Mitochondrial Oxidative Phosphorylation Activity Research Articles

The ω-3 polyunsaturated fatty acid docosahexaenoic acid enhances NK-cell antitumor effector functions.

ω-3 polyunsaturated fatty acids (PUFAs) are known to directly repress tumour development and progression. In this study, we explored whether docosahexaenoic acid (DHA), a type of ω-3 PUFA, had an immunomodulatory role in promoting tumour growth in immunocompetent mice. The number of natural killer (NK) cells but not the number of T or B cells was decreased by DHA supplementation in various tissues under physiological conditions. Although the frequency and number of NK cells were comparable, IFN-γ production by NK cells in both the spleen and lung was increased in DHA-supplemented mice in the mouse B16F10 melanoma tumour model. Single-cell RNA sequencing (scRNA-seq) revealed that DHA promoted effector function and oxidative phosphorylation in NK cells but had no obvious effects on other immune cells. Using Rag2-/- mice and NK-cell depletion by PK136 antibody injection, we demonstrated that the suppression of B16F10 melanoma tumour growth in the lung by DHA supplementation was dependent mainly on NK cells. In vitro experiments showed that DHA directly enhanced IFN-γ production, CD107a expression and mitochondrial oxidative phosphorylation (OXPHOS) activity, and slightly increased proliferator-activated receptor gamma coactivator-1α (PGC-1α) protein expression in NK cells. The PGC-1α inhibitor SR-18292 in vitro and NK cell-specific knockout of PGC-1α in mice reversed the antitumour effects of DHA. In summary, our findings broaden the current knowledge on how DHA supplementation protects against cancer growth from the perspective of immunomodulation by upregulating PGC-1α signalling-mediated mitochondrial OXPHOS activity in NK cells.

Targeting Erbin-mitochondria axis in platelets/megakaryocytes promotes B cell-mediated antitumor immunity

The roles of platelets/megakaryocytes (MKs), the key components in the blood system, in the tumor microenvironment and antitumor immunity are unclear. In patients with colorectal cancer, the number of platelets was significantly increased in patients with metastasis, and Erbin expression was highly expressed in platelets from patients with metastases. Moreover, Erbin knockout in platelets/MKs suppressed lung metastasis in mice and promoted aggregations of platelets. Mechanistically, Erbin-deficient platelets have increasing mitochondrial oxidative phosphorylation and secrete lipid metabolites like acyl-carnitine (Acar) by abolishing interaction with prothrombotic protein ESAM. Notably, Acar enhanced the activity of mitochondrial electron transport chain complex and mitochondrial oxidative phosphorylation in B cells by acetylation of H3K27 epigenetically. Targeting Erbin in platelets/MKs by a nanovesicle system dramatically attenuated lung metastasis in mice invivo. Our study identifies an Erbin-mitochondria axis in platelets/MKs, which suppresses B cell-mediated antitumor immunity, suggesting a new way for the treatment of metastasis.

Abstract C049: Loss of RNF43 creates an OXPHOS dependency in early pancreatic neoplasia

Abstract Pancreatic ductal adenocarcinoma (PDAC) has a dismal 5-year survival of 12%. RNF43 is frequently mutated in pancreatic cystic neoplasms, including intraductal papillary mucinous neoplasms (IPMNs), which are precursor lesions of PDAC. RNF43 encodes for an E3 ubiquitin ligase and was initially identified as a negative Wnt regulator. To elucidate the role of RNF43-mutated neoplasms in an organ specific context, we have generated a genetically engineered mouse model which has pancreas specific loss of RNF43 (Hosein, Gastroenterology 2022). In this study we examine some of the metabolic dependencies created by Rnf43 loss on the background of mutant Kras, and how the Kras;Rnf43 model differs from the commonly used Kras;p53 model of PDAC. We have generated cell lines harboring mutant Kras and bi-allelic loss of Rnf43 from the resulting lesions in these mice (henceforth referred to as Kras;Rnf43 lines).Isogenic Kras;Rnf43 cell lines with re-expression of full-length Rnf43 (Kras;Rnf43-RNF43OE) were generated to confirm if observed phenotypes were Rnf43 dependent. Single-cell RNA sequencing (scRNA-seq) was performed for comparison between murine PDAC arising in Kras;Rnf43 versus Kras;p53 mice. We further compared metabolic parameters in Kras;Rnf43 and Kras;Rnf43-RNF43OE cells using the Seahorse platform. Mitochondrial ultrastructure by transmission electron microscopy (TEM) was analyzed in Kras;Rnf43 compared to Kras;p53 cells. To visualize endoplasmic reticulum (ER)-mitochondria contact sites (ERMCS), a split green fluorescent protein-based contact site sensor (SPLICS) was transfected and analyzed. Compared to Kras;p53 PDAC, Kras;Rnf43 tumors demonstrated upregulated mitochondrial transcripts and gene signatures of ER stress. Further, the ER stress response protein IRE1 was markedly elevated in Kras;Rnf43 cells versus Kras;p53 cells. The Kras;Rnf43 lines had enhanced mitochondrial oxidative phosphorylation (OXPHOS) activity and demonstrated evidence of enhanced mitochondrial quality control. ERMCS is a dynamic contact region between ER and mitochondria, which regulates biological processes including calcium homeostasis, ER stress and mitochondrial dynamics. The Kras;Rnf43 cells had significantly increased ERMCS compared to Kras;p53 cells. Finally, using IACS-010759, a small molecule inhibitor of OXPHOS, we demonstrate that Kras;Rnf43 cells had both increased in vitro sensitivity as well as in vivo susceptibility to tumor growth inhibition in orthotopic models, which translated into increased overall survival of mice. In conclusion, we provide evidence showing that bi-allelic loss of RNF43 is associated with increased ER stress and enhanced IRE1 dependent stress response. ER stress is mitigated via increased mitochondrial OXPHOS and ERMCS. Importantly, our results suggest that this creates a metabolic synthetic essentiality in the context of RNF43 loss, providing an avenue to suppress the progression of RNF43-mutated IPMNs, and potentially other solid cancers by targeting mitochondrial OXPHOS. Citation Format: Akiko Sagara, Brandon Chen, Nathaniel G. Yee, Megan J. Siemann, Costas A. Lyssiotis, Yatrik M. Shah, Sonja M. Woermann, Anirban Maitra. Loss of RNF43 creates an OXPHOS dependency in early pancreatic neoplasia [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C049.

ACOX1-mediated peroxisomal fatty acid oxidation contributes to metabolic reprogramming and survival in chronic lymphocytic leukemia.

Chronic lymphocytic leukemia (CLL) is still an incurable disease, with many patients developing resistance to conventional and targeted therapies. To better understand the physiology of CLL and facilitate the development of innovative treatment options, we examined specific metabolic features in the tumor CLL B-lymphocytes. We observed metabolic reprogramming, characterized by a high level of mitochondrial oxidative phosphorylation activity, a low glycolytic rate, and the presence of C2- to C6-carnitine end-products revealing an unexpected, essential role for peroxisomal fatty acid beta-oxidation (pFAO). Accordingly, downmodulation of ACOX1 (a rate-limiting pFAO enzyme overexpressed in CLL cells) was enough to shift the CLL cells' metabolism from lipids to a carbon- and amino-acid-based phenotype. Complete blockade of ACOX1 resulted in lipid droplet accumulation and caspase-dependent death in CLL cells, including those from individuals with poor cytogenetic and clinical prognostic factors. In a therapeutic translational approach, ACOX1 inhibition spared non-tumor blood cells from CLL patients but led to the death of circulating, BCR-stimulated CLL B-lymphocytes and CLL B-cells receiving pro-survival stromal signals. Furthermore, a combination of ACOX1 and BTK inhibitors had a synergistic killing effect. Overall, our results highlight a less-studied but essential metabolic pathway in CLL and pave the way towards the development of new, metabolism-based treatment options.

Loss of Fatty Acid Degradation by Astrocytic Mitochondria as a Mechanism of Neuroinflammation and Neurodegeneration

AbstractBackgroundAstrocytes provide key neuronal support, and their phenotypic transformation is strongly implicated in neurodegenerative disorders including Alzheimer’s disease (AD). Metabolically, astrocytes possess modest mitochondrial oxidative phosphorylation (OxPhos) activity, yet the pathological role of astrocytic OxPhos in neurodegeneration remains to be defined.MethodWe generated the TfamAKO mice, in which the transcription factor A mitochondrial (Tfam) is deleted selectively in astrocytes. Behavioral, electrophysiological, immunostaining, transcriptomics, metabolomics, and magnetic resonance imaging analyses were employed to characterize AD‐relevant phenotypes of TfamAKO mice, which were further compared to an AD mouse model (5xFAD). Primary cell cultures and co‐cultures were used to determine the cell autonomous and non‐autonomous mechanisms by which disrupted astrocytic OxPhos induces astrocyte reactivity, neuroinflammation and neurodegeneration.ResultHere we show that the brain critically depends on astrocytic OxPhos to degrade fatty acids (FAs) and maintain lipid homeostasis. Aberrant astrocytic OxPhos induces lipid droplet (LD) accumulation followed by neurodegeneration that recapitulates key features of AD including reactive astrogliosis, synaptic loss, microgliosis, demyelination, and cognitive impairment. Mechanistically, when FA load overwhelms astrocytic OxPhos capacity, elevated acetyl‐CoA levels induce astrocyte reactivity by enhancing STAT3 acetylation and activation. Intercellularly, lipid‐laden reactive astrocytes stimulate neuronal FA oxidation and oxidative stress, activate microglia via IL‐3 signaling, and inhibit the biosynthesis of FAs and phospholipids required for myelin replenishment. Moreover, the metabolic and transcriptional signatures of the hippocampus of TfamAKO mice highly overlap with that of 5xFAD mice.ConclusionWe reveal a lipid‐centric, AD‐resembling mechanism by which astrocytic mitochondrial dysfunction progressively induces neuroinflammation and neurodegeneration.

Status of Mitochondrial Oxidative Phosphorylation during the Development of Heart Failure.

Mitochondria are specialized organelles, which serve as the "Power House" to generate energy for maintaining heart function. These organelles contain various enzymes for the oxidation of different substrates as well as the electron transport chain in the form of Complexes I to V for producing ATP through the process of oxidative phosphorylation (OXPHOS). Several studies have shown depressed OXPHOS activity due to defects in one or more components of the substrate oxidation and electron transport systems which leads to the depletion of myocardial high-energy phosphates (both creatine phosphate and ATP). Such changes in the mitochondria appear to be due to the development of oxidative stress, inflammation, and Ca2+-handling abnormalities in the failing heart. Although some investigations have failed to detect any changes in the OXPHOS activity in the failing heart, such results appear to be due to a loss of Ca2+ during the mitochondrial isolation procedure. There is ample evidence to suggest that mitochondrial Ca2+-overload occurs, which is associated with impaired mitochondrial OXPHOS activity in the failing heart. The depression in mitochondrial OXPHOS activity may also be due to the increased level of reactive oxygen species, which are formed as a consequence of defects in the electron transport complexes in the failing heart. Various metabolic interventions which promote the generation of ATP have been reported to be beneficial for the therapy of heart failure. Accordingly, it is suggested that depression in mitochondrial OXPHOS activity plays an important role in the development of heart failure.

Small molecule activator of Serca2a improves myocardial bioenergetics and lipid metabolism in diabetic mice

Background: Altered calcium homeostasis, insulin resistance, and dysregulated energy metabolism are major causes of diabetic cardiomyopathy. The expression and activity of Sarco/endoplasmic reticulum Ca2+-ATPase 2a (SERCA2a) are decreased in the diabetic heart failure. Increasing SERCA2a function reverses both systolic and diastolic dysfunction. However, the mechanisms and consequences underlying the role of SERCA2a in the diabetic failing heart are not clear yet. Objective: To examine the effect of pharmacological activation of SERCA2a on the diabetic heart. Methods and Results: To restore calcium abnormality in leptin-deficient (ob/ob) diabetic mice, we employed and contrasted two different models to elevate the restoration of SERCA2a function: 1) activation of SERCA2 with a novel allosteric agonist, CDN1163 or 2) overexpression of SERCA2a using cardiac-specific AAV9-mediated gene transfer. We demonstrate that SERCA2a activation with CDN1163 or AAV9 repressed the expression of genes involved in lipid synthesis and fatty acid oxidation in obese mice, leading to improved lipid homeostasis. Increased SERCA2a function improved mitochondrial function through elevation of mitochondrial biogenesis, mitochondrial DNA content, oxidative phosphorylation, and ATPase activity in the heart of obese mice. SERCA2a also restored mitochondrial membrane potential to normal levels in cultured H9C2 myocytes in the presence of high glucose and H2O2. SERCA2a ameliorated intracellular lipid toxicity and cell damage, possibly through the upregulation of the gene expression of antioxidant enzymes, and attenuated ROS generation by repression of NADPH oxidase in the obese heart. Furthermore, these molecular changes were paralleled by improvement in diabetes-induced diastolic dysfunction following CDN1163 activation of SERCA2a or AAV9-SERCA2a overexpression in the obese mice. Conclusion: These results suggest that calcium resolving diabetes-induced calcium dyshomeostasis by pharmacological activation of SERCA2a in obese individuals may be a highly effective therapeutic modality for treating obesity-induced diabetes. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Metabolic shift and the effect of mitochondrial respiration on the osteogenic differentiation of dental pulp stem cells.

Metabolism shifts from glycolysis to mitochondrial oxidative phosphorylation are vital during the differentiation of stem cells. Mitochondria have a direct function in differentiation. However, the metabolic shift and the effect of mitochondria in regulating the osteogenic differentiation of human dental pulp stem cells (hDPSCs) remain unclear. Human dental pulp stem cells were collected from five healthy donors. Osteogenic differentiation was induced by osteogenic induction medium. The activities of alkaline phosphatase, hexokinase, pyruvate kinase, and lactate dehydrogenase were analyzed by enzymatic activity kits. The extracellular acidification rate and the mitochondrial oxygen consumption rate were measured. The mRNA levels of COL-1, ALP, TFAM, and NRF1 were analyzed. The protein levels of p-AMPK and AMPK were detected by western blotting. Glycolysis decreased after a slight increase, while mitochondrial oxidative phosphorylation continued to increase when cells grew in osteogenic induction medium. Therefore, the metabolism of differentiating cells switched to mitochondrial respiration. Next, inhibiting mitochondrial respiration with carbonyl cyanide-chlorophenylhydrazone, a mitochondrial uncoupler inhibited hDPSCs differentiation with less ALP activity and decreased ALP and COL-1 mRNA expression. Furthermore, mitochondrial uncoupling led to AMPK activation. 5-Aminoimidazole-4-carboxamide ribonucleotide, an AMPK activator, simulated the effect of mitochondrial uncoupling by inhibiting osteogenic differentiation, mitochondrial biogenesis, and mitochondrial morphology. Mitochondrial uncoupling and activation of AMPK depressed mitochondrial oxidative phosphorylation and inhibited differentiation, suggesting that they may serve as regulators to halt osteogenic differentiation from impaired mitochondrial oxidative phosphorylation.

Abstract 388: Acquired sensitivity to ONC201/TIC10 in ER+ breast cancer progressing on the mTOR inhibitor everolimus

Abstract The mTOR inhibitor everolimus has become an important component for clinical management of metastatic ER+ breast cancer. Despite the improved patient outcomes, progression and resistance will still develop. Therefore, it is important to research strategies that can increase response durability and effectiveness of this therapy. Here we developed everolimus resistance models and performed pre-clinical evaluation of the small molecule ONC201/TIC10, a drug candidate showing promising results in clinical trials with advanced cancer patients. ONC201/TIC10 targets mitochondrial function and metabolism and activates stress response, however its efficacy has not been studied in everolimus resistant breast cancer. Transcriptomic analysis in everolimus resistant tumors identified sustained mitochondrial oxidative phosphorylation activity suggesting increased sensitivity to ONC201/TIC10. Our results show that combination treatment of ONC201/TIC10 with everolimus inhibits the growth of sensitive as well as everolimus resistant cells in 2D and 3D in vitro studies. The increased response to combination therapy was confirmed in primary cells from patients progressing on endocrine and mTOR therapy, supporting clinical relevance. We further show that the mechanism of ONC201/TIC10 anti-proliferative activity involves disruption of mitochondrial function and increased levels of the pro-apoptotic transcription factors CHOP and ATF4. Importantly, several resistant cell lines demonstrated increased dependency on mitochondrial respiration compared to sensitive cells which contributes to a vulnerability to ONC201/TIC10. In conclusion, we used pre-clinical models to characterize acquired sensitivity to mTOR inhibition. Combining patient derived data with resistant cell line driven experiments, our study provides validated findings in various settings strengthening the potential for clinical applications of ONC201/TIC10. We propose that ONC201/TIC10 and modulation of mitochondrial function is effective in drug resistant cancer cells and can enhance the anti-tumor activity of standard of care therapy in progressing patients. Citation Format: Eleni Farmaki, Rena Emond, Aritro Nath, Vince K. Grolmusz, Patrick A. Cosgrove, Andrea H. Bild. Acquired sensitivity to ONC201/TIC10 in ER+ breast cancer progressing on the mTOR inhibitor everolimus [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 388.

Loss of fatty acid degradation by astrocytic mitochondria triggers neuroinflammation and neurodegeneration.

Astrocytes provide key neuronal support, and their phenotypic transformation is implicated in neurodegenerative diseases. Metabolically, astrocytes possess low mitochondrial oxidative phosphorylation (OxPhos) activity, but its pathophysiological role in neurodegeneration remains unclear. Here, we show that the brain critically depends on astrocytic OxPhos to degrade fatty acids (FAs) and maintain lipid homeostasis. Aberrant astrocytic OxPhos induces lipid droplet (LD) accumulation followed by neurodegeneration that recapitulates key features of Alzheimer's disease (AD), including synaptic loss, neuroinflammation, demyelination and cognitive impairment. Mechanistically, when FA load overwhelms astrocytic OxPhos capacity, elevated acetyl-CoA levels induce astrocyte reactivity by enhancing STAT3 acetylation and activation. Intercellularly, lipid-laden reactive astrocytes stimulate neuronal FA oxidation and oxidative stress, activate microglia through IL-3 signalling, and inhibit the biosynthesis of FAs and phospholipids required for myelin replenishment. Along with LD accumulation and impaired FA degradation manifested in an AD mouse model, we reveal a lipid-centric, AD-resembling mechanism by which astrocytic mitochondrial dysfunction progressively induces neuroinflammation and neurodegeneration.

Combined Effects of Fluoride and Arsenic on Mitochondrial Function in the Liver of Rat.

Biochemical and/or molecular mechanisms of arsenic or fluoride toxicity in experimental animals have been widely investigated in the recent past. However, their combined effects on target cells/organelle are poorly understood. The present study was executed to delineate their combined effects on mitochondrial function in the liver of rat. Female Wistar rats (140 ± 20 g) were force fed individually or in combination with sodium arsenate (4 mg/kg body weight) and sodium fluoride (4 mg/kg body weight) for 90 days. Thereafter, established markers of mitochondrial function viz. mitochondrial lipid peroxidation, oxidative phosphorylation, ATPase, succinic dehydrogenase, and caspase-3 activity were determined. Cytochrome C release and oxidative DNA damage were also estimated in the liver of respective groups of rats. The study showed significant differences in these results amongst the three groups. Observations on parameters viz. LPO, cytochrome-C, caspase-3, and 8-OHdG suggested an antagonistic relationship between these two elements. Results on ATPase, SDH, and ADP:O ratio indicated synergism. It is concluded that AsIII + F in combination may express differential effects on signalling pathways and proapoptotic/antiapoptotic proteins/genes that contribute to liver cell death. Interaction of As and F with mitochondria.

Deterioration of mitochondrial biogenesis and degradation in the endometrium is a cause of subfertility in cows.

To investigate possible causes of reproductive failure, we conducted global endometrial gene expression analyses in fertile and subfertile cows. Ingenuity pathway analysis showed that RICTOR and SIRT3 are significant upstream regulators for highly expressed genes in fertile cows, and are predicted to be activated upstream regulators of normal mitochondrial respiration. Canonical pathway analysis revealed that these highly expressed genes are involved in the activation of mitochondrial oxidative phosphorylation. Therefore, in subfertile cows, the inactivation of RICTOR and SIRT3 may correlate with decreased capacity of mitochondrial respiration. Furthermore, the expression levels of most mitochondrial DNA genes and nuclear genes encoding mitochondrial proteins were higher in subfertile cows. The mitochondrial DNA copy number was significantly higher in the endometrium of subfertile cows, whereas the ATP content did not differ between fertile and subfertile cows. Quantitative reverse transcription-PCRanalysis demonstrated that the expression of PGC1a, TFAM, MFN1, FIS1, and BCL2L13 were significantly lower in subfertile cows. In addition, transmission electron microscopy images showed mitochondrial swelling in the endometrial cells of the subfertile cow. These results suggest that poor-quality mitochondria accumulate in the endometrium owing to a reduced capacity for mitochondrial biogenesis, fusion, fission, and degradation in subfertile cows, and may contribute to infertility.

"Gingival Soft Tissue Integrative" Lithium Disilicate Glass-Ceramics with High Mechanical Properties and Sustained-Release Lithium Ions.

Due to their good mechanical performances and high biocompatibility, all-ceramic materials are widely applied in clinics, especially in orthopedic and dental areas. However, the "hard" property negatively affects its integration with "soft" tissue, which greatly limits its application in soft tissue-related areas. For example, dental implant all-ceramic abutments should be well integrated with the surrounding gingival soft tissue to prevent the invasion of bacteria. Mimicking the gingival soft tissue and dentine integration progress, we applied the modified ion-exchange technology to "activate" the biological capacity of lithium disilicate glass-ceramics, via introducing OH- to weaken the stability of Si-O bonds and release lithium ions to promote multi-reparative functions of gingival fibroblasts. The underlying mechanism was found to be closely related to the activation of mitochondrial activity and oxidative phosphorylation. In addition, during the ion-exchange process, the larger radius sodium ions (Na+) replaced the smaller radius lithium ions (Li+), so that the residual compressive stress was applied to the glass-ceramics surface to counteract the tensile stress, thus improving the mechanical properties. This successful case in simultaneous improvement of mechanical properties and biological activities proves the feasibility of developing "soft tissue integrative" all-ceramic materials with high mechanical properties. It proposes a new strategy to develop advanced bioactive and high strength all-ceramic materials by modified ion-exchange, which can pave the way for the extended applications of such all-ceramic materials in soft tissue-related areas.

Astrocyte heterogeneity within white matter tracts and a unique subpopulation of optic nerve head astrocytes.

Much of what we know about astrocyte form and function is derived from the study of gray matter protoplasmic astrocytes, whereas white matter fibrous astrocytes remain relatively unexplored. Here, we used the ribotag approach to isolate ribosome-associated mRNA and investigated the transcriptome of uninjured fibrous astrocytes from three regions: unmyelinated optic nerve head, myelinated optic nerve proper, and corpus callosum. Astrocytes from each region were transcriptionally distinct and we identified region-specific astrocyte genes and pathways. Energy metabolism, particularly oxidative phosphorylation and mitochondrial protein translation emerged as key differentiators of astrocyte populations. Optic nerve astrocytes expressed higher levels of neuroinflammatory pathways than corpus callosum astrocytes and we further identified CARTPT as a new marker of optic nerve head astrocytes. These previously uncharacterized transcriptional profiles of white matter astrocyte types reveal their functional diversity and a greater heterogeneity than previously appreciated.

ITCH deficiency clinical phenotype expansion and mitochondrial dysfunction

Autoimmune Disease, Multisystem, with Facial Dysmorphism (ADMFD) is an autosomal recessive disorder due to pathogenic variants in the ITCH gene. It is characterized by failure to thrive, dysmorphic facial features, developmental delay, and systemic autoimmunity that can manifest variably with autoimmune hepatitis, thyroiditis, and enteropathy, among other organ manifestations. It was originally described in 10 consanguineous Old Order Amish patients, and more recently in two patients of White British and Black German ethnicities. While the role of ITCH protein in apoptosis and inflammation has previously been characterized, a defect in cellular bioenergetics has not yet been reported in ITCH deficiency. Here we present a Caucasian female originally evaluated for possible mitochondrial respiratory chain deficiency, who ultimately was found to have two novel variants in ITCH with absence of ITCH protein in patient derived fibroblasts. Clinical studies of patient muscle showed mitochondrial DNA copy number of 57% compared to controls. Functional studies in skin fibroblasts revealed decreased activity of mitochondrial fatty acid oxidation and oxidative phosphorylation, and decreased overall ATP production. Our findings confirm mitochondrial energy dysfunction in a patient with ITCH deficiency offering the opportunity to assess alternative therapeutic options.

Modulating p-AMPK/mTOR Pathway of Mitochondrial Dysfunction Caused by MTERF1 Abnormal Expression in Colorectal Cancer Cells.

Human mitochondrial transcription termination factor 1 (MTERF1) has been demonstrated to play an important role in mitochondrial gene expression regulation. However, the molecular mechanism of MTERF1 in colorectal cancer (CRC) remains largely unknown. Here, we found that MTERF1 expression was significantly increased in colon cancer tissues compared with normal colorectal tissue by Western blotting, immunohistochemistry, and tissue microarrays (TMA). Overexpression of MTERF1 in the HT29 cell promoted cell proliferation, migration, invasion, and xenograft tumor formation, whereas knockdown of MTERF1 in HCT116 cells appeared to be the opposite phenotype to HT29 cells. Furthermore, MTERF1 can increase mitochondrial DNA (mtDNA) replication, transcription, and protein synthesis in colorectal cancer cells; increase ATP levels, the mitochondrial crista density, mitochondrial membrane potential, and oxygen consumption rate (OCR); and reduce the ROS production in colorectal cancer cells, thereby enhancing mitochondrial oxidative phosphorylation (OXPHOS) activity. Mechanistically, we revealed that MTERF1 regulates the AMPK/mTOR signaling pathway in cancerous cell lines, and we also confirmed the involvement of the AMPK/mTOR signaling pathway in both xenograft tumor tissues and colorectal cancer tissues. In summary, our data reveal an oncogenic role of MTERF1 in CRC progression, indicating that MTERF1 may represent a new therapeutic target in the future.

Targeting HOTAIRM1 ameliorates glioblastoma by disrupting mitochondrial oxidative phosphorylation and serine metabolism

SummarySerine hydroxymethyltransferase 2 (SHMT2), which catalyzes the conversion of serine to glycine and one-carbon transfer reactions in mitochondria, is significantly upregulated in glioblastoma (GBM). However, the mechanism by which the stability of SHMT2 gene expression is maintained to drive GBM tumorigenesis has not been clarified. Herein, through microarray screening, we identified that HOXA Transcript Antisense RNA, Myeloid-Specific 1 (HOTAIRM1) modulates the SHMT2 level in various GBM cell lines. Serine catabolism and mitochondrial oxidative phosphorylation activities were decreased by HOTAIRM1 inhibition. Mechanistically, according to our mass spectrometry and eCLIP-seq results, HOTAIRM1 can bind to PTBP1 and IGF2BP2. Furthermore, HOTAIRM1 maintains the stability of SHMT2 by promoting the recognition of an m6A site and the interaction of PTBP1/IGF2BP2 with SHMT2 mRNA. The stability of HOTAIRM1 can also be enhanced and results in positive feedback regulation to support the progression of GBM. Thus, targeting HOTAIRM1 could be a promising metabolic therapy for GBM.

NAD + salvage governs mitochondrial metabolism, invigorating natural killer cell antitumor immunity.

Natural killer (NK) cells are key players in tumor immunosurveillance, and metabolic adaptation manipulates their fate and functional state. The nicotinamide adenine dinucleotide (NAD + ) has emerged as a vital factor to link cellular metabolism and signaling transduction. Here, we identified NAD + metabolism as a central hub to determine the homeostasis and function of NK cells. NAD + level was elevated in activated NK cells. NAD + supplementation not only enhanced cytokine production and cytotoxicity but also improved the proliferation and viability of NK cells. Intriguingly, the salvage pathway was involved in maintaining NAD + homeostasis in activated NK cells. Genetic ablation or pharmacological blockade of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the NAD + salvage pathway, markedly destroyed the viability and function of NK cells. Mechanistically, NAD + salvage dictated the mitochondrial homeostasis and oxidative phosphorylation activity to support the optimal function of NK cells. However, in human HCC tissues, NAMPT expression and NAD + level were significantly down-regulated in tumor-infiltrating NK cells, which negatively correlated with patient survival. And lactate accumulation in the tumor microenvironment was at least partially responsible for the transcriptional repression of NAMPT in NK cells. Further, deficiency of Nampt in NK cells accelerated the growth of HCC and melanoma. Supplementation of the NAD + precursor nicotinamide mononucleotide (NMN) significantly improved NK antitumor response in both mouse and human cell-derived xenografts. These findings reveal NAD + salvage as an essential factor for NK-cell homeostasis and function, suggesting a potential strategy for invigorating NK cell-based immunotherapy.

Mice selected for a high basal metabolic rate evolved larger guts but not more efficient mitochondria.

Intra-specific variation in both the basal metabolic rate (BMR) and mitochondrial efficiency (the amount of ATP produced per unit of oxygen consumed) has profound evolutionary and ecological consequences. However, the functional mechanisms responsible for this variation are not fully understood. Mitochondrial efficiency is negatively correlated with BMR at the interspecific level but it is positively correlated with performance capacity at the intra-specific level. This discrepancy is surprising, as theories explaining the evolution of endothermy assume a positive correlation between BMR and performance capacity. Here, we quantified mitochondrial oxidative phosphorylation activity and efficiency in two lines of laboratory mice divergently selected for either high (H-BMR) or low (L-BMR) levels of BMR. H-BMR mice had larger livers and kidneys (organs that are important predictors of BMR). H-BMR mice also showed higher oxidative phosphorylation activity in liver mitochondria but this difference can be hypothesized to be a direct effect of selection only if the heritability of this trait is low. However, mitochondrial efficiency in all studied organs did not differ between the two lines. We conclude that the rapid evolution of BMR can reflect changes in organ size rather than mitochondrial properties, and does not need to be accompanied obligatorily by changes in mitochondrial efficiency.

Integrating spatial transcriptomics with single-cell transcriptomics reveals a spatiotemporal gene landscape of the human developing kidney

BackgroundResearch on spatiotemporal gene landscape can provide insights into the spatial characteristics of human kidney development and facilitate kidney organoid cultivation. Here, we profiled the spatiotemporal gene programs of the human embryonic kidneys at 9 and 18 post-conception weeks (PCW) by integrating the application of microarray-based spatial transcriptomics and single-cell transcriptomics.ResultsWe mapped transcriptomic signatures of scRNA-seq cell types upon the 9 and 18 PCW kidney sections based on cell-type deconvolution and multimodal intersection analyses, depicting a spatial landscape of developing cell subpopulations. We established the gene characteristics in the medullary regions and revealed a strong mitochondrial oxidative phosphorylation and glycolysis activity in the deeper medullary region. We also built a regulatory network centered on GDNF-ETV4 for nephrogenic niche development based on the weighted gene co-expression network analysis and highlighted the key roles of Wnt, FGF, and JAG1-Notch2 signaling in maintaining renal branching morphogenesis.ConclusionsOur findings obtained by this spatiotemporal gene program are expected to improve the current understanding of kidney development.