Tetramethylpyrazine blocks TFAM degradation and up-regulates mitochondrial DNA copy number by interacting with TFAM

Deregulation of mitochondrial gene expression in cancer: mechanisms and therapeutic opportunities

"Reprogramming of energy metabolism" was first considered an emerging hallmark of cancer in 2011 by Hanahan & Weinberg and is now considered a core hallmark of cancer. Mitochondria are the hubs of metabolism, crucial for energetic functions and cellular homeostasis. The mitochondrion's bacterial origin and preservation of their own genome, which encodes proteins and RNAs essential to their function, make them unique organelles. Successful generation of mitochondrial gene products requires coordinated functioning of the mitochondrial 'central dogma,' encompassing all steps necessary for mtDNA to yield mitochondrial proteins. Each of these processes has several levels of regulation, including mtDNA accessibility and protection through mtDNA packaging and epigenetic modifications, mtDNA copy number through mitochondrial replication, mitochondrial transcription through mitochondrial transcription factors, and mitochondrial translation through mitoribosome formation. Deregulation of these mitochondrial processes in the context of cancers has only recently been appreciated, with most studies being correlative in nature. Nonetheless, numerous significant associations of the mitochondrial central dogma with pro-tumor phenotypes have been documented. Several studies have even provided mechanistic insights and further demonstrated successful pharmacologic targeting strategies. Based on the emergent importance of mitochondria for cancer biology and therapeutics, it is becoming increasingly important that we gain an understanding of the underpinning mechanisms so they can be successfully therapeutically targeted. It is expected that this mechanistic understanding will result in mitochondria-targeting approaches that balance anticancer potency with normal cell toxicity. This review will focus on current evidence for the dysregulation of mitochondrial gene expression in cancers, as well as therapeutic opportunities on the horizon.

CKIP-1 silencing suppresses OSCC via mitochondrial homeostasis-associated TFAM/cGAS-STING signalling axis

Limited effective targets have challenged the treatment of oral squamous cell carcinoma (OSCC). Casein kinase 2 interacting protein 1 (CKIP-1) is a scaffold protein involved in various diseases. However, the role of CKIP-1 in OSCC remains unclear. The aim of this study was to explore the regulatory role of CKIP-1 in OSCC, as well as the involved mechanism. First, higher expression of CKIP-1 in OSCC tissues and cell lines were found. Series of gain- and loss-of-function experiments demonstrated suppressed malignant behaviours and enhanced apoptosis of OSCC cells when CKIP-1 was silenced. Also, inhibited tumour growth in CKIP-1-silenced group were proved. Further, mitochondrial transcription factor A (TFAM) downregulation, increased ROS production, decreased mitochondrial membrane potential and cGAS-STING activation in CKIP-1-silenced group were observed. The involvement of mitochondrial homeostasis-related TFAM/cGAS-STING axis in CKIP-1-silenced OSCC cells was finally demonstrated by tetramethylpyrazine (TMP) that inhibits TFAM degradation. Taken together, our study demonstrated that CKIP-1 silencing could significantly antagonize OSCC via TFAM/cGAS-STING axis, which may provide a candidate target for OSCC treatment.

Mitochondria transcription and cancer

Mitochondria are major organelles involved in several processes related to energy supply, metabolism, and cell proliferation. The mitochondria function is transcriptionally regulated by mitochondria DNA (mtDNA), which encodes the key proteins in the electron transport chain that is indispensable for oxidative phosphorylation (OXPHOS). Mitochondrial transcriptional abnormalities are closely related to a variety of human diseases, such as cardiovascular diseases, and diabetes. The mitochondria transcription is regulated by the mtDNA, mitochondrial RNA polymerase (POLRMT), two transcription factors (TFAM and TF2BM), one transcription elongation (TEFM), and one known transcription termination factor (mTERFs). Dysregulation of these factors directly leads to altered expression of mtDNA in tumor cells, resulting in cellular metabolic reprogramming and mitochondrial dysfunction. This dysregulation plays a role in modulating tumor progression. Therefore, understanding the role of mitochondrial transcription in cancer can have implications for cancer diagnosis, prognosis, and treatment. Targeting mitochondrial transcription or related pathways may provide potential therapeutic strategies for cancer treatment. Additionally, assessing mitochondrial transcriptional profiles or biomarkers in cancer cells or patient samples may offer diagnostic or prognostic information.

Miriplatin-loaded liposome, as a novel mitophagy inducer, suppresses pancreatic cancer proliferation through blocking POLG and TFAM-mediated mtDNA replication

Pancreatic cancer is a more aggressive and refractory malignancy. Resistance and toxicity limit drug efficacy. Herein, we report a lower toxic and higher effective miriplatin (MPt)-loaded liposome, LMPt, exhibiting totally different anti-cancer mechanism from previously reported platinum agents. Both in gemcitabine (GEM)-resistant/sensitive (GEM-R/S) pancreatic cancer cells, LMPt exhibits prominent anti-cancer activity, led by faster cellular entry-induced larger accumulation of MPt. The level of caveolin-1 (Cav-1) determines entry rate and switch of entry pathways of LMPt, indicating a novel role of Cav-1 in nanoparticle entry. After endosome-lysosome processing, in unchanged metabolite, MPt is released and targets mitochondria to enhance binding of mitochondria protease LONP1 with POLG and TFAM, to degrade POLG and TFAM. Then, via PINK1-Parkin axis, mitophagy is induced by POLG and TFAM degradation-initiated mitochondrial DNA (mtDNA) replication blocking. Additionally, POLG and TFAM are identified as novel prognostic markers of pancreatic cancer, and mtDNA replication-induced mitophagy blocking mediates their pro-cancer activity. Our findings reveal that the target of this liposomal platinum agent is mitochondria but not DNA (target of most platinum agents), and totally distinct mechanism of MPt and other formulations of MPt. Self-assembly offers LMPt special efficacy and mechanisms. Prominent action and characteristic mechanism make LMPt a promising cancer candidate.

Photobiomodulation promotes repair following spinal cord injury by restoring neuronal mitochondrial bioenergetics via AMPK/PGC-1α/TFAM pathway

Background: Insufficient neuronal mitochondrial bioenergetics supply occurs after spinal cord injury (SCI), leading to neuronal apoptosis and impaired motor function. Previous reports have shown that photobiomodulation (PBM) could reduce neuronal apoptosis and promote functional recovery, but the underlying mechanism remains unclear. Therefore, we aimed to investigate whether PBM improved prognosis by promoting neuronal mitochondrial bioenergetics after SCI.

Methods: Sprague Dawley rats were randomly divided into four groups: a Sham group, an SCI group, an SCI + PBM group and an SCI + PBM + Compound C group. After SCI model was established, PBM and Compound C (an AMPK inhibitor) injection were carried out. The level of neuron apoptosis, the recovery of motor function and mitochondrial function were observed at different times (7, 14, and 28 days). The AMPK/PGC-1α/TFAM pathway was hypothesized to be a potential target through which PBM could affect neuronal mitochondrial bioenergetics. In vitro, ventral spinal cord 4.1 (VSC4.1) cells were irradiated with PBM and cotreated with Compound C after oxygen and glucose deprivation (OGD).

Results: PBM promoted the recovery of mitochondrial respiratory chain complex activity, increased ATP production, alleviated neuronal apoptosis and reversed motor dysfunction after SCI. The activation of the AMPK/PGC-1α/TFAM pathway after SCI were facilitated by PBM but inhibited by Compound C. Equally important, PBM could inhibit OGD-induced VSC4.1 cell apoptosis by increasing ATP production whereas these changes could be abolished by Compound C.

Conclusion: PBM activated AMPK/PGC-1α/TFAM pathway to restore mitochondrial bioenergetics and exerted neuroprotective effects after SCI.

TFAM loss induces nuclear actin assembly upon mDia2 malonylation to promote liver cancer metastasis

The mechanisms underlying cancer metastasis remain poorly understood. Here, we report that TFAM deficiency rapidly and stably induced spontaneous lung metastasis in mice with liver cancer. Interestingly, unexpected polymerization of nuclear actin was observed in TFAM-knockdown HCC cells when cytoskeleton was examined. Polymerization of nuclear actin is causally linked to the high-metastatic ability of HCC cells by modulating chromatin accessibility and coordinating the expression of genes associated with extracellular matrix remodeling, angiogenesis, and cell migration. Mechanistically, TFAM deficiency blocked the TCA cycle and increased the intracellular malonyl-CoA levels. Malonylation of mDia2, which drives actin assembly, promotes its nuclear translocation. Importantly, inhibition of malonyl-CoA production or nuclear actin polymerization significantly impeded the spread of HCC cells in mice. Moreover, TFAM was significantly downregulated in metastatic HCC tissues and was associated with overall survival and time to tumor recurrence of HCC patients. Taken together, our study connects mitochondria to the metastasis of human cancer via uncovered mitochondria-to-nucleus retrograde signaling, indicating that TFAM may serve as an effective target to block HCC metastasis.

Mitochondrial DNA stress triggers autophagy-dependent ferroptotic death

Pancreatic cancer tends to be highly resistant to current therapy and remains one of the great challenges in biomedicine with very low 5-year survival rates. Here, we report that zalcitabine, an antiviral drug for human immunodeficiency virus infection, can suppress the growth of primary and immortalized human pancreatic cancer cells through the induction of ferroptosis, an iron-dependent form of regulated cell death. Mechanically, this effect relies on zalcitabine-induced mitochondrial DNA stress, which activates the STING1/TMEM173-mediated DNA sensing pathway, leading to macroautophagy/autophagy-dependent ferroptotic cell death via lipid peroxidation, but not a type I interferon response. Consequently, the genetic and pharmacological inactivation of the autophagy-dependent ferroptosis pathway diminishes the anticancer effects of zalcitabine in cell culture and animal models. Together, these findings not only provide a new approach for pancreatic cancer therapy but also increase our understanding of the interplay between autophagy and DNA damage response in shaping cell death.Abbreviations: ALOX: arachidonate lipoxygenase; ARNTL/BMAL1: aryl hydrocarbon receptor nuclear translocator-like; ATM: ATM serine/threonine kinase; ATG: autophagy-related; cGAMP: cyclic GMP-AMP; CGAS: cyclic GMP-AMP synthase; ER: endoplasmic reticulum; FANCD2: FA complementation group D2; GPX4: glutathione peroxidase 4; IFNA1/IFNα: interferon alpha 1; IFNB1/IFNβ: interferon beta 1; MAP1LC3B/LC3: microtubule-associated protein 1 light chain 3 beta; MDA: malondialdehyde; mtDNA: mitochondrial DNA; NCOA4: nuclear receptor coactivator 4; PDAC: pancreatic ductal adenocarcinoma; POLG: DNA polymerase gamma, catalytic subunit; qRT-PCR: quantitative polymerase chain reaction; RCD: regulated cell death; ROS: reactive oxygen species; SLC7A11: solute carrier family 7 member 11; STING1/TMEM173: stimulator of interferon response cGAMP interactor 1; TFAM: transcription factor A, mitochondrial.

Mitochondrial unfolded protein response: An emerging pathway in human diseases

Mitochondrial unfolded protein response (UPR^mt) is a mitochondria stress response, which the transcriptional activation programs of mitochondrial chaperone proteins and proteases are initiated to maintain proteostasis in mitochondria. Additionally, the activation of UPR^mt delays aging and extends lifespan by maintaining mitochondrial proteostasis. Growing evidences suggests that UPR^mt plays an important role in diverse human diseases, especially ageing-related diseases. Therefore, this review focuses on the role of UPR^mt in ageing and ageing-related neurodegenerative diseases such as Alzheimer's disease, Huntington's disease and Parkinson's disease. The activation of UPR^mt and the high expression of UPR^mt components contribute to longevity extension. The activation of UPR^mt may ameliorate Alzheimer's disease, Parkinson's disease and Huntington's disease. Besides, UPR^mt is also involved in the occurrence and development of cancers and heart diseases. UPR^mt contributes to the growth, invasive and metastasis of cancers. UPR^mt has paradoxical roles in heart diseases. UPR^mt not only protects against heart damage, but may sometimes aggravates the development of heart diseases. Considering the pleiotropic actions of UPR^mt system, targeting UPR^mt pathway may be a potent therapeutic avenue for neurodegenerative diseases, cancers and heart diseases.

Higher proteotoxic stress rather than mitochondrial damage is involved in higher neurotoxicity of bortezomib compared to carfilzomib

Proteasome inhibitors have great success for their therapeutic potential against hematologic malignancies. First generation proteasome inhibitor bortezomib induced peripheral neuropathy is considered as a limiting factor in chemotherapy and its second-generation counterpart carfilzomib is associated with lower rates of neurotoxicity. The mitochondrial toxicity (mitotoxicity) hypothesis arises from studies with animal models of bortezomib induced peripheral neuropathy. However, molecular mechanisms are not fully elucidated and the role of mitotoxicity in bortezomib and carfilzomib induced neurotoxicity has not been investigated comparatively. Herein, we characterized the neurotoxic effects of bortezomib and carfilzomib at the molecular level in human neuronal cells using LC-MS/MS analysis, flow cytometry, RT-qPCR, confocal microscopy and western blotting. We showed that bortezomib and carfilzomib affected the human neuronal proteome differently, and bortezomib caused higher proteotoxic stress via protein oxidation, protein K48-ubiquitination, heat shock protein expression upregulation and reduction of mitochondria membrane potential. Bortezomib and carfilzomib did not affect the gene expression levels related to mitochondrial dynamics (optic atrophy 1; OPA1, mitofusin 1; MFN1, mitofusin 2; MFN2, fission 1; FIS1, dynamin-related protein 1; DRP1) and overall mitophagy rate whereas, PINK1/Parkin mediated mitophagy gene expressions were altered with both drugs. Bortezomib and carfilzomib caused downregulation of the contents of mitochondrial oxidative phosphorylation complexes, voltage-dependent anion channel 1 (VDAC1) and uncoupling protein 2 (UCP2) similarly. Our findings suggest that, both drugs induce mitotoxicity besides proteotoxic stress in human neuronal cells and the higher incidence of neurotoxicity with bortezomib than carfilzomib is not directly related to mitochondrial pathways.

The biology of Lonp1: More than a mitochondrial protease

Initially discovered as a protease responsible for degradation of misfolded or damaged proteins, the mitochondrial Lon protease (Lonp1) turned out to be a multifaceted enzyme, that displays at least three different functions (proteolysis, chaperone activity, binding of mtDNA) and that finely regulates several cellular processes, within and without mitochondria. Indeed, LONP1 in humans is ubiquitously expressed, and is involved in regulation of response to oxidative stress and, heat shock, in the maintenance of mtDNA, in the regulation of mitophagy. Furthermore, its proteolytic activity can regulate several biochemical pathways occurring totally or partially within mitochondria, such as TCA cycle, oxidative phosphorylation, steroid and heme biosynthesis and glutamine production. Because of these multiple activities, Lon protease is highly conserved throughout evolution, and mutations occurring in its gene determines severe diseases in humans, including a rare syndrome characterized by Cerebral, Ocular, Dental, Auricular and Skeletal anomalies (CODAS). Finally, alterations of LONP1 regulation in humans can favor tumor progression and aggressiveness, further highlighting the crucial role of this enzyme in mitochondrial and cellular homeostasis.

Artemisinin suppresses hepatocellular carcinoma cell growth, migration and invasion by targeting cellular bioenergetics and Hippo-YAP signaling

The primary liver cancer (PLC) is one of the leading causes of cancer-related death worldwide. The predominant form of PLC is hepatocellular carcinoma (HCC), which accounts for about 85% of all PLC. Artemisinin (ART) was clinically used as anti-malarial agents. Recently, it was demonstrated to inhibit cell growth and migration in multiple cancer types. However, the molecular mechanism underlying these anti-cancer activity remains largely unknown. Herein, it is discovered that ART dramatically suppresses HCC cell growth in vitro through arresting cell cycle progression, and represses cell migration and invasion via regulating N-cadherin-Snail-E-cadherin axis. In addition, the disruption of cellular bioenergetics contributed to ART-caused cell growth, migration and invasion inhibition. Moreover, ART (100 mg/kg, intraperitoneally) substantially inhibits HCC xenograft growth in vivo. Importantly, Hippo-YAP signal transduction is remarkably inactivated in HCC cells upon ART administration. Collectively, these data reveal a novel mechanism of ART in regulating HCC cell growth, migration, and invasion, which indicates that ART could be considered as a potential drug for the treatment of HCC.

Effects of eicosapentaenoic acid and docosahexaenoic acid on C2C12 cell adipogenesis and inhibition of myotube formation

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) modulate cellular metabolic functions and gene expression. This study investigated the impacts of EPA and DHA on gene expression and morphological changes during adipogenic inducement in C2C12 myoblasts. Cells were cultured and treated with differentiation medium with and without 50 μM EPA and DHA. Cells treated with fatty acids had noticeable lipid droplets, but no formation of myotubes compared to control group cells. The expression levels of key genes relevant to adipogenesis and inflammation were significantly higher (P < 0.05) in cells treated with fatty acids. Genes associated with myogenesis and mitochondrial biosynthesis and function had lower (P < 0.05) expression with fatty acids supplementation. Moreover, fatty acid treatment reduced (P < 0.05) oxygen consumption rate in the differentiated cells. This suggested blocking myotube formation through supplementation with EPA and DHA drove myoblasts to enter the quiescent state and enabled adipogenic trans-differentiation of the myoblasts. Data also suggested that overdosage of EPA and DHA during gestation may drive fetal mesenchymal stem cell differentiation to the fate of adipogenesis and have a long-term effect on childhood obesity.

Melatonin reduces intramuscular fat deposition by promoting lipolysis and increasing mitochondrial function

In obesity and diabetes, intramuscular fat (IMF) content correlates markedly with insulin sensitivity, which makes IMF manipulation an area of therapeutic interest. Melatonin, an important circadian rhythm-regulating hormone, reportedly regulates fat deposition, but its effects on different types of adipose vary. Little is known about the role of melatonin in IMF deposition. Here, using intramuscular preadipocytes in pigs, we investigated to determine whether melatonin affects or regulates IMF deposition. We found that melatonin greatly inhibited porcine intramuscular preadipocyte proliferation. Although melatonin administration significantly upregulated the expression of adipogenic genes, smaller lipid droplets were formed in intramuscular adipocytes. Additional investigation demonstrated that melatonin promoted lipolysis of IMF by activating protein kinase A and the signaling of ERK1/2. Moreover, melatonin increased thermogenesis in intramuscular adipocytes by enhancing mitochondrial biogenesis and mitochondrial respiration. A mouse model, in which untreated controls were compared with mice that received 3 weeks of melatonin treatment, verified the effect of melatonin on IMF deposition. In conclusion, melatonin reduces IMF deposition by upregulating lipolysis and mitochondrial bioactivities. These data establish a link between melatonin signaling and lipid metabolism in mammalian models and suggest the potential for melatonin administration to treat or prevent obesity and related diseases.

Mitochondrial Nucleoids: Superresolution microscopy analysis

The mitochondrion owns an autonomous genome. Double-stranded circular mitochondrial DNA (mtDNA) is organized in complexes with a packing/stabilizing transcription factor TFAM, having multiple roles, and proteins of gene expression machinery in structures called nucleoids. From hundreds to thousands nucleoids exist distributed in the matrix of mitochondrial reticulum network. A single mtDNA molecule contained within the single nucleoid is a currently preferred but questioned model. Nevertheless, mtDNA replication should lead transiently to its doubling within a nucleoid. However, nucleoid division has not yet been documented in detail. A 3D superresolution microscopy is required to resolve nucleoid biology occurring in ∼100 nm space, having an advantage over electron microscopy tomography in resolving the particular protein components. We discuss stochastic vs. stimulated emission depletion microscopy yielding wide vs. narrow nucleoid size distribution, respectively. Nucleoid clustering into spheroids fragmented from the continuous mitochondrial network, likewise possible nucleoid attachment to the inner membrane is reviewed.

Tetramethylpyrazine Showed Therapeutic Effects on Sepsis-Induced Acute Lung Injury in Rats by Inhibiting Endoplasmic Reticulum Stress Protein Kinase RNA-Like Endoplasmic Reticulum Kinase (PERK) Signaling-Induced Apoptosis of Pulmonary Microvascular Endothelial Cells

Background

Acute lung injury (ALI) is a life-threatening complication of sepsis. Tetramethylpyrazine (TMP) has been used in the clinical treatment of vascular diseases. The aim of this study was to investigate the therapeutic effects and possible involved mechanisms on ALI.

Material/Methods

Cecal ligation and puncture (CLP) was used to establish a sepsis model in rats. TMP at various dosages were administrated to rats using a intragastric method. Animal survival rate was calculated. The lung functions were evaluated by lung weight/dry weight ratio (W/D), PaO₂, dynamic compliance (DC), and airway resistance index (ARI). Pulmonary microvascular endothelial cells (PMVECs) were isolated from lungs harvested from rats with sepsis. TUNEL assay was used to detect apoptosis. Protein expression and phosphorylation levels were assessed by western blotting.

Results

TMP administration increased the survival rate of septic rats. TMP also decreased W/D and DC, but increased PaO₂ and ARI in septic rats. Moreover, PMVECs apoptosis was inhibited in septic rats that received TMP treatment. The expression levels of GRP78, ATF4, caspase-12, active caspase-3, as well as the phosphorylation levels of PERK and eIF2α were suppressed in PMVECs isolated from TMP-treated septic rats.

Conclusions

TMP alleviated sepsis-induced ALI by suppressing PMVECs apoptosis via PERK/eIF2α/ATF4/CHOP apoptotic signaling in endoplasmic reticulum stress.

Mitochondrial Lon Protease and Cancer

ATP-dependent Lon protease of mitochondrial matrix is encoded by nuclear DNA and highly evolutionarily conserved throughout all organisms, which is involved in the quality control of proteins by selective degradation of misfolded, oxidized, and short-lived regulatory proteins within mitochondrial matrix, maintenance of mitochondrial genome (mtDNA), and folding of mitochondria proteins. Various stimuli such as hypoxia and oxidative and ER stress lead to upregulation of Lon expression. Inhibition of protease activity or downregulation of Lon promotes cancer cell death and enhances sensitivity of cancer cells to anticancer drugs through metabolic reprogramming, thus reducing the viability of cancer cell in tumor microenvironment and epithelial to mesenchymal transition (EMT). Moreover, mitochondrial ATP-dependent Lon protease may serve as a potential biomarker for cancer diagnosis and novel target for the development of anticancer drugs and for predicting of the efficiency and effectiveness of chemotherapy of a variety of cancers.