Prohibitin overexpression in adipocytes induces mitochondrial biogenesis, leads to obesity development, and affects glucose homeostasis in a sex-specific manner

Mitochondrial fractions located in the cytoplasmic and peridroplet areas of white adipocytes have distinct roles

The role of mitochondria in white adipocytes (WAs) has not been fully explored. A recent study revealed that brown adipocytes contain functionally distinct mitochondrial fractions, cytoplasmic mitochondria, and peridroplet mitochondria. However, it is not known whether such a functional division of mitochondria exists in WA. Herein, we observed that mitochondria could be imaged and mitochondrial DNA and protein detected in pellets obtained from the cytoplasmic layer and oil layer of WAs after centrifugation. The mitochondria in each fraction were designated as cytoplasmic mitochondria (CMw) and peridroplet mitochondria (PDMw) in WAs, respectively. CMw had higher β-oxidation activity than PDMw, and PDMw was associated with diacylglycerol acyltransferase 2. Therefore, CMw may be involved in β-oxidation and PDMw in droplet expansion in WAs.

Prohibitions in the meta-inflammatory response: a review

Prohibitins are the central regulatory element of cellular homeostasis, especially by modulating the response at different levels: Nucleus, mitochondria and membranes. Their localization and interaction with various proteins, homons, transcription and nuclear factors, and mtDNA indicate the globality and complexity of their pleiotropic properties, which remain to be investigated. A more detailed deciphering of cellular metabolism in relation to prohibitins under normal conditions and in various metabolic diseases will allow us to understand the precise role of prohibitins in the signaling cascades of PI3K/Akt, Raf/MAP/ERK, STAT3, p53, and others and to fathom their mutual influence. A valuable research perspective is to investigate the role of prohibitins in the molecular and cellular interactions between the two major players in the pathogenesis of obesity-adipocytes and macrophages - that form the basis of the meta-inflammatory response. Investigating the subtle intercellular communication and molecular cascades triggered in these cells will allow us to propose new therapeutic strategies to eliminate persistent inflammation, taking into account novel molecular genetic approaches to activate/inactivate prohibitins.

Molecular-Level Dysregulation of Insulin Pathways and Inflammatory Processes in Peripheral Blood Mononuclear Cells by Circadian Misalignment

Circadian misalignment due to night work has been associated with an elevated risk for chronic diseases. We investigated the effects of circadian misalignment using shotgun protein profiling of peripheral blood mononuclear cells taken from healthy humans during a constant routine protocol, which was conducted immediately after participants had been subjected to a 3-day simulated night shift schedule or a 3-day simulated day shift schedule. By comparing proteomic profiles between the simulated shift conditions, we identified proteins and pathways that are associated with the effects of circadian misalignment and observed that insulin regulation pathways and inflammation-related proteins displayed markedly different temporal patterns after simulated night shift. Further, by integrating the proteomic profiles with previously assessed metabolomic profiles in a network-based approach, we found key associations between circadian dysregulation of protein-level pathways and metabolites of interest in the context of chronic metabolic diseases. Endogenous circadian rhythms in circulating glucose and insulin differed between the simulated shift conditions. Overall, our results suggest that circadian misalignment is associated with a tug of war between central clock mechanisms controlling insulin secretion and peripheral clock mechanisms regulating insulin sensitivity, which may lead to adverse long-term outcomes such as diabetes and obesity. Our study provides a molecular-level mechanism linking circadian misalignment and adverse long-term health consequences of night work.

Self-Assembled Oligopeptoplex-Loaded Dissolving Microneedles for Adipocyte-Targeted Anti-Obesity Gene Therapy

Advancements in gene delivery systems are pivotal for gene-based therapeutics in oncological, inflammatory, and infectious diseases. This study delineates the design of a self-assembled oligopeptoplex (SA-OP) optimized for shRNA delivery to adipocytes, targeting obesity and associated metabolic syndromes. Conventional systems face challenges, including instability due to electrostatic interactions between genetic materials and cationic oligopeptides. Additionally, repeated injections induce discomfort and compromise patient well-being. To circumvent these issues, a dissolvable hyaluronic acid-based, self-locking microneedle (LMN) patch is developed, with improved micro-dose efficiency, for precise SA-OP delivery. This platform offers pain-free administration and improved SA-OP storage stability. In vitro studies in 3T3-L1 cells demonstrated improvements in SA-OP preservation and gene silencing efficacy. In vivo evaluation in a mice model of diet-induced type 2 diabetes yielded significant gene silencing in adipose tissue and a 21.92 ± 2.51% reduction in body weight with minimum relapse risk at 6-weeks post-treatment, representing a superior therapeutic efficacy in a truncated timeframe relative to the GLP-1 analogues currently available on the market. Additionally, SA-OP (LMN) mitigated insulin resistance, inflammation, and hepatic steatosis. These findings establish SA-OP (LMN) as a robust, minimally invasive transdermal gene delivery platform with prolonged storage stability for treating obesity and its metabolic comorbidities.

Novel effects of prohibitin 1 expression level on cholesterol and lipid homeostasis

Prohibitin 1 (PHB1) plays an important role in maintaining liver health and function. The PHB1 level is decreased in patients with various liver diseases. In this study, liver cancer was induced in liver-specific Phb1 knock-out mice, which were then subjected to hepatic gene and metabolomic analysis. The reduced expression of mRNA expression level of Phb1 induced down-regulation of cholesterol and lipid metabolism. This result was confirmed in a cell model. The expression of Hmgcr and Srebp2 in normal cells decreased when they were treated with cholesterol. In HepG2 cells in which the expression of Phb1 was lowered using siPhb1, the mRNA expression of Hmgcr and Srebp2 also decreased when the cells were treated with cholesterol. Furthermore, in the Phb1 knock-out group, the expression of Fasn and Srebp1 related to lipid metabolism increased but the expression of Ldlr decreased. The expression of Cat and Gpx in cells increased when the expression of Phb1 decreased. Altogether, a decreased expression of Phb1 induces down-regulation of cholesterol- and lipid metabolism-related genes and cholesterol homeostasis is not achieved, particularly in a cholesterol-rich environment. The decrease in Phb1 expression causes excessive oxidative stress in cholesterol and lipid metabolism. Therefore, maintaining a normal level of PHB1 expression is crucial for maintaining cholesterol homeostasis in the liver. Thus, PHB1 may become an important target for non-alcoholic fatty liver disease and lipid metabolism in the future.

Activation of AMP-activated protein kinase (AMPK) through inhibiting interaction with prohibitins

5'-Adenosine monophosphate-activated protein kinase (AMPK) is a potential therapeutic target for various medical conditions. We here identify a small-molecule compound (RX-375) that activates AMPK and inhibits fatty acid synthesis in cultured human hepatocytes. RX-375 does not bind to AMPK but interacts with prohibitins (PHB1 and PHB2), which were found to form a complex with AMPK. RX-375 induced dissociation of this complex, and PHBs knockdown resulted in AMPK activation, in the cultured cells. Administration of RX-375 to obese mice activated AMPK and ameliorated steatosis in the liver. High-throughput screening based on disruption of the AMPK-PHB interaction identified a second small-molecule compound that activates AMPK, confirming the importance of this interaction in the regulation of AMPK. Our results thus indicate that PHBs are previously unrecognized negative regulators of AMPK, and that compounds that prevent the AMPK-PHB interaction constitute a class of AMPK activator.

Human RSPO1 Mutation Represses Beige Adipocyte Thermogenesis and Contributes to Diet-Induced Adiposity

Recent genetic evidence has linked WNT downstream mutations to fat distribution. However, the roles of WNTs in human obesity remain unclear. Here, the authors screen all Wnt-related paracrine factors in 1994 obese cases and 2161 controls using whole-exome sequencing (WES) and identify that 12 obese patients harbor the same mutations in RSPO1 (p.R219W/Q) predisposing to human obesity. RSPO1 is predominantly expressed in visceral fat, primarily in the fibroblast cluster, and is increased with adiposity. Mice overexpressing human RSPO1 in adipose tissues develop obesity under a high-fat diet (HFD) due to reduced brown/beige fat thermogenesis. In contrast, Rspo1 ablation resists HFD-induced adiposity by increasing thermogenesis. Mechanistically, RSPO1 overexpression or administration significantly inhibits adipocyte mitochondrial respiration and thermogenesis via LGR4-Wnt/β-catenin signaling pathway. Importantly, humanized knockin mice carrying the hotspot mutation (p.R219W) display suppressed thermogenesis and recapitulate the adiposity feature of obese carriers. The mutation disrupts RSPO1's electrostatic interaction with the extracellular matrix, leading to excessive RSPO1 release that activates LGR4-Wnt/β-catenin signaling and attenuates thermogenic capacity in differentiated beige adipocytes. Therefore, these findings identify that gain-of-function mutations and excessive expression of RSPO1, acting as a paracrine Wnt activator, suppress fat thermogenesis and contribute to obesity in humans.

Ovarian Cancer: A Landscape of Mitochondria with Emphasis on Mitochondrial Dynamics

Ovarian cancer (OC) represents the main cause of death from gynecological malignancies in western countries. Altered cellular and mitochondrial metabolism are considered hallmarks in cancer disease. Several mitochondrial aspects have been found altered in OC, such as the oxidative phosphorylation system, oxidative stress and mitochondrial dynamics. Mitochondrial dynamics includes cristae remodeling, fusion, and fission processes forming a dynamic mitochondrial network. Alteration of mitochondrial dynamics is associated with metabolic change in tumour development and, in particular, the mitochondrial shaping proteins appear also to be responsible for the chemosensitivity and/or chemoresistance in OC. In this review a focus on the mitochondrial dynamics in OC cells is presented.

Prohibitins in neurodegeneration and mitochondrial homeostasis

The incidence of age-related neurodegenerative disorders has risen with the increase of life expectancy. Unfortunately, the diagnosis of such disorders is in most cases only possible when the neurodegeneration status is already advanced, and symptoms are evident. Although age-related neurodegeneration is a common phenomenon in living animals, the cellular and molecular mechanisms behind remain poorly understood. Pathways leading to neurodegeneration usually diverge from a common starting point, mitochondrial stress, which can serve as a potential target for early diagnosis and treatments. Interestingly, the evolutionarily conserved mitochondrial prohibitin (PHB) complex is a key regulator of ageing and metabolism that has been associated with neurodegenerative diseases. However, its role in neurodegeneration is still not well characterized. The PHB complex shows protective or toxic effects in different genetic and physiological contexts, while mitochondrial and cellular stress promote both up and downregulation of PHB expression. With this review we aim to shed light into the complex world of PHB’s function in neurodegeneration by putting together the latest advances in neurodegeneration and mitochondrial homeostasis associated with PHB. A better understanding of the role of PHB in neurodegeneration will add knowledge to neuron deterioration during ageing and help to identify early molecular markers of mitochondrial stress. This review will deepen our understanding of age-related neurodegeneration and provide questions to be addressed, relevant to human health and to improve the life quality of the elderly.

Deletion of adipocyte prohibitin 1 exacerbates high-fat diet-induced steatosis but not liver inflammation and fibrosis

Adipose tissue dysfunction is closely associated with the development and progression of nonalcoholic fatty liver disease (NAFLD). Recent studies have implied an important role of prohibitin-1 (PHB1) in adipose tissue function. In the current study, we aimed to explore the function of adipocyte PHB1 in the development and progression of NAFLD. The PHB1 protein levels in adipose tissues were markedly decreased in mice fed a high-fat diet (HFD) compared to those fed a chow diet. To explore the function of adipocyte PHB1 in the progression of NAFLD, mice with adipocyte-specific (adipo) deletion of Phb1 (Phb1^adipo-/- mice) were generated. Notably, Phb1^adipo-/- mice did not develop obesity but displayed severe liver steatosis under HFD feeding. Compared to HFD-fed wild-type (WT) mice, HFD-fed Phb1^adipo-/- mice displayed dramatically lower fat mass with significantly decreased levels of total adipose tissue inflammation, including macrophage and neutrophil number as well as the expression of inflammatory mediators. To our surprise, although liver steatosis in Phb1^adipo-/- mice was much more severe, liver inflammation and fibrosis were similar to WT mice after HFD feeding. RNA sequencing analyses revealed that the interferon pathway was markedly suppressed while the bone morphogenetic protein 2 pathway was significantly up-regulated in the liver of HFD-fed Phb1^adipo-/- mice compared with HFD-fed WT mice. Conclusion: HFD-fed Phb1^adipo-/- mice display a subtype of the lean NAFLD phenotype with severe hepatic steatosis despite low adipose mass. This subtype of the lean NAFLD phenotype has similar inflammation and fibrosis as obese NAFLD in HFD-fed WT mice; this is partially due to reduced total adipose tissue inflammation and the hepatic interferon pathway.

Endothelial Prohibitin Mediates Bidirectional Long-Chain Fatty Acid Transport in White and Brown Adipose Tissues

The function of prohibitin-1 (PHB1) in adipocyte mitochondrial respiration, adaptive thermogenesis, and long-chain fatty acid (LCFA) metabolism has been reported. While intracellular PHB1 expression is ubiquitous, cell surface PHB1 localization is selective for adipocytes and endothelial cells of adipose tissue. The importance of PHB1 in adipose endothelium has not been investigated, and its vascular cell surface function has remained unclear. Here, we generated and analyzed mice with PHB1 knock-out specifically in endothelial cells (PHB1 EC-KO). Despite the lack of endothelial PHB1, mice developed normally and had normal vascularization in both white adipose tissue and brown adipose tissue (BAT). Tumor and ex vivo explant angiogenesis assays also have not detected a functional defect in PHB1 KO endothelium. No metabolic phenotype was observed in PHB1 EC-KO mice raised on a regular diet. We show that both male and female PHB1 EC-KO mice have normal body composition and adaptive thermogenesis. However, PHB1 EC-KO mice displayed higher insulin sensitivity and increased glucose clearance when fed a high-fat diet. We demonstrate that the efficacy of LCFA deposition by adipocytes is decreased by PHB1 EC-KO, in particular in BAT. Consistent with that, EC-KO mice have a defect in clearing triglycerides from systemic circulation. Free fatty acid release upon lipolysis induction was also found to be reduced in PHB1 EC-KO mice. Our results demonstrate that PHB1 in endothelial cells regulates bidirectional LCFA transport and thereby suppresses glucose utilization.

The intracellular cholesterol pool in steroidogenic cells plays a role in basal steroidogenesis

The framework of steroidogenesis across steroidogenic cells is constructed around cholesterol - the precursor substrate molecule for all steroid hormones - including its cellular uptake, storage in intracellular lipid droplets, mobilization upon steroidogenic stimulation, and finally, its transport to the mitochondria, where steroidogenesis begins. Thus, cholesterol and the mitochondria are highly interconnected in steroidogenic cells. Moreover, accruing evidence suggests that autophagy and mitochondrial dynamics are important cellular events in the regulation of trophic hormone-induced cholesterol homeostasis and steroidogenesis. However, a potential role of cholesterol in itself in the regulation of steroidogenic factors and events remain largely unexplored. We tested the hypothesis that cholesterol plays a role in the regulation of cell-intrinsic factors and events involving steroidogenesis. Here, we show that depleting the intracellular cholesterol pool in steroidogenic cells induces autophagy, affects mitochondrial dynamics, and upregulates steroidogenic factors and basal steroidogenesis in three different steroidogenic cell types producing different steroid hormones. Notably, the cholesterol insufficiency-induced changes in different steroidogenic cell types occur independent of pertinent hormone stimulation and work in a dynamic and temporal manner with or without hormonal stimulation. Such effects of cholesterol deprivation on autophagy and mitochondrial dynamics were not observed in the non-steroidogenic cells, indicating that cholesterol insufficiency-induced changes in steroidogenic cells are specific to steroidogenesis. Thus, our data suggests a role of cholesterol in steroidogenesis beyond being a mere substrate for steroid hormones. The implications of our findings are broad and offer new insights into trophic hormone-dependent and hormone-independent steroidogenesis during development, as well as in health and disease.

Sex differences in the intergenerational inheritance of metabolic traits

Strong evidence suggests that early-life exposures to suboptimal environmental factors, including those in utero, influence our long-term metabolic health. This has been termed developmental programming. Mounting evidence suggests that the growth and metabolism of male and female fetuses differ. Therefore, sexual dimorphism in response to pre-conception or early-life exposures could contribute to known sex differences in susceptibility to poor metabolic health in adulthood. However, until recently, many studies, especially those in animal models, focused on a single sex, or, often in the case of studies performed during intrauterine development, did not report the sex of the animal at all. In this review, we (a) summarize the evidence that male and females respond differently to a suboptimal pre-conceptional or in utero environment, (b) explore the potential biological mechanisms that underlie these differences and (c) review the consequences of these differences for long-term metabolic health, including that of subsequent generations.

Prohibitin-1 plays a regulatory role in Leydig cell steroidogenesis

Mitochondria are essential for steroidogenesis. In steroidogenic cells, the initiation of steroidogenesis from cholesterol occurs on the matrix side of the inner mitochondrial membrane by the enzyme P450scc. This requires cholesterol import from the cytoplasm through the outer mitochondrial membrane, facilitated by the StAR protein. The subsequent steps leading to P450scc remain elusive. Here we report that the male transgenic mice that expressed a mutant form of a mitochondrial protein prohibitin-1 (PHB1^Tyr114Phe) from the Fabp-4 gene promoter displayed smaller testes, higher testosterone, and lower gonadotropin levels compared with PHB1-expressing and wild-type mice. A subsequent analysis of the testis and Leydig cells from the mice revealed that PHB1 played a previously unknown regulatory role in Leydig cell steroidogenesis. This includes a role in coordinating cell signaling, cholesterol homeostasis, and mitochondrial biology pertaining to steroidogenesis. The implications of our finding are broad as the initial stages of steroidogenesis are indistinguishable across steroidogenic cells.

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Tyr114Phe-PHB-1 transgenic male mice reveal PHB-1’s role in testosterone production

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PHB-1 coordinates steroidogenic signaling and events in testosterone biosynthesis

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Tyr114 residue in PHB-1 plays a regulatory role in testosterone production

Nonalcoholic fatty liver disease shows significant sex dimorphism

Nonalcoholic fatty liver disease (NAFLD), which has been renamed metabolic dysfunction-associated fatty liver disease, is a growing global medical problem. The incidence of NAFLD and its associated end-stage liver disease is increasing each year, and many research advancements have been achieved to date. This review focuses on the current knowledge of the sex differences in NAFLD and does not elaborate on areas without differences. Studies have revealed significant sex differences in the prevalence, influencing factors, pathophysiology, complications and therapies of NAFLD. Men have a higher incidence than women. Compared with women, men exhibit increased visceral fat deposition, are more susceptible to leptin resistance, lack estrogen receptors, and tend to synthesize fatty acids into fat storage. Male patients will experience more severe hepatic fibrosis and a higher incidence of liver cancer. However, once NAFLD occurs, women show a faster progression of liver fibrosis, higher levels of liver cell damage and inflammation and are less likely to undergo liver transplantation than men. In general, men have more risk factors and more severe pathophysiological reactions than women, whereas the development of NAFLD is faster in women, and the treatments for women are more limited than those for men. Thus, whether sex differences should be considered in the individualized prevention and treatment of NAFLD in the future is worth considering.

Prohibitin Inactivation in Adipocytes Results in Reduced Lipid Metabolism and Adaptive Thermogenesis Impairment

Prohibitin-1 (PHB) is a multifunctional protein previously reported to be important for adipocyte function. PHB is expressed on the surface of adipose cells, where it interacts with a long-chain fatty acid (LCFA) transporter. Here, we show that mice lacking PHB in adipocytes (PHB adipocyte [Ad]-knockout [KO]) have a defect in fat tissue accumulation despite having larger lipid droplets in adipocytes due to reduced lipolysis. Although PHB Ad-KO mice do not display glucose intolerance, they are insulin resistant. We show that PHB Ad-KO mice are lipid intolerant due to a decreased capacity of adipocytes for LCFA uptake. Instead, PHB Ad-KO mice have increased expression of GLUT1 in various tissues and use glucose as a preferred energy source. We demonstrate that PHB Ad-KO mice have defective brown adipose tissue, are intolerant to cold, and display reduced basal energy expenditure. Systemic repercussions of PHB inactivation in adipocytes were observed in both males and females. Consistent with lower cellular mitochondrial content and reduced uncoupling protein 1 protein expression, brown adipocytes lacking PHB display decreased proton leak and switch from aerobic metabolism to glycolysis. Treatment of differentiating brown adipocytes with small molecules targeting PHB suppressed mitochondrial respiration and uncoupling. Our results demonstrate that PHB in adipocytes is essential for normal fatty acid uptake, oxidative metabolism, and adaptive thermogenesis. We conclude that PHB inhibition could be investigated as an approach to altering energy substrate utilization.

The Mitochondrial Prohibitin (PHB) Complex in C. elegans Metabolism and Ageing Regulation

The mitochondrial prohibitin (PHB) complex, composed of PHB-1 and PHB-2, is an evolutionarily conserved context-dependent modulator of longevity. This extremely intriguing phenotype has been linked to alterations in mitochondrial function and lipid metabolism. The true biochemical function of the mitochondrial PHB complex remains elusive, but it has been shown to affect membrane lipid composition. Recent work, using large-scale biochemical approaches, has highlighted a broad effect of PHB on the C. elegans metabolic network. Collectively, the biochemical data support the notion that PHB modulates, at least partially, worm longevity through the moderation of fat utilisation and energy production via the mitochondrial respiratory chain. Herein, we review, in a systematic manner, recent biochemical insights into the impact of PHB on the C. elegans metabolome.

Prohibitin-1 Is a Dynamically Regulated Blood Protein With Cardioprotective Effects in Sepsis

Background In sepsis, circulating cytokines and lipopolysaccharide elicit mitochondrial dysfunction and cardiomyopathy, a major cause of morbidity and mortality with this condition. Emerging research places the PHB1 (lipid raft protein prohibitin-1) at the nexus of inflammation, metabolism, and oxidative stress. PHB1 has also been reported in circulation, though its function in this compartment is completely unknown. Methods and Results Using a wide-ranging approach across multiple in vitro and in vivo models, we interrogated the functional role of intracellular and circulating PHB1 in the heart during sepsis, and elucidated some of the mechanisms involved. Upon endotoxin challenge or sepsis induction in rodent models, PHB1 translocates from mitochondria to nucleus in cardiomyocytes and is secreted into the circulation from the liver in a manner dependent on nuclear factor (erythroid-derived 2)-like 2, a key transcriptional regulator of the antioxidant response. Overexpression or treatment with recombinant human PHB1 enhances the antioxidant/anti-inflammatory response and protects HL-1 cardiomyocytes from mitochondrial dysfunction and toxicity from cytokine stress. Importantly, administration of recombinant human PHB1 blunted inflammation and restored cardiac contractility and ATP production in mice following lipopolysaccharide challenge. This cardioprotective, anti-inflammatory effect of recombinant human PHB1 was determined to be independent of nuclear factor (erythroid-derived 2)-like 2, but partially dependent on PI3K/AKT  signaling in the heart. Conclusions These findings reveal a previously unknown cardioprotective effect of PHB1 during sepsis, and illustrate a pro-survival, protective role for PHB1 in the circulation. Exploitation of circulating PHB1 as a biomarker and/or therapeutic could have widespread benefit in the clinical management of sepsis and other severe inflammatory disorders.

Mitochondrial unfolded protein response: A novel pathway in metabolism and immunity

Mitochondrial unfolded protein response (mitoUPR) is a mitochondria stress response to maintain mitochondrial proteostasis during stress. Increasing evidence suggests that mitoUPR participates in diverse physiological processes especially metabolism and immunity. Although mitoUPR regulates metabolism in many aspects, it is mainly reflected in the regulation of energy metabolism. During stress, mitoUPR alters energy metabolism via suppressing oxidative phosphorylation (OXPHOS) or increasing glycolysis. MitoUPR also alters energy metabolism and regulates diverse metabolic diseases such as diabetes, cancers, fatty liver and obesity. In addition, mitoUPR also participates in immune process during stress. MitoUPR can induce innate immune response during various infections and may regulate inflammatory response during diverse inflammations. Considering the pleiotropic actions of mitoUPR, mitoUPR may supply diverse therapeutic targets for metabolic diseases and immune diseases.

The current landscape of coronavirus-host protein-protein interactions

In less than 20 years, three deadly coronaviruses, SARS-CoV, MERS-CoV and SARS-CoV-2, have emerged in human population causing hundreds to hundreds of thousands of deaths. Other coronaviruses are causing epizootic representing a significant threat for both domestic and wild animals. Members of this viral family have the longest genome of all RNA viruses, and express up to 29 proteins establishing complex interactions with the host proteome. Deciphering these interactions is essential to identify cellular pathways hijacked by these viruses to replicate and escape innate immunity. Virus-host interactions also provide key information to select targets for antiviral drug development. Here, we have manually curated the literature to assemble a unique dataset of 1311 coronavirus-host protein–protein interactions. Functional enrichment and network-based analyses showed coronavirus connections to RNA processing and translation, DNA damage and pathogen sensing, interferon production, and metabolic pathways. In particular, this global analysis pinpointed overlooked interactions with translation modulators (GIGYF2-EIF4E2), components of the nuclear pore, proteins involved in mitochondria homeostasis (PHB, PHB2, STOML2), and methylation pathways (MAT2A/B). Finally, interactome data provided a rational for the antiviral activity of some drugs inhibiting coronaviruses replication. Altogether, this work describing the current landscape of coronavirus-host interactions provides valuable hints for understanding the pathophysiology of coronavirus infections and developing effective antiviral therapies.

Functional Mechanisms of Mitochondrial Respiratory Chain Supercomplex Assembly Factors and Their Involvement in Muscle Quality

Impairment of skeletal muscle function causes disabilities in elderly people. Therefore, in an aged society, prevention and treatment of sarcopenia are important for expanding healthy life expectancy. In addition to aging, adipose tissue disfunction and inflammation also contribute to the pathogenesis of sarcopenia by causing the combined state called ‘sarcopenic obesity’. Muscle quality as well as muscle mass contributes to muscle strength and physical performance. Mitochondria in the skeletal muscles affect muscle quality by regulating the production of energy and reactive oxygen species. A certain portion of the mitochondrial respiratory chain complexes form a higher-order structure called a “supercomplex”, which plays important roles in efficient energy production, stabilization of respiratory chain complex I, and prevention of reactive oxygen species (ROS) generation. Several molecules including phospholipids, proteins, and certain chemicals are known to promote or stabilize mitochondrial respiratory chain supercomplex assembly directly or indirectly. In this article, we review the distinct mechanisms underlying the promotion or stabilization of mitochondrial respiratory chain supercomplex assembly by supercomplex assembly factors. Further, we introduce regulatory pathways of mitochondrial respiratory chain supercomplex assembly and discuss the roles of supercomplex assembly factors and regulatory pathways in skeletal muscles and adipose tissues, believing that this will lead to discovery of potential targets for prevention and treatment of muscle disorders such as sarcopenia.

HDAC6 promotes sepsis development by impairing PHB1-mediated mitochondrial respiratory chain function

OBJECTIVE

This study was aimed at investigating the regulation of mitochondrial function by histone deacetylase 6 (HDAC6) and the role of HDAC6 in the development and progression of sepsis.

RESULTS

HDAC6 downregulated PHB1 and subsequently promoted the development of CLP-induced sepsis. Inhibition of HDAC6 significantly attenuated CLP-induced sepsis through inhibition of mitochondrial dysfunction and reduced oxidant production, thus protecting the rats from oxidative injury.

CONCLUSIONS

In this sepsis model, HDAC6 inhibits the expression and function of PHB1 and alters the function of the mitochondrial respiratory chain mediated by PHB1, thus enhancing the production of oxidants and increasing oxidative stress and thereby leading to severe oxidative injury in multiple organs.

METHODS

The expression of HDAC6 and prohibitin 1 (PHB1) in humans and in a rat model of sepsis was measured by quantitative reverse-transcription PCR and western blotting. Sepsis induction by cecal ligation and puncture (CLP) was confirmed by histological analysis. Concentrations of different sepsis markers were measured by an enzyme-linked immunosorbent assay, and mitochondrial function was assessed via the mitochondrial respiratory control rate.

Mitochondrial Dysfunction in Age-Related Metabolic Disorders

Aging is a natural biological process in living organisms characterized by receding bioenergetics. Mitochondria are crucial for cellular bioenergetics and thus an important contributor to age-related energetics deterioration. In addition, mitochondria play a major role in calcium signaling, redox homeostasis, and thermogenesis making this organelle a major cellular component that dictates the fate of a cell. To maintain its quantity and quality, mitochondria undergo multiple processes such as fission, fusion, and mitophagy to eliminate or replace damaged mitochondria. While this bioenergetics machinery is properly protected, the functional decline associated with age and age-related metabolic diseases is mostly a result of failure in such protective mechanisms. In addition, metabolic by-products like reactive oxygen species also aid in this destructive pathway. Mitochondrial dysfunction has always been thought to be associated with diseases. Moreover, studies in recent years have pointed out that aging contributes to the decay of mitochondrial health by promoting imbalances in key mitochondrial-regulated pathways. Hence, it is crucial to understand the nexus of mitochondrial dysfunction in age-related diseases. This review focuses on various aspects of basic mitochondrial biology and its status in aging and age-related metabolic diseases.

Prohibitin 2 deficiency impairs cardiac fatty acid oxidation and causes heart failure

Fatty acids are the most major substrate source for adult cardiac energy generation. Prohibitin 2 (PHB2), a highly conserved protein located in mitochondrial inner membrane, plays key roles in cellular energy metabolic homeostasis. However, its functions in regulating cardiac fatty acid metabolism have remained largely unknown. Our study demonstrates that cardiac-specific knockout of Phb2 leads to accumulation of lipid droplets and causes heart failure. Mechanistically, ablation of PHB2 impairs cardiac fatty acid oxidation (FAO) through downregulating carnitine palmitoyltransferase1b (CPT1b), a rate-limiting enzyme of cardiac mitochondrial FAO. Moreover, overexpression of CPT1b alleviates impaired FAO in PHB2-deficient cardiomyocytes. Thus, our study provides direct evidence for the link between PHB2 and cardiac fatty acid metabolism. Our study points out that PHB2 is a potential FAO regulator in cardiac mitochondrial inner membrane, as well as the connection between PHB2 and CPT1b and their relationships to cardiac pathology especially to cardiac fatty acid metabolic disorder.

White adipose tissue mitochondrial metabolism in health and in obesity

White adipose tissue is one of the largest organs of the body. It plays a key role in whole-body energy status and metabolism; it not only stores excess energy but also secretes various hormones and metabolites to regulate body energy balance. Healthy adipose tissue capable of expanding is needed for metabolic well-being and to prevent accumulation of triglycerides to other organs. Mitochondria govern several important functions in the adipose tissue. We review the derangements of mitochondrial function in white adipose tissue in the obese state. Downregulation of mitochondrial function or biogenesis in the white adipose tissue is a central driver for obesity-associated metabolic diseases. Mitochondrial functions compromised in obesity include oxidative functions and renewal and enlargement of the adipose tissue through recruitment and differentiation of adipocyte progenitor cells. These changes adversely affect whole-body metabolic health. Dysfunction of the white adipose tissue mitochondria in obesity has long-term consequences for the metabolism of adipose tissue and the whole body. Understanding the pathways behind mitochondrial dysfunction may help reveal targets for pharmacological or nutritional interventions that enhance mitochondrial biogenesis or function in adipose tissue.

A Putative Prohibitin-Calcium Nexus in β-Cell Mitochondria and Diabetes

The role of mitochondria in apoptosis is well known; however, the mechanisms linking mitochondria to the proapoptotic effects of proinflammatory cytokines, hyperglycemia, and glucolipotoxicity are not completely understood. Complex Ca²⁺ signaling has emerged as a critical contributor to these proapoptotic effects and has gained significant attention in regulating the signaling processes of mitochondria. In pancreatic β-cells, Ca²⁺ plays an active role in β-cell function and survival. Prohibitin (PHB), a mitochondrial chaperone, is actively involved in maintaining the architecture of mitochondria. However, its possible interaction with Ca²⁺-activated signaling pathways has not been explored. The present review aims to examine potential crosstalk between Ca²⁺ signaling and PHB function in pancreatic β-cells. Moreover, this review will focus on the effects of cytokines and glucolipotoxicity on Ca²⁺ signaling and its possible interaction with PHB. Improved understanding of this important mitochondrial protein may aid in the design of more targeted drugs to identify specific pathways involved with stress-induced dysfunction in the β-cell.

Human Ovarian Cancer Tissue Exhibits Increase of Mitochondrial Biogenesis and Cristae Remodeling

Ovarian cancer (OC) is the most lethal gynecologic cancer characterized by an elevated apoptosis resistance that, potentially, leads to chemo-resistance in the recurrent disease. Mitochondrial oxidative phosphorylation was found altered in OC, and mitochondria were proposed as a target for therapy. Molecular evidence suggests that the deregulation of mitochondrial biogenesis, morphology, dynamics, and apoptosis is involved in carcinogenesis. However, these mitochondrial processes remain to be investigated in OC. Eighteen controls and 16 OC tissues (serous and mucinous) were collected. Enzymatic activities were performed spectrophotometrically, mitochondrial DNA (mtDNA) content was measured by real-time-PCR, protein levels were determined by Western blotting, and mitochondrial number and structure were measured by electron microscopy. Statistical analysis was performed using Student’s t-test, Mann-Whitney U test, and principal component analysis (PCA). We found, in OC, that increased mitochondrial number associated with increased peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) and mitochondrial transcription factor A (TFAM) protein levels, as well as mtDNA content. The OC mitochondria presented an increased maximum length, as well as reduced cristae width and junction diameter, associated with increased optic atrophy 1 protein (OPA1) and prohibitin 2 (PHB2) protein levels. In addition, in OC tissues, augmented cAMP and sirtuin 3 (SIRT3) protein levels were observed. PCA of the 25 analyzed biochemical parameters classified OC patients in a distinct group from controls. We highlight a “mitochondrial signature” in OC that could result from cooperation of the cAMP pathway with the SIRT3, OPA1, and PHB2 proteins.

Prohibitin: a prime candidate for a pleiotropic effector that mediates sex differences in obesity, insulin resistance, and metabolic dysregulation

Adipocytes and macrophages, the two major constituents of adipose tissue, exhibit sex differences and work in synergy in adipose tissue physiology and pathophysiology, including obesity-linked insulin resistance and metabolic dysregulation. Sex steroid hormones play a major role in sex differences in adipose tissue biology. However, our knowledge of the molecules that mediate these effects in adipose tissue remains limited. Consequently, it remains unclear whether these effector molecules in different adipose and immune cell types are distinct or if there are also pleiotropic effectors. Recently, a protein named prohibitin (PHB) with cell compartment- and tissue-specific functions has been found to play a role in sex differences in adipose and immune functions. Transgenic (Tg) mouse models overexpressing PHB (PHB-Tg) and a phospho-mutant PHB (mPHB-Tg) from the fatty acid binding protein-4 (Fabp-4) gene promoter display sex-neutral obesity; however, obesity-related insulin resistance and metabolic dysregulation are male-specific. Intriguingly, with aging, the male PHB-Tg mice developed hepatic steatosis and subsequently liver tumors whereas the male mPHB-Tg mice developed lymph node tumors and splenomegaly. Unlike the male transgenic mice, the female PHB-Tg and mPHB-Tg mice remain protected from obesity-related metabolic dysregulation and tumor development. In conclusion, the sex-dimorphic metabolic and immune phenotypes of PHB-Tg and mPHB-Tg mice have revealed PHB as a pleiotropic effector of sex differences in adipose and immune functions. In this mini-review, we will discuss the pleiotropic attributes of PHB and potential mechanisms that may have contributed to the sex-dimorphic metabolic phenotypes in PHB-Tg and mPHB-Tg mice, which warrant future research. We propose that PHB is a prime candidate for a pleiotropic mediator of sex differences in adipose and immune functions in both physiology and pathophysiology, including obesity, insulin resistance, and metabolic dysregulation.

Prohibitin: A hypothetical target for sex-based new therapeutics for metabolic and immune diseases

IMPACT STATEMENT

Traditional sex-related biases in research are now obsolete, and it is important to identify the sex of humans, animals, and even cells in research protocols, due to the role of sex as a fundamental facet of biology, predisposition to disease, and response to therapy. Genetic sex, epigenetics and hormonal regulations, generate sex-dimorphisms. Recent investigations acknowledge sex differences in metabolic and immune health as well as chronic diseases. Prohibitin, an evolutionarily conserved molecule, has pleotropic functions in mitochondrial housekeeping, plasma membrane signaling, and nuclear genetic transcription. Studies in adipocytes, macrophages, and transgenic mice indicate that prohibitin interacts with sex steroids and plays a role in mediating sex differences in adipose tissues and immune cell types. Prohibitin may, depending on context, modulate predisposition to chronic metabolic diseases and malignancy and, because of these attributes, could be a target for sex-based therapies of metabolic and immune-related diseases as well as cancer.

Prohibitins: A Critical Role in Mitochondrial Functions and Implication in Diseases

Prohibitin 1 (PHB1) and prohibitin 2 (PHB2) are proteins that are ubiquitously expressed, and are present in the nucleus, cytosol, and mitochondria. Depending on the cellular localization, PHB1 and PHB2 have distinctive functions, but more evidence suggests a critical role within mitochondria. In fact, PHB proteins are highly expressed in cells that heavily depend on mitochondrial function. In mitochondria, these two proteins assemble at the inner membrane to form a supra-macromolecular structure, which works as a scaffold for proteins and lipids regulating mitochondrial metabolism, including bioenergetics, biogenesis, and dynamics in order to determine the cell fate, death, or life. PHB alterations have been found in aging and cancer, as well as neurodegenerative, cardiac, and kidney diseases, in which significant mitochondrial impairments have been observed. The molecular mechanisms by which prohibitins regulate mitochondrial function and their role in pathology are reviewed and discussed herein.

Obesity-Linked Cancers: Current Knowledge, Challenges and Limitations in Mechanistic Studies and Rodent Models

The worldwide prevalence of obesity has doubled during the last 50 years, and according to the World Obesity Federation, one third of the people on Earth will be obese by the year 2025. Obesity is described as a chronic, relapsing and multifactorial disease that causes metabolic, biomechanical, and psychosocial health consequences. Growing evidence suggests that obesity is a risk factor for multiple cancer types and rivals smoking as the leading preventable cause for cancer incidence and mortality. The epidemic of obesity will likely generate a new wave of obesity-related cancers with high aggressiveness and shortened latency. Observational studies have shown that from cancer risk to disease prognosis, an individual with obesity is consistently ranked worse compared to their lean counterpart. Mechanistic studies identified similar sets of abnormalities under obesity that may lead to cancer development, including ectopic fat storage, altered adipokine profiles, hormone fluctuations and meta-inflammation, but could not explain how these common mechanisms produce over 13 different cancer types. A major hurdle in the mechanistic underpinning of obesity-related cancer is the lack of suitable pre-clinical models that spontaneously develop obesity-linked cancers like humans. Current approaches and animal models fall short when discerning the confounders that often coexist in obesity. In this mini-review, we will briefly survey advances in the different obesity-linked cancers and discuss the challenges and limitations in the rodent models employed to study their relationship. We will also provide our perspectives on the future of obesity-linked cancer research.

The mitochondrial unfolded protein response and mitohormesis: a perspective on metabolic diseases

Mitochondria perform essential roles as crucial organelles for cellular and systemic energy homeostasis, and as signaling hubs, which coordinate nuclear transcriptional responses to the intra- and extra-cellular environment. Complex human diseases, including diabetes, obesity, fatty liver disease and aging-related degenerative diseases are associated with alterations in mitochondrial oxidative phosphorylation (OxPhos) function. However, a recent series of studies in animal models have revealed that an integrated response to tolerable mitochondrial stress appears to render cells less susceptible to subsequent aging processes and metabolic stresses, which is a key feature of mitohormesis. The mitochondrial unfolded protein response (UPRmt) is a central part of the mitohormetic response and is a retrograde signaling pathway, which utilizes the mitochondria-to-nucleus communication network. Our understanding of the UPRmt has contributed to elucidating the role of mitochondria in metabolic adaptation and lifespan regulation. In this review, we discuss and integrate recent data from the literature on the present status of mitochondrial OxPhos function in the development of metabolic diseases, relying on evidence from human and other animal studies, which points to alterations in mitochondrial function as a key factor in the regulation of metabolic diseases and conclude with a discussion on the specific roles of UPRmt and mitohormesis as a novel therapeutic strategy for the treatment of obesity and insulin resistance.

Gonadectomy in Mito-Ob mice revealed a sex-dimorphic relationship between prohibitin and sex steroids in adipose tissue biology and glucose homeostasis

Background

Recently, we have developed a novel transgenic mouse model by overexpressing prohibitin (PHB) in adipocytes, which developed obesity due to upregulation of mitochondrial biogenesis in adipocytes, hence named “Mito-Ob.” Interestingly, only male Mito-Ob mice developed obesity-related impaired glucose homeostasis and insulin sensitivity, whereas female Mito-Ob mice did not. The observed sex differences in metabolic dysregulation suggest a potential involvement of sex steroids. Thus, the main aim of this study is to investigate the role of sex steroids on the overall phenotype of Mito-Ob mice through gonadectomy, as well as direct effect of sex steroids on adipocytes from Mito-Ob mice in vitro.

Methods

Mito-Ob mice and wild-type CD-1 mice were gonadectomized at 12 weeks of age. Age- and sex-matched sham-operated mice were used as controls. Body weight, white adipose tissue, glucose tolerance, and insulin sensitivity were analyzed 3 months post-surgery. Differentiation of adipocytes isolated from female and male Mito-Ob mice were studied with and without sex steroids.

Results

Gonadectomy significantly reduced body weight in Mito-Ob mice compared with sham-operated mice, whereas the opposite trend was observed in wild-type mice. These changes occurred independent of food intake. A corresponding decrease in adipose tissue weight was found in gonadectomized Mito-Ob mice, but depot-specific differences were observed in male and female. Gonadectomy improved glucose tolerance in male wild-type and Mito-Ob mice, but the effect was more pronounced in wild-type mice. Gonadectomy did not alter insulin sensitivity in male Mito-Ob mice, but it was improved in male wild-type mice. In primary cell cultures, testosterone inhibited adipocyte differentiation to a lesser extent in male Mito-Ob preadipocytes compared with the wild-type mice. On the other hand, preadipocytes from female wild-type mice showed better differentiation potential than those from female Mito-Ob mice in the presence of 17β-estradiol.

Conclusions

PHB requires sex steroids for the development of obese phenotype in Mito-Ob mice, which differentially affect glucose homeostasis and insulin sensitivity in male and female. It appears that PHB plays sex- and adipose depot-specific roles and involves additional factors. In vitro studies suggested that PHB differently influenced adipocyte differentiation in the presence and absence of sex steroids. Overall, this study along with available information in the literature indicated that a multifaceted relationship exists between PHB and sex steroids, which may work in a cell/tissue type- and sex-specific manner.

Accumulation of prohibitin is a common cellular response to different stressing stimuli and protects melanoma cells from ER stress and chemotherapy-induced cell death

Melanoma is responsible for most deaths among skin cancers and conventional and palliative care chemotherapy are limited due to the development of chemoresistance. We used proteomic analysis to identify cellular responses that lead to chemoresistance of human melanoma cell lines to cisplatin. A systems approach to the proteomic data indicated the participation of specific cellular processes such as oxidative phosphorylation, mitochondrial organization and homeostasis, as well as the unfolded protein response (UPR) to be required for the survival of cells treated with cisplatin. Prohibitin (PHB) was among the proteins consistently accumulated, interacting with the functional clusters associated with resistance to cisplatin. We showed PHB accumulated at different levels in melanoma cell lines under stressing stimuli, such as (i) treatment with temozolomide (TMZ), dacarbazine (DTIC) and cisplatin; (ii) serum deprivation; (iii) tunicamycin, an UPR inducer. Prohibitin accumulated in the mitochondria of melanoma cells after cisplatin and tunicamycin treatment and its de novo accumulation led to chemoresistance melanoma cell lines. In contrast, PHB knock-down sensitized melanoma cells to cisplatin and tunicamycin treatment. We conclude that PHB participates in the survival of cells exposed to different stress stimuli, and can therefore serve as a target for the sensitization of melanoma cells to chemotherapy.

Elucidation of the 14-3-3ζ interactome reveals critical roles of RNA-splicing factors during adipogenesis

Adipogenesis involves a complex signaling network requiring strict temporal and spatial organization of effector molecules. Molecular scaffolds, such as 14-3-3 proteins, facilitate such organization, and we have previously identified 14-3-3ζ as an essential scaffold in adipocyte differentiation. The interactome of 14-3-3ζ is large and diverse, and it is possible that novel adipogenic factors may be present within it, but this possibility has not yet been tested. Herein, we generated mouse embryonic fibroblasts from mice overexpressing a tandem affinity purification (TAP) epitope-tagged 14-3-3ζ molecule. After inducing adipogenesis, TAP-14-3-3ζ complexes were purified, followed by MS analysis to determine the 14-3-3ζ interactome. We observed more than 100 proteins that were unique to adipocyte differentiation, 56 of which were novel interacting partners. Among these, we were able to identify previously established regulators of adipogenesis (i.e. Ptrf/Cavin1) within the 14-3-3ζ interactome, confirming the utility of this approach to detect adipogenic factors. We found that proteins related to RNA metabolism, processing, and splicing were enriched in the interactome. Analysis of transcriptomic data revealed that 14-3-3ζ depletion in 3T3-L1 cells affected alternative splicing of mRNA during adipocyte differentiation. siRNA-mediated depletion of RNA-splicing factors within the 14-3-3ζ interactome, that is, of Hnrpf, Hnrpk, Ddx6, and Sfpq, revealed that they have essential roles in adipogenesis and in the alternative splicing of Pparg and the adipogenesis-associated gene Lpin1 In summary, we have identified novel adipogenic factors within the 14-3-3ζ interactome. Further characterization of additional proteins within the 14-3-3ζ interactome may help identify novel targets to block obesity-associated expansion of adipose tissues.

Prohibitin: a potential therapeutic target in tyrosine kinase signaling

Prohibitin is a pleiotropic protein that has roles in fundamental cellular processes, such as cellular proliferation and mitochondrial housekeeping, and in cell- or tissue-specific functions, such as adipogenesis and immune cell functions. The different functions of prohibitin are mediated by its cell compartment-specific attributes, which include acting as an adaptor molecule in membrane signaling, a scaffolding protein in mitochondria, and a transcriptional co-regulator in the nucleus. However, the precise relationship between its distinct cellular localization and diverse functions remain largely unknown. Accumulating evidence suggests that the phosphorylation of prohibitin plays a role in a number of cell signaling pathways and in intracellular trafficking. Herein, we discuss the known and potential importance of the site-specific phosphorylation of prohibitin in regulating these features. We will discuss this in the context of new evidence from tissue-specific transgenic mouse models of prohibitin, including a mutant prohibitin lacking a crucial tyrosine phosphorylation site. We conclude with the opinion that prohibitin can be used as a potential target for tyrosine kinase signal transduction-targeting therapy, including in insulin, growth factors, and immune signaling pathways.

Characterization of mitochondrial prohibitin from Boleophthalmus pectinirostris and evaluation of its possible role in spermatogenesis

Prohibitin (PHB) is an evolutionarily conserved mitochondrial membrane protein. It plays a vital role in cell proteolysis, senescence, and apoptosis and is associated with spermatogenesis and sperm quality control in mammals. To study the characteristics of the PHB gene and its potential roles during spermatogenesis in Boleophthalmus pectinirostris, we cloned a 1153-bp full-length cDNA from the testis of B. pectinirostris with an open reading frame of 816 bp, which encodes 272 amino acid residues. Real-time quantitative PCR (qPCR) analysis revealed the presence of phb mRNA in all the tissues examined, with higher expression levels found in the testis, kidney, intestine, and muscle tissues. We examined the localization of phb mRNA during spermatogenesis by in situ hybridization (ISH), showing that phb mRNA was distributed in the periphery of the nucleus in primary and secondary spermatocytes. In spermatid and mature sperm, the phb mRNA gradually moved toward one side, where the flagellum is formed. Immunofluorescence (IF) results showed co-localization of the PHB and mitochondria at different stages during spermatogenesis of B. pectinirostris. The signals obtained for PHB decreased as spermatogenesis proceeded; the strongest detection signal was found in secondary spermatocytes, with lower levels of staining in other stages. Additionally, in the mature germ cells, the PHB signals were weak and aggregate in the midpiece of the flagellum.

Prohibitin-induced obesity leads to anovulation and polycystic ovary in mice

Polycystic ovary syndrome (PCOS) is a prevalent endocrine disorder and the most common cause of female infertility. However, its etiology and underlying mechanisms remain unclear. Here we report that a transgenic obese mouse (Mito-Ob) developed by overexpressing prohibitin in adipocytes develops polycystic ovaries. Initially, the female Mito-Ob mice were equally fertile to their wild-type littermates. The Mito-Ob mice began to gain weight after puberty, became significantly obese between 3-6 months of age, and ∼25% of them had become infertile by 9 months of age. Despite obesity, female Mito-Ob mice maintained glucose homeostasis and insulin sensitivity similar to their wild-type littermates. Mito-Ob mice showed morphologically distinct polycystic ovaries and elevated estradiol, but normal testosterone and insulin levels. Histological analysis of the ovaries showed signs of impaired follicular dynamics, such as preantral follicular arrest and reduced number, or absence, of corpus luteum. The ovaries of the infertile Mito-Ob mice were closely surrounded by periovarian adipose tissue, suggesting a potential role in anovulation. Collectively, these data suggest that elevated estradiol and obesity per se might lead to anovulation and polycystic ovaries independent of hyperinsulinemia and hyperandrogenism. As obesity often coexists with other abnormalities known to be involved in the development of PCOS such as insulin resistance, compensatory hyperinsulinemia and hyperandrogenism, the precise role of these factors in PCOS remains unclear. Mito-Ob mice provide an opportunity to study the effects of obesity on anovulation and ovarian cyst formation independent of the major drivers of obesity-linked PCOS.

Summary: Obesity-related overgrowth of periovarian adipose tissue and elevated estradiol levels cause anovulation and ovarian cyst formation in mice, independent of hyperinsulinemia and hyperandrogenism.

Prohibitin - At the crossroads of obesity-linked diabetes and cancer

The promoter of a gene that is selectively expressed in just a few cell types provides unique opportunities to study: (1) the pleiotropic function of a protein in two different cell types including the cell compartment specific function, and (2) the crosstalk between two cell/tissue types at the systemic level. This is not possible with a ubiquitous or a highly specific gene promoter. The adipocyte protein-2 ( aP2) is one such gene. It is primarily expressed in adipocytes, but also selectively in monocytic macrophages and dendritic cells, among various immune cell types. Thus, the adipocyte protein-2 gene promoter provides an opportunity to simultaneously manipulate adipose and immune functions in a transgenic animal. Prohibitin (PHB) is a pleiotropic protein that has roles in both adipocytes and immune cells. Adipocyte specific functions of prohibitin are mediated through its mitochondrial function, whereas its immune functions are mediated in a phosphorylation-dependent manner. We capitalized on this attribute of prohibitin to explore the crosstalk between adipose and immune functions, and to discern mitochondrial and plasma membrane-associated cell signaling functions of prohibitin, by expressing wild type prohibitin (Mito-Ob) and a phospho-mutant form of prohibitin (m-Mito-Ob) from the protein-2 gene promoter, individually. Both transgenic mice develop obesity in a sex-neutral manner, but develop obesity-related metabolic dysregulation in a male sex-specific manner. Subsequently, the male Mito-Ob mice spontaneously developed type 2 diabetes and liver cancer, whereas the male m-Mito-Ob mice developed lymph node tumors or autoimmune diabetes in a context-dependent manner. This review provides a point of view on the role of prohibitin in mediating sex differences in adipose and immune functions at the systemic level. We discuss the unique attributes of prohibitin and provide a new paradigm in adipose-immune crosstalk mediated through a pleiotropic protein. Impact statement Prohibitin (PHB) is ubiquitously expressed and plays a role in adipocyte-immune cell cross-talk. Both male and female transgenic mice expressing wild-type PHB in adipose tissue and in macrophages are obese, but only males develop diabetes and liver cancer. When the mice express PHB mutated on tyrosine-114 in adipocytes and macrophages, both males and females are still obese, but none develops liver cancer; instead, males develop lymph node tumors. Adipocyte specific functions of PHB are mediated through its mitochondrial function, whereas its immune functions are mediated in a phosphorylation-dependent manner. Thus, PHB appears to be an important molecule linking obesity, diabetes, and cancer. In addition, this link appears to be affected by sex steroids. Therefore, targeting PHB may lead to a better understanding of the pathogenesis of obesity, diabetes and cancer.

Differences in Beef Quality between Angus (Bos taurus taurus) and Nellore (Bos taurus indicus) Cattle through a Proteomic and Phosphoproteomic Approach

Proteins are the major constituents of muscle and are key molecules regulating the metabolic changes during conversion of muscle to meat. Brazil is one of the largest exporters of beef and most Brazilian cattle are composed by zebu (Nellore) genotype. Bos indicus beef is generally leaner and tougher than Bos taurus such as Angus. The aim of this study was to compare the muscle proteomic and phosphoproteomic profile of Angus and Nellore. Seven animals of each breed previously subjected the same growth management were confined for 84 days. Proteins were extracted from Longissimus lumborum samples collected immediately after slaughter and separated by two-dimensional electrophoresis. Pro-Q Diamond stain was used in phosphoproteomics. Proteins identification was performed using matrix assisted laser desorption/ionization time-of-flight mass spectrometry. Tropomyosin alpha-1 chain, troponin-T, myosin light chain-1 fragment, cytoplasmic malate dehydrogenase, alpha-enolase and 78 kDa glucose-regulated protein were more abundant in Nellore, while myosin light chain 3, prohibitin, mitochondrial stress-70 protein and heat shock 70 kDa protein 6 were more abundant in Angus (P<0.05). Nellore had higher phosphorylation of myosin regulatory light chain-2, alpha actin-1, triosephosphate isomerase and 14-3-3 protein epsilon. However, Angus had greater phosphorylation of phosphoglucomutase-1 and troponin-T (P<0.05). Therefore, proteins involved in contraction and muscle organization, myofilaments expressed in fast or slow-twitch fibers and heat shock proteins localized in mitochondria or sarcoplasmic reticulum and involved in cell flux of calcium and apoptosis might be associated with differences in beef quality between Angus and Nellore. Furthermore, prohibitin appears to be a potential biomarker of intramuscular fat in cattle. Additionally, differences in phosphorylation of myofilaments and glycolytic enzymes could be involved with differences in muscle contraction force, susceptibility to calpain, apoptosis and postmortem glycolysis, which might also be related to differences in beef quality among Angus and Nellore.

Prohibitin overexpression improves myocardial function in diabetic cardiomyopathy

Prohibitin (PHB) is a highly conserved protein implicated in various cellular functions including proliferation, apoptosis, tumor suppression, transcription, and mitochondrial protein folding. However, its function in diabetic cardiomyopathy (DCM) is still unclear. In vivo, type 2 diabetic rat model was induced by using a high-fat diet and low-dose streptozotocin. Overexpression of the PHB protein in the model rats was achieved by injecting lentivirus carrying PHB cDNA via the jugular vein. Characteristics of type 2 DCM were evaluated by metabolic tests, echocardiography and histopathology. Rats with DCM showed severe insulin resistance, left ventricular dysfunction, fibrosis and apoptosis. PHB overexpression ameliorated the disease. Cardiofibroblasts (CFs) and H9c2 cardiomyoblasts were used in vitro to investigate the mechanism of PHB in altered function. In CFs treated with HG, PHB overexpression decreased expression of collagen, matrix metalloproteinase activity, and proliferation. In H9c2 cardiomyoblasts, PHB overexpression inhibited apoptosis induced by HG. Furthermore, the increased phosphorylation of extracellular signal–regulated kinase (ERK) 1/2 was significantly decreased and the inhibited phosphorylation of Akt was restored in DCM. Therefore, PHB may be a new therapeutic target for human DCM.

Prohibitin in Adipose and Immune Functions

Prohibitin (PHB) was discovered in a quest to find genes with antiproliferative functions. However, the attribute of PHB that is responsible for its antiproliferative function remains elusive. Meanwhile, recent studies have established PHB as a pleiotropic protein with roles in metabolism, immunity, and senescence. PHB has cell compartment-specific functions, acting as a scaffolding protein in mitochondria, an adaptor molecule in membrane signaling, and a transcriptional coregulator in the nucleus. However, it remains unclear whether different functions and locations of PHB are interrelated or independent from each other, or if PHB works in a tissue-specific manner. Here, we discuss new findings on the role of PHB in adipose-immune interaction and an unexpected role in sex differences in adipose and immune functions.

Prohibitin/annexin 2 interaction regulates fatty acid transport in adipose tissue

We have previously identified prohibitin (PHB) and annexin A2 (ANX2) as proteins interacting on the surface of vascular endothelial cells in white adipose tissue (WAT) of humans and mice. Here, we demonstrate that ANX2 and PHB also interact in adipocytes. Mice lacking ANX2 have normal WAT vascularization, adipogenesis, and glucose metabolism but display WAT hypotrophy due to reduced fatty acid uptake by WAT endothelium and adipocytes. By using cell culture systems in which ANX2/PHB binding is disrupted either genetically or through treatment with a blocking peptide, we show that fatty acid transport efficiency relies on this protein complex. We also provide evidence that the interaction between ANX2 and PHB mediates fatty acid transport from the endothelium into adipocytes. Moreover, we demonstrate that ANX2 and PHB form a complex with the fatty acid transporter CD36. Finally, we show that the colocalization of PHB and CD36 on adipocyte surface is induced by extracellular fatty acids. Together, our results suggest that an unrecognized biochemical interaction between ANX2 and PHB regulates CD36-mediated fatty acid transport in WAT, thus revealing a new potential pathway for intervention in metabolic diseases.

Prohibitin: an unexpected role in sex dimorphic functions

Sex differences are known to exist in adipose and immune functions in the body, and sex steroid hormones are known to be involved in sexually dimorphic biological and pathological processes related to adipose-immune interaction. However, our knowledge of proteins that mediate such differences is poor. Two novel obese mice models, Mito-Ob and m-Mito-Ob, that have been reported recently have revealed an unexpected role of a pleiotropic protein, prohibitin (PHB), in sex differences in adipose and immune functions. This discovery points towards a role of pleiotropic proteins and their potential interplay with sex steroid hormones in mediating sexually dimorphic adipose-immune interaction.

Prohibitin-induced, obesity-associated insulin resistance and accompanying low-grade inflammation causes NASH and HCC

Obesity increases the risk for nonalcoholic steatohepatitis (NASH) and hepatocarcinogenesis. However, the underlying mechanisms involved in the disease process remain unclear. Recently, we have developed a transgenic obese mouse model (Mito-Ob) by prohibitin mediated mitochondrial remodeling in adipocytes. The Mito-Ob mice develop obesity in a sex-neutral manner, but obesity-associated adipose inflammation and metabolic dysregulation in a male sex-specific manner. Here we report that with aging, the male Mito-Ob mice spontaneously develop obesity-linked NASH and hepatocellular carcinoma (HCC). In contrast, the female Mito-Ob mice maintained normal glucose and insulin levels and did not develop NASH and HCC. The anti-inflammatory peptide ghrelin was significantly upregulated in the female mice and down regulated in the male mice compared with respective control mice. In addition, a reduction in the markers of mitochondrial content and function was found in the liver of male Mito-Ob mice with NASH/HCC development. We found that ERK1/2 signaling was significantly upregulated whereas STAT3 signaling was significantly down regulated in the tumors from Mito-Ob mice. These data provide a proof-of-concept that the metabolic and inflammatory status of the adipose tissue and their interplay at the systemic and hepatic level play a central role in the pathogenesis of obesity-linked NASH and HCC.

Expression of a mutant prohibitin from the aP2 gene promoter leads to obesity-linked tumor development in insulin resistance-dependent manner

A critical unmet need for the study of obesity-linked cancer is the lack of preclinical models that spontaneously develop obesity and cancer sequentially. Prohibitin (PHB) is a pleiotropic protein that has a role in adipose and immune functions. We capitalized on this attribute of PHB to develop a mouse model for obesity-linked tumor. We achieved this by expressing Y114F-PHB (m-PHB) from the aP2 gene promoter for simultaneous manipulation of adipogenic and immune signaling functions. The m-PHB mice develop obesity in a sex-neutral manner, but only male mice develop impaired glucose homeostasis and hyperinsulinemia similar to transgenic mice expressing PHB. Interestingly, only male m-PHB mice develop histiocytosis with lymphadenopathy, suggesting that metabolic dysregulation or m-PHB alone is not sufficient for the tumor development and that both are required for tumorigenesis. Moreover, ovariectomy in female m-PHB mice resulted in impaired glucose homeostasis, hyperinsulinemia and consequently tumor development similar to male m-PHB mice. These changes were not observed in sham-operated control m-Mito-Ob mice, further confirming the role of obesity-related metabolic dysregulation in tumor development in m-PHB mice. Our data provide a proof-of-concept that obesity-associated hyperinsulinemia promotes tumor development by facilitating dormant mutant to manifest and reveals a sex-dimorphic role of PHB in adipose-immune interaction or immunometabolism. Targeting PHB may provide a unique opportunity for the modulation of immunometabolism in obesity, cancer and in immune diseases.