Hepatic-specific Pgc-1α ablation drives fibrosis in a MASH model.

BACKGROUND & AIMS: Metabolic dysfunction-associated steatohepatitis (MASH) is a growing cause of chronic liver disease, characterized by fat accumulation, inflammation and fibrosis, which development depends on mitochondrial dysfunction and oxidative stress. Highly expressed in the liver during fasting, peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) regulates mitochondrial and oxidative metabolism. Given the relevant role of mitochondrial function in MASH, we investigated the relationship between PGC-1α and steatohepatitis. METHODS: We measured the hepatic expression of Pgc-1α in both MASH patients and wild-type mice fed a western diet (WD) inducing steatosis and fibrosis. We then generated a pure C57BL6/J strain loss of function mouse model in which Pgc-1α is selectively deleted in the liver and we fed these mice with a WD supplemented with sugar water that accurately mimics human MASH. RESULTS: We observed that the hepatic expression of Pgc-1α is strongly reduced in MASH, in both humans and mice. Moreover, the hepatic ablation of Pgc-1α promotes a considerable reduction of the hepatic mitochondrial respiratory capacity, setting up a bioenergetic harmful environment for liver diseases. Indeed, the lack of Pgc-1α decreases mitochondrial function and increases inflammation, fibrosis and oxidative stress in the scenario of MASH. Intriguingly, this profibrotic phenotype is not linked with obesity, insulin resistance and lipid disbalance. CONCLUSIONS: In a MASH model the hepatic ablation of Pgc-1α drives fibrosis independently from lipid and glucose metabolism. These results add a novel mechanistic piece to the puzzle of the specific and crucial role of mitochondrial function in MASH development.

Pivotal role of intestinal cholesterol and nuclear receptor LXR in metabolic liver steatohepatitis and hepatocarcinoma.

Hepatocellular carcinoma (HCC) incidence is continuously increasing worldwide, due to the rise of metabolic dysfunction-associated steatohepatitis (MASH) cases. Cholesterol is an essential driver of the metabolic dysregulations that promote HCC progression. Liver X Receptor (LXR) is a nuclear receptor best known for the regulation of lipid and cholesterol homeostasis, with a prominent function in the liver and in the intestine. Here, we aimed to explore whether modifications in intestinal lipid metabolism may contribute to the onset of HCC, particularly taking into account cholesterol metabolism and LXRs. To study the progression of MASH to HCC, we induced metabolic HCC in wild-type male mice and mice carrying an intestinal chronic activation of LXRα. Also, we analysed human hepatic transcriptome datasets. The increased consumption of fat and carbohydrates drives the intestinal activation of LXRα and accelerates the onset of the hepatic tumours. Chronic intestinal-specific activation of LXRα enhances HCC progression only in the presence of a high cholesterol intake. In HCC, despite the increased hepatic cholesterol content, LXR is not active, thus driving liver cancer development. Intriguingly, in line with these results in the mouse model, LXR transcriptome is also downregulated in human hepatocarcinoma and its expression level in liver tumours directly correlates with a decreased survival rate in patients. Overall, our findings establish the relevance of the intestine in influencing the susceptibility to MASH-HCC and point to intestinal LXRα activation as a driver of metabolic liver cancer in the presence of dietary cholesterol.

Intestinal Pgc1α ablation protects from liver steatosis and fibrosis.

Background & Aims: The gut-liver axis modulates the progression of metabolic dysfunction-associated steatotic liver disease (MASLD), a spectrum of conditions characterised by hepatic steatosis and a progressive increase of inflammation and fibrosis, culminating in metabolic dysfunction-associated steatohepatitis. Peroxisome proliferator-activated receptor-gamma coactivator 1α (Pgc1α) is a transcriptional co-regulator of mitochondrial activity and lipid metabolism. Here, the intestinal-specific role of Pgc1α was analysed in liver steatosis and fibrosis. Methods: We used a mouse model in which Pgc1α was selectively deleted from the intestinal epithelium. We fed these mice and their wild-type littermates a Western diet to recapitulate the major features of liver steatosis (after 2 months of diet) and metabolic dysfunction-associated steatohepatitis (after 4 months of diet). The chow diet was administered as a control diet. Results: In humans and mice, low expression of intestinal Pgc1α is inversely associated with liver steatosis, inflammation, and fibrosis. Intestinal disruption of Pgc1α impairs the transcription of a wide number of genes, including the cholesterol transporter Niemann-Pick C1-like 1 (Npc1l1), thus limiting the uptake of cholesterol from the gut. This results in a lower cholesterol accretion in the liver and a decreased production of new fatty acids, which protect the liver from lipotoxic lipid species accumulation, inflammation, and related fibrotic processes. Conclusions: In humans and mice, intestinal Pgc1α induction during Western diet may be another culprit driving hepatic steatosis and fibrosis. Here, we show that enterocyte-specific Pgc1α ablation protects the liver from steatosis and fibrosis by reducing intestinal cholesterol absorption, with subsequent decrease of cholesterol and de novo fatty acid accumulation in the liver. Impact and implications: Liver diseases result from several insults, including signals from the gut. Although the incidence of liver diseases is continuously increasing worldwide, effective drug therapy is still lacking. Here, we showed that the modulation of an intestinal coactivator regulates the liver response to a Western diet, by limiting the uptake of dietary cholesterol. This results in a lower accumulation of hepatic lipids together with decreased inflammation and fibrosis, thus limiting the progression of liver steatosis and fibrosis towards severe end-stage diseases.

Platelets from patients with visceral obesity promote colon cancer growth.

Several studies highlighted the importance of platelets in the tumor microenvironment due to their ability to interact with other cell types such as leukocytes, endothelial, stromal and cancer cells. Platelets can influence tumor development and metastasis formation through several processes consisting of the secretion of growth factors and cytokines and/or via direct interaction with cancer cells and endothelium. Patients with visceral obesity (VO) are susceptible to pro-thrombotic and pro-inflammatory states and to development of cancer, especially colon cancer. These findings provide us with the impetus to analyze the role of platelets isolated from VO patients in tumor growth and progression with the aim to explore a possible link between platelet activation, obesity and colon cancer. Here, using xenograft colon cancer models, we prove that platelets from patients with visceral obesity are able to strongly promote colon cancer growth. Then, sequencing platelet miRNome, we identify miR-19a as the highest expressed miRNA in obese subjects and prove that miR-19a is induced in colon cancer. Last, administration of miR-19a per se in the xenograft colon cancer model is able to promote colon cancer growth. We thus elect platelets with their specific miRNA abundance as important factors in the tumor promoting microenvironment of patients with visceral obesity.

Enterocyte superoxide dismutase 2 deletion drives obesity.

Compelling evidence support an involvement of oxidative stress and intestinal inflammation as early events in the predisposition and development of obesity and its related comorbidities. Here, we show that deficiency of the major mitochondrial antioxidant enzyme superoxide dismutase 2 (SOD2) in the gastrointestinal tract drives spontaneous obesity. Intestinal epithelium-specific Sod2 ablation in mice induced adiposity and inflammation via phospholipase A2 (PLA2) activation and increased release of omega-6 polyunsaturated fatty acid arachidonic acid. Remarkably, this obese phenotype was rescued when fed an essential fatty acid-deficient diet, which abrogates de novo biosynthesis of arachidonic acid. Data from clinical samples revealed that the negative correlation between intestinal Sod2 mRNA levels and obesity features appears to be conserved between mice and humans. Collectively, our findings suggest a role of intestinal Sod2 levels, PLA2 activity, and arachidonic acid in obesity presenting new potential targets of therapeutic interest in the context of this metabolic disorder.

Adhesion of Platelets to Colon Cancer Cells Is Necessary to Promote Tumor Development in Xenograft, Genetic and Inflammation Models.

Platelets represent the linkage between tissue damage and inflammatory response with a putative role in tumorigenesis. Given the importance of the microenvironment in colon cancer development, we elucidated the eventual role of platelets-cancer cells crosstalk in in vivo colon cancermodels. To evaluate the involvement of platelets in intestinal tumorigenesis, we first analyzed if the ablation of ß-integrin P-selectin that drives platelets-cell adhesion, would contribute to platelets-colon cancer cell interaction and drive cancer progression. In a xenograft tumor model, we observed that when tumors are inoculated with platelets, the ablation of P-selectin significantly reduced tumor growth compared to control platelets. Furthermore, in genetic models, as well as in chronic colitis-associated colorectal carcinogenesis, P-selectin ablated mice displayed a significant reduction in tumor number and size compared to control mice. Taken together, our data highlights the importance of platelets in the tumor microenvironment for intestinal tumorigenesis. These results support the hypothesis that a strategy aimed to inhibit platelets adhesion to tumor cells are able to block tumor growth and could represent a novel therapeutic approach to colon cancer treatment.

Uridine and pyruvate protect T cells' proliferative capacity from mitochondrial toxic antibiotics: a clinical pilot study.

Antibiotics that inhibit bacterial protein or nucleic acid synthesis and function can exert an off-target action on mitochondria (mitotoxic antibiotics), making actively dividing mammalian cells dependent on uridine and pyruvate supplementation. Based on this rationale, we carried out, for the first time, a randomized pilot study in 55 patients with asymptomatic bacteriuria or positive sperm culture, each treated with a single mitotoxic antibiotic with or without oral supplementation of uridine + pyruvate (Uripyr, Mitobiotix, Italy). The in vivo and ex vivo data show a a 3.4-fold higher value in the differential (before and after the antibiotic treatment) lymphocytes count and a 3.7-fold increase in the percentage of dividing T cells, respectively, in the Uripyr vs the control group. Our findings lay the groundwork to enhance the synergy between antibiotics and the immune system in order to optimize the administration protocols and widen the application potentials of antibiotic therapies as well as to re-evaluate old "forgotten" molecules to fight bacterial infections in the antibiotics resistance era.

PGC-1s in the Spotlight with Parkinson's Disease.

Parkinson's disease is one of the most common neurodegenerative disorders worldwide, characterized by a progressive loss of dopaminergic neurons mainly localized in the substantia nigra pars compacta. In recent years, the detailed analyses of both genetic and idiopathic forms of the disease have led to a better understanding of the molecular and cellular pathways involved in PD, pointing to the centrality of mitochondrial dysfunctions in the pathogenic process. Failure of mitochondrial quality control is now considered a hallmark of the disease. The peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1) family acts as a master regulator of mitochondrial biogenesis. Therefore, keeping PGC-1 level in a proper range is fundamental to guarantee functional neurons. Here we review the major findings that tightly bond PD and PGC-1s, raising important points that might lead to future investigations.

let-7e downregulation characterizes early phase colonic adenoma in APCMin/+ mice and human FAP subjects.

The crypt-villus axis represents the essential unit of the small intestine, which integrity and functions are fundamental to assure tissue and whole-body homeostasis. Disruption of pathways regulating the fine balance between proliferation and differentiation results in diseases development. Nowadays, it is well established that microRNAs (miRNAs) play a crucial role in the homeostasis maintenance and perturbation of their levels may promote tumor development. Here, by using microarray technology, we analysed the miRNAs differentially expressed between the crypt and the villus in mice ileum. The emerged miRNAs were further validated by Real Time qPCR in mouse model (ApcMin/+), human cell lines and human tissue samples (FAP) of colorectal cancer (CRC). Our results indicated that miRNAs more expressed in the villi compartment are negatively regulated in tumor specimens, thus suggesting a close association between these microRNAs and the differentiation process. Particularly, from our analysis let-7e appeared to be a promising target for possible future therapies and a valuable marker for tumor staging, being upregulated in differentiated cells and downregulated in early-stage colonic adenoma samples.

Extra-Virgin Olive Oil from Apulian Cultivars and Intestinal Inflammation.

Inflammatory bowel disease (IBD) is a multifactorial intestinal disorder characterized by chronic intestinal inflammation. The etiology of IBD is still unclear, although genetic, environmental and host factors have been associated to the disease. Extra-virgin olive oil (EVO) is a central component of the Mediterranean diet and it decreases chronic inflammation by interfering with arachidonic acid and NF-κB signaling pathways. Specifically, the different components of EVO are able to confer advantages in terms of health in their site of action. For instance, oleic acid displays a protective effect in liver dysfunction and gut inflammation, whereas phenolic compounds protect colon cells against oxidative damage and improve the symptoms of chronic inflammation in IBD. Given the biological properties of EVO, we investigated whether its administration is able to confer protection in a mouse model of dextrane sodium sulfate (DSS)-induced colitis. Four EVO cultivars from the Apulian Region of Italy, namely Ogliarola (Cima di Bitonto), Coratina, Peranzana and Cima di Mola, respectively, were used. Administration of EVO resulted in reduced body weight loss in our colitis model. Furthermore, mice treated with Ogliarola, Coratina and Cima di Mola EVO displayed a reduction of rectal bleeding and IL-1ß, TGFß, IL-6 gene expression levels. Furthermore, Ogliarola, Coratina and Peranzana EVO administration ameliorated intestinal permeability and histopathological features of inflammation. Our data further validate the well-known positive effects of EVO supplementation in promoting human health and suggest the bona fide contribution of EVO in preventing onset and reducing progression of intestinal inflammation.

Hepatic microRNA Expression by PGC-1α and PGC-1ß in the Mouse.

The fine-tuning of liver metabolism is essential to maintain the whole-body homeostasis and to prevent the onset of diseases. The peroxisome proliferator-activated receptor-γ coactivators (PGC-1s) are transcriptional key players of liver metabolism, able to regulate mitochondrial function, gluconeogenesis and lipid metabolism. Their activity is accurately modulated by post-translational modifications. Here, we showed that specific PGC-1s expression can lead to the upregulation of different microRNAs widely implicated in liver physiology and diseases development and progression, thus offering a new layer of complexity in the control of hepatic metabolism.

PGC-1ß Induces Susceptibility To Acetaminophen-Driven Acute Liver Failure.

Acetaminophen (APAP) is a worldwide commonly used painkiller drug. However, high doses of APAP can lead to acute hepatic failure and, in some cases, death. Previous studies indicated that different factors, including life-style and metabolic diseases, could predispose to the risk of APAP-induced liver failure. However, the molecular process that could favor APAP hepatotoxicity remains understood. Here, we reported that a short-term high fat-enriched diet worsens APAP-induced liver damage, by promoting liver accumulation of lipids that induces the activation of peroxisome proliferator-activated receptor gamma coactivator 1-beta (PGC-1ß). Therefore, we challenged mice with hepatic-specific PGC-1ß overexpression on a chow diet with a subtoxic dose of APAP and we found that PGC-1ß overexpression renders the liver more sensitive to APAP damage, mainly due to intense oxidative stress, finally ending up with liver necrosis and mice death. Overall, our results indicated that during high fat feeding, PGC-1ß adversely influences the ability of the liver to overcome APAP toxicity by orchestrating different metabolic pathways that finally lead to fatal outcome.

PGC-1α induced browning promotes involution and inhibits lactation in mammary glands.

The PPARγ coactivator 1α (PGC-1α) is a transcriptional regulator of mitochondrial biogenesis and oxidative metabolism. Recent studies have highlighted a fundamental role of PGC-1α in promoting breast cancer progression and metastasis, but the physiological role of this coactivator in the development of mammary glands is still unknown. First, we show that PGC-1α is highly expressed during puberty and involution, but nearly disappeared in pregnancy and lactation. Then, taking advantage of a newly generated transgenic mouse model with a stable and specific overexpression of PGC-1α in mammary glands, we demonstrate that the re-expression of this coactivator during the lactation stage leads to a precocious regression of the mammary glands. Thus, we propose that PGC-1α action is non-essential during pregnancy and lactation, whereas it is indispensable during involution. The rapid preadipocyte-adipocyte transition, together with an increased rate of apoptosis promotes a premature mammary glands involution that cause lactation defects and pup growth retardation. Overall, we provide new insights in the comprehension of female reproductive cycles and lactation deficiency, thus opening new roads for mothers that cannot breastfeed.

Metabolic aspects in NAFLD, NASH and hepatocellular carcinoma: the role of PGC1 coactivators.

Alterations of hepatic metabolism are critical to the development of liver disease. The peroxisome proliferator-activated receptor-γ coactivators (PGC1s) are able to orchestrate, on a transcriptional level, different aspects of liver metabolism, such as mitochondrial oxidative phosphorylation, gluconeogenesis and fatty acid synthesis. As modifications affecting both mitochondrial and lipid metabolism contribute to the initiation and/or progression of liver steatosis, nonalcoholic fatty liver disease (NAFLD), nonalcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC), a link between disrupted PGC1 pathways and onset of these pathological conditions has been postulated. However, despite the large quantity of studies, the scenario is still not completely understood, and some issues remain controversial. Here, we discuss the roles of PGC1s in healthy liver and explore their contribution to the pathogenesis and future therapy of NASH and HCC.

Uncoupling FoxO3A mitochondrial and nuclear functions in cancer cells undergoing metabolic stress and chemotherapy.

While aberrant cancer cell growth is frequently associated with altered biochemical metabolism, normal mitochondrial functions are usually preserved and necessary for full malignant transformation. The transcription factor FoxO3A is a key determinant of cancer cell homeostasis, playing a dual role in survival/death response to metabolic stress and cancer therapeutics. We recently described a novel mitochondrial arm of the AMPK-FoxO3A axis in normal cells upon nutrient shortage. Here, we show that in metabolically stressed cancer cells, FoxO3A is recruited to the mitochondria through activation of MEK/ERK and AMPK, which phosphorylate serine 12 and 30, respectively, on FoxO3A N-terminal domain. Subsequently, FoxO3A is imported and cleaved to reach mitochondrial DNA, where it activates expression of the mitochondrial genome to support mitochondrial metabolism. Using FoxO3A-/- cancer cells generated with the CRISPR/Cas9 genome editing system and reconstituted with FoxO3A mutants being impaired in their nuclear or mitochondrial subcellular localization, we show that mitochondrial FoxO3A promotes survival in response to metabolic stress. In cancer cells treated with chemotherapeutic agents, accumulation of FoxO3A into the mitochondria promoted survival in a MEK/ERK-dependent manner, while mitochondrial FoxO3A was required for apoptosis induction by metformin. Elucidation of FoxO3A mitochondrial vs. nuclear functions in cancer cell homeostasis might help devise novel therapeutic strategies to selectively disable FoxO3A prosurvival activity.

Hepatic peroxisome proliferator-activated receptor γ coactivator 1ß drives mitochondrial and anabolic signatures that contribute to hepatocellular carcinoma progression in mice.

The peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1ß (PGC-1 ß) is a master regulator of mitochondrial biogenesis and oxidative metabolism as well as of antioxidant defense. Specifically, in the liver, PGC-1ß also promotes de novo lipogenesis, thus sustaining cellular anabolic processes. Given the relevant pathogenic role of mitochondrial and fatty acid metabolism in hepatocarcinoma (HCC), here we pointed to PGC-1ß as a putative novel transcriptional player in the development and progression of HCC. For this purpose, we generated both hepatic-specific PGC-1ß-overexpressing (LivPGC-1ß) and PGC-1ß knockout (LivPGC-1ßKO) mice, and we challenged them with both chemical and genetic models of hepatic carcinogenesis. Our results demonstrate a pivotal role of PGC-1ß in driving liver tumor development. Indeed, whereas mice overexpressing PGC-1ß show greater tumor susceptibility, PGC-1ß knockout mice are protected from carcinogenesis. High levels of PGC-1ß are able to boost reactive oxygen species (ROS) scavenger expression, therefore limiting the detrimental ROS accumulation and, consequently, apoptosis. Moreover, it supports tumor anabolism, enhancing the expression of genes involved in fatty acid and triglyceride synthesis. Accordingly, the specific hepatic ablation of PGC-1ß promotes the accumulation of ROS-driven macromolecule damage, finally limiting tumor growth. CONCLUSION: The present data elect hepatic PGC-1ß as a transcriptional gatekeeper of mitochondrial function and redox status in HCC, orchestrating different metabolic programs that allow tumor progression. (Hepatology 2018;67:884-898).

Is hepatic lipogenesis fundamental for NAFLD/NASH? A focus on the nuclear receptor coactivator PGC-1ß.

Non-alcoholic fatty liver diseases are the hepatic manifestation of metabolic syndrome. According to the classical pattern of NAFLD progression, de novo fatty acid synthesis has been incriminated in NAFLD progression. However, this hypothesis has been challenged by the re-evaluation of NAFLD development mechanisms together with the description of the role of lipogenic genes in NAFLD and with the recent observation that PGC-1ß, a nuclear receptor/transcription factor coactivator involved in the transcriptional regulation of lipogenesis, displays protective effects against NAFLD/NASH progression. In this review, we focus on the implication of lipogenesis and triglycerides synthesis on the development of non-alcoholic fatty liver diseases and discuss the involvement of these pathways in the protective role of PGC-1ß toward these hepatic manifestations.

Generation of Rho Zero Cells: Visualization and Quantification of the mtDNA Depletion Process.

Human mitochondrial DNA (mtDNA) is located in discrete DNA-protein complexes, so called nucleoids. These structures can be easily visualized in living cells by utilizing the fluorescent stain PicoGreen. In contrary, cells devoid of endogenous mitochondrial genomes (ρ° cells) display no mitochondrial staining in the cytoplasm. A modified restriction enzyme can be targeted to mitochondria to cleave the mtDNA molecules in more than two fragments, thereby activating endogenous nucleases. By applying this novel enzymatic approach to generate mtDNA-depleted cells the destruction of mitochondrial nucleoids in cultured cells could be detected in a time course. It is clear from these experiments that mtDNA-depleted cells can be seen as early as 48 h post-transfection using the depletion system. To prove that mtDNA is degraded during this process, mtDNA of transfected cells was quantified by real-time PCR. A significant decline could be observed 24 h post-transfection. Combination of both results showed that mtDNA of transfected cells is completely degraded and, therefore, ρ° cells were generated within 48 h. Thus, the application of a mitochondrially-targeted restriction endonuclease proves to be a first and fast, but essential step towards a therapy for mtDNA disorders.

Adenomatous polyposis coli (APC)-induced apoptosis of HT29 colorectal cancer cells depends on mitochondrial oxidative metabolism.

Adenomatous polyposis coli (APC) is a tumor suppressor involved in the Wnt signaling, the primary driving force of the intestinal epithelium homeostasis. Alterations of components of the Wnt pathway, and in most cases mutations of APC, have been reported to promote colorectal cancer (CRC). During differentiation the enterocytes migrate from the crypt to the tip of the villus where they undergo apoptosis thus ensuring the continual renewal of the intestinal mucosa. The differentiation process is characterized by an activation gradient of the Wnt signaling pathway accompanied by a metabolic switch from glycolysis to mitochondrial oxidative phosphorylation along the crypt-villus axis. In the present work, we study the relationship between the expression of wild type APC protein and mitochondrial oxidative metabolism in HT29 colorectal cancer cells, originally carrying endogenous inactive APC alleles. By generating mtDNA-depleted (rho0) APC-inducible HT29 cells, we demonstrate for the first time that the APC-dependent apoptosis requires the production of reactive oxygen species (ROS) by the mitochondrial respiratory chain. The possible role of mitochondria as putative target in the prevention and/or therapy of colorectal cancer is herein discussed.

PGC-1ß promotes enterocyte lifespan and tumorigenesis in the intestine.

The mucosa of the small intestine is renewed completely every 3-5 d throughout the entire lifetime by small populations of adult stem cells that are believed to reside in the bottom of the crypts and to migrate and differentiate into all the different populations of intestinal cells. When the cells reach the apex of the villi and are fully differentiated, they undergo cell death and are shed into the lumen. Reactive oxygen species (ROS) production is proportional to the electron transfer activity of the mitochondrial respiration chain. ROS homeostasis is maintained to control cell death and is finely tuned by an inducible antioxidant program. Here we show that peroxisome proliferator-activated receptor-γ coactivator-1ß (PGC-1ß) is highly expressed in the intestinal epithelium and possesses dual activity, stimulating mitochondrial biogenesis and oxygen consumption while inducing antioxidant enzymes. To study the role of PGC-1ß gain and loss of function in the gut, we generated both intestinal-specific PGC-1ß transgenic and PGC-1ß knockout mice. Mice overexpressing PGC-1ß present a peculiar intestinal morphology with very long villi resulting from increased enterocyte lifespan and also demonstrate greater tumor susceptibility, with increased tumor number and size when exposed to carcinogens. PGC-1ß knockout mice are protected from carcinogenesis. We show that PGC-1ß triggers mitochondrial respiration while protecting enterocytes from ROS-driven macromolecule damage and consequent apoptosis in both normal and dysplastic mucosa. Therefore, PGC-1ß in the gut acts as an adaptive self-point regulator, capable of providing a balance between enhanced mitochondrial activity and protection from increased ROS production.