts, including elevated long-chain fatty acids, which influenced osteoclast differentiation and activity. These findings suggest a systemic mechanism connecting environmental temperature and BAT metabolism with bone physiology, providing new insights into the metabolic and environmental determinants of bone health. Future research could lead to novel bone disease therapies targeting these pathways.

Inhibition of Crif1 protects fatty acid-induced POMC neuron-like cell-line damage by increasing CPT-1 function

Hypothalamic proopiomelanocortin (POMC) neurons are sensors of signals that reflect the energy stored in the body. Inducing mild stress in proopiomelanocortin neurons protects them from the damage promoted by the consumption of a high-fat diet, mitigating the development of obesity; however, the cellular mechanisms behind these effects are unknown. Here, we induced mild stress in a proopiomelanocortin neuron cell line by inhibiting Crif1. In proopiomelanocortin neurons exposed to high levels of palmitate, the partial inhibition of Crif1 reverted the defects in mitochondrial respiration and ATP production; this was accompanied by improved mitochondrial fusion/fission cycling. Furthermore, the partial inhibition of Crif1 resulted in increased reactive oxygen species production, increased fatty acid oxidation, and reduced dependency on glucose for mitochondrial respiration. These changes were dependent on the activity of CPT-1. Thus, we identified a CPT-1-dependent metabolic shift toward greater utilization of fatty acids as substrates for respiration as the mechanism behind the protective effect of mild stress against palmitate-induced damage of proopiomelanocortin neurons.NEW & NOTEWORTHY Saturated fats can damage hypothalamic neurons resulting in positive energy balance, and this is mitigated by mild cellular stress; however, the mechanisms behind this protective effect are unknown. Using a proopiomelanocortin cell line, we show that under exposure to a high concentration of palmitate, the partial inhibition of the mitochondrial protein Crif1 results in protection due to a metabolic shift warranted by the increased expression and activity of the mitochondrial fatty acid transporter CPT-1.

CRIF1 deficiency induces FOXP3LOW inflammatory non-suppressive regulatory T cells, thereby promoting antitumor immunity

Recently identified human FOXP3lowCD45RA- inflammatory non-suppressive (INS) cells produce proinflammatory cytokines, exhibit reduced suppressiveness, and promote antitumor immunity unlike conventional regulatory T cells (Tregs). In spite of their implication in tumors, the mechanism for generation of FOXP3lowCD45RA- INS cells in vivo is unclear. We showed that the FOXP3lowCD45RA- cells in human tumors demonstrate attenuated expression of CRIF1, a vital mitochondrial regulator. Mice with CRIF1 deficiency in Tregs bore Foxp3lowINS-Tregs with mitochondrial dysfunction and metabolic reprograming. The enhanced glutaminolysis activated α-ketoglutarate-mTORC1 axis, which promoted proinflammatory cytokine expression by inducing EOMES and SATB1 expression. Moreover, chromatin openness of the regulatory regions of the Ifng and Il4 genes was increased, which facilitated EOMES/SATB1 binding. The increased α-ketoglutarate-derived 2-hydroxyglutarate down-regulated Foxp3 expression by methylating the Foxp3 gene regulatory regions. Furthermore, CRIF1 deficiency-induced Foxp3lowINS-Tregs suppressed tumor growth in an IFN-γ-dependent manner. Thus, CRIF1 deficiency-mediated mitochondrial dysfunction results in the induction of Foxp3lowINS-Tregs including FOXP3lowCD45RA- cells that promote antitumor immunity.

Mitochondrial bioenergetics, metabolism, and beyond in pancreatic β-cells and diabetes

In Type 1 and Type 2 diabetes, pancreatic β-cell survival and function are impaired. Additional etiologies of diabetes include dysfunction in insulin-sensing hepatic, muscle, and adipose tissues as well as immune cells. An important determinant of metabolic health across these various tissues is mitochondria function and structure. This review focuses on the role of mitochondria in diabetes pathogenesis, with a specific emphasis on pancreatic β-cells. These dynamic organelles are obligate for β-cell survival, function, replication, insulin production, and control over insulin release. Therefore, it is not surprising that mitochondria are severely defective in diabetic contexts. Mitochondrial dysfunction poses challenges to assess in cause-effect studies, prompting us to assemble and deliberate the evidence for mitochondria dysfunction as a cause or consequence of diabetes. Understanding the precise molecular mechanisms underlying mitochondrial dysfunction in diabetes and identifying therapeutic strategies to restore mitochondrial homeostasis and enhance β-cell function are active and expanding areas of research. In summary, this review examines the multidimensional role of mitochondria in diabetes, focusing on pancreatic β-cells and highlighting the significance of mitochondrial metabolism, bioenergetics, calcium, dynamics, and mitophagy in the pathophysiology of diabetes. We describe the effects of diabetes-related gluco/lipotoxic, oxidative and inflammation stress on β-cell mitochondria, as well as the role played by mitochondria on the pathologic outcomes of these stress paradigms. By examining these aspects, we provide updated insights and highlight areas where further research is required for a deeper molecular understanding of the role of mitochondria in β-cells and diabetes.

The role of the mitochondrial ribosomal protein family in detecting hepatocellular carcinoma and predicting prognosis, immune features, and drug sensitivity

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most common types of malignant tumors, with a slow onset, rapid progression, and frequent recurrence. Previous research has implicated mitochondrial ribosomal genes in the development, metastasis, and prognosis of various cancers. However, further research is necessary to establish a link between mitochondrial ribosomal protein (MRP) family expression and HCC diagnosis, prognosis, ferroptosis-related gene (FRG) expression, m6A modification-related gene expression, tumor immunity, and drug sensitivity.

METHODS

Bioinformatics resources were used to analyze data from patients with HCC retrieved from the TCGA, ICGC, and GTEx databases (GEPIA, UALCAN, Xiantao tool, cBioPortal, STRING, Cytoscape, TISIDB, and GSCALite).

RESULTS

Among the 82 MRP family members, 14 MRP genes (MRPS21, MRPS23, MRPL9, DAP3, MRPL13, MRPL17, MRPL24, MRPL55, MRPL16, MRPL14, MRPS17, MRPL47, MRPL21, and MRPL15) were significantly upregulated differentially expressed genes (DEGs) in HCC tumor samples in comparison to normal samples. Receiver-operating characteristic curve analysis indicated that all 14 DEGs show good diagnostic performance. Furthermore, TCGA analysis revealed that the mRNA expression of 39 MRPs was associated with overall survival (OS) in HCC. HCC was divided into two molecular subtypes (C1 and C2) with distinct prognoses using clustering analysis. The clusters showed different FRG expression and m6A methylation profiles and immune features, and prognostic models showed that the model integrating 5 MRP genes (MRPS15, MRPL3, MRPL9, MRPL36, and MRPL37) and 2 FRGs (SLC1A5 and SLC5A11) attained a greater clinical net benefit than three other prognostic models. Finally, analysis of the CTRP and GDSC databases revealed several potential drugs that could target prognostic MRP genes.

CONCLUSION

We identified 14 MRP genes as HCC diagnostic markers. We investigated FRG and m6A modification-related gene expression profiles and immune features in patients with HCC, and developed and validated a model incorporating MRP and FRG expression that accurately and reliably predicts HCC prognosis and may predict disease progression and treatment response.

Cardiovascular aging: spotlight on mitochondria

Mitochondria are cellular organelles critical for ATP production and are particularly relevant to cardiovascular diseases including heart failure, atherosclerosis, ischemia-reperfusion injury, and cardiomyopathies. With advancing age, even in the absence of clinical disease, mitochondrial homeostasis becomes disrupted (e.g., redox balance, mitochondrial DNA damage, oxidative metabolism, and mitochondrial quality control). Mitochondrial dysregulation leads to the accumulation of damaged and dysfunctional mitochondria, producing excessive reactive oxygen species and perpetuating mitochondrial dysfunction. In addition, mitochondrial DNA, cardiolipin, and N-formyl peptides are potent activators of cell-intrinsic and -extrinsic inflammatory pathways. These age-related mitochondrial changes contribute to the development of cardiovascular diseases. This review covers the impact of aging on mitochondria and links these mechanisms to therapeutic implications for age-associated cardiovascular diseases.

CR6-Interacting Factor-1 Promotes Osteoclastogenesis Through the NF-κB Signaling Pathway after Irradiation

Radiation exposure arising from radiotherapy may induce rapid bone loss and an increase in the extent of bone resorption. Reactive oxygen species (ROS) caused by radiation exposure play a crucial role during the process of osteoclastogenesis. However, the pathological mechanisms underlying radiation-induced osteoclastogenesis have yet to be fully elucidated. CR6-interacting factor-1 (Crif1) as a multifunctional protein is involved in regulating multiple biological functions in cells. Here, we investigated the role of Crif1 in radiation-induced osteoclastogenesis and found that radiation exposure induced an increase in the expression level of Crif1 and enhanced osteoclastogenesis in osteoclast progenitors. Crif1 and NF-κB p65 co-localized in the cytoplasm after radiation exposure. Crif1 knockdown did not affect the phosphorylation and total protein levels of extracellular signal-regulated kinases (ERK), c-Jun amino (N)-terminal kinases (JNK), p38, and IκB-α before and after irradiation. However, Crif1 knockdown did lead to the reduced phosphorylation and nuclear translocation of NF-κB p65 after irradiation and resulted in a reduced level of osteoclastogenesis in RAW264.7 cells after irradiation. In vivo studies involving Lyz2Cre;Crif1fl/fl mice possessing the myeloid-specific deletion of Crif1 demonstrated the alleviation of bone loss after irradiation when compared with Crif1fl/fl mice. Our findings demonstrate that Crif1 mediated the phosphorylation and nuclear translocation of NF-κB p65 and promoted osteoclastogenesis via the NF-κB signaling pathway after radiation exposure. Thus, our analysis revealed a specific role for Crif1 in the mediation of radiation-induced bone loss and may provide new insight into potential therapeutic strategies for radiation-induced bone loss.

Crif1 deficiency in dopamine neurons triggers early-onset parkinsonism

Mitochondrial dysfunction has been implicated in Parkinson's Disease (PD) progression; however, the mitochondrial factors underlying the development of PD symptoms remain unclear. One candidate is CR6-interacting factor1 (CRIF1), which controls translation and membrane insertion of 13 mitochondrial proteins involved in oxidative phosphorylation. Here, we found that CRIF1 mRNA and protein expression were significantly reduced in postmortem brains of elderly PD patients compared to normal controls. To evaluate the effect of Crif1 deficiency, we produced mice lacking the Crif1 gene in dopaminergic neurons (DAT-CRIF1-KO mice). From 5 weeks of age, DAT-CRIF1-KO mice began to show decreased dopamine production with progressive neuronal degeneration in the nigral area. At ~10 weeks of age, they developed PD-like behavioral deficits, including gait abnormalities, rigidity, and resting tremor. L-DOPA, a medication used to treat PD, ameliorated these defects at an early stage, although it was ineffective in older mice. Taken together, the observation that CRIF1 expression is reduced in human PD brains and deletion of CRIF1 in dopaminergic neurons leads to early-onset PD with stepwise PD progression support the conclusion that CRIF1-mediated mitochondrial function is important for the survival of dopaminergic neurons.

Biofactors regulating mitochondrial function and dynamics in podocytes and podocytopathies

Podocytes are terminally differentiated kidney cells acting as the main gatekeepers of the glomerular filtration barrier; hence, inhibiting proteinuria. Podocytopathies are classified as kidney diseases caused by podocyte damage. Different genetic and environmental risk factors can cause podocyte damage and death. Recent evidence shows that mitochondrial dysfunction also contributes to podocyte damage. Understanding alterations in mitochondrial metabolism and function in podocytopathies and whether altered mitochondrial homeostasis/dynamics is a cause or effect of podocyte damage are issues that need in-depth studies. This review highlights the roles of mitochondria and their bioenergetics in podocytes. Then, factors/signalings that regulate mitochondria in podocytes are discussed. After that, the role of mitochondrial dysfunction is reviewed in podocyte injury and the development of different podocytopathies. Finally, the mitochondrial therapeutic targets are considered.

Mitochondrial Factors in the Cell Nucleus

The origin of eukaryotic organisms involved the integration of mitochondria into the ancestor cell, with a massive gene transfer from the original proteobacterium to the host nucleus. Thus, mitochondrial performance relies on a mosaic of nuclear gene products from a variety of genomes. The concerted regulation of their synthesis is necessary for metabolic housekeeping and stress response. This governance involves crosstalk between mitochondrial, cytoplasmic, and nuclear factors. While anterograde and retrograde regulation preserve mitochondrial homeostasis, the mitochondria can modulate a wide set of nuclear genes in response to an extensive variety of conditions, whose response mechanisms often merge. In this review, we summarise how mitochondrial metabolites and proteins-encoded either in the nucleus or in the organelle-target the cell nucleus and exert different actions modulating gene expression and the chromatin state, or even causing DNA fragmentation in response to common stress conditions, such as hypoxia, oxidative stress, unfolded protein stress, and DNA damage.

PCK1 Protects against Mitoribosomal Defects in Diabetic Nephropathy in Mouse Models

SIGNIFICANCE STATEMENT

Renal gluconeogenesis plays an important role in the pathogenesis of diabetic nephropathy (DN). Proximal tubular phosphoenolpyruvate carboxykinase1 (PEPCK1) is the rate-limiting enzyme in gluconeogenesis. However, the functions of PEPCK1 have not been elucidated. We describe the novel role of PEPCK1 as a mitoribosomal protector using Pck1 transgenic (TG) mice and knockout mice. Pck1 blocks excessive glycolysis by suppressing the upregulation of excess HK2 (the rate-limiting enzyme of glycolysis). Notably, Pck1 overexpression retains mitoribosomal function and suppresses renal fibrosis. The renal and mitoribosomal protective roles of Pck1 may provide important clues for understanding DN pathogenesis and provide novel therapeutic targets.

BACKGROUND

Phosphoenolpyruvate carboxykinase (PEPCK) is part of the gluconeogenesis pathway, which maintains fasting glucose levels and affects renal physiology. PEPCK consists of two isoforms-PEPCK1 and PEPCK2-that the Pck1 and Pck2 genes encode. Gluconeogenesis increases in diabetic nephropathy (DN), escalating fasting and postprandial glucose levels. Sodium-glucose cotransporter-2 inhibitors increase hepatic and renal gluconeogenesis. We used genetically modified mice to investigate whether renal gluconeogenesis and Pck1 activity are renoprotective in DN.

METHODS

We investigated the expression of Pck1 in the proximal tubule (PTs) of streptozotocin (STZ)-treated diabetic mice. We studied the phenotypic changes in PT-specific transgenic (TG) mice and PT-specific Pck1 conditional knockout (CKO) mice.

RESULTS

The expression of Pck1 in PTs was downregulated in STZ-treated diabetic mice when they exhibited albuminuria. TG mice overexpressing Pck1 had improved albuminuria, concomitant with the mitigation of PT cell apoptosis and deposition of peritubular type IV collagen. Moreover, CKO mice exhibited PT cell apoptosis and type IV collagen deposition, findings also observed in STZ-treated mice. Renal fibrotic changes in CKO mice were associated with increasing defects in mitochondrial ribosomes (mitoribosomes). The TG mice were protected against STZ-induced mitoribosomal defects.

CONCLUSION

PCK1 preserves mitoribosomal function and may play a novel protective role in DN.

Recent Advances in Proteinuric Kidney Disease/Nephrotic Syndrome: Lessons from Knockout/Transgenic Mouse Models

Proteinuria is known to be associated with all-cause and cardiovascular mortality, and nephrotic syndrome is defined by the level of proteinuria and hypoalbuminemia. With advances in medicine, new causative genes for genetic kidney diseases are being discovered increasingly frequently. We reviewed articles on proteinuria/nephrotic syndrome, focal segmental glomerulosclerosis, membranous nephropathy, diabetic kidney disease/nephropathy, hypertension/nephrosclerosis, Alport syndrome, and rare diseases, which have been studied in mouse models. Significant progress has been made in understanding the genetics and pathophysiology of kidney diseases thanks to advances in science, but research in this area is ongoing. In the future, genetic analyses of patients with proteinuric kidney disease/nephrotic syndrome may ultimately lead to personalized treatment options.

CRIF1 siRNA-Encapsulated PLGA Nanoparticles Suppress Tumor Growth in MCF-7 Human Breast Cancer Cells

Mitochondrial oxidative phosphorylation (OXPHOS) system dysfunction in cancer cells has been exploited as a target for anti-cancer therapeutic intervention. The downregulation of CR6-interacting factor 1 (CRIF1), an essential mito-ribosomal factor, can impair mitochondrial function in various cell types. In this study, we investigated whether CRIF1 deficiency induced by siRNA and siRNA nanoparticles could suppress MCF-7 breast cancer growth and tumor development, respectively. Our results showed that CRIF1 silencing decreased the assembly of mitochondrial OXPHOS complexes I and II, which induced mitochondrial dysfunction, mitochondrial reactive oxygen species (ROS) production, mitochondrial membrane potential depolarization, and excessive mitochondrial fission. CRIF1 inhibition reduced p53-induced glycolysis and apoptosis regulator (TIGAR) expression, as well as NADPH synthesis, leading to additional increases in ROS production. The downregulation of CRIF1 suppressed cell proliferation and inhibited cell migration through the induction of G0/G1 phase cell cycle arrest in MCF-7 breast cancer cells. Similarly, the intratumoral injection of CRIF1 siRNA-encapsulated PLGA nanoparticles inhibited tumor growth, downregulated the assembly of mitochondrial OXPHOS complexes I and II, and induced the expression of cell cycle protein markers (p53, p21, and p16) in MCF-7 xenograft mice. Thus, the inhibition of mitochondrial OXPHOS protein synthesis through CRIF1 deletion destroyed mitochondrial function, leading to elevated ROS levels and inducing antitumor effects in MCF-7 cells.

Mitochondrial division inhibitor (mdivi-1) inhibits proliferation and epithelial-mesenchymal transition via the NF-κB pathway in thyroid cancer cells

Excessively fragmented mitochondria have been reported in thyroid cancer (TC). Mitochondrial division inhibitor (mdivi-1), a putative inhibitor of dynamin-related protein 1 (Drp1), prevents mitochondrial fission and thereby restricts cell proliferation across several types of primary cancer. However, the role of mdivi-1 on TC has not been sufficiently studied. This research is intended to explore the therapeutic effect of mdivi-1 in TC cells. Results demonstrated that highly invasive TC cells displayed excessive mitochondrial fission with more fragmented mitochondria. Treatment with mdivi-1 inhibited mitochondrial fission in 8505C cells as indicated by transmission electron microscope (TEM). It also impaired the proliferation and increased apoptosis in 8505C and K1 cells as shown by plate cloning assay, cell viability assay, and apoptosis assay. Mdivi-1 treatment also attenuated migratory and invasive abilities in 8505C and K1 cells as shown by the transwell assay and the wound healing assay. And we noticed the same inhibition of mdivi-1 in cell migration and cell viability after the knockdown of Drp1 in 8505C cells. This demonstrated that mdivi-1 exerted an anti-tumor effect independently of Drp1 in 8505C cells. Moreover, mdivi-1 treatment reversed epithelial-mesenchymal transition (EMT) by inhibiting the NF-κB pathway in 8505C cells. The present findings demonstrate that mdivi-1 has a therapeutic role in thyroid carcinoma.

Integrated transcriptomics and metabolomics analysis reveals the biomolecular mechanisms associated to the antitumoral potential of a novel silver-based core@shell nanosystem

A combination of omics techniques (transcriptomics and metabolomics) has been used to elucidate the mechanisms responsible for the antitumor action of a nanosystem based on a Ag core coated with mesoporous silica on which transferrin has been anchored as a targeting ligand against tumor cells (Ag@MSNs-Tf). Transcriptomics analysis has been carried out by gene microarrays and RT-qPCR, while high-resolution mass spectrometry has been used for metabolomics. This multi-omics strategy has enabled the discovery of the effect of this nanosystem on different key molecular pathways including the glycolysis, the pentose phosphate pathway, the oxidative phosphorylation and the synthesis of fatty acids, among others.

Multifunctions of CRIF1 in cancers and mitochondrial dysfunction

Sustaining proliferative signaling and enabling replicative immortality are two important hallmarks of cancer. The complex of cyclin-dependent kinase (CDK) and its cyclin plays a decisive role in the transformation of the cell cycle and is also critical in the initiation and progression of cancer. CRIF1, a multifunctional factor, plays a pivotal role in a series of cell biological progresses such as cell cycle, cell proliferation, and energy metabolism. CRIF1 is best known as a negative regulator of the cell cycle, on account of directly binding to Gadd45 family proteins or CDK2. In addition, CRIF1 acts as a regulator of several transcription factors such as Nur77 and STAT3 and partly determines the proliferation of cancer cells. Many studies showed that the expression of CRIF1 is significantly altered in cancers and potentially regarded as a tumor suppressor. This suggests that targeting CRIF1 would enhance the selectivity and sensitivity of cancer treatment. Moreover, CRIF1 might be an indispensable part of mitoribosome and is involved in the regulation of OXPHOS capacity. Further, CRIF1 is thought to be a novel target for the underlying mechanism of diseases with mitochondrial dysfunctions. In summary, this review would conclude the latest aspects of studies about CRIF1 in cancers and mitochondria-related diseases, shed new light on targeted therapy, and provide a more comprehensive holistic view.

Neuron-periphery mitochondrial stress communication in aging and diseases

The nervous system is the central hub of the body, detecting environmental and internal stimuli to regulate organismal metabolism via communications to the peripheral tissues. Mitochondria play an essential role in neuronal activity by supplying energy, maintaining cellular metabolism, and buffering calcium levels. A variety of mitochondrial conditions are associated with aging and age-related neurological disorders. Beyond regulating individual neuron cells, mitochondria also coordinate signaling in tissues and organs during stress conditions to mediate systemic metabolism and enable organisms to adapt to such stresses. In addition, peripheral organs and immune cells can also produce signaling molecules to modulate neuronal function. Recent studies have found that mitokines released upon mitochondrial stresses affect metabolism and the physiology of different tissues and organs at a distance. Here, we summarize recent advances in understanding neuron-periphery mitochondrial stress communication and how mitokine signals contribute to the systemic regulation of metabolism and aging with potential implications for therapeutic strategies.

CRIF1 promotes the progression of non-small-cell lung cancer by SIRT3- mediated deacetylation of PYCR1

Lung cancer is the cancer with the highest mortality in the world. So further exploration of the pathogenesis of lung cancer is of great significance. In this study, the specific role and related mechanism of CRIF1 in non-small cell lung cancer (NSCLC) were explored in this research. TheRT-PCR, western blot and IHC assays were used to examine the expression level of CRIF1 in NSCLC tissue, tissue adjacent to carcinoma, NSCLC cell lines and human normal lung epithelial cells. Next, colony formation assay, Alamar blue Kit and EdU assays were employed to examine the proliferation of transfected A549 and NCI-H2009 cells. Measurement of mitochondrial permeability transition pore opening, ATP production and cellular oxygen consumption were used to evaluate the mitochondrial apoptosis of transfected NSCLC cells. Enzymatic activity assays for PYCR1, western blot and flow cytometry assays were used to explore the relationship between PYCR1 and CRIF1. The subcutaneous xenograft tumor mice model was established to explore the role of CRIF1 in vivo. Collectively, results revealed that CRIF1 was upregulated in NSCLC cells and tissues (p < 0.001). CRIF1 promoted proliferation of NSCLC cells (p < 0.001). CRIF1 inhibited mitochondrial apoptosis in NSCLC cells (p < 0.05). Moreover, CRIF1 promoted PYCR1 deacetylation and increased its activity through SIRT3 (p < 0.05). Deacetylation of PYCR1 reversed the antitumor effect of CRIF1 knockdown (p < 0.05). Finally, knockdown of CRIF1 inhibited the tumor growth of NSCLC in vivo (p < 0.05).This research found that CRIF1 promoted the progression of non-small-cell lung cancer by SIRT3- mediated deacetylation of PYCR1.

Mitoribosome insufficiency in β cells is associated with type 2 diabetes-like islet failure

Genetic variations in mitoribosomal subunits and mitochondrial transcription factors are related to type 2 diabetes. However, the role of islet mitoribosomes in the development of type 2 diabetes has not been determined. We investigated the effects of the mitoribosomal gene on β-cell function and glucose homeostasis. Mitoribosomal gene expression was analyzed in datasets from the NCBI GEO website (GSE25724, GSE76894, and GSE76895) and the European Nucleotide Archive (ERP017126), which contain the transcriptomes of type 2 diabetic and nondiabetic organ donors. We found deregulation of most mitoribosomal genes in islets from individuals with type 2 diabetes, including partial downregulation of CRIF1. The phenotypes of haploinsufficiency in a single mitoribosomal gene were examined using β-cell-specific Crif1 (Mrpl59) heterozygous-deficient mice. Crif1^beta+/− mice had normal glucose tolerance, but their islets showed a loss of first-phase glucose-stimulated insulin secretion. They also showed increased β-cell mass associated with higher expression of Reg family genes. However, Crif1^beta+/− mice showed earlier islet failure in response to high-fat feeding, which was exacerbated by aging. Haploinsufficiency of a single mitoribosomal gene predisposes rodents to glucose intolerance, which resembles the early stages of type 2 diabetes in humans.

Disruptions in the mitochondrial protein synthesis machinery give rise to metabolic disturbances that lay the foundation for type 2 diabetes. As physiological glucose levels rise, the energy-generating machinery of the mitochondria responds with increased activity, which stimulates insulin secretion. Many proteins responsible for mitochondrial metabolism are produced by ribosomes within this cellular organelle. Researchers led by Hyun Jin Kim and Minho Shong at Chungnam National University, Daejon, South Korea, have determined that mutations affecting a mitochondrial ribosomal protein called CRIF1 can lead to impaired insulin release. Mice with reduced CRIF1 were initially healthy, but as they aged, exhibited signs of impaired pancreatic function similar to those seen in patients with early-stage diabetes. This process was accelerated by consumption of a high-fat diet, and the researchers propose that this mechanism may be directly relevant to human disease.

Skeletal muscle mitoribosomal defects are linked to low bone mass caused by bone marrow inflammation in male mice

BACKGROUND

Mitochondrial oxidative phosphorylation (OxPhos) is a critical regulator of skeletal muscle mass and function. Although muscle atrophy due to mitochondrial dysfunction is closely associated with bone loss, the biological characteristics of the relationship between muscle and bone remain obscure. We showed that muscle atrophy caused by skeletal muscle-specific CR6-interacting factor 1 knockout (MKO) modulates the bone marrow (BM) inflammatory response, leading to low bone mass.

METHODS

MKO mice with lower muscle OxPhos were fed a normal chow or high-fat diet and then evaluated for muscle mass and function, and bone mineral density. Immunophenotyping of BM immune cells was also performed. BM transcriptomic analysis was used to identify key factors regulating bone mass in MKO mice. To determine the effects of BM-derived CXCL12 (C-X-C motif chemokine ligand 12) on regulation of bone homeostasis, a variety of BM niche-resident cells were treated with recombinant CXCL12. Vastus lateralis muscle and BM immune cell samples from 14 patients with hip fracture were investigated to examine the association between muscle function and BM inflammation.

RESULTS

MKO mice exhibited significant reductions in both muscle mass and expression of OxPhos subunits but increased transcription of mitochondrial stress response-related genes in the extensor digitorum longus (P < 0.01). MKO mice showed a decline in grip strength and a higher drop rate in the wire hanging test (P < 0.01). Micro-computed tomography and von Kossa staining revealed that MKO mice developed a low mass phenotype in cortical and trabecular bone (P < 0.01). Transcriptomic analysis of the BM revealed that mitochondrial stress responses in skeletal muscles induce an inflammatory response and adipogenesis in the BM and that the CXCL12-CXCR4 (C-X-C chemokine receptor 4) axis is important for T-cell homing to the BM. Antagonism of CXCR4 attenuated BM inflammation and increased bone mass in MKO mice. In humans, patients with low body mass index (BMI = 17.2 ± 0.42 kg/m² ) harboured a larger population of proinflammatory and cytotoxic senescent T-cells in the BMI (P < 0.05) and showed reduced expression of OxPhos subunits in the vastus lateralis, compared with controls with a normal BMI (23.7 ± 0.88 kg/m² ) (P < 0.01).

CONCLUSIONS

Defects in muscle mitochondrial OxPhos promote BM inflammation in mice, leading to decreased bone mass. Muscle mitochondrial dysfunction is linked to BM inflammatory cytokine secretion via the CXCL12-CXCR4 signalling axis, which is critical for inducing low bone mass.

Mitoribosomal defects aggravate liver cancer via aberrant glycolytic flux and T cell exhaustion

BACKGROUND

Mitochondria are involved in cancer energy metabolism, although the mechanisms underlying the involvement of mitoribosomal dysfunction in hepatocellular carcinoma (HCC) remain poorly understood. Here, we investigated the effects of mitoribosomal impairment-mediated alterations on the immunometabolic characteristics of liver cancer.

METHODS

We used a mouse model of HCC, liver tissues from patients with HCC, and datasets from The Cancer Genome Atlas (TCGA) to elucidate the relationship between mitoribosomal proteins (MRPs) and HCC. In a mouse model, we selectively disrupted expression of the mitochondrial ribosomal protein CR6-interacting factor 1 (CRIF1) in hepatocytes to determine the impact of hepatocyte-specific impairment of mitoribosomal function on liver cancer progression. The metabolism and immunophenotype of liver cancer was assessed by glucose flux assays and flow cytometry, respectively.

RESULTS

Single-cell RNA-seq analysis of tumor tissue and TCGA HCC transcriptome analysis identified mitochondrial defects associated with high-MRP expression and poor survival outcomes. In the mouse model, hepatocyte-specific disruption of the mitochondrial ribosomal protein CRIF1 revealed the impact of mitoribosomal dysfunction on liver cancer progression. Crif1 deficiency promoted programmed cell death protein 1 expression by immune cells in the hepatic tumor microenvironment. A [U-¹³C₆]-glucose tracer demonstrated enhanced glucose entry into the tricarboxylic acid cycle and lactate production in mice with mitoribosomal defects during cancer progression. Mice with hepatic mitoribosomal defects also exhibited enhanced progression of liver cancer accompanied by highly exhausted tumor-infiltrating T cells. Crif1 deficiency induced an environment unfavorable to T cells, leading to exhaustion of T cells via elevation of reactive oxygen species and lactate production.

CONCLUSIONS

Hepatic mitoribosomal defects promote glucose partitioning toward glycolytic flux and lactate synthesis, leading to T cell exhaustion and cancer progression. Overall, the results suggest a distinct role for mitoribosomes in regulating the immunometabolic microenvironment during HCC progression.

B cell-specific deletion of Crif1 drives lupus-like autoimmunity by activation of IL-17, IL-6, and pathogenic Tfh cells

OBJECTIVE

CR6-interacting factor 1 (Crif1) is a nuclear transcriptional regulator and a mitochondrial inner membrane protein; however, its functions in B lymphocytes have been poorly defined. In this study, we investigated the effects of Crif1 on B-cell metabolic regulation, cell function, and autoimmune diseases.

METHODS

Using mice with B cell-specific deletion of Crif1 (Crif1^ΔCD19 ), we assessed the relevance of Crif1 function for lupus disease parameters including anti-double-stranded DNA, cytokines, and kidney pathology. RNA sequencing was performed on B cells from Crif1^ΔCD19 mice. The phenotypic and metabolic changes in immune cells were evaluated in Crif1^ΔCD19 mice. Roquin^san/+ mice crossed with Crif1^ΔCD19 mice were monitored to assess the functionality of Crif1-deficient B cells in lupus development.

RESULTS

Crif1^ΔCD19 mice showed an autoimmune lupus-like phenotype, including high levels of autoantibodies to double-stranded DNA and severe lupus nephritis with increased mesangial hypercellularity. While loss of Crif1 in B cells showed impaired mitochondrial oxidative function, Crif1-deficient B cells promoted the production of IL-17 and IL-6 and was more potent in helping T cells develop into T follicular helper cells. In an autoimmune lupus mouse model, depletion of Crif1 in B cells exacerbated lupus severity and Crif1 overexpression prevented lupus development in Roquin^san/san mice.

CONCLUSION

These results showed that Crif1 was negatively correlated with disease severity, and overexpression of Crif1 ameliorated disease development. Our findings suggest that Crif1 is essential for preventing lupus development by maintaining B cell self-tolerance.

CRIF1 Deficiency Increased Homocysteine Production by Disrupting Dihydrofolate Reductase Expression in Vascular Endothelial Cells

Elevated plasma homocysteine levels can induce vascular endothelial dysfunction; however, the mechanisms regulating homocysteine metabolism in impaired endothelial cells are currently unclear. In this study, we deleted the essential mitoribosomal gene CR6 interacting factor 1 (CRIF1) in human umbilical vein endothelial cells (HUVECs) and mice to induce endothelial cell dysfunction; then, we monitored homocysteine accumulation. We found that CRIF1 downregulation caused significant increases in intracellular and plasma concentrations of homocysteine, which were associated with decreased levels of folate cycle intermediates such as 5-methyltetrahydrofolate (MTHF) and tetrahydrofolate (THF). Moreover, dihydrofolate reductase (DHFR), a key enzyme in folate-mediated metabolism, exhibited impaired activity and decreased protein expression in CRIF1 knockdown endothelial cells. Supplementation with folic acid did not restore DHFR expression levels or MTHF and homocysteine concentrations in endothelial cells with a CRIF1 deletion or DHFR knockdown. However, the overexpression of DHFR in CRIF1 knockdown endothelial cells resulted in decreased accumulation of homocysteine. Taken together, our findings suggest that CRIF1-deleted endothelial cells accumulated more homocysteine, compared with control cells; this was primarily mediated by the disruption of DHFR expression.

CRIF1 deficiency suppresses endothelial cell migration via upregulation of RhoGDI2

Rho GDP-dissociation inhibitor (RhoGDI), a downregulator of Rho family GTPases, prevents nucleotide exchange and membrane association. It is responsible for the activation of Rho GTPases, which regulate a variety of cellular processes, such as migration. Although RhoGDI2 has been identified as a tumor suppressor gene involved in cellular migration and invasion, little is known about its role in vascular endothelial cell (EC) migration. CR6-interacting factor 1 (CRIF1) is a CR6/GADD45-interacting protein with important mitochondrial functions and regulation of cell growth. We examined the expression of RhoGDI2 in CRIF1-deficient human umbilical vein endothelial cells (HUVECs) and its role in cell migration. Expression of RhoGDI2 was found to be considerably higher in CRIF1-deficient HUVECs along with suppression of cell migration. Moreover, the phosphorylation levels of Akt and CREB were decreased in CRIF1-silenced cells. The Akt-CREB signaling pathway was implicated in the changes in endothelial cell migration caused by CRIF1 downregulation. In addition to RhoGDI2, we identified another factor that promotes migration and invasion of ECs. Adrenomedullin2 (ADM2) is an autocrine/paracrine factor that regulates vascular tone and other vascular functions. Endogenous ADM2 levels were elevated in CRIF1-silenced HUVECs with no effect on cell migration. However, siRNA-mediated depletion of RhoGDI2 or exogenous ADM2 administration significantly restored cell migration via the Akt-CREB signaling pathway. In conclusion, RhoGDI2 and ADM2 play important roles in the migration of CRIF1-deficient endothelial cells.

Hearing Impairment in a Mouse Model of Diabetes Is Associated with Mitochondrial Dysfunction, Synaptopathy, and Activation of the Intrinsic Apoptosis Pathway

Although previous studies continuously report an increased risk of hearing loss in diabetes patients, the impact of the disease on the inner ear remains unexplored. Herein, we examine the pathophysiology of diabetes-associated hearing impairment and cochlear synaptopathy in a mouse model of diabetes. Male B6.BKS(D)-Lepr^db/J (db/db, diabetes) and heterozygote (db/+, control) mice were assigned into each experimental group (control vs. diabetes) based on the genotype and tested for hearing sensitivity every week from 6 weeks of age. Each cochlea was collected for histological and biological assays at 14 weeks of age. The diabetic mice exerted impaired hearing and a reduction in cochlear blood flow and C-terminal-binding protein 2 (CtBP2, a presynaptic ribbon marker) expression. Ultrastructural images revealed severely damaged mitochondria from diabetic cochlea accompanied by a reduction in Cytochrome c oxidase subunit 4 (COX4) and CR6-interacting factor 1 (CRIF1). The diabetic mice presented significantly decreased levels of platelet endothelial cell adhesion molecule (PECAM-1), B-cell lymphoma 2 (BCL-2), and procaspase-9, but not procaspase-8. Importantly, significant changes were not found in necroptotic programmed cell death markers (receptor-interacting serine/threonine-protein kinase 1, RIPK1; RIPK3; and mixed lineage kinase domain-like pseudokinase, MLKL) between the groups. Taken together, diabetic hearing loss is accompanied by synaptopathy, microangiopathy, damage to the mitochondrial structure/function, and activation of the intrinsic apoptosis pathway. Our results imply that mitochondrial dysfunction is deeply involved in diabetic hearing loss, and further suggests the potential benefits of therapeutic strategies targeting mitochondria.

Mitochondrial HSP70 Chaperone System-The Influence of Post-Translational Modifications and Involvement in Human Diseases

Since their discovery, heat shock proteins (HSPs) have been identified in all domains of life, which demonstrates their importance and conserved functional role in maintaining protein homeostasis. Mitochondria possess several members of the major HSP sub-families that perform essential tasks for keeping the organelle in a fully functional and healthy state. In humans, the mitochondrial HSP70 chaperone system comprises a central molecular chaperone, mtHSP70 or mortalin (HSPA9), which is actively involved in stabilizing and importing nuclear gene products and in refolding mitochondrial precursor proteins, and three co-chaperones (HSP70-escort protein 1-HEP1, tumorous imaginal disc protein 1-TID-1, and Gro-P like protein E-GRPE), which regulate and accelerate its protein folding functions. In this review, we summarize the roles of mitochondrial molecular chaperones with particular focus on the human mtHsp70 and its co-chaperones, whose deregulated expression, mutations, and post-translational modifications are often considered to be the main cause of neurological disorders, genetic diseases, and malignant growth.

Mitochondrial Metabolic Signatures in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer death worldwide. HCC progression and metastasis are closely related to altered mitochondrial metabolism, including mitochondrial stress responses, metabolic reprogramming, and mitoribosomal defects. Mitochondrial oxidative phosphorylation (OXPHOS) defects and reactive oxygen species (ROS) production are attributed to mitochondrial dysfunction. In response to oxidative stress caused by increased ROS production, misfolded or unfolded proteins can accumulate in the mitochondrial matrix, leading to initiation of the mitochondrial unfolded protein response (UPR^mt). The mitokines FGF21 and GDF15 are upregulated during UPR^mt and their levels are positively correlated with liver cancer development, progression, and metastasis. In addition, mitoribosome biogenesis is important for the regulation of mitochondrial respiration, cell viability, and differentiation. Mitoribosomal defects cause OXPHOS impairment, mitochondrial dysfunction, and increased production of ROS, which are associated with HCC progression in mouse models and human HCC patients. In this paper, we focus on the role of mitochondrial metabolic signatures in the development and progression of HCC. Furthermore, we provide a comprehensive review of cell autonomous and cell non-autonomous mitochondrial stress responses during HCC progression and metastasis.

CD4+ T-cell differentiation and function: Unifying glycolysis, fatty acid oxidation, polyamines NAD mitochondria

The progression through different steps of T-cell development, activation, and effector function is tightly bound to specific cellular metabolic processes. Previous studies established that T-effector cells have a metabolic bias toward aerobic glycolysis, whereas naive and regulatory T cells mainly rely on oxidative phosphorylation. More recently, the field of immunometabolism has drifted away from the notion that mitochondrial metabolism holds little importance in T-cell activation and function. Of note, T cells possess metabolic promiscuity, which allows them to adapt their nutritional requirements according to the tissue environment. Altogether, the integration of these metabolic pathways culminates in the generation of not only energy but also intermediates, which can regulate epigenetic programs, leading to changes in T-cell fate. In this review, we discuss the recent literature on how glycolysis, amino acid catabolism, and fatty acid oxidation work together with the tricarboxylic acid cycle in the mitochondrion. We also emphasize the importance of the electron transport chain for T-cell immunity. We also discuss novel findings highlighting the role of key enzymes, accessory pathways, and posttranslational protein modifications that distinctively regulate T-cell function and might represent prominent candidates for therapeutic purposes.

Mitochondrial Dysfunction in Podocytes Caused by CRIF1 Deficiency Leads to Progressive Albuminuria and Glomerular Sclerosis in Mice

Recent studies have implicated mitochondrial disruption in podocyte dysfunction, which is a characteristic feature of primary and diabetic glomerular diseases. However, the mechanisms by which primary mitochondrial dysfunction in podocytes affects glomerular renal diseases are currently unknown. To investigate the role of mitochondrial oxidative phosphorylation (OxPhos) in podocyte dysfunction, glomerular function was examined in mice carrying a loss of function mutation of the gene encoding CR6-interacting factor-1 (CRIF1), which is essential for intramitochondrial production and the subsequent insertion of OxPhos polypeptides into the inner mitochondrial membrane. Homozygotic deficiency of CRIF1 in podocytes resulted in profound and progressive albuminuria from 3 weeks of age; the CRIF1-deficient mice also developed glomerular and tubulointerstitial lesions by 10 weeks of age. Furthermore, marked glomerular sclerosis and interstitial fibrosis were observed in homozygous CRIF1-deficient mice at 20 weeks of age. In cultured mouse podocytes, loss of CRIF1 resulted in OxPhos dysfunction and marked loss or abnormal aggregation of F-actin. These findings indicate that the OxPhos status determines the integrity of podocytes and their ability to maintain a tight barrier and control albuminuria. Analyses of the glomerular function of the podocyte-specific primary OxPhos dysfunction model mice demonstrate a link between podocyte mitochondrial dysfunction, progressive glomerular sclerosis, and tubulointerstitial diseases.

Mitochondrial Unfolded Protein Responses in White Adipose Tissue: Lipoatrophy, Whole-Body Metabolism and Lifespan

The mitochondrial unfolded protein response (UPR^mt) is a stress response mediated by the expression of genes such as chaperones, proteases, and mitokines to maintain mitochondrial proteostasis. Certain genetically modified mice, which defect mitochondrial proteins specifically in adipocytes, developed atrophy of the white adipose tissue, resisted diet-induced obesity, and had altered whole-body metabolism. UPR^mt, which has beneficial functions for living organisms, is termed "mitohormesis", but its specific characteristics and detailed regulatory mechanism have not been elucidated to date. In this review, we discuss the function of UPR^mt in adipose atrophy (lipoatrophy), whole-body metabolism, and lifespan based on the concept of mitohormesis.

Differential roles of GDF15 and FGF21 in systemic metabolic adaptation to the mitochondrial integrated stress response

Perturbation of mitochondrial proteostasis provokes cell autonomous and cell non-autonomous responses that contribute to homeostatic adaptation. Here, we demonstrate distinct metabolic effects of hepatic metabokines as cell non-autonomous factors in mice with mitochondrial OxPhos dysfunction. Liver-specific mitochondrial stress induced by a loss-of-function mutation in Crif1 (LKO) leads to aberrant oxidative phosphorylation and promotes the mitochondrial unfolded protein response. LKO mice are highly insulin sensitive and resistant to diet-induced obesity. The hepatocytes of LKO mice secrete large quantities of metabokines, including GDF15 and FGF21, which confer metabolic benefits. We evaluated the metabolic phenotypes of LKO mice with global deficiency of GDF15 or FGF21 and show that GDF15 regulates body and fat mass and prevents diet-induced hepatic steatosis, whereas FGF21 upregulates insulin sensitivity, energy expenditure, and thermogenesis in white adipose tissue. This study reveals that the mitochondrial integrated stress response (ISR^mt) in liver mediates metabolic adaptation through hepatic metabokines.

Mitohormesis in Hypothalamic POMC Neurons Mediates Regular Exercise-Induced High-Turnover Metabolism

Low-grade mitochondrial stress can promote health and longevity, a phenomenon termed mitohormesis. Here, we demonstrate the opposing metabolic effects of low-level and high-level mitochondrial ribosomal (mitoribosomal) stress in hypothalamic proopiomelanocortin (POMC) neurons. POMC neuron-specific severe mitoribosomal stress due to Crif1 homodeficiency causes obesity in mice. By contrast, mild mitoribosomal stress caused by Crif1 heterodeficiency in POMC neurons leads to high-turnover metabolism and resistance to obesity. These metabolic benefits are mediated by enhanced thermogenesis and mitochondrial unfolded protein responses (UPRmt) in distal adipose tissues. In POMC neurons, partial Crif1 deficiency increases the expression of β-endorphin (β-END) and mitochondrial DNA-encoded peptide MOTS-c. Central administration of MOTS-c or β-END recapitulates the adipose phenotype of Crif1 heterodeficient mice, suggesting these factors as potential mediators. Consistently, regular running exercise at moderate intensity stimulates hypothalamic MOTS-c/β-END expression and induces adipose tissue UPRmt and thermogenesis. Our findings indicate that POMC neuronal mitohormesis may underlie exercise-induced high-turnover metabolism.

Cellular and Intercellular Homeostasis in Adipose Tissue with Mitochondria-Specific Stress

Paracrine interactions are imperative for the maintenance of adipose tissue intercellular homeostasis, and intracellular organelle dysfunction results in local and systemic alterations in metabolic homeostasis. It is currently accepted that mitochondrial proteotoxic stress activates the mitochondrial unfolded protein response (UPRmt) in vitro and in vivo. The induction of mitochondrial chaperones and proteases during the UPRmt is a key cell-autonomous mechanism of mitochondrial quality control. The UPRmt also affects systemic metabolism through the secretion of cell non-autonomous peptides and cytokines (hereafter, metabokines). Mitochondrial function in adipose tissue plays a pivotal role in whole-body metabolism and human diseases. Despite continuing interest in the role of the UPRmt and quality control pathways of mitochondria in energy metabolism, studies on the roles of the UPRmt and metabokines in white adipose tissue are relatively sparse. Here, we describe the role of the UPRmt in adipose tissue, including adipocytes and resident macrophages, and the interactive roles of cell non-autonomous metabokines, particularly growth differentiation factor 15, in local adipose cellular homeostasis and systemic energy metabolism.

Downregulation of CR6-interacting factor 1 suppresses keloid fibroblast growth via the TGF-β/Smad signaling pathway

Keloids are a type of aberrant skin scarring characterized by excessive accumulation of collagen and extracellular matrix (ECM), arising from uncontrolled wound healing responses. While typically non-pathogenic, keloids are occasionally regarded as a form of benign tumor. CR6-interacting factor 1 (CRIF1) is a well-known CR6/GADD45-interacting protein, that has both nuclear and mitochondrial functions, and also exerts regulatory effects on cell growth and apoptosis. In this study, cell proliferation, cell migration, collagen production and TGF-β signaling was compared between normal fibroblasts (NFs) and keloid fibroblasts (KFs). Subsequently, the effects of CRIF1 deficiency were investigated in both NFs and KFs. Cell proliferation, cell migration, collagen production and protein expressions of TGF-β, phosphorylation of Smad2 and Smad3 were all found to be higher in KFs compared to NFs. CRIF1 deficiency in NFs and KFs inhibited cell proliferation, migration, and collagen production. In addition, phosphorylation of Smad2 and Smad3, which are transcription factors of collagen, was decreased. In contrast, mRNA expression levels of Smad7 and SMURF2, two important inhibitory proteins of Smad2/3, were increased, suggesting that CRIF1 may regulate collagen production. CRIF1 deficiency decreases the proliferation and migration of KFs, thereby inhibiting their overgrowth via the transforming growth factor-β (TGF-β)/Smad pathway. CRIF1 may therefore represent a potential therapeutic target in keloid pathogenesis.

SIRT1 Activation Attenuates the Cardiac Dysfunction Induced by Endothelial Cell-Specific Deletion of CRIF1

The CR6-interacting factor1 (CRIF1) mitochondrial protein is indispensable for peptide synthesis and oxidative phosphorylation. Cardiomyocyte-specific deletion of CRIF1 showed impaired mitochondrial function and cardiomyopathy. We developed an endothelial cell-specific CRIF1 deletion mouse to ascertain whether dysfunctional endothelial CRIF1 influences cardiac function and is mediated by the antioxidant protein sirtuin 1 (SIRT1). We also examined the effect of the potent SIRT1 activator SRT1720 on cardiac dysfunction. Mice with endothelial cell-specific CRIF1 deletion showed an increased heart-to-body weight ratio, increased lethality, and markedly reduced fractional shortening of the left ventricle, resulting in severe cardiac dysfunction. Moreover, endothelial cell-specific CRIF1 deletion resulted in mitochondrial dysfunction, reduced ATP levels, inflammation, and excessive oxidative stress in heart tissues, associated with decreased SIRT1 expression. Intraperitoneal injection of SRT1720 ameliorated cardiac dysfunction by activating endothelial nitric oxide synthase, reducing oxidative stress, and inhibiting inflammation. Furthermore, the decreased endothelial junction-associated protein zonula occludens-1 in CRIF1-deleted mice was significantly recovered after SRT1720 treatment. Our results suggest that endothelial CRIF1 plays an important role in maintaining cardiac function, and that SIRT1 induction could be a therapeutic strategy for endothelial dysfunction-induced cardiac dysfunction.

Human X chromosome exome sequencing identifies BCORL1 as contributor to spermatogenesis

BACKGROUND

Infertility affects approximately 15% of couples worldwide with male infertility being responsible for approximately 50% of cases. Although accumulating evidence demonstrates the critical role of the X chromosome in spermatogenesis during the last few decades, the expression patterns and potential impact of the X chromosome, together with X linked genes, on male infertility are less well understood.

METHODS

We performed X chromosome exome sequencing followed by a two-stage independent population validation in 1333 non-obstructive azoospermia cases and 1141 healthy controls to identify variant classes with high likelihood of pathogenicity. To explore the functions of these candidate genes in spermatogenesis, we first knocked down these candidate genes individually in mouse spermatogonial stem cells (SSCs) using short interfering RNA oligonucleotides and then generated candidate genes knockout mice by CRISPR-Cas9 system.

RESULTS

Four low-frequency variants were identified in four genes (BCORL1, MAP7D3, ARMCX4 and H2BFWT) associated with male infertility. Functional studies of the mouse SSCs revealed that knocking down Bcorl1 or Mtap7d3 could inhibit SSCs self-renewal and knocking down Armcx4 could repress SSCs differentiation in vitro. Using CRISPR-Cas9 system, Bcorl1 and Mtap7d3 knockout mice were generated. Excitingly, Bcorl1 knockout mice were infertile with impaired spermatogenesis. Moreover, Bcorl1 knockout mice exhibited impaired sperm motility and sperm cells displayed abnormal mitochondrial structure.

CONCLUSION

Our data indicate that the X-linked genes are associated with male infertility and involved in regulating SSCs, which provides a new insight into the role of X-linked genes in spermatogenesis.

A Novel Nanoproteomic Approach for the Identification of Molecular Targets Associated with Thyroid Tumors

A thyroid nodule is the most common presentation of thyroid cancer; thus, it is extremely important to differentiate benign from malignant nodules. Within malignant lesions, classification of a thyroid tumor is the primary step in the assessment of the prognosis and selection of treatment. Currently, fine-needle aspiration biopsy (FNAB) is the preoperative test most commonly used for the initial thyroid nodule diagnosis. However, due to some limitations of FNAB, different high-throughput “omics” approaches have emerged that could further support diagnosis based on histopathological patterns. In the present work, formalin-fixed paraffin-embedded (FFPE) tissue specimens from normal (non-neoplastic) thyroid (normal controls (NCs)), benign tumors (follicular thyroid adenomas (FTAs)), and some common types of well-differentiated thyroid carcinoma (follicular thyroid carcinomas (FTCs), conventional or classical papillary thyroid carcinomas (CV-PTCs), and the follicular variant of papillary thyroid carcinomas (FV-PTCs)) were analyzed. For the first time, FFPE thyroid samples were deparaffinized using an easy, fast, and non-toxic method. Protein extracts from thyroid tissue samples were analyzed using a nanoparticle-assisted proteomics approach combined with shotgun LC-MS/MS. The differentially regulated proteins found to be specific for the FTA, FTC, CV-PTC, and FV-PTC subtypes were analyzed with the bioinformatic tools STRING and PANTHER showing a profile of proteins implicated in the thyroid cancer metabolic reprogramming, cancer progression, and metastasis. These proteins represent a new source of potential molecular targets related to thyroid tumors.

DNAJA3/Tid1 Is Required for Mitochondrial DNA Maintenance and Regulates Migration and Invasion of Human Gastric Cancer Cells

BACKGROUND

Gastric cancer is a common health issue. Deregulated cellular energetics is regarded as a cancer hallmark and mitochondrial dysfunction might contribute to cancer progression. Tid1, a mitochondrial co-chaperone, may play a role as a tumor suppressor in various cancers, but the role of Tid1 in gastric cancers remains under investigated.

METHODS

The clinical TCGA online database and immunohistochemical staining for Tid1 expression in tumor samples of gastric cancer patients were analyzed. Tid1 knockdown by siRNA was applied to investigate the role of Tid1 in gastric cancer cells.

RESULTS

Low Tid1 protein-expressing gastric cancer patients had a poorer prognosis and higher lymph node invasion than high Tid1-expressing patients. Knockdown of Tid1 did not increase cell proliferation, colony/tumor sphere formation, or chemotherapy resistance in gastric cancer cells. However, Tid1 knockdown increased cell migration and invasion. Moreover, Tid1 knockdown reduced the mtDNA copy number of gastric cancer cells. In addition, the Tid1-galectin-7-MMP-9 axis might be associated with Tid1 knockdown-induced cell migration and invasion of gastric cancer cells.

CONCLUSIONS

Tid1 is required for mtDNA maintenance and regulates migration and invasion of gastric cancer cells. Tid1 deletion may be a poor prognostic factor in gastric cancers and could be further investigated for development of gastric cancer treatments.

Tetracycline Antibiotics Induce Host-Dependent Disease Tolerance to Infection

Several classes of antibiotics have long been known to have beneficial effects that cannot be explained strictly on the basis of their capacity to control the infectious agent. Here, we report that tetracycline antibiotics, which target the mitoribosome, protected against sepsis without affecting the pathogen load. Mechanistically, we found that mitochondrial inhibition of protein synthesis perturbed the electron transport chain (ETC) decreasing tissue damage in the lung and increasing fatty acid oxidation and glucocorticoid sensitivity in the liver. Using a liver-specific partial and acute deletion of Crif1, a critical mitoribosomal component for protein synthesis, we found that mice were protected against sepsis, an observation that was phenocopied by the transient inhibition of complex I of the ETC by phenformin. Together, we demonstrate that mitoribosome-targeting antibiotics are beneficial beyond their antibacterial activity and that mitochondrial protein synthesis inhibition leading to ETC perturbation is a mechanism for the induction of disease tolerance.

•

Doxycycline protects from sepsis beyond its direct antibacterial activity

•

Doxycycline protection from infection is microbiome-independent

•

Inhibition of mitochondrial protein synthesis induces disease tolerance

•

Mild and transient perturbations of the mitochondrial ETC induce disease tolerance

Endothelial-specific Crif1 deletion induces BBB maturation and disruption via the alteration of actin dynamics by impaired mitochondrial respiration

Cerebral endothelial cells (ECs) require junctional proteins to maintain blood-brain barrier (BBB) integrity, restricting toxic substances and controlling peripheral immune cells with a higher concentration of mitochondria than ECs of peripheral capillaries. The mechanism underlying BBB disruption by defective mitochondrial oxidative phosphorylation (OxPhos) is unclear in a mitochondria-related gene-targeted animal model. To assess the role of EC mitochondrial OxPhos function in the maintenance of the BBB, we developed an EC-specific CR6-interactin factor1 (Crif1) deletion mouse. We clearly observed defects in motor behavior, uncompacted myelin and leukocyte infiltration caused by BBB maturation and disruption in this mice. Furthermore, we investigated the alteration in the actin cytoskeleton, which interacts with junctional proteins to support BBB integrity. Loss of Crif1 led to reorganization of the actin cytoskeleton and a decrease in tight junction-associated protein expression through an ATP production defect in vitro and in vivo. Based on these results, we suggest that mitochondrial OxPhos is important for the maturation and maintenance of BBB integrity by supplying ATP to cerebral ECs.

CRIF1 overexpression facilitates tumor growth and metastasis through inducing ROS/NFκB pathway in hepatocellular carcinoma

CR6-interacting factor 1 (Crif1) is a mitochondrial protein which is required for the assembly of oxidative phosphorylation (OXPHOS) complexes. Our bioinformatics analysis based on Cancer Genome Atlas (TCGA) database revealed an aberrant overexpression of CRIF1 in hepatocellular carcinoma (HCC). However, the clinical significance and biological functions of CRIF1 are still unclear in this malignancy. Here, we report that CRIF1 is frequently overexpressed in HCC cells mainly due to the downregulation of miR-497-5p, which is associated with poor prognosis of patients with HCC. CRIF1-promoted HCC growth and metastasis by suppressing cell apoptosis and inducing cell cycle progression and epithelial to mesenchymal transition (EMT). Mechanistically, increased mitochondrial ROS production and consequently activation of the NFκB signaling pathway was found to be involved in the promotion of growth and metastasis by CRIF1 in HCC cells. In summary, CRIF1 plays an oncogenic role in HCC progression through activating ROS/NFKB pathway, implying CRIF1 as a potential prognostic factor and therapeutic target in HCC.

The role of mitochondrial-related nuclear genes in age-related common disease

Mitochondria are critical organelles that provide energy as ATP to the cell. Besides 37 genes encoded by mitochondrial genome, it has been estimated that over 1500 nuclear genes are required for mitochondrial structure and function. Thus, mutations of many genes in the nuclear genome cause dysfunction of mitochondria that can lead to many severe conditions. Mitochondrial dysfunction often results in reduced ATP synthesis, higher levels of reactive oxygen species (ROS), imbalanced mitochondrial dynamics, and other detrimental effects. In addition to rare primary mitochondrial disorders, these mitochondrial-related genes are often associated with many common diseases. For example, in neurodegenerative diseases such as Parkinson's, Alzheimer's, and Huntington disease, mitochondrialand energy metabolism abnormalities can greatly affect brain function. Cancer cells are also known to exhibit repressed mitochondrial ATP production in favor of glycolysis, which fuels the aggressive proliferation and metastasis of tumor tissues, leading many to speculate on a possible relationship between compromised mitochondrial function and cancer. The association between mitochondrial dysfunction and diabetes is also unsurprising, given the organelle's crucial role in cellular energy utilization. Here, we will discuss the multiple lines of evidence connecting mitochondrial dysfunction associated with mitochondria-related nuclear genes to many of the well-known disease genes that also underlie common disease.

Deficiency of Crif1 in hair follicle stem cells retards hair growth cycle in adult mice

Hair growth is the cyclically regulated process that is characterized by growing phase (anagen), regression phase (catagen) and resting phase (telogen). Hair follicle stem cells (HFSCs) play pivotal role in the control of hair growth cycle. It has been notified that stem cells have the distinguished metabolic signature compared to differentiated cells, such as the preference to glycolysis rather than mitochondrial respiration. Crif1 is a mitochondrial protein that regulates the synthesis and insertion of oxidative phosphorylation (OXPHOS) polypeptides to inner membrane of mitochondria. Several studies demonstrate that tissue-specific knockout of Crif1 leads to mitochondrial dysfunction. In this study, we investigated the effect of mitochondrial dysfunction in terms of Crif1 deficiency on the hair growth cycle of adult mice. We created two kinds of inducible conditional knockout (icKO) mice. In epidermal specific icKO mice (Crif1 K14icKO), hair growth cycle was significantly retarded compared to wild type mice. Similarly, HFSC specific icKO mice (Crif1 K15icKO) showed significant retardation of hair growth cycle in depilation-induced anagen model. Interestingly, flow cytometry revealed that HFSC populations were maintained in Crif1 K15icKO mice. These results suggest that mitochondrial function in HFSCs is important for the progression of hair growth cycle, but not for maintenance of HFSCs.

An adipocyte-specific defect in oxidative phosphorylation increases systemic energy expenditure and protects against diet-induced obesity in mouse models

AIMS/HYPOTHESIS

Mitochondrial oxidative phosphorylation (OxPhos) is essential for energy production and survival. However, the tissue-specific and systemic metabolic effects of OxPhos function in adipocytes remain incompletely understood.

METHODS

We used adipocyte-specific Crif1 (also known as Gadd45gip1) knockout (AdKO) mice with decreased adipocyte OxPhos function. AdKO mice fed a normal chow or high-fat diet were evaluated for glucose homeostasis, weight gain and energy expenditure (EE). RNA sequencing of adipose tissues was used to identify the key mitokines affected in AdKO mice, which included fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15). For in vitro analysis, doxycycline was used to pharmacologically decrease OxPhos in 3T3L1 adipocytes. To identify the effects of GDF15 and FGF21 on the metabolic phenotype of AdKO mice, we generated AdKO mice with global Gdf15 knockout (AdGKO) or global Fgf21 knockout (AdFKO).

RESULTS

Under high-fat diet conditions, AdKO mice were resistant to weight gain and exhibited higher EE and improved glucose tolerance. In vitro pharmacological and in vivo genetic inhibition of OxPhos in adipocytes significantly upregulated mitochondrial unfolded protein response-related genes and secretion of mitokines such as GDF15 and FGF21. We evaluated the metabolic phenotypes of AdGKO and AdFKO mice, revealing that GDF15 and FGF21 differentially regulated energy homeostasis in AdKO mice. Both mitokines had beneficial effects on obesity and insulin resistance in the context of decreased adipocyte OxPhos, but only GDF15 regulated EE in AdKO mice.

CONCLUSIONS/INTERPRETATION

The present study demonstrated that the adipose tissue adaptive mitochondrial stress response affected systemic energy homeostasis via cell-autonomous and non-cell-autonomous pathways. We identified novel roles for adipose OxPhos and adipo-mitokines in the regulation of systemic glucose homeostasis and EE, which facilitated adaptation of an organism to local mitochondrial stress.

CR6-interacting factor 1 deficiency reduces endothelial nitric oxide synthase activity by inhibiting biosynthesis of tetrahydrobiopterin

Downregulation of CR6 interacting factor 1 (CRIF1) has been reported to induce mitochondrial dysfunction, resulting in reduced activity of endothelial nitric oxide synthase (eNOS) and NO production in endothelial cells. Tetrahydrobiopterin (BH4) is an important cofactor in regulating the balance between NO (eNOS coupling) and superoxide production (eNOS uncoupling). However, whether the decreased eNOS and NO production in CRIF1-deficient cells is associated with relative BH4 deficiency-induced eNOS uncoupling remains completely unknown. Our results showed that CRIF1 deficiency increased eNOS uncoupling and depleted levels of total biopterin and BH4 by reducing the enzymes of BH4 biosynthesis (GCH-1, PTS, SPR, and DHFR) in vivo and vitro, respectively. Supplementation of CRIF1-deficient cells with BH4 significantly increased the recovery of Akt and eNOS phosphorylation and NO synthesis. In addition, scavenging ROS with MitoTEMPO treatment replenished BH4 levels by elevating levels of GCH-1, PTS, and SPR, but with no effect on the level of DHFR. Downregulation of DHFR synthesis regulators p16 or p21 in CRIF1-deficient cells partially recovered the DHFR expression. In summary, CRIF1 deficiency inhibited BH4 biosynthesis and exacerbated eNOS uncoupling. This resulted in reduced NO production and increased oxidative stress, which contributes to endothelial dysfunction and is involved in the pathogenesis of cardiovascular diseases.