bims-mitper Biomed News
on Mitochondrial Permeabilization
Issue of 2023‒01‒22
five papers selected by
Bradley Irizarry
Thomas Jefferson University

  1. Bioessays. 2023 Jan 17. e2200221
      The pore-forming BCL-2 family proteins are effectors of mitochondrial poration in apoptosis initiation. Two atypical effectors-BOK and truncated BID (tBID)-join the canonical effectors BAK and BAX. Gene knockout revealed developmental phenotypes in the absence the effectors, supporting their roles in vivo. During apoptosis effectors are activated and change shape from dormant monomers to dynamic oligomers that associate with and permeabilize mitochondria. BID is activated by proteolysis, BOK accumulates on inhibition of its degradation by the E3 ligase gp78, while BAK and BAX undergo direct activation by BH3-only initiators, autoactivation, and crossactivation. Except tBID, effector oligomers on the mitochondria appear as arcs and rings in super-resolution microscopy images. The BH3-in-groove dimers of BAK and BAX, the tBID monomers, and uncharacterized BOK species are the putative building blocks of apoptotic pores. Effectors interact with lipids and bilayers but the mechanism of membrane poration remains elusive. I discuss effector-mediated mitochondrial poration.
    Keywords:  arc and ring oligomerization; effector activation; effector dimerization; effector oligomerization; mitochondrial apoptosis; mitochondrial poration; pore-forming effector BCL-2 family proteins
  2. Exp Mol Med. 2023 Jan 19.
      Mitochondrial DNA (mtDNA) released through protein oligomers, such as voltage-dependent anion channel 1 (VDAC1), triggers innate immune activation and thus contributes to liver fibrosis. Here, we investigated the role of Parkin, an important regulator of mitochondria, and its regulation of VDAC1-mediated mtDNA release in liver fibrosis. The circulating mitochondrial DNA (mtDNA) and protein levels of liver Parkin and VDAC1 were upregulated in patients with liver fibrosis. A 4-week CCl4 challenge induced release of mtDNA, activation of STING signaling, a decline in autophagy, and apoptosis in mouse livers, and the knockout of Parkin aggravated these effects. In addition, Parkin reduced mtDNA release and prevented VDAC1 oligomerization in a manner dependent on its E3 activity in hepatocytes. We found that site-specific ubiquitination of VDAC1 at lysine 53 by Parkin interrupted VDAC1 oligomerization and prevented mtDNA release into the cytoplasm under stress. The ubiquitination-defective VDAC1 K53R mutant predominantly formed oligomers that resisted suppression by Parkin. Hepatocytes expressing VDAC1 K53R exhibited mtDNA release and thus activated the STING signaling pathway in hepatic stellate cells, and this effect could not be abolished by Parkin. We propose that the ubiquitination of VDAC1 at a specific site by Parkin confers protection against liver fibrosis by interrupting VDAC1 oligomerization and mtDNA release.
  3. Cells. 2023 Jan 04. pii: 204. [Epub ahead of print]12(2):
      The brief opening mode of the mitochondrial permeability transition pore (mPTP) serves as a calcium (Ca2+) release valve to prevent mitochondrial Ca2+ (mCa2+) overload. Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a stress-induced arrhythmic syndrome due to mutations in the Ca2+ release channel complex of ryanodine receptor 2 (RyR2). We hypothesize that inhibiting the mPTP opening in CPVT exacerbates the disease phenotype. By crossbreeding a CPVT model of CASQ2 knockout (KO) with a mouse missing CypD, an activator of mPTP, a double KO model (DKO) was generated. Echocardiography, cardiac histology, and live-cell imaging were employed to assess the severity of cardiac pathology. Western blot and RNAseq were performed to evaluate the contribution of various signaling pathways. Although exacerbated arrhythmias were reported, the DKO model did not exhibit pathological remodeling. Myocyte Ca2+ handling was similar to that of the CASQ2 KO mouse at a low pacing frequency. However, increased ROS production, activation of the CaMKII pathway, and hyperphosphorylation of RyR2 were detected in DKO. Transcriptome analysis identified altered gene expression profiles associated with electrical instability in DKO. Our study provides evidence that genetic inhibition of mPTP exacerbates RyR2 dysfunction in CPVT by increasing activation of the CaMKII pathway and subsequent hyperphosphorylation of RyR2.
    Keywords:  CPVT; EC-coupling; calcium signaling; mitochondria
  4. Rheumatology (Oxford). 2023 Jan 16. pii: kead015. [Epub ahead of print]
      OBJECTIVES: Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) includes granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA). ANCA triggers neutrophil extracellular trap formation, which releases either mitochondrial (mt) DNA or nuclear DNA (n) DNA, contributing to inflammation. Our aim was to prospectively examine the extent and nature of circulating DNA in AAV and the clinical utility of DNA quantification.METHODS: DNA was isolated from platelet-free plasma of consecutive GPA and MPA patients and healthy controls (HC). mtDNA and nDNA copy numbers were quantified by PCR. Clinical data including the Birmingham Vasculitis Activity Score (BVAS), were collected.
    RESULTS: Ninety-two HC (median age 51 years, 58.7% female) and 101 AAV patients (80 GPA, 21 MPA, median age 64 years, 50.5% female, BVAS range: 0-30) were included. Median mtDNA copies were 13-fold higher in AAV than HC; nDNA concentrations did not differ. Patients with active AAV (BVAS > 0) had 4-fold higher median mtDNA copies than patients in remission (P= 0.03). mtDNA, unlike nDNA, correlated with BVAS (r = 0.30, P= 0.002) and was associated with AAV activity at multivariable analysis. Receiver operating characteristic curve analysis indicates that mtDNA quantification differentiates active AAV (BVAS >0) from HC with 96.1% sensitivity and 98.9% specificity (AUC 0.99). In 27 AAV patients with follow-up, mtDNA changes but not CRP or ANCA-titers correlated with BVAS changes (r = 0.56, P= 0.002).
    CONCLUSIONS: mtDNA, unlike nDNA, is elevated in the plasma of AAV patients and may contribute to systemic inflammation. mtDNA could be superior to established biomarkers in the laboratory monitoring of AAV activity.
    Keywords:  ANCA-associated vasculitis; disease activity; innate immunity; mitochondrial DNA; neutrophil extracellular traps
  5. Am J Physiol Lung Cell Mol Physiol. 2023 Jan 17.
      Idiopathic Pulmonary Fibrosis is increasingly associated with nerve-driven processes and endogenous innate immune ligands such as mitochondrial DNA (mtDNA). Interestingly, a connection between these entities has not been explored. Here we report that noradrenaline (NA) derived from the lung's adrenergic nerve supply drives αSMA-expressing fibroblast accumulation via mechanisms involving α1 adrenoreceptors and mtDNA. Using the bleomycin model, we compared ablation of the lung's adrenergic nerve supply to surgical adrenal resection and found that NA derived from local but not adrenal sources drives experimentally induced lung fibrosis and the emergence of an αSMA+ fibroblast population expressing adrenoreceptor alpha-1D (ADRA1D). Therapeutic delivery of the α1 adrenoreceptor antagonist terazosin reversed these changes and suppressed extracellular mtDNA accumulation. Cultured normal human lung fibroblasts displayed α1 adrenoreceptors and in response to co-stimulation with TGFβ1 and NA adopted ACTA2 expression and extracellular mtDNA release. These findings were opposed by terazosin. IPF patients prescribed α1 adrenoreceptor antagonists for non-pulmonary indications demonstrated improved survival and reduced plasma mtDNA. Our observations link nerve-derived NA, α1 adrenoreceptors, extracellular mtDNA, and lung fibrogenesis in mouse models, cultured cells, and humans with IPF. Further study of this neuroinnate connection may yield new avenues for investigation in the clinical and basic science realms.
    Keywords:  alpha-1 adrenoreceptor; mitochondrial DNA; neuroinnate; pulmonary fibrosis