Pathogenic mutations in mitochondrial (mt) tRNA genes that compromise oxidative phosphorylation (OXPHOS) exhibit heteroplasmy and cause a range of multisyndromic conditions. Although mitochondrial ...disease patients are known to suffer from abnormal immune responses, how heteroplasmic mtDNA mutations affect the immune system at the molecular level is largely unknown. Here, in mice carrying pathogenic C5024T in mt-tRNA
Ala
and in patients with mitochondrial encephalomyopathy, lactic acidosis, stroke-like episodes (MELAS) syndrome carrying A3243G in mt-tRNA
Leu
, we found memory T and B cells to have lower pathogenic mtDNA mutation burdens than their antigen-inexperienced naive counterparts, including after vaccination. Pathogenic burden reduction was less pronounced in myeloid compared with lymphoid lineages, despite C5024T compromising macrophage OXPHOS capacity. Rapid dilution of the C5024T mutation in T and B cell cultures could be induced by antigen receptor–triggered proliferation and was accelerated by metabolic stress conditions. Furthermore, we found C5024T to dysregulate CD8
+
T cell metabolic remodeling and IFN-γ production after activation. Together, our data illustrate that the generation of memory lymphocytes shapes the mtDNA landscape, wherein pathogenic variants dysregulate the immune response.
Over-activated microglia and chronic neuroinflammation contribute to dopaminergic neuron degeneration and progression of Parkinson's disease (PD). Leucine-rich repeat kinase 2 (LRRK2), a kinase ...mutated in autosomal dominantly inherited and sporadic PD cases, is highly expressed in immune cells, in which it regulates inflammation through a yet unclear mechanism.
Here, using pharmacological inhibition and cultured Lrrk2 (-/-) primary microglia cells, we validated LRRK2 as a positive modulator of inflammation and we investigated its specific function in microglia cells.
Inhibition or genetic deletion of LRRK2 causes reduction of interleukin-1β and cyclooxygenase-2 expression upon lipopolysaccharide-mediated inflammation. LRRK2 also takes part of the signaling trigged by α-synuclein fibrils, which culminates in induction of inflammatory mediators. At the molecular level, loss of LRRK2 or inhibition of its kinase activity results in increased phosphorylation of nuclear factor kappa-B (NF-κB) inhibitory subunit p50 at S337, a protein kinase A (PKA)-specific phosphorylation site, with consequent accumulation of p50 in the nucleus.
Taken together, these findings point to a role of LRRK2 in microglia activation and sustainment of neuroinflammation and in controlling of NF-κB p50 inhibitory signaling. Understanding the molecular pathways coordinated by LRRK2 in activated microglia cells after pathological stimuli such us fibrillar α-synuclein holds the potential to provide novel targets for PD therapeutics.
Abstract
Background and Aims
Chronic kidney disease (CKD) and kidney failure are connected to increased oxidative stress and vascular calcification, which are indicators for development of ...comorbidities and mortality outcome. Mitochondrial (mt)DNA copy number has been reported as independent predictor for frailty and mortality outcome of various cardiovascular diseases (CVD) and cancer.
We aimed that mtDNA copy number in whole blood of kidney failure patients can be correlated to coronary artery media calcification score and coronary artery calcium (CAC) score and be used as an independent predictor for comorbidities and mortality outcome.
Method
Quantitative PCR (qPCR) with TaqMan® probes for three mtDNA genes (mtND1, mtND4 and mtCOX1) and two single locus genes on nuclear DNA (hemoglobin subunit beta and 18S), for normalization, is performed on DNA samples isolated from collected blood of 196 kidney transplant donors and 211 recipients at basal timepoint and 32 at 1-year-follow-up timepoint, included in the KaroKidney biobank. Resulting mtDNA copy number is investigated for correlation to CAC score, patient mortality outcome, biological age determined by skin autofluorescence and other clinical parameters.
Results
In our Swedish kidney transplant cohort we can see statistically significant difference in mtDNA copy number between kidney failure patients (recipients) and healthy controls (donors). No obvious difference between females and males was observed. mtDNA copy number correlates to biological age determined by skin autofluorescence, CAC score and Framingham CVD risk score. In the 32 1-year-follow-up samples we could see significant increase/recovery of mtDNA copy number for male patients compared to their baseline before receiving a transplant.
Conclusion
In this study we show that mtDNA copy number in kidney failure patients correlates to biological age and CAC score, affirming mtDNA copy number as an independent predictor of frailty in this Swedish cohort of CKD patients. Additionally, we can see that a kidney transplant can lead to a significant increase of mtDNA copy number in blood one year later, suggesting a general increase in health quality.
Highlights • The molecular pathways involved in Parkinson's disease are extensively described. • The aforementioned pathways are linked to the oxidative chemistry of dopamine. • The reactions of ...dopamine-derived quinones with cellular targets are emphasized. • Dopamine-derived quinones could contribute to the progression of Parkinson's disease.
The mammalian respiratory chain complexes I, III2, and IV (CI, CIII2, and CIV) are critical for cellular bioenergetics and form a stable assembly, the respirasome (CI-CIII2-CIV), that is ...biochemically and structurally well documented. The role of the respirasome in bioenergetics and the regulation of metabolism is subject to intense debate and is difficult to study because the individual respiratory chain complexes coexist together with high levels of respirasomes. To critically investigate the in vivo role of the respirasome, we generated homozygous knockin mice that have normal levels of respiratory chain complexes but profoundly decreased levels of respirasomes. Surprisingly, the mutant mice are healthy, with preserved respiratory chain capacity and normal exercise performance. Our findings show that high levels of respirasomes are dispensable for maintaining bioenergetics and physiology in mice but raise questions about their alternate functions, such as those relating to the regulation of protein stability and prevention of age-associated protein aggregation.
Display omitted
•Three amino acids (EED) in UQCRC1 of complex III2 control respirasome stability•Homozygous Uqcrc1delEED knockin mice have drastically reduced respirasome levels•Profound depletion of respirasomes does not impair oxidative phosphorylation•Mice with a profound depletion of respirasomes have apparently normal physiology
The role of the mammalian respirasome, a stable assembly of a complete respiratory chain, is much debated. Milenkovic et al. have generated knockin mice with a profound depletion of respirasomes. Very unexpectedly, the mutant mice have preserved oxidative phosphorylation capacity and physiology, arguing that respirasomes may be dispensable for normal bioenergetics.
Cancer cells depend on mitochondria to sustain their increased metabolic need and mitochondria therefore constitute possible targets for cancer treatment. We recently developed small‐molecule ...inhibitors of mitochondrial transcription (IMTs) that selectively impair mitochondrial gene expression. IMTs have potent antitumor properties in vitro and in vivo, without affecting normal tissues. Because therapy‐induced resistance is a major constraint to successful cancer therapy, we investigated mechanisms conferring resistance to IMTs. We employed a CRISPR‐Cas9 (clustered regularly interspaced short palindromic repeats)‐(CRISP‐associated protein 9) whole‐genome screen to determine pathways conferring resistance to acute IMT1 treatment. Loss of genes belonging to von Hippel–Lindau (VHL) and mammalian target of rapamycin complex 1 (mTORC1) pathways caused resistance to acute IMT1 treatment and the relevance of these pathways was confirmed by chemical modulation. We also generated cells resistant to chronic IMT treatment to understand responses to persistent mitochondrial gene expression impairment. We report that IMT1‐acquired resistance occurs through a compensatory increase of mitochondrial DNA (mtDNA) expression and cellular metabolites. We found that mitochondrial transcription factor A (TFAM) downregulation and inhibition of mitochondrial translation impaired survival of resistant cells. The identified susceptibility and resistance mechanisms to IMTs may be relevant for different types of mitochondria‐targeted therapies.
Synopsis
A CRISPR‐Cas9 screen shows that mTORC1 loss increases OXPHOS and prevents IMT1‐induced cell death whereas loss of VHL confers resistance in an OXPHOS‐independent fashion.
A CRISPR‐Cas9 screen shows that loss of mTORC1 or VHL cause resistance to the inhibition of mtDNA transcription in cancer cells.
Rapamycin promotes survival of IMT1‐treated cancer cells by enhancing mtDNA expression and OXPHOS.
Cells with chronic IMT1 resistance have increased mtDNA levels and OXPHOS capacity.
Decreased mtDNA levels or impaired mitochondrial translation sensitize cancer cells to IMT1 treatment.
A CRISPR‐Cas9 screen shows that mTORC1 loss increases OXPHOS and prevents IMT1‐induced cell death whereas loss of VHL confers resistance in an OXPHOS‐independent fashion.
Parkinson disease is a debilitating and incurable neurodegenerative disorder affecting ∼1-2% of people over 65 years of age. Oxidative damage is considered to play a central role in the progression ...of Parkinson disease and strong evidence links chronic exposure to the pesticide paraquat with the incidence of the disease, most probably through the generation of oxidative damage. In this work, we demonstrated in human SH-SY5Y neuroblastoma cells the beneficial role of superoxide dismutase (SOD) enzymes against paraquat-induced toxicity, as well as the therapeutic potential of the SOD-mimetic compound M40403. Having verified the beneficial effects of superoxide dismutation in cells, we then evaluated the effects using Drosophila melanogaster as an in vivo model. Besides protecting against the oxidative damage induced by paraquat treatment, our data demonstrated that in Drosophila M40403 was able to compensate for the loss of endogenous SOD enzymes, acting both at a cytosolic and mitochondrial level. Because previous clinical trials have indicated that the M40403 molecule is well tolerated in humans, this study may have important implication for the treatment of Parkinson disease.
Abstract
The in vivo role for RNase H1 in mammalian mitochondria has been much debated. Loss of RNase H1 is embryonic lethal and to further study its role in mtDNA expression we characterized a ...conditional knockout of Rnaseh1 in mouse heart. We report that RNase H1 is essential for processing of RNA primers to allow site-specific initiation of mtDNA replication. Without RNase H1, the RNA:DNA hybrids at the replication origins are not processed and mtDNA replication is initiated at non-canonical sites and becomes impaired. Importantly, RNase H1 is also needed for replication completion and in its absence linear deleted mtDNA molecules extending between the two origins of mtDNA replication are formed accompanied by mtDNA depletion. The steady-state levels of mitochondrial transcripts follow the levels of mtDNA, and RNA processing is not altered in the absence of RNase H1. Finally, we report the first patient with a homozygous pathogenic mutation in the hybrid-binding domain of RNase H1 causing impaired mtDNA replication. In contrast to catalytically inactive variants of RNase H1, this mutant version has enhanced enzyme activity but shows impaired primer formation. This finding shows that the RNase H1 activity must be strictly controlled to allow proper regulation of mtDNA replication.
Abstract
Reactive oxygen species exert important functions in regulating several cellular signalling pathways. However, an excessive accumulation of reactive oxygen species can perturb the redox ...homeostasis leading to oxidative stress, a condition which has been associated to many neurodegenerative disorders. Accordingly, alterations in the redox state of cells and mitochondrial homeostasis are established hallmarks in both familial and sporadic Parkinson's disease cases. PINK1 and Parkin are two genes which account for a large fraction of autosomal recessive early-onset forms of Parkinson's disease and are now firmly associated to both mitochondria and redox homeostasis. In this study we explored the hypothesis that superoxide anions participate in the generation of the Parkin and PINK1 associated phenotypic effect by testing the capacity of endogenous and exogenous superoxide dismutating molecules to rescue the toxic effects induced by loss of PINK1 or Parkin, in both cellular and fly models. Our results demonstrate the positive effect of an increased level of superoxide dismutase proteins on the pathological phenotypes, both in vitro and in vivo. A more pronounced effectiveness for mitochondrial SOD2 activity points to the superoxide radicals generated in the mitochondrial matrix as the prime suspect in the definition of the observed phenotypes. Moreover, we also demonstrate the efficacy of a SOD-mimetic compound, M40403, to partially ameliorate PINK1/Parkin phenotypes in vitro and in vivo. These results support the further exploration of SOD-mimetic compounds as a therapeutic strategy against Parkinson's disease.
PDF
