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Liver‐X‐receptor (LXR) agonists are known to bear anti‐tumor activity. However, their efficacy is limited and additional insights regarding the underlying mechanism are necessary. By performing transcriptome analysis coupled with global polar metabolite screening, we show that LXR agonists, LXR623 and GW3965, enhance synergistically the anti‐proliferative effect of BH3 mimetics in solid tumor malignancies, which is predominantly mediated by cell death with features of apoptosis and is rescued by exogenous cholesterol. Extracellular flux analysis and carbon tracing experiments (U‐ 13 C‐glucose and U‐ 13 C‐glutamine) reveal that within 5 h, activation of LXRβ results in reprogramming of tumor cell metabolism, leading to suppression of mitochondrial respiration, a phenomenon not observed in normal human astrocytes. LXR activation elicits a suppression of respiratory complexes at the protein level by reducing their stability. In turn, energy starvation drives an integrated stress response (ISR) that up‐regulates pro‐apoptotic Noxa in an ATF4‐dependent manner. Cholesterol and nucleotides rescue from the ISR elicited by LXR agonists and from cell death induced by LXR agonists and BH3 mimetics. In conventional and patient‐derived xenograft models of colon carcinoma, melanoma, and glioblastoma, the combination treatment of ABT263 and LXR agonists reduces tumor sizes significantly stronger than single treatments. Therefore, the combination treatment of LXR agonists and BH3 mimetics might be a viable efficacious treatment approach for solid malignancies. Synopsis Liver‐X‐receptor agonists display limited anti‐tumor activity. The present study uncovers the synthetic lethality triggered by combining activation of liver‐X‐receptor and Bcl‐xL inhibition. Activation of LXR‐receptors resulted in suppression of gene‐sets related to mitochondrial translation, metabolism, transcription and regulators of intrinsic apoptosis associated, with an increase in cholesterol efflux signature. In the TCGA datasets, high levels of the LXR target ABCA1 correlated with low levels of group of genes related to mitochondrial transcription, translation and metabolism. Liver‐X‐receptors activation led to early reprogramming of oxidative energy metabolism, resulting in energy deprivation and solid tumor cells sensitization to glucose withdrawal. Suppression of the electron transport chain by LXRβ activation lowered the apoptotic threshold and sensitized solid tumor cells to the cytotoxic effects of BH3‐mimetics. The combination treatment of ABT263 and LXR623 reduced tumor growth in patient‐derived xenograft model systems. Graphical Abstract Liver‐X‐receptor agonists display limited anti‐tumor activity. The present study uncovers the synthetic lethality triggered by combining activation of liver‐X‐receptor and Bcl‐xL inhibition.

Coenzyme Q (CoQ) is an electron acceptor for sulfide‐quinone reductase (SQR), the first enzyme of the hydrogen sulfide oxidation pathway. Here, we show that lack of CoQ in human skin fibroblasts causes impairment of hydrogen sulfide oxidation, proportional to the residual levels of CoQ. Biochemical and molecular abnormalities are rescued by CoQ supplementation in vitro and recapitulated by pharmacological inhibition of CoQ biosynthesis in skin fibroblasts and ADCK3 depletion in HeLa cells. Kidneys of Pdss2 kd/kd mice, which only have ~15% residual CoQ concentrations and are clinically affected, showed (i) reduced protein levels of SQR and downstream enzymes, (ii) accumulation of hydrogen sulfides, and (iii) glutathione depletion. These abnormalities were not present in brain, which maintains ~30% residual CoQ and is clinically unaffected. In Pdss2 kd/kd mice, we also observed low levels of plasma and urine thiosulfate and increased blood C4‐C6 acylcarnitines. We propose that impairment of the sulfide oxidation pathway induced by decreased levels of CoQ causes accumulation of sulfides and consequent inhibition of short‐chain acyl‐CoA dehydrogenase and glutathione depletion, which contributes to increased oxidative stress and kidney failure. Synopsis Coenzyme Q (CoQ) is an electron acceptor for sulfide‐quinone reductase (SQR), the first enzyme of the hydrogen sulfide oxidation pathway. Lack of CoQ is here shown to cause impairment of hydrogen sulfide oxidation in vitro and in vivo . Reduced levels of CoQ in vitro cause impairment of the hydrogen sulfide oxidation pathway and increased protein persulfhydration levels. Reduced levels of CoQ in vivo impair the sulfide oxidation pathway determining accumulation of sulfides and consequent inhibition of short‐chain acyl‐CoA dehydrogenase. Graphical Abstract Coenzyme Q (CoQ) is an electron acceptor for sulfide‐quinone reductase (SQR), the first enzyme of the hydrogen sulfide oxidation pathway. Lack of CoQ is here shown to cause impairment of hydrogen sulfide oxidation in vitro and in vivo .

Mutations in mitochondrial DNA (mtDNA) have been linked to a variety of metabolic, neurological and muscular diseases which can present at any time throughout life. MtDNA is replicated by DNA polymerase gamma (Pol γ), twinkle helicase and mitochondrial single-stranded binding protein (mtSSB). The Pol γ holoenzyme is a heterotrimer consisting of the p140 catalytic subunit and a p55 homodimeric accessory subunit encoded by the nuclear genes POLG and POLG2, respectively. The accessory subunits enhance DNA binding and promote processive DNA synthesis of the holoenzyme. Mutations in either POLG or POLG2 are linked to disease and adversely affect maintenance of the mitochondrial genome, resulting in depletion, deletions and/or point mutations in mtDNA. A homozygous mutation located at Chr17: 62492543G>A in POLG2, resulting in R182W substitution in p55, was previously identified to cause mtDNA depletion and fatal hepatic liver failure. Here we characterize this homozygous R182W p55 mutation using in vivo cultured cell models and in vitro biochemical assessments. Compared to control fibroblasts, homozygous R182W p55 primary dermal fibroblasts exhibit a two-fold slower doubling time, reduced mtDNA copy number and reduced levels of POLG and POLG2 transcripts correlating with the reported disease state. Expression of R182W p55 in HEK293 cells impairs oxidative-phosphorylation. Biochemically, R182W p55 displays DNA binding and association with p140 similar to WT p55. R182W p55 mimics the ability of WT p55 to stimulate primer extension, support steady-state nucleotide incorporation, and suppress the exonuclease function of Pol γ in vitro. However, R182W p55 has severe defects in protein stability as determined by differential scanning fluorimetry and in stimulating function as determined by thermal inactivation. These data demonstrate that the Chr17: 62492543G>A mutation in POLG2, R182W p55, severely impairs stability of the accessory subunit and is the likely cause of the disease phenotype.

Recent data suggest that glioblastomas (GBM) activate the c-MET signaling pathway and display increased levels in anti-apoptotic Bcl-2 family members. Therefore, targeting these two deregulated pathways for therapy might yield synergistic treatment responses. We applied extracellular flux analysis to assess tumor metabolism. We found that combined treatment with ABT263 and Crizotinib synergistically reduces the proliferation of glioblastoma cells, which was dependent on dual inhibition of Bcl-2 and Bcl-xL. The combination treatment led to enhanced apoptosis with loss of mitochondrial membrane potential and activation of caspases. On the molecular level, c-MET-inhibition results in significant energy deprivation with a reduction in oxidative phosphorylation, respiratory capacity and a suppression of intracellular energy production (ATP). In turn, loss of energy levels suppresses protein synthesis, causing a decline in anti-apoptotic Mcl-1 levels. Silencing of Mcl-1 enhanced ABT263 and MET-inhibitor mediated apoptosis, but marginally the combination treatment, indicating that Mcl-1 is the central factor for the induction of cell death induced by the combination treatment. Finally, combined treatment with BH3-mimetics and c-MET inhibitors results in significantly smaller tumors than each treatment alone in a PDX model system of glioblastoma. These results suggest that c-MET inhibition causes a selective vulnerability of GBM cells to Bcl-2/Bcl-xL inhibition.

Amoxicillin, a low-molecular-weight compound, is able to interact with dendritic cells inducing semi-maturation in vitro. Specific antigens and TLR ligands can synergistically interact with dendritic cells (DC), leading to complete maturation and more efficient T-cell stimulation. The aim of the study was to evaluate the synergistic effect of amoxicillin and the TLR2, 4 and 7/8 agonists (PAM, LPS and R848, respectively) in TLR expression, DC maturation and specific T-cell response in patients with delayed-type hypersensitivity (DTH) reactions to amoxicillin. Monocyte-derived DC from 15 patients with DTH to amoxicillin and 15 controls were cultured with amoxicillin in the presence or absence of TLR2, 4 and 7/8 agonists (PAM, LPS and R848, respectively). We studied TLR1-9 gene expression by RT-qPCR, and DC maturation, lymphocyte proliferation and cytokine production by flow cytometry. DC from both patients and controls expressed all TLRs except TLR9. The amoxicillin plus TLR2/4 or TLR7/8 ligands showed significant differences, mainly in patients: AX+PAM+LPS induced a decrease in TLR2 and AX+R848 in TLR2, 4, 7 and 8 mRNA levels. AX+PAM+LPS significantly increased the percentage of maturation in patients (75%) vs. controls (40%) (p=0.036) and T-cell proliferation (80.7% vs. 27.3% of cases; p=0.001). Moreover, the combinations AX+PAM+LPS and AX+R848 produced a significant increase in IL-12p70 during both DC maturation and T-cell proliferation. These results indicate that in amoxicillin-induced maculopapular exanthema, the presence of different TLR agonists could be critical for the induction of the innate and adaptive immune responses and this should be taken into account when evaluating allergic reactions to these drugs.

Acute coronary syndrome (ACS) is the leading cause of mortality in developed countries. Mitochondrial dysfunction is a hallmark of various cardiometabolic diseases, including ACS. Emerging evidence suggests that evaluating mitochondrial biomarkers in plasma may offer valuable insights into the pathophysiology and management of these conditions. The present study aims to analyse the effect of ACS, sex and their interaction on plasma levels of mitochondrial markers, such as peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), mitochondrial open reading frame of the 12S rRNA type-c (MOTS-c) and citrate syntetase (CS). A total of 18 ACS patients (8 women and 10 men) and 20 controls (8 women and 12 men) were included in this study. Venous blood samples were collected from participants after a 12-h overnight fast. Plasma levels of mitochondrial PGC-1α, MOTS-c and CS were measured. ACS significantly reduced plasma levels of PGC-1α and MOTS-c. Sex did not shown a significant effect on these markers. Additionally, MOTS-c positively correlated with the first troponin and hemoglobin, PGC-1α negatively correlated with glucose and positively with HDL-cholesterol, and CS showed negative correlations with NT-proBNP, C-reactive protein, and hemoglobin. Mitochondria markers, MOTS-c and PGC-1α, are altered in ACS patients, with no observed sex differences. These findings represent an initial step toward integrating personalized medicine into the clinical management of ACS. Nonetheless, further studies are required to fully elucidate the role of these markers in this pathology.

Aortic valve disease (AVD) is a common condition that leads to pressure and/or volume overload in the left ventricle. Aortic valve replacement is the standard treatment, as no pharmacological therapies are currently available. The incidence of AVD is increasing in developed countries, making the discovery of new biomarkers for early detection crucial. The importance of mitochondria in heart function is well established, and various cardiovascular pathologies are associated with mitochondrial dysfunction. In this cross-sectional study, we evaluated for the first time the role of mitochondria in AVD, aiming to identify new pathways involved in the disease and discover potential biomarkers. We recruited 17 patients diagnosed with AVD and scheduled for aortic valve replacement, and 22 healthy controls. Plasma levels of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) and mitochondrial open reading frame of the 12S rRNA type-c peptide (MOTS-c) were measured by ELISA. We observed significantly reduced levels of both proteins in patients, suggesting that substantial mitochondrial dysfunction occurs in AVD patients, independent of sex or age, but directly related to the disease. Mitochondria may represent a promising target for studying new pathways involved in AVD. We propose PGC1α and MOTS-c as potential plasma biomarkers for AVD detection. Further studies, including early-stage patients, are necessary to confirm the significance of our findings.

Abstract Autosomal recessive thymidine kinase 2 (TK2) mutations causes TK2 deficiency, which typically manifests as a progressive and fatal mitochondrial myopathy in infants and children. Treatment with deoxycytidine and thymidine ameliorates mitochondrial defects and extends lifespan of Tk2 knock-in mouse (TK2−/−); however, efficacy is limited by age- and tissue-dependent expression of the cytosolic enzymes Tk1 and Dck. Thus, therapies aimed at systemic restoration of TK2 activity are needed. Here, we demonstrate that delivery of human TK2 cDNA to Tk2−/− mice using AAV9 efficiently rescued Tk2 activity in all the tissues tested except kidney, delayed disease onset, and increased lifespan. Sequential treatment of Tk2−/− mice with AAV9 first followed by AAV2 at different ages allowed us to reduce the viral dose while further prolonging the lifespan. Furthermore, addition of deoxycytidine and deoxythymidine supplementation to AAV9 + AAV2 treated Tk2−/− mice dramatically improved mtDNA copy numbers in liver and kidney, animal growth, and lifespan. These data indicate that combined pharmacological and gene therapies may be highly efficacious for human TK2 deficiency.

Amoxicillin, a low-molecular-weight compound, is able to interact with dendritic cells inducing semi-maturation in vitro. Specific antigens and TLR ligands can synergistically interact with dendritic cells (DC), leading to complete maturation and more efficient T-cell stimulation. The aim of the study was to evaluate the synergistic effect of amoxicillin and the TLR2, 4 and 7/8 agonists (PAM, LPS and R848, respectively) in TLR expression, DC maturation and specific T-cell response in patients with delayed-type hypersensitivity (DTH) reactions to amoxicillin. Monocyte-derived DC from 15 patients with DTH to amoxicillin and 15 controls were cultured with amoxicillin in the presence or absence of TLR2, 4 and 7/8 agonists (PAM, LPS and R848, respectively). We studied TLR1-9 gene expression by RT-qPCR, and DC maturation, lymphocyte proliferation and cytokine production by flow cytometry. DC from both patients and controls expressed all TLRs except TLR9. The amoxicillin plus TLR2/4 or TLR7/8 ligands showed significant differences, mainly in patients: AX+PAM+LPS induced a decrease in TLR2 and AX+R848 in TLR2, 4, 7 and 8 mRNA levels. AX+PAM+LPS significantly increased the percentage of maturation in patients (75%) vs. controls (40%) (p=0.036) and T-cell proliferation (80.7% vs. 27.3% of cases; p=0.001). Moreover, the combinations AX+PAM+LPS and AX+R848 produced a significant increase in IL-12p70 during both DC maturation and T-cell proliferation. These results indicate that in amoxicillin-induced maculopapular exanthema, the presence of different TLR agonists could be critical for the induction of the innate and adaptive immune responses and this should be taken into account when evaluating allergic reactions to these drugs.

Mitochondria are key cellular organelles whose main function is maintaining cell bioenergetics by producing ATP through oxidative phosphorylation. However, mitochondria are involved in a much higher number of cellular processes. Mitochondria are the home of key metabolic pathways like the tricarboxylic acid cycle and β-oxidation of fatty acids, as well as biosynthetic pathways of key products like nucleotides and amino acids, the control of the redox balance of the cell and detoxifying the cell from H2S and NH3. This plethora of critical functions within the cell is the reason mitochondrial function is involved in several complex disorders (apart from pure mitochondrial disorders), among them inflammatory bowel diseases (IBD). IBD are a group of chronic, inflammatory disorders of the gut, mainly composed of ulcerative colitis and Crohn’s disease. In this review, we present the current knowledge regarding the impact of mitochondrial dysfunction in the context of IBD. The role of mitochondria in both intestinal mucosa and immune cell populations are discussed, as well as the role of mitochondrial function in mechanisms like mucosal repair, the microbiota– and brain–gut axes and the development of colitis-associated colorectal cancer.