MTERF2 contributes to MPP+-induced mitochondrial dysfunction and cell damage

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.

MTERF3 contributes to MPP+-induced mitochondrial dysfunction in SH-SY5Y cells

Parkinson's disease (PD) is a neurodegenerative disorder causing severe social and economic burdens. The origin of PD has been usually attributed to mitochondrial dysfunction. To this end, mitochondrial transcription regulators become attractive subjects for understanding PD pathogenesis. Previously, we found that the expression of mitochondrial transcription termination factor 3 (MTERF3) was reduced in MPP+-induced mice model of PD. In the present study, we probe the function of MTERF3 and its role in MPP+-induced cellular model of PD. Initially, we observe that MTERF3 expression is also reduced in MPP+-induced cellular model of PD, which can be mainly attributed to the increase of MTERF3 degradation. Next, we examine the effect of MTERF3 knockdown and overexpression on the replication, transcription, and translation of mitochondrial DNA (mtDNA). We show that knockdown and overexpression of MTERF3 have opposite effects on mtDNA transcript level but similar effects on mtDNA expression level, in line with MTERF3's dual roles in mtDNA transcription and translation. In addition, we examine the effect of MTERF3 knockdown and overexpression on mitochondrial function with and without MPP+ treatment, and find that MTERF3 seems to play a generally protective role in MPP+-induced mitochondrial dysfunction. Together, this work suggests a regulatory role of MTERF3 in MPP+-induced cellular model of PD and may provide clues in designing novel therapeutics against PD.

PGC1α regulates mitochondrial oxidative phosphorylation involved in cisplatin resistance in ovarian cancer cells via nucleo-mitochondrial transcriptional feedback

Mitochondria play an important role in effective cell energy production and cell survival under stress conditions, such as treatment with chemotherapeutic drugs. Mitochondrial biogenesis is increased in ovarian cancer tissues, which is accompanied by alteration of mitochondrial energy metabolism, structure, and dynamics. These factors are involved in tumorigenesis and apoptosis resistance, highlighting the role of mitochondria in resisting cisplatin toxicity. Cisplatin-resistant ovarian cancer cells are dependent on mitochondrial OXPHOS for energy supply, and intracellular PGC1α-mediated mitochondrial biogenesis levels are increased in this cell line, indicating the important role of mitochondrial oxidative phosphorylation in cisplatin resistance. As PGC1α is a key molecule for integrating and coordinating nuclear DNA and mitochondrial DNA transcriptional machinery, an investigation into the regulatory mechanism PGC1α in mitochondrial energy metabolism via transcription may provide new clues for solving chemotherapy resistance. In the present study, it was demonstrated that inhibiting the expression of PGC1α decreased nuclear and mitochondrial DNA transcription factor expression, leading to increased lactic acid production and decreased cellular oxygen consumption and mitochondrial oxidative phosphorylation. Furthermore, mitochondrial stress-induced ROS production, as a feedback signal from mitochondria to the cell nucleus, increased PGC1α expression in SKOV3/DDP cells, which was involved in mitochondrial oxidative phosphorylation regulation. Collectively, the present study provides evidence that PGC1α-mediated nuclear and mitochondrial transcription feedback regulates energy metabolism and is involved in ovarian cancer cells escaping apoptosis during cisplatin treatment.

Marek's Disease Virus Infection Induced Mitochondria Changes in Chickens

Mitochondria are crucial cellular organelles in eukaryotes and participate in many cell processes including immune response, growth development, and tumorigenesis. Marek’s disease (MD), caused by an avian alpha-herpesvirus Marek’s disease virus (MDV), is characterized with lymphomas and immunosuppression. In this research, we hypothesize that mitochondria may play roles in response to MDV infection. To test it, mitochondrial DNA (mtDNA) abundance and gene expression in immune organs were examined in two well-defined and highly inbred lines of chickens, the MD-susceptible line 7₂ and the MD-resistant line 6₃. We found that mitochondrial DNA contents decreased significantly at the transformation phase in spleen of the MD-susceptible line 7₂ birds in contrast to the MD-resistant line 6₃. The mtDNA-genes and the nucleus-genes relevant to mtDNA maintenance and transcription, however, were significantly up-regulated. Interestingly, we found that POLG2 might play a potential role that led to the imbalance of mtDNA copy number and gene expression alteration. MDV infection induced imbalance of mitochondrial contents and gene expression, demonstrating the indispensability of mitochondria in virus-induced cell transformation and subsequent lymphoma formation, such as MD development in chicken. This is the first report on relationship between virus infection and mitochondria in chicken, which provides important insights into the understanding on pathogenesis and tumorigenesis due to viral infection.

Long non-coding RNA-p21 regulates MPP+-induced neuronal injury by targeting miR-625 and derepressing TRPM2 in SH-SY5Y cells

Parkinson's disease (PD), the second most prevalent age-related neurodegenerative disease, occurs as a result of the loss of dopaminergic neurons in the substantia nigra. Long non-coding RNA-p21 (lnc-p21) has been demonstrated to be upregulated in PD. However, its role in PD is unknown. Here, the results showed that lnc-p21 was highly expressed in human neuroblastoma SH-SY5Y cells treated with MPP⁺. Knockdown of lnc-p21 attenuated the cytotoxicity and cell apoptosis induced by MPP⁺ as shown by enhanced cell viability, decreased LDH release and cell apoptosis rate, accompanying with reduction of caspase-3 activity and Bax expression, and enhancement of Bcl-2 expression. Furthermore, knockdown of lnc-p21 mitigated MPP⁺-induced oxidative stress and neuroinflammation, as evidenced by the decrease in ROS generation, increase in SOD activity and decline in TNF-α, IL-1β and IL-6 levels. Conversely, overexpression of lnc-p21 resulted in the opposite effect. miR-625 was identified as a target of lnc-p21. lnc-p21 overturned the inhibitory effect of miR-625 on MPP⁺-induced neuronal injury in SH-SY5Y cells. Additionally, lnc-p21 positively regulated TRPM2 expression by targeting miR-625, and knockdown of TRPM2 inhibited MPP⁺-induced neuronal injury. Overall, our study identified a new lnc-p21-miR-625-TRPM2 regulatory network that lnc-p21 regulated MPP + -induced neuronal injury by sponging miR-625 and upregulating TRPM2 in SH-SY5Y cells, which provide a better understanding for the pathogenesis of PD.

An adverse outcome pathway for parkinsonian motor deficits associated with mitochondrial complex I inhibition

Epidemiological studies have observed an association between pesticide exposure and the development of Parkinson's disease, but have not established causality. The concept of an adverse outcome pathway (AOP) has been developed as a framework for the organization of available information linking the modulation of a molecular target [molecular initiating event (MIE)], via a sequence of essential biological key events (KEs), with an adverse outcome (AO). Here, we present an AOP covering the toxicological pathways that link the binding of an inhibitor to mitochondrial complex I (i.e., the MIE) with the onset of parkinsonian motor deficits (i.e., the AO). This AOP was developed according to the Organisation for Economic Co-operation and Development guidelines and uploaded to the AOP database. The KEs linking complex I inhibition to parkinsonian motor deficits are mitochondrial dysfunction, impaired proteostasis, neuroinflammation, and the degeneration of dopaminergic neurons of the substantia nigra. These KEs, by convention, were linearly organized. However, there was also evidence of additional feed-forward connections and shortcuts between the KEs, possibly depending on the intensity of the insult and the model system applied. The present AOP demonstrates mechanistic plausibility for epidemiological observations on a relationship between pesticide exposure and an elevated risk for Parkinson's disease development.

Linking mitochondrial dysfunction, metabolic syndrome and stress signaling in Neurodegeneration

Mounting evidence suggests a link between metabolic syndrome (MetS) such as diabetes, obesity, non-alcoholic fatty liver disease in the progression of Alzheimer's disease (AD), Parkinson's disease (PD) and other neurodegenerative diseases (NDDs). For instance, accumulated Aβ oligomer is enhancing neuronal Ca²⁺ release and neural NO where increased NO level in the brain through post translational modification is modulating the level of insulin production. It has been further confirmed that irrespective of origin; brain insulin resistance triggers a cascade of the neurodegeneration phenomenon which can be aggravated by free reactive oxygen species burden, ER stress, metabolic dysfunction, neuorinflammation, reduced cell survival and altered lipid metabolism. Moreover, several studies confirmed that MetS and diabetic sharing common mechanisms in the progression of AD and NDDs where mitochondrial dynamics playing a critical role. Any mutation in mitochondrial DNA, exposure of environmental toxin, high-calorie intake, homeostasis imbalance, glucolipotoxicity is causative factors for mitochondrial dysfunction. These cumulative pleiotropic burdens in mitochondria leads to insulin resistance, increased ROS production; enhanced stress-related enzymes that is directly linked MetS and diabetes in neurodegeneration. Since, the linkup mechanism between mitochondrial dysfunction and disease phenomenon of both MetS and NDDs is quite intriguing, therefore, it is pertinent for the researchers to identify and implement the therapeutic interventions for targeting MetS and NDDs. Herein, we elucidated the pertinent role of MetS induced mitochondrial dysfunction in neurons and their consequences in NDDs. Further, therapeutic potential of well-known biomolecules and chaperones to target altered mitochondria has been comprehensively documented. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.