Disruption of the uncoupling protein-2 gene in mice reveals a role in immunity and reactive oxygen species production

Reduction of hyperglycemia in STZ-induced diabetic mice by prophylactic treatment with heat-killed Mycobacterium aurum: possible effects on glucose utilization, mitochondrial uncoupling, and oxidative stress in liver and skeletal muscle

Background

In addition to conventional treatment and modifications in physical activity and diet, alternative strategies have been investigated to manage, prevent, or delay diabetes in humans. In this regard, one strategy has relied on the immunomodulatory properties of mycobacteria, whereby Bacillus Calmette-Guerin, an attenuated live strain of Mycobacterium bovis, has been shown to improve glycemic control in patients with diabetes and to alleviate hyperglycemia in selected murine models of diabetes. A novel heat-killed (HK) whole-cell preparation of Mycobacterium aurum (M. aurum) is currently under development as a potential food supplement; nevertheless, its potential bioactivity remains largely unknown. Thus, the present study investigated the potential prophylactic anti-diabetic effects of HK M. aurum in streptozotocin (STZ)-induced diabetic mice.

Methods

Mice were divided into three groups: the STZ-induced diabetic group was injected with a single intraperitoneal high dose of STZ, the HK M. aurum-treated diabetic group was prophylactically treated with three doses of HK M. aurum 6 weeks before STZ injection, and the control non-diabetic group was given three intradermal injections of borate-buffered saline and an intraperitoneal injection of citrate buffer. Liver lactate dehydrogenase (LDH), uncoupling protein 2 (UCP2), and glucose transporter 2 (GLUT2) and skeletal muscle LDH, UCP3, and GLUT4 protein expression levels in different mouse groups were determined by Western blot.

Results

Our results indicated that HK M. aurum did not cause any significant changes in glycemic levels of normal non-diabetic mice. Prophylactic administration of three doses of HK M. aurum to diabetic mice resulted in a significant reduction in their blood glucose levels when compared to those in control diabetic mice. Prophylactic treatment of diabetic mice with HK M. aurum significantly restored their disturbed protein expression levels of liver UCP2 and LDH as well as of skeletal muscle UCP3. On the other hand, prophylactic treatment of diabetic mice with HK M. aurum had no significant effect on their liver GLUT2 and skeletal muscle GLUT4 and LDH protein expression levels.

Conclusions

Our findings provide the first evidence that HK M. aurum possesses a hyperglycemia-lowering capacity and might support its future use as a food supplement for the amelioration of diabetes.

Mitochondrial Physiology of Cellular Redox Regulations

Mitochondria (mt) represent the vital hub of the molecular physiology of the cell, being decision-makers in cell life/death and information signaling, including major redox regulations and redox signaling. Now we review recent advances in understanding mitochondrial redox homeostasis, including superoxide sources and H2O2 consumers, i.e., antioxidant mechanisms, as well as exemplar situations of physiological redox signaling, including the intramitochondrial one and mt-to-cytosol redox signals, which may be classified as acute and long-term signals. This review exemplifies the acute redox signals in hypoxic cell adaptation and upon insulin secretion in pancreatic beta-cells. We also show how metabolic changes under these circumstances are linked to mitochondrial cristae narrowing at higher intensity of ATP synthesis. Also, we will discuss major redox buffers, namely the peroxiredoxin system, which may also promote redox signaling. We will point out that pathological thresholds exist, specific for each cell type, above which the superoxide sources exceed regular antioxidant capacity and the concomitant harmful processes of oxidative stress subsequently initiate etiology of numerous diseases. The redox signaling may be impaired when sunk in such excessive pro-oxidative state.

Misaligned feeding uncouples daily rhythms within brown adipose tissue and between peripheral clocks

Extended food consumption during the rest period perturbs the phase relationship between circadian clocks in the periphery and the brain, leading to adverse health effects. Beyond the liver, how metabolic organs respond to a timed hypocaloric diet is largely unexplored. We investigated how feeding schedules impacted circadian gene expression in epididymal white and brown adipose tissue (eWAT and BAT) compared to the liver and hypothalamus. We restricted food to either daytime or nighttime in C57BL/6J male mice, with or without caloric restriction. Unlike the liver and eWAT, rhythmic clock genes in the BAT remained insensitive to feeding time, similar to the hypothalamus. We uncovered an internal split within the BAT in response to conflicting environmental cues, displaying inverted oscillations on a subset of metabolic genes without modifying its local core circadian machinery. Integrating tissue-specific responses on circadian transcriptional networks with metabolic outcomes may help elucidate the mechanism underlying the health burden of eating at unusual times.

The role of sirtuins and uncoupling proteins on vascular aging: The Northern Manhattan Study experience

Aging affects all organs. Arteries, in particular, are among the most affected. Vascular aging (VA) is defined as age-associated changes in function and structure of vessels. Classical VA phenotypes are carotid intima-media thickness (IMT), carotid plaque (CP), and arterial stiffness (STIFF). Individuals have different predisposition to these VA phenotypes and their associated risk of cardiovascular events. Some develop an early vascular aging (EVA), and others are protected and identified as having supernormal vascular aging (SUPERNOVA). The mechanisms leading to these phenotypes are not well understood. In the Northern Manhattan Study (NOMAS), we found genetic variants in the 7 Sirtuins (SIRT) and 5 Uncoupling Proteins (UCP) to be differently associated with risk to developing VA phenotypes. In this article, we review the results of genetic-epidemiology studies to better understand which of the single nucleotide polymorphisms (SNPs) in SIRT and UCP are responsible for both EVA and SUPERNOVA.

UCP2 polymorphisms, daily step count, and number of teeth associated with all-cause mortality risk in Sado City: A hospital-based cohort study

Objective

Uncoupling protein 2 (UCP2) is an ion/anion transporter in the mitochondrial inner membrane that plays a crucial role in immune response, regulation of oxidative stress, and cellular metabolism. UCP2 polymorphisms are linked to chronic inflammation, obesity, diabetes, heart disease, exercise efficiency, and longevity. Daily step count and number of teeth are modifiable factors that reduce mortality risk, although the role of UCP2 in this mechanism is unknown. This study aimed to assess the possible effects of UCP2 polymorphisms on the association between daily step count and number of teeth with all-cause mortality.

Methods

This study was conducted as a cohort project involving adult Japanese outpatients at Sado General Hospital (PROST). The final number of participants was 875 (mean age: 69 y). All-cause mortality during thirteen years (from June 2008 to August 2021) was recorded. The functional UCP2 genotypes rs659366 and rs660339 were identified using the Japonica Array®. Survival analyses were performed using multivariate Cox proportional hazard models.

Results

There were 161 deaths (mean observation period: 113 months). Age, sex, daily step count, and the number of teeth were significantly associated with mortality. In females, UCP2 polymorphisms were associated with mortality independent of other factors (rs659366 GA compared to GG + AA; HR = 2.033, p = 0.019, rs660339 C T compared to CC + TT; HR = 1.911, p = 0.029). Multivariate models, with and without UCP2 genotypes, yielded similar results. The interaction terms between UCP2 genotype and daily step count or number of teeth were not significantly associated with mortality.

Conclusion

The effects of UCP2 polymorphisms on the association between daily step count or the number of teeth and all-cause mortality were not statistically significant. In females, UCP2 polymorphisms were significantly associated with all-cause mortality. Our findings confirmed the importance of physical activity and oral health and suggested a role of UCP2 in mortality risk independently with those factors.

UCP2, a Member of the Mitochondrial Uncoupling Proteins: An Overview from Physiological to Pathological Roles

UCP2 is an uncoupling protein homolog to UCP1. Unlike UCP1, which participates in non-shivering thermogenesis by uncoupling oxidative phosphorylation (OXPHOS), UCP2 does not perform a canonical H+ leak, consuming the protonmotive force (Δp) through the inner mitochondrial membrane. The UCP2 biological role is elusive. It can counteract oxidative stress, acting with a "mild uncoupling" process to reduce ROS production, and, in fact, UCP2 activities are related to inflammatory processes, triggering pathological conditions. However, the Δp dissipation by UCP2 activity reduces the mitochondrial ATP production and rewires the bioenergetic metabolism of the cells. In all likelihood, UCP2 works as a carrier of metabolites with four carbon atoms (C4), reversing the anaerobic glycolysis-dependent catabolism to OXPHOS. Indeed, UCP2 can perform catalysis in dual mode: mild uncoupling of OXPHOS and metabolite C4 exchange of mitochondria. In vivo, the UCP2 features in the biology of mitochondria promote healthy ageing, increased lifespan, and can assure cerebro- and cardiovascular protection. However, the pathological conditions responsible for insulin secretion suppression are dependent on UCP2 activity. On balance, the uncertain biochemical mechanisms dependent on UCP2 do not allow us to depict the protective role in mitochondrial bioenergetics.

Mitochondrial Reactive Oxygen Species in Infection and Immunity

Reactive oxygen species (ROS) contain at least one oxygen atom and one or more unpaired electrons and include singlet oxygen, superoxide anion radical, hydroxyl radical, hydroperoxyl radical, and free nitrogen radicals. Intracellular ROS can be formed as a consequence of several factors, including ultra-violet (UV) radiation, electron leakage during aerobic respiration, inflammatory responses mediated by macrophages, and other external stimuli or stress. The enhanced production of ROS is termed oxidative stress and this leads to cellular damage, such as protein carbonylation, lipid peroxidation, deoxyribonucleic acid (DNA) damage, and base modifications. This damage may manifest in various pathological states, including ageing, cancer, neurological diseases, and metabolic disorders like diabetes. On the other hand, the optimum levels of ROS have been implicated in the regulation of many important physiological processes. For example, the ROS generated in the mitochondria (mitochondrial ROS or mt-ROS), as a byproduct of the electron transport chain (ETC), participate in a plethora of physiological functions, which include ageing, cell growth, cell proliferation, and immune response and regulation. In this current review, we will focus on the mechanisms by which mt-ROS regulate different pathways of host immune responses in the context of infection by bacteria, protozoan parasites, viruses, and fungi. We will also discuss how these pathogens, in turn, modulate mt-ROS to evade host immunity. We will conclude by briefly giving an overview of the potential therapeutic approaches involving mt-ROS in infectious diseases.

UCP2 and pancreatic cancer: conscious uncoupling for therapeutic effect

Pancreatic cancer has an exaggerated dependence on mitochondrial metabolism, but methods to specifically target the mitochondria without off target effects in normal tissues that rely on these organelles is a significant challenge. The mitochondrial uncoupling protein 2 (UCP2) has potential as a cancer-specific drug target, and thus, we will review the known biology of UCP2 and discuss its potential role in the pathobiology and future therapy of pancreatic cancer.

The mechanisms of mitochondrial abnormalities that contribute to sleep disorders and related neurodegenerative diseases

Sleep is a highly intricate biological phenomenon, and its disorders play a pivotal role in numerous diseases. However, the specific regulatory mechanisms remain elusive. In recent years, the role of mitochondria in sleep disorders has gained considerable attention. Sleep deprivation not only impairs mitochondrial morphology but also decreases the number of mitochondria and triggers mitochondrial dysfunction. Furthermore, mitochondrial dysfunction has been implicated in the onset and progression of various sleep disorder-related neurological diseases, especially neurodegenerative conditions. Therefore, a greater understanding of the impact of sleep disorders on mitochondrial dysfunction may reveal new therapeutic targets for neurodegenerative diseases. In this review, we comprehensively summarize the recent key findings on the mechanisms underlying mitochondrial dysfunction caused by sleep disorders and their role in initiating or exacerbating common neurodegenerative diseases. In addition, we provide fresh insights into the diagnosis and treatment of sleep disorder-related diseases.

Deletion of the Clock Gene Bmal2 Leads to Alterations in Hypothalamic Clocks, Circadian Regulation of Feeding, and Energy Balance

BMAL2 (ARNTL2) is a paralog of BMAL1 that can form heterodimers with the other circadian factors CLOCK and NPAS2 to activate transcription of clock and clock-controlled genes. To assess a possible role of Bmal2 in the circadian regulation of metabolism, we investigated daily variations of energy metabolism, feeding behavior, and locomotor behavior, as well as ability to anticipate restricted food access in male mice knock-out for Bmal2 (B2KO). While their amount of food intake and locomotor activity were normal compared with wild-type mice, B2KO mice displayed increased adiposity (1.5-fold higher) and fasted hyperinsulinemia (fourfold higher) and tended to have lower energy expenditure at night. Impairment of the master clock in the suprachiasmatic nuclei was evidenced by the shorter free-running period (-14 min/cycle) of B2KO mice compared with wild-type controls and by a loss of daily rhythmicity in expression of intracellular metabolic regulators (e.g., Lipoprotein lipase and Uncoupling protein 2). The circadian window of eating was longer in B2KO mice. The circadian patterns of food intake and meal numbers were bimodal in control mice but not in B2KO mice. In response to restricted feeding, food-anticipatory activity was almost prevented in B2KO mice, suggesting altered food clock that controls anticipation of food availability. In the mediobasal hypothalamus of B2KO mice, expression of genes coding orexigenic neuropeptides (including Neuropeptide y and Agouti-Related Peptide) was downregulated, while Lipoprotein lipase expression lost its rhythmicity. Together, these data highlight that BMAL2 has major impacts on brain regulation of metabolic rhythms, sleep-wake cycle, and food anticipation.

The Effect of Orally Administered Multi-Strain Probiotic Formulation (Lactobacillus, Bifidobacterium) on the Phagocytic Activity and Oxidative Metabolism of Peripheral Blood Granulocytes and Monocytes in Lambs

Probiotic feed additives have attracted considerable research interest in recent years because the effectiveness of probiotics can differ across microbial strains and the supplemented macroorganisms. The present study was conducted on 16 lambs divided equally into two groups (C-control and E-experimental). The examined lambs were aged 11 days at the beginning of the experiment and 40 days at the end of the experiment. The diet of group E lambs was supplemented with a multi-strain probiotic formulation (Lactobacillus plantarum AMT14, Lactobacillus plantarum AMT4, Lactobacillus rhamnosus AMT15, and Bifidobacterium animalis AMT30), whereas group C lambs did not receive the probiotic additive. At the beginning of the experiment (day 0) and on experimental days 15 and 30, blood was sampled from the jugular vein to determine and compare: phagocytic activity (Phagotest) and oxidative metabolism (Phagoburst) of peripheral blood granulocytes and monocytes by flow cytometry. An analysis of the phagocytic activity of granulocytes and monocytes revealed significantly higher levels of phagocytic activity (expressed as the percentage of phagocytic cells and mean fluorescence intensity) in lambs that were administered the multi-strain probiotic formulation compared with lambs in the control group. The probiotic feed additive also exerted a positive effect on the oxidative metabolism of both granulocytes and monocytes (expressed as the percentage of oxidative metabolism and mean fluorescence intensity) after stimulation with Escherichia coli bacteria and with PMA (4-phorbol-12-β-myristate-13-acetate). These findings suggest that the tested probiotic formulation may have a positive effect on the immune status of lambs.

Glycerol 3-phosphate dehydrogenases (1 and 2) in cancer and other diseases

The glycerol 3-phosphate shuttle (GPS) is composed of two different enzymes: cytosolic NAD+-linked glycerol 3-phosphate dehydrogenase 1 (GPD1) and mitochondrial FAD-linked glycerol 3-phosphate dehydrogenase 2 (GPD2). These two enzymes work together to act as an NADH shuttle for mitochondrial bioenergetics and function as an important bridge between glucose and lipid metabolism. Since these genes were discovered in the 1960s, their abnormal expression has been described in various metabolic diseases and tumors. Nevertheless, it took a long time until scientists could investigate the causal relationship of these enzymes in those pathophysiological conditions. To date, numerous studies have explored the involvement and mechanisms of GPD1 and GPD2 in cancer and other diseases, encompassing reports of controversial and non-conventional mechanisms. In this review, we summarize and update current knowledge regarding the functions and effects of GPS to provide an overview of how the enzymes influence disease conditions. The potential and challenges of developing therapeutic strategies targeting these enzymes are also discussed.

Mitochondrial uncoupling proteins protect human airway epithelial ciliated cells from oxidative damage

Apical cilia on epithelial cells defend the lung by propelling pathogens and particulates out of the respiratory airways. Ciliated cells produce ATP that powers cilia beating by densely grouping mitochondria just beneath the apical membrane. However, this efficient localization comes at a cost because electrons leaked during oxidative phosphorylation react with molecular oxygen to form superoxide, and thus, the cluster of mitochondria creates a hotspot for oxidant production. The relatively high oxygen concentration overlying airway epithelia further intensifies the risk of generating superoxide. Thus, airway ciliated cells face a unique challenge of producing harmful levels of oxidants. However, surprisingly, highly ciliated epithelia produce less reactive oxygen species (ROS) than epithelia with few ciliated cells. Compared to other airway cell types, ciliated cells express high levels of mitochondrial uncoupling proteins, UCP2 and UCP5. These proteins decrease mitochondrial protonmotive force and thereby reduce production of ROS. As a result, lipid peroxidation, a marker of oxidant injury, decreases. However, mitochondrial uncoupling proteins exact a price for decreasing oxidant production; they decrease the fraction of mitochondrial respiration that generates ATP. These findings indicate that ciliated cells sacrifice mitochondrial efficiency in exchange for safety from damaging oxidation. Employing uncoupling proteins to prevent oxidant production, instead of relying solely on antioxidants to decrease postproduction oxidant levels, may offer an advantage for targeting a local area of intense ROS generation.

Glucose transport, transporters and metabolism in diabetic retinopathy

Diabetic retinopathy (DR) is the most common reason for blindness in working-age individuals globally. Prolonged high blood glucose is a main causative factor for DR development, and glucose transport is prerequisite for the disturbances in DR caused by hyperglycemia. Glucose transport is mediated by its transporters, including the facilitated transporters (glucose transporter, GLUTs), the "active" glucose transporters (sodium-dependent glucose transporters, SGLTs), and the SLC50 family of uniporters (sugars will eventually be exported transporters, SWEETs). Glucose transport across the blood-retinal barrier (BRB) is crucial for nourishing the neuronal retina in the context of retinal physiology. This physiological process primarily relies on GLUTs and SGLTs, which mediate the glucose transportation across both the cell membrane of retinal capillary endothelial cells and the retinal pigment epithelium (RPE). Under diabetic conditions, increased accumulation of extracellular glucose enhances the retinal cellular glucose uptake and metabolism via both glycolysis and glycolytic side branches, which activates several biochemical pathways, including the protein kinase C (PKC), advanced glycation end-products (AGEs), polyol pathway and hexosamine biosynthetic pathway (HBP). These activated biochemical pathways further increase the production of reactive oxygen species (ROS), leading to oxidative stress and activation of Poly (ADP-ribose) polymerase (PARP). The activated PARP further affects all the cellular components in the retina, and finally resulting in microangiopathy, neurodegeneration and low-to-moderate grade inflammation in DR. This review aims to discuss the changes of glucose transport, glucose transporters, as well as its metabolism in DR, which influences the retinal neurovascular unit (NVU) and implies the possible therapeutic strategies for treating DR.

Uncoupling Protein 3 Catalyzes the Exchange of C4 Metabolites Similar to UCP2

Uncoupling protein 3 (UCP3) belongs to the mitochondrial carrier protein superfamily SLC25 and is abundant in brown adipose tissue (BAT), the heart, and muscles. The expression of UCP3 in tissues mainly dependent on fatty acid oxidation suggests its involvement in cellular metabolism and has drawn attention to its possible transport function beyond the transport of protons in the presence of fatty acids. Based on the high homology between UCP2 and UCP3, we hypothesized that UCP3 transports C4 metabolites similar to UCP2. To test this, we measured the transport of substrates against phosphate (32Pi) in proteoliposomes reconstituted with recombinant murine UCP3 (mUCP3). We found that mUCP3 mainly transports aspartate and sulfate but also malate, malonate, oxaloacetate, and succinate. The transport rates calculated from the exchange of 32Pi against extraliposomal aspartate and sulfate were 23.9 ± 5.8 and 17.5 ± 5.1 µmol/min/mg, respectively. Using site-directed mutagenesis, we revealed that mutation of R84 resulted in impaired aspartate/phosphate exchange, demonstrating its critical role in substrate transport. The difference in substrate preference between mUCP2 and mUCP3 may be explained by their different tissue expression patterns and biological functions in these tissues.

Sensing the oxygen and temperature in the adipose tissues - who's sensing what?

Adipose tissues, composed of various cell types, including adipocytes, endothelial cells, neurons, and immune cells, are organs that are exposed to dynamic environmental challenges. During diet-induced obesity, white adipose tissues experience hypoxia due to adipocyte hypertrophy and dysfunctional vasculature. Under these conditions, cells in white adipose tissues activate hypoxia-inducible factor (HIF), a transcription factor that activates signaling pathways involved in metabolism, angiogenesis, and survival/apoptosis to adapt to such an environment. Exposure to cold or activation of the β-adrenergic receptor (through catecholamines or chemicals) leads to heat generation, mainly in brown adipose tissues through activating uncoupling protein 1 (UCP1), a proton uncoupler in the inner membrane of the mitochondria. White adipose tissues can undergo a similar process under this condition, a phenomenon known as 'browning' of white adipose tissues or 'beige adipocytes'. While UCP1 expression has largely been confined to adipocytes, HIF can be expressed in many types of cells. To dissect the role of HIF in specific types of cells during diet-induced obesity, researchers have generated tissue-specific knockout (KO) mice targeting HIF pathways, and many studies have commonly revealed that intact HIF-1 signaling in adipocytes and adipose tissue macrophages exacerbates tissue inflammation and insulin resistance. In this review, we highlight some of the key findings obtained from these transgenic mice, including Ucp1 KO mice and other models targeting the HIF pathway in adipocytes, macrophages, or endothelial cells, to decipher their roles in diet-induced obesity.

Age-related hearing loss and its potential drug candidates: a systematic review

BACKGROUND

Age-related hearing loss (ARHL) is one of the main illnesses afflicting the aged population and has a significant negative impact on society, economy, and health. However, there is presently no appropriate therapeutic treatment of ARHL due to the absence of comprehensive trials.

OBJECTIVES

The goal of this review is to systematically evaluate and analyze recent statistics on the pathologic classifications, risk factors, treatment strategies, and drug candidates of ARHL, including that from traditional Chinese medicine (TCM), to provide potential new approaches for preventing and treating ARHL.

METHODS

Literature related to ARHL was conducted in databases such as PubMed, WOS, China National Knowledge Infrastructure (CNKI), and Wanfang from the establishment of the database to Jan, 2023. The pathology, causal factor, pathophysiological mechanism, treatment strategy, and the drug candidate of ARHL were extracted and pooled for synthesis.

RESULTS

Many hypotheses about the etiology of ARHL are based on genetic and environmental elements. Most of the current research on the pathology of ARHL focuses on oxidative damage, mitochondrial dysfunction, inflammation, cochlear blood flow, ion homeostasis, etc. In TCM, herbs belonging to the kidney, lung, and liver meridians exhibit good hearing protection. Seven herbs belonging to the kidney meridian, 9 belonging to the lung meridian, and 4 belonging to the liver meridian were ultimately retrieved in this review, such as Polygonum multiflorum Thunb., Panax ginseng C.A. Mey, and Pueraria lobata (Willd.) Ohwi. Their active compounds, 2,3,4',5-Tetrahydroxystilbene-2-O-D-glucoside, ginsenoside Rb1, and puerarin, may act as the molecular substance for their anti-ARHL efficacy, and show anti-oxidative, neuroprotective, anti-inflammatory, anti-apoptotic, or mitochondrial protective effects.

CONCLUSION

Anti-oxidants, modulators of mitochondrial function, anti-inflammation agents, vasodilators, K+ channel openers, Ca2+ channel blockers, JNK inhibitors, and nerve growth factors/neurotrophic factors all contribute to hearing protection, and herbs are an important source of potential anti-ARHL drugs.

Progress on mechanisms of age-related hearing loss

Age-related hearing loss, or presbycusis, is a common cause of hearing loss in elderly people worldwide. It typically presents as progressive, irreversible, and usually affects the high frequencies of hearing, with a tremendous impact on the quality of life. Presbycusis is a complex multidimensional disorder, in addition to aging, multiple factors including exposure to noise, or ototoxic agents, genetic susceptibility, metabolic diseases and lifestyle can influence the onset and severity of presbycusis. With the aging of the body, its ability to clean up deleterious substances produced in the metabolic process is weakened, and the self-protection and repair function of the body is reduced, which in turn leads to irreversible damage to the cochlear tissue, resulting in the occurrence of presbycusis. Presently, oxidative stress (OS), mitochondrial DNA damage, low-grade inflammation, decreased immune function and stem cell depletion have been demonstrated to play a critical role in developing presbycusis. The purpose of this review is to illuminate the various mechanisms underlying this age-related hearing loss, with the goal of advancing our understanding, prevention, and treatment of presbycusis.

Cellular heterogeneity and plasticity during NAFLD progression

Nonalcoholic fatty liver disease (NAFLD) is a progressive liver disease that can progress to nonalcoholic steatohepatitis (NASH), NASH-related cirrhosis, and hepatocellular carcinoma (HCC). NAFLD ranges from simple steatosis (or nonalcoholic fatty liver [NAFL]) to NASH as a progressive form of NAFL, which is characterized by steatosis, lobular inflammation, and hepatocellular ballooning with or without fibrosis. Because of the complex pathophysiological mechanism and the heterogeneity of NAFLD, including its wide spectrum of clinical and histological characteristics, no specific therapeutic drugs have been approved for NAFLD. The heterogeneity of NAFLD is closely associated with cellular plasticity, which describes the ability of cells to acquire new identities or change their phenotypes in response to environmental stimuli. The liver consists of parenchymal cells including hepatocytes and cholangiocytes and nonparenchymal cells including Kupffer cells, hepatic stellate cells, and endothelial cells, all of which have specialized functions. This heterogeneous cell population has cellular plasticity to adapt to environmental changes. During NAFLD progression, these cells can exert diverse and complex responses at multiple levels following exposure to a variety of stimuli, including fatty acids, inflammation, and oxidative stress. Therefore, this review provides insights into NAFLD heterogeneity by addressing the cellular plasticity and metabolic adaptation of hepatocytes, cholangiocytes, hepatic stellate cells, and Kupffer cells during NAFLD progression.

Rats lacking Ucp1 present a novel translational tool for the investigation of thermogenic adaptation during cold challenge

AIM

Valuable studies have tested the role of UCP1 on body temperature maintenance in mice, and we sought to knockout Ucp1 in rats (Ucp1-/- ) to provide insight into thermogenic mechanisms in larger mammals.

METHODS

We used CRISPR/Cas9 technology to create Ucp1-/- rats. Body weight and adiposity were measured, and rats were subjected to indirect calorimetry. Rats were maintained at room temperature or exposed to 4°C for either 24 h or 14 days. Analyses of brown and white adipose tissue and skeletal muscle were conducted via histology, western blot comparison of oxidative phosphorylation proteins, and qPCR to compare mitochondrial DNA levels and mRNA expression profiles. RNA-seq was performed in skeletal muscle.

RESULTS

Ucp1-/- rats withstood 4°C for 14 days, but core temperature steadily declined. All rats lost body weight after 14 days at 4°C, but controls increased food intake more robustly than Ucp1-/- rats. Brown adipose tissue showed signs of decreased activity in Ucp1-/- rats, while mitochondrial lipid metabolism markers in white adipose tissue and skeletal muscle were increased. Ucp1-/- rats displayed more visible shivering and energy expenditure than controls at 4°C. Skeletal muscle transcriptomics showed more differences between genotypes at 23°C than at 4°C.

CONCLUSION

Room temperature presented sufficient cold stress to rats lacking UCP1 to activate compensatory thermogenic mechanisms in skeletal muscle, which were only activated in control rats following exposure to 4°C. These results provide novel insight into thermogenic responses to UCP1 deficiency; and highlight Ucp1-/- rats as an attractive translational model for the study of thermogenesis.

Surviving without oxygen involves major tissue specific changes in the proteome of crucian carp (Carassius carassius)

The crucian carp (Carassius carassius) can survive complete oxygen depletion (anoxia) for several months at low temperatures, making it an excellent model for studying molecular adaptations to anoxia. Still, little is known about how its global proteome responds to anoxia and reoxygenation. By applying mass spectrometry-based proteome analyses on brain, heart and liver tissue from crucian carp exposed to normoxia, five days anoxia, and reoxygenation, we found major changes in particularly cardiac and hepatic protein levels in response to anoxia and reoxygenation. These included tissue-specific differences in mitochondrial proteins involved in aerobic respiration and mitochondrial membrane integrity. Enzymes in the electron transport system (ETS) decreased in heart and increased massively in liver during anoxia and reoxygenation but did not change in the brain. Importantly, the data support a special role for the liver in succinate handling upon reoxygenation, as suggested by a drastic increase of components of the ETS and uncoupling protein 2, which could allow for succinate metabolism without excessive formation of reactive oxygen species (ROS). Also during reoxygenation, the levels of proteins involved in the cristae junction organization of the mitochondria changed in the heart, possibly functioning to suppress ROS formation. Furthermore, proteins involved in immune (complement) system activation changed in the anoxic heart compared to normoxic controls. The results emphasize that responses to anoxia are highly tissue-specific and related to organ function.

The emerging role for metabolism in fueling neutrophilic inflammation

Neutrophils are a critical element of host defense and are rapidly recruited to inflammatory sites. Such sites are frequently limited in oxygen and/or nutrient availability, presenting a metabolic challenge for infiltrating cells. Long believed to be uniquely dependent on glycolysis, it is now clear that neutrophils possess far greater metabolic plasticity than previously thought, with the capacity to generate energy stores and utilize extracellular proteins to fuel central carbon metabolism and biosynthetic activity. Out-with cellular energetics, metabolic programs have also been implicated in the production of neutrophils and their progenitors in the bone marrow compartment, activation of neutrophil antimicrobial responses, inflammatory and cell survival signaling cascades, and training of the innate immune response. Thus, understanding the mechanisms by which metabolic processes sustain changes in neutrophil effector functions and how these are subverted in disease states provides exciting new avenues for the treatment of dysfunctional neutrophilic inflammation which are lacking in clinical practice to date.

Mitochondrial Dysfunction in Cardiac Arrhythmias

Electrophysiological and structural disruptions in cardiac arrhythmias are closely related to mitochondrial dysfunction. Mitochondria are an organelle generating ATP, thereby satisfying the energy demand of the incessant electrical activity in the heart. In arrhythmias, the homeostatic supply-demand relationship is impaired, which is often accompanied by progressive mitochondrial dysfunction leading to reduced ATP production and elevated reactive oxidative species generation. Furthermore, ion homeostasis, membrane excitability, and cardiac structure can be disrupted through pathological changes in gap junctions and inflammatory signaling, which results in impaired cardiac electrical homeostasis. Herein, we review the electrical and molecular mechanisms of cardiac arrhythmias, with a particular focus on mitochondrial dysfunction in ionic regulation and gap junction action. We provide an update on inherited and acquired mitochondrial dysfunction to explore the pathophysiology of different types of arrhythmias. In addition, we highlight the role of mitochondria in bradyarrhythmia, including sinus node dysfunction and atrioventricular node dysfunction. Finally, we discuss how confounding factors, such as aging, gut microbiome, cardiac reperfusion injury, and electrical stimulation, modulate mitochondrial function and cause tachyarrhythmia.

A lncRNA-encoded mitochondrial micropeptide exacerbates microglia-mediated neuroinflammation in retinal ischemia/reperfusion injury

As a common pathology of many ocular disorders such as diabetic retinopathy and glaucoma, retinal ischemia/reperfusion (IR) triggers inflammation and microglia activation that lead to irreversible retinal damage. The detailed molecular mechanism underlying retinal IR injury, however, remains poorly understood at present. Here we report the bioinformatic identification of a lncRNA 1810058I24Rik (181-Rik) that was shown to encode a mitochondrion-located micropeptide Stmp1. Its deficiency in mice protected retinal ganglion cells from retinal IR injury by attenuating the activation of microglia and the Nlrp3 inflammasome pathway. Moreover, its genetic knockout in mice or knockdown in primary microglia promoted mitochondrial fusion, impaired mitochondrial membrane potential, and reactive oxygen species (ROS) production, diminished aerobic glycolysis, and ameliorated inflammation. It appears that 181-Rik may trigger the Nlrp3 inflammasome activation by controlling mitochondrial functions through inhibiting expression of the metabolic sensor uncoupling protein 2 (Ucp2) and activating expression of the Ca²⁺ sensors S100a8/a9. Together, our findings shed new light on the molecular pathogenesis of retinal IR injury and may provide a fresh therapeutic target for IR-associated neurodegenerative diseases.

Innate sensing and cellular metabolism: role in fine tuning antiviral immune responses

Several studies over the last decade have identified intimate links between cellular metabolism and macrophage function. Metabolism has been shown to both drive and regulate macrophage function by producing bioenergetic and biosynthetic precursors as well as metabolites (and other bioactive molecules) that regulate gene expression and signal transduction. Many studies have focused on lipopolysaccharide-induced reprogramming, assuming that it is representative of most inflammatory responses. However, emerging evidence suggests that diverse pathogen-associated molecular patterns (PAMPs) are associated with unique metabolic profiles, which may drive pathogen specific immune responses. Further, these metabolic pathways and processes may act as a rheostat to regulate the magnitude of an inflammatory response based on the biochemical features of the local microenvironment. In this review, we will discuss recent work examining the relationship between cellular metabolism and macrophage responses to viral PAMPs and describe how these processes differ from lipopolysaccharide-associated responses. We will also discuss how an improved understanding of the specificity of these processes may offer new insights to fine-tune macrophage function during viral infections or when using viral PAMPs as therapeutics.

Pleiotrophin deficiency protects against high-fat diet-induced neuroinflammation: Implications for brain mitochondrial dysfunction and aberrant protein aggregation

Metabolic Syndrome (MetS) is a risk factor for the development of neurodegenerative diseases. Neuroinflammation associated with MetS may contribute significantly to neurodegeneration. Pleiotrophin (PTN) is a neurotrophic factor that modulates neuroinflammation and is a key player in regulating energy metabolism and thermogenesis, suggesting that PTN could be important in the connection between MetS and neuroinflammation. We have now used a high-fat diet (HFD)-induced obesity model in Ptn^-/- mice. HFD and Ptn deletion caused alterations in circulating hormones including GIP, leptin and resistin. HFD produced in Ptn^+/+ mice a neuroinflammatory state as observed in cerebral quantifications of proinflammatory markers, including Il1β, Tnfα and Ccl2. The upregulation of neuroinflammatory markers was prevented in Ptn^-/- mice. Changes induced by HFD in genes related to mitochondrial biogenesis and dynamics were less pronounced in the brain of Ptn^-/- mice and were accompanied by significant increases in the protein expression of mitochondrial oxidative phosphorylation (OXPHOS) complexes I and IV. HFD-induced changes in genes related to the elimination of protein aggregates were also less pronounced in the brain of Ptn^-/- mice. This study provides substantial evidence that Ptn deletion protects against HFD-induced neuroinflammation, mitochondrial dysfunction, and aberrant protein aggregation, prominent features in neurodegenerative diseases.

Mitochondrial Energy Metabolism in the Regulation of Thermogenic Brown Fats and Human Metabolic Diseases

Brown fats specialize in thermogenesis by increasing the utilization of circulating blood glucose and fatty acids. Emerging evidence suggests that brown adipose tissue (BAT) prevents the incidence of obesity-associated metabolic diseases and several types of cancers in humans. Mitochondrial energy metabolism in brown/beige adipocytes regulates both uncoupling protein 1 (UCP1)-dependent and -independent thermogenesis for cold adaptation and the utilization of excess nutrients and energy. Many studies on the quantification of human BAT indicate that mass and activity are inversely correlated with the body mass index (BMI) and visceral adiposity. Repression is caused by obesity-associated positive and negative factors that control adipocyte browning, de novo adipogenesis, mitochondrial energy metabolism, UCP1 expression and activity, and noradrenergic response. Systemic and local factors whose levels vary between lean and obese conditions include growth factors, inflammatory cytokines, neurotransmitters, and metal ions such as selenium and iron. Modulation of obesity-associated repression in human brown fats is a promising strategy to counteract obesity and related metabolic diseases through the activation of thermogenic capacity. In this review, we highlight recent advances in mitochondrial metabolism, thermogenic regulation of brown fats, and human metabolic diseases.

Free radicals: Relationship to Human Diseases and Potential Therapeutic applications

Reactive species are highly-reactive enzymatically, or non-enzymatically produced compounds with important roles in physiological and pathophysiological cellular processes. Although reactive species represent an extensively researched topic in biomedical sciences, many aspects of their roles and functions remain unclear. This review aims to systematically summarize findings regarding the biochemical characteristics of various types of reactive species and specify the localization and mechanisms of their production in cells. In addition, we discuss the specific roles of free radicals in cellular physiology, focusing on the current lines of research that aim to identify the reactive oxygen species-initiated cascades of reactions resulting in adaptive or pathological cellular responses. Finally, we present recent findings regarding the therapeutic modulations of intracellular levels of reactive oxygen species, which may have substantial significance in developing novel agents for treating several diseases.

UCP2 as a Cancer Target through Energy Metabolism and Oxidative Stress Control

Despite numerous therapies, cancer remains one of the leading causes of death worldwide due to the lack of markers for early detection and response to treatment in many patients. Technological advances in tumor screening and renewed interest in energy metabolism have allowed us to identify new cellular players in order to develop personalized treatments. Among the metabolic actors, the mitochondrial transporter uncoupling protein 2 (UCP2), whose expression is increased in many cancers, has been identified as an interesting target in tumor metabolic reprogramming. Over the past decade, a better understanding of its biochemical and physiological functions has established a role for UCP2 in (1) protecting cells from oxidative stress, (2) regulating tumor progression through changes in glycolytic, oxidative and calcium metabolism, and (3) increasing antitumor immunity in the tumor microenvironment to limit cancer development. With these pleiotropic roles, UCP2 can be considered as a potential tumor biomarker that may be interesting to target positively or negatively, depending on the type, metabolic status and stage of tumors, in combination with conventional chemotherapy or immunotherapy to control tumor development and increase response to treatment. This review provides an overview of the latest published science linking mitochondrial UCP2 activity to the tumor context.

Selenium and selenoproteins in thermogenic adipocytes

Selenium (Se) is involved in energy metabolism in the liver, white adipose tissue, and skeletal muscle, and may also play a role in thermogenic adipocytes, i.e. brown and beige adipocytes. Thereby this micronutrient is a key nutritional target to aid in combating obesity and metabolic diseases. In thermogenic adipocytes, particularly in brown adipose tissue (BAT), the selenoprotein type 2 iodothyronine deiodinase (DIO2) is essential for the activation of adaptive thermogenesis. Recent evidence has suggested that additional selenoproteins may also be participating in this process, and a role for Se itself through its metabolic pathways is also envisioned. In this review, we discuss the recognized effects and the knowledge gaps in the involvement of Se metabolism and selenoproteins in the mechanisms of adaptive thermogenesis in thermogenic (brown and beige) adipocytes.

The heterogeneity of astrocytes in glaucoma

Glaucoma is a leading cause of blindness with progressive degeneration of retinal ganglion cells. Aging and increased intraocular pressure (IOP) are major risk factors. Lowering IOP does not always stop the disease progression. Alternative ways of protecting the optic nerve are intensively studied in glaucoma. Astrocytes are macroglia residing in the retina, optic nerve head (ONH), and visual brain, which keep neuronal homeostasis, regulate neuronal activities and are part of the immune responses to the retina and brain insults. In this brief review, we discuss the activation and heterogeneity of astrocytes in the retina, optic nerve head, and visual brain of glaucoma patients and animal models. We also discuss some recent transgenic and gene knockout studies using glaucoma mouse models to clarify the role of astrocytes in the pathogenesis of glaucoma. Astrocytes are heterogeneous and play crucial roles in the pathogenesis of glaucoma, especially in the process of neuroinflammation and mitochondrial dysfunction. In astrocytes, overexpression of Stat3 or knockdown of IκKβ/p65, caspase-8, and mitochondrial uncoupling proteins (Ucp2) can reduce ganglion cell loss in glaucoma mouse models. Based on these studies, therapeutic strategies targeting the heterogeneity of reactive astrocytes by enhancing their beneficial reactivity or suppressing their detrimental reactivity are alternative options for glaucoma treatment in the future.

Therapeutic targeting of microglia mediated oxidative stress after neurotrauma

Inflammation is a primary component of the central nervous system injury response. Traumatic brain and spinal cord injury are characterized by a pronounced microglial response to damage, including alterations in microglial morphology and increased production of reactive oxygen species (ROS). The acute activity of microglia may be beneficial to recovery, but continued inflammation and ROS production is deleterious to the health and function of other cells. Microglial nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX), mitochondria, and changes in iron levels are three of the most common sources of ROS. All three play a significant role in post-traumatic brain and spinal cord injury ROS production and the resultant oxidative stress. This review will evaluate the current state of therapeutics used to target these avenues of microglia-mediated oxidative stress after injury and suggest avenues for future research.

UCP2 KO mice exhibit ameliorated obesity and inflammation induced by high-fat diet feeding

Uncoupling protein 2 (Ucp2) was first introduced as a member of Uncoupling protein family and a regulator of ROS formation; however, its role in adipose tissue is not fully understood. In the present study, we have investigated the role of Ucp2 against high-fat diet (HFD)-induced obesity in epididymal white adipose tissue (eWAT) and browning of inguinal white adipose tissue (iWAT). Diet-induced obesity is closely related to macrophage infiltration and the secretion of pro-inflammatory cytokines. Macrophages surround adipocytes and form a crown-like-structure (CLS). Some reports have suggested that CLS formation requires adipocyte apoptosis. After 12 weeks of HFD challenge, Ucp2 knockout (KO) mice maintained relatively lean phenotypes compared to wild-type (WT) mice. In eWAT, macrophage infiltration, CLS formation, and inflammatory cytokines were reduced in HFD KO mice compared to HFD WT mice. Surprisingly, we found that apoptotic signals were also reduced in the Ucp2 KO mice. Our study suggests that Ucp2 deficiency may prevent diet-induced obesity by regulating adipocyte apoptosis. However, Ucp2 deficiency did not affect the browning capacity of iWAT.

UCP2 silencing restrains leukemia cell proliferation through glutamine metabolic remodeling

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy derived from early T cell progenitors. Since relapsed T-ALL is associated with a poor prognosis improving initial treatment of patients is essential to avoid resistant selection of T-ALL. During initiation, development, metastasis and even in response to chemotherapy, tumor cells face strong metabolic challenges. In this study, we identify mitochondrial UnCoupling Protein 2 (UCP2) as a tricarboxylic acid (TCA) cycle metabolite transporter controlling glutamine metabolism associated with T-ALL cell proliferation. In T-ALL cell lines, we show that UCP2 expression is controlled by glutamine metabolism and is essential for their proliferation. Our data show that T-ALL cell lines differ in their substrate dependency and their energetic metabolism (glycolysis and oxidative). Thus, while UCP2 silencing decreases cell proliferation in all leukemia cells, it also alters mitochondrial respiration of T-ALL cells relying on glutamine-dependent oxidative metabolism by rewiring their cellular metabolism to glycolysis. In this context, the function of UCP2 in the metabolite export of malate enables appropriate TCA cycle to provide building blocks such as lipids for cell growth and mitochondrial respiration. Therefore, interfering with UCP2 function can be considered as an interesting strategy to decrease metabolic efficiency and proliferation rate of leukemia cells.

Mechanisms underlying paclitaxel-induced neuropathic pain: Channels, inflammation and immune regulations

Paclitaxel is a chemotherapeutic agent widely used for many types of malignancies. However, when paclitaxel is used to treat tumors, patients commonly experience severe neuropathic pain that is difficult to manage. The mechanism underlying paclitaxel-induced neuropathic pain remains unclear. Evidence demonstrates correlations between mechanisms of paclitaxel-mediated pain and associated actions of ion channels, neuroinflammation, mitochondrial damage, and other factors. This review provides a comprehensive analysis of paclitaxel-induced neuropathic pain mechanisms and suggestions for effective interventions.

Mitochondrial uncoupling protein-2 reprograms metabolism to induce oxidative stress and myofibroblast senescence in age-associated lung fibrosis

Mitochondrial dysfunction has been associated with age-related diseases, including idiopathic pulmonary fibrosis (IPF). We provide evidence that implicates chronic elevation of the mitochondrial anion carrier protein, uncoupling protein-2 (UCP2), in increased generation of reactive oxygen species, altered redox state and cellular bioenergetics, impaired fatty acid oxidation, and induction of myofibroblast senescence. This pro-oxidant senescence reprogramming occurs in concert with conventional actions of UCP2 as an uncoupler of oxidative phosphorylation with dissipation of the mitochondrial membrane potential. UCP2 is highly expressed in human IPF lung myofibroblasts and in aged fibroblasts. In an aging murine model of lung fibrosis, the in vivo silencing of UCP2 induces fibrosis regression. These studies indicate a pro-fibrotic function of UCP2 in chronic lung disease and support its therapeutic targeting in age-related diseases associated with impaired tissue regeneration and organ fibrosis.

Expression and hormone regulation of UCP2 in goat uterus

Pregnancy success is closely related to the molecular mechanisms that control energy metabolism balance. However, the mechanisms have not been fully understood. Uncoupling protein 2 (UCP2) plays a physiological role by regulating energy metabolism in numerous tissues. In this study, we determined the expression and hormone regulation of UCP2 in goat uterus. UCP2 is expressed in the luminal and glandular epithelia of goat uterus during early pregnancy, as revealed by in situ hybridization and immunohistochemistry conducted on pregnant goats. The signals were detected from day 0 (D0) to D30 of pregnancy, though weak on D16 (the adhesion period). The low levels of UCP2 on D16 were confirmed by RT-qPCR and western blot. In goat uterus and endometrial epithelial cells (EECs), UCP2 was up-regulated by progesterone and estrogen. In addition, after goat EECs were treated with genipin (an inhibitor of UCP2), not only UCP2 expression but also cell proliferation was inhibited. Collectively, UCP2 is dynamically expressed in goat uterus and can affect EEC proliferation, suggesting that it may participate in regulating the energy metabolism balance of goat uterus during early pregnancy.

Caffeine Citrate Protects Against Sepsis-Associated Encephalopathy and Inhibits the UCP2/NLRP3 Axis in Astrocytes

Sepsis-associated encephalopathy (SAE) is a diffuse brain dysfunction without overt central nervous system infection. Caffeine citrate has therapeutic effect on different brain diseases, while its role in SAE remains unclear. The expression levels of interleukin (IL)-18 and IL-1β were upregulated in the cerebrospinal fluid of the subjects. In this study, a rat model of SAE was established by cecal ligation and puncture. Caffeine citrate inhibited SAE-induced neuronal apoptosis and astrocytic activation, decreased reactive oxygen species (ROS) generation, and elevated mitochondrial membrane potential (MMP) level in the cerebral cortex. In vitro, primary astrocytes were isolated from rat cerebral cortex and incubated with lipopolysaccharide (LPS) and interferon-γ (IFN-γ). Caffeine citrate reduced ROS and MMP levels and mitochondrial complex enzyme activities in LPS plus IFN-γ-induced astrocytes. Moreover, caffeine citrate inhibited the activation of nucleotide-binding and oligomerization domain (NOD)-like receptor (NLRP3) inflammasome and decreased the production of IL-1β and IL-18 in vivo and in vitro. Notably, caffeine citrate promoted UCP2 expression in astrocytes. The neuroprotective role of UCP2 has been reported in several experimental brain diseases. These results suggest that caffeine citrate inhibits neuronal apoptosis, astrocytic activation, mitochondrial dysfunction in rat cerebral cortex, thereby alleviating SAE. The protection of caffeine citrate against SAE may be achieved by the UCP2-mediated NLRP3 pathway inhibition in astrocytes.

Strategies for Hypothermia Compensation in Altricial and Precocial Newborn Mammals and Their Monitoring by Infrared Thermography

Thermoregulation in newborn mammals is an essential species-specific mechanism of the nervous system that contributes to their survival during the first hours and days of their life. When exposed to cold weather, which is a risk factor associated with mortality in neonates, pathways such as the hypothalamic–pituitary–adrenal axis (HPA) are activated to achieve temperature control, increasing the circulating levels of catecholamine and cortisol. Consequently, alterations in blood circulation and mechanisms to produce or to retain heat (e.g., vasoconstriction, piloerection, shivering, brown adipocyte tissue activation, and huddling) begin to prevent hypothermia. This study aimed to discuss the mechanisms of thermoregulation in newborn domestic mammals, highlighting the differences between altricial and precocial species. The processes that employ brown adipocyte tissue, shivering, thermoregulatory behaviors, and dermal vasomotor control will be analyzed to understand the physiology and the importance of implementing techniques to promote thermoregulation and survival in the critical post-birth period of mammals. Also, infrared thermography as a helpful method to perform thermal measurements without animal interactions does not affect these parameters.

Role of Uncoupling Protein 2 Gene Polymorphisms on the Risk of Ischemic Stroke in a Sardinian Population

The mitochondrial uncoupling protein 2 (UCP2) acts as an anion transporter and as an antioxidant factor able to reduce the reactive oxygen species level. Based on its effects, UCP2 prevents the membrane lipids, proteins, and DNA damage while preserving normal cellular functions. Many variants have been identified within the human UCP2. Some of them were associated with a higher risk of obesity, diabetes and cardiovascular diseases in different populations. UCP2 appears a suitable candidate also for the risk of ischemic stroke. In the current study, we investigated the possible association between few variants of UCP2 (rs659366, rs660339, rs1554995310) and the risk of ischemic stroke in a genetically homogenous cohort of cases and controls selected in Sardinia Island. This population has been previously analysed for other candidate genes. A total of 250 cases of ischemic stroke and 241 controls were enrolled in the study. The allelic/genotypic distribution of the 3 UCP2 variants was characterized and compared among cases and controls. The results of our study confirmed known risk factors for ischemic stroke: age, history of smoking, hypertension, hypercholesterolemia, and atrial fibrillation. No association was found between the 3 UCP2 variants and the risk of ischemic stroke in our Sardinian cohort.

Mitochondrial function in spinal cord injury and regeneration

Many people around the world suffer from some form of paralysis caused by spinal cord injury (SCI), which has an impact on quality and life expectancy. The spinal cord is part of the central nervous system (CNS), which in mammals is unable to regenerate, and to date, there is a lack of full functional recovery therapies for SCI. These injuries start with a rapid and mechanical insult, followed by a secondary phase leading progressively to greater damage. This secondary phase can be potentially modifiable through targeted therapies. The growing literature, derived from mammalian and regenerative model studies, supports a leading role for mitochondria in every cellular response after SCI: mitochondrial dysfunction is the common event of different triggers leading to cell death, cellular metabolism regulates the immune response, mitochondrial number and localization correlate with axon regenerative capacity, while mitochondrial abundance and substrate utilization regulate neural stem progenitor cells self-renewal and differentiation. Herein, we present a comprehensive review of the cellular responses during the secondary phase of SCI, the mitochondrial contribution to each of them, as well as evidence of mitochondrial involvement in spinal cord regeneration, suggesting that a more in-depth study of mitochondrial function and regulation is needed to identify potential targets for SCI therapeutic intervention.

Activation of UCP2 by anethole trithione suppresses neuroinflammation after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating disease, in which neuroinflammation substantially contributes to brain injury. Uncoupling protein 2 (UCP2) is a member of the mitochondrial anion carrier family, which uncouples oxidative phosphorylation from ATP synthesis by facilitating proton leak across the mitochondrial inner membrane. UCP2 has been reported to modulate inflammation. In this study we investigated whether and how UCP2 modulated neuroinflammation through microglia/macrophages following ICH in vitro and in vivo. We used an in vitro neuroinflammation model in murine BV2 microglia to mimic microglial activation following ICH. ICH in vivo model was established in mice through collagenase infusion into the left striatum. ICH mice were treated with anetholetrithione (ADT, 50 mg· kg^-1 ·d^-1, ip) or the classical protonophoric uncoupler FCCP (injected into hemorrhagic striatum). We showed that the expression and mitochondrial location of microglial UCP2 were not changed in both in vitro and in vivo ICH models. Knockdown of UCP2 exacerbated neuroinflammation in BV2 microglia and mouse ICH models, suggesting that endogenous UCP2 inhibited neuroinflammation and therefore played a protective role following ICH. ADT enhanced mitochondrial ROS production thus inducing mitochondrial uncoupling and activating UCP2 in microglia. ADT robustly suppressed neuroinflammation, attenuated brain edema and improved neurological deficits following ICH, and these effects were countered by striatal knockdown of UCP2. ADT enhanced AMP-activated protein kinase (AMPK) activation in the hemorrhagic brain, which was abrogated by striatal knockdown of UCP2. Moreover, striatal knockdown of AMPK abolished the suppression of neuroinflammation by ADT following ICH. On the other hand, FCCP-induced mitochondrial uncoupling was independent of UCP2 in microglia; and striatal knockdown of UCP2 did not abrogate the suppression of neuroinflammation by FCCP in ICH mice. In conclusion, the uncoupling activity is essential for suppression of neuroinflammation by UCP2. We prove for the first time the concept that activators of endogenous UCP2 such as anetholetrithione are a new class of uncouplers with translational significance.

Regulation of Aging and Longevity by Ion Channels and Transporters

Despite significant advances in our understanding of the mechanisms that underlie age-related physiological decline, our ability to translate these insights into actionable strategies to extend human healthspan has been limited. One of the major reasons for the existence of this barrier is that with a few important exceptions, many of the proteins that mediate aging have proven to be undruggable. The argument put forth here is that the amenability of ion channels and transporters to pharmacological manipulation could be leveraged to develop novel therapeutic strategies to combat aging. This review delves into the established roles for ion channels and transporters in the regulation of aging and longevity via their influence on membrane excitability, Ca2+ homeostasis, mitochondrial and endolysosomal function, and the transduction of sensory stimuli. The goal is to provide the reader with an understanding of emergent themes, and prompt further investigation into how the activities of ion channels and transporters sculpt the trajectories of cellular and organismal aging.

Uncoupling Protein 2 as a Pathogenic Determinant and Therapeutic Target in Cardiovascular and Metabolic Diseases

Uncoupling protein 2 (UCP2) is a mitochondrial protein that acts as an anion carrier. It is involved in the regulation of several processes, including mitochondrial membrane potential, generation of reactive oxygen species within the inner mitochondrial membrane and calcium homeostasis. UCP2 expression can be regulated at different levels: genetic (gene variants), transcriptional [by peroxisome proliferator-activated receptors (PPARs) and microRNAs], and post-translational. Experimental evidence indicates that activation of UCP2 expression through the AMPK/PPAR-α axis exerts a protective effect toward renal damage and stroke occurrence in an animal model of ischemic stroke (IS) associated with hypertension. UCP2 plays a key role in heart diseases (myocardial infarction and cardiac hypertrophy) and metabolic disorders (obesity and diabetes). In humans, UCP2 genetic variants (-866G/A and Ala55Val) associate with an increased risk of type 2 diabetes mellitus and IS development. Over the last few years, many agents that modulate UCP2 expression have been identified. Some of them are natural compounds of plant origin, such as Brassica oleracea, curcumin, berberine and resveratrol. Other molecules, currently used in clinical practice, include anti-diabetic (gliptin) and chemotherapeutic (doxorubicin and taxol) drugs. This evidence highlights the relevant role of UCP2 for the treatment of a wide range of diseases, which affect the national health systems of Western countries. We will review current knowledge on the physiological and pathological implications of UCP2 with particular regard to cardiovascular and metabolic disorders and will focus on the available therapeutic approaches affecting UCP2 level for the treatment of human diseases.

Skeletal Muscle Uncoupling Proteins in Mice Models of Obesity

Obesity and accompanying type 2 diabetes are among major and increasing worldwide problems that occur fundamentally due to excessive energy intake during its expenditure. Endotherms continuously consume a certain amount of energy to maintain core body temperature via thermogenic processes, mainly in brown adipose tissue and skeletal muscle. Skeletal muscle glucose utilization and heat production are significant and directly linked to body glucose homeostasis at rest, and especially during physical activity. However, this glucose balance is impaired in diabetic and obese states in humans and mice, and manifests as glucose resistance and altered muscle cell metabolism. Uncoupling proteins have a significant role in converting electrochemical energy into thermal energy without ATP generation. Different homologs of uncoupling proteins were identified, and their roles were linked to antioxidative activity and boosting glucose and lipid metabolism. From this perspective, uncoupling proteins were studied in correlation to the pathogenesis of diabetes and obesity and their possible treatments. Mice were extensively used as model organisms to study the physiology and pathophysiology of energy homeostasis. However, we should be aware of interstrain differences in mice models of obesity regarding thermogenesis and insulin resistance in skeletal muscles. Therefore, in this review, we gathered up-to-date knowledge on skeletal muscle uncoupling proteins and their effect on insulin sensitivity in mouse models of obesity and diabetes.

Antioxidant Effects of Irisin in Liver Diseases: Mechanistic Insights

Oxidative stress is a crucial factor in the development of various liver diseases. Irisin, a metabolic hormone discovered in 2012, is mainly produced by proteolytic cleavage of fibronectin type III domain containing 5 (FNDC5) in skeletal muscles. Irisin is induced by physical exercise, and a rapidly growing body of literature suggests that irisin is, at least partially, responsible for the beneficial effects of regular exercise. The major biological function of irisin is believed to be involved in the maintenance of metabolic homeostasis. However, recent studies have suggested the therapeutic potential of irisin against a variety of liver diseases involving its antioxidative function. In this review, we aim to summarize the accumulating evidence demonstrating the antioxidative effects of irisin in liver diseases, with an emphasis on the current understanding of the potential molecular mechanisms.

Genetic variation in satiety signaling and hypothalamic inflammation: merging fields for the study of obesity

Although obesity has been a longstanding health crisis, the genetic architecture of the disease remains poorly understood. Genome-wide association studies have identified many genomic loci associated with obesity, with genes being enriched in the brain, particularly in the hypothalamus. This points to the role of the central nervous system (CNS) in predisposition to obesity, and we emphasize here several key genes along the satiety signaling pathway involved in genetic susceptibility. Interest has also risen regarding the chronic, low-grade obesity-associated inflammation, with a growing concern toward inflammation in the hypothalamus as a precursor to obesity. Recent studies have found that genetic variation in inflammatory genes play a role in obesity susceptibility, and we highlight here several key genes. Despite the interest in the genetic variants of these pathways individually, there is a lack of research that investigates the relationship between the two. Understanding the interplay between genetic variation in obesity genes enriched in the CNS and inflammation genes will advance our understanding of obesity etiology and heterogeneity, improve genetic risk prediction analyses, and highlight new drug targets for the treatment of obesity. Additionally, this increased knowledge will assist in physician's ability to develop personalized nutrition and medication strategies for combating the obesity epidemic. Though it often seems to present universally, obesity is a highly individual disease, and there remains a need in the field to develop methods to treat at the individual level.

Maternal Isocaloric High-Fat Diet Induces Liver Mitochondria Maladaptations and Homeostatic Disturbances Intensifying Mitochondria Damage in Response to Fructose Intake in Adult Male Rat Offspring

SCOPE

Perinatal maternal obesity and excessive fructose consumption have been associated with liver metabolic diseases. We investigated whether moderate maternal high-fat diet affects the liver mitochondria responses to fructose intake in adult offspring.

METHODS AND RESULTS

Wistar female rats received a standard diet (mSTD) or high-fat diet (mHFD) (9% and 28.6% fat, respectively), before mating until the end of lactation. Male offspring were fed standard diet from weaning to adulthood and received water or fructose-drinking water (15%) from 120 to 150 days old. Fructose induced liver mitochondrial ultrastructural alterations with higher intensity in mHFD offspring, accompanied by reduced autophagy markers. Isolated mitochondria respirometry showed unaltered ATP-coupled oxygen consumption with increased Atp5f1b mRNA only in mHFD offspring. Fructose increased basal respiration and encoding complex I-III mRNA, only in mSTD offspring. Uncoupled respiration was lower in mHFD mitochondria that were unable to exhibit fructose-induced increase Ucp2 mRNA. Fructose decreased antioxidative defense markers, increased unfolded protein response and insulin resistance only in mHFD offspring without fructose-induced hepatic lipid accumulation.

CONCLUSION

Mitochondrial dysfunction and homeostatic disturbances in response to fructose are early events evidencing the higher risk of fructose damage in the liver of adult offspring from dams fed an isocaloric moderate high-fat diet. This article is protected by copyright. All rights reserved.

The Precision Interventions for Severe and/or Exacerbation-Prone (PrecISE) Asthma Network: An overview of Network organization, procedures, and interventions

Asthma is a heterogeneous disease, with multiple underlying inflammatory pathways and structural airway abnormalities that impact disease persistence and severity. Recent progress has been made in developing targeted asthma therapeutics, especially for subjects with eosinophilic asthma. However, there is an unmet need for new approaches to treat patients with severe and exacerbation-prone asthma, who contribute disproportionately to disease burden. Extensive deep phenotyping has revealed the heterogeneous nature of severe asthma and identified distinct disease subtypes. A current challenge in the field is to translate new and emerging knowledge about different pathobiologic mechanisms in asthma into patient-specific therapies, with the ultimate goal of modifying the natural history of disease. Here, we describe the Precision Interventions for Severe and/or Exacerbation-Prone Asthma (PrecISE) Network, a groundbreaking collaborative effort of asthma researchers and biostatisticians from around the United States. The PrecISE Network was designed to conduct phase II/proof-of-concept clinical trials of precision interventions in the population with severe asthma, and is supported by the National Heart, Lung, and Blood Institute of the National Institutes of Health. Using an innovative adaptive platform trial design, the PrecISE Network will evaluate up to 6 interventions simultaneously in biomarker-defined subgroups of subjects. We review the development and organizational structure of the PrecISE Network, and choice of interventions being studied. We hope that the PrecISE Network will enhance our understanding of asthma subtypes and accelerate the development of therapeutics for severe asthma.

Glutamine-Derived Aspartate Biosynthesis in Cancer Cells: Role of Mitochondrial Transporters and New Therapeutic Perspectives

Simple Summary

In recent years, aspartate has been increasingly acknowledged as a critical player in the metabolism of cancer cells which use this metabolite for nucleotide and protein synthesis and for redox homeostasis. Most intracellular aspartate derives from the mitochondrial catabolism of glutamine. To date at least four mitochondrial transporters have been involved in this metabolic pathway. Their involvement appears to be cancer type-specific and dependent on glutamine availability. Targeting these mitochondrial transporters may represent a new attractive strategy to fight cancer. The aim of this review is to dissect the role of each of these transporters in relation to the type of cancer and the availability of nutrients in the tumoral microenvironment.

Abstract

Aspartate has a central role in cancer cell metabolism. Aspartate cytosolic availability is crucial for protein and nucleotide biosynthesis as well as for redox homeostasis. Since tumor cells display poor aspartate uptake from the external environment, most of the cellular pool of aspartate derives from mitochondrial catabolism of glutamine. At least four transporters are involved in this metabolic pathway: the glutamine (SLC1A5_var), the aspartate/glutamate (AGC), the aspartate/phosphate (uncoupling protein 2, UCP2), and the glutamate (GC) carriers, the last three belonging to the mitochondrial carrier family (MCF). The loss of one of these transporters causes a paucity of cytosolic aspartate and an arrest of cell proliferation in many different cancer types. The aim of this review is to clarify why different cancers have varying dependencies on metabolite transporters to support cytosolic glutamine-derived aspartate availability. Dissecting the precise metabolic routes that glutamine undergoes in specific tumor types is of upmost importance as it promises to unveil the best metabolic target for therapeutic intervention.