Prohibitin has an important role in adipocyte differentiation

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.

The Role of Epicardial Adipose Tissue-Derived MicroRNAs in the Regulation of Cardiovascular Disease: A Narrative Review

Cardiovascular diseases have been leading cause of death worldwide for many decades, and obesity has been acknowledged as a risk factor for cardiovascular diseases. In the present review, human epicardial adipose tissue-derived miRNAs reported to be differentially expressed under pathologic conditions are discussed and summarized. The results of the literature review indicate that some of the epicardial adipose tissue-derived miRNAs are believed to be cardioprotective, while some others show quite the opposite effects depending on the underlying pathologic conditions. Furthermore, they suggest that that the epicardial adipose tissue-derived miRNAs have great potential as both a diagnostic and therapeutic modality. Nevertheless, mainly due to highly limited availability of human samples, it is very difficult to make any generalized claims on a given miRNA in terms of its overall impact on the cardiovascular system. Therefore, further functional investigation of a given miRNA including, but not limited to, the study of its dose effect, off-target effects, and potential toxicity is required. We hope that this review can provide novel insights to transform our current knowledge on epicardial adipose tissue-derived miRNAs into clinically viable therapeutic strategies for preventing and treating cardiovascular diseases.

Adipocytolytic Polymer Nanoparticles for Localized Fat Reduction

The demand for body fat reduction is increasing. However, conventional lipolytic approaches fail to control adipose tissue reduction and cause severe side effects in adjacent nonadipose tissues. A strategy to specifically reduce subcutaneous fat using adipocytolytic polymer nanoparticles in a minimally invasive manner is reported here. The polymer nanoparticles are designed to generate carbon dioxide gas when selectively absorbed by adipocytes. The carbon dioxide gas generated within late endosomes/lysosomes induces adipocytolysis, thereby reducing the number of cells. Localized injection of the adipocytolytic nanoparticles substantially reduces subcutaneous fat in a high-fat diet-induced obese mouse model, without significant changes in hematological or serum biochemical parameters. The adipocytolytic efficacy of the nanoparticles is also evaluated in a porcine model. This strategy addresses the need to develop safe and effective adipocytolytic agents using functional polymer nanoparticles.

The function of prohibitins in mitochondria and the clinical potentials

Prohibitins (PHBs) are a class of highly evolutionarily conserved proteins that widely distribute in prokaryotes and eukaryotes. PHBs function in cell growth and proliferation or differentiation, regulating metabolism and signaling pathways. PHBs have different subcellular localization in eukaryotes, but they are mainly located in mitochondria. In the mitochondria, PHBs stabilize the structure of the mitochondrial membrane and regulate mitochondrial autophagy, mitochondrial dynamics, mitochondrial biogenesis and quality control, and mitochondrial unfolded protein response. PHBs has shown to be associated with many diseases, such as mitochondria diseases, cancers, infectious diseases, and so on. Some molecule targets of PHBs can interfere with the occurrence and development of diseases. Therefore, this review clarifies the functions of PHBs in mitochondria, and provides a summary of the potential values in clinics.

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.

Saturated Fatty Acid-Induced Impairment of Hepatic Lipid Metabolism Is Worsened by Prohibitin 1 Deficiency in Hepatocytes

Obesity-associated nonalcoholic fatty liver disease (NAFLD) is characterized by excessive intrahepatic lipid accumulation. Despite the increasing prevalence of NAFLD and obesity, the pathogenesis of NAFLD has not yet been clearly elucidated. Prohibitin 1 (PHB1) is mainly expressed in the inner membrane of mitochondria and is known to play an important role in hepatocyte proliferation and lipid metabolism. In this study, we investigated how PHB1 affects lipid metabolism in murine hepatocytes. To reduce the expression of PHB1, Phb1 small interfering RNA was transfected into normal murine hepatocytes (AML12), and the cells were treated with the saturated fatty acid (SFA), palmitic acid (PA), for 24 h. When PHB1 was inhibited, the cell viability decreased by ∼20%, and it was found that it diminished further after PA treatment in both control and peroxisome proliferator-activated receptor gamma (Ppar-γ) knockdown cell groups. Examination of the mRNA expression levels of key enzymes involved in lipid metabolism revealed that PHB1 led to increased stearoyl-coenzyme A desaturase-1 (Scd1) mRNA levels, which leads to an increase in the synthesis of triglycerides (TGs). It also activates the endoplasmic reticulum (ER) stress response through upregulating C/EBP homologous protein (Chop) mRNA levels. PPAR-γ, which has been reported to be upregulated in NAFLD patients, also showed elevated expression. The expression of carnitine palmitoyltransferase 1A, which is involved in the conversion of excess intracellular SFA to fatty acid by catabolism, was downregulated in the PHB1-deficient group. Furthermore, TG synthesis was further promoted by a marked increase in SCD1 mRNA levels, which was further exacerbated by elevated Chop mRNA levels and Ppar-γ disruption. Taken together, PHB1 deficiency led to altered lipid metabolism, resulting in the increased intracellular lipid accumulation and ER stress. These cytotoxic effects were shown to be further exacerbated by excessive PA treatment.

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.

The Combined Partial Knockdown of CBS and MPST Genes Induces Inflammation, Impairs Adipocyte Function-Related Gene Expression and Disrupts Protein Persulfidation in Human Adipocytes

Recent studies in mice and humans demonstrated the relevance of H₂S synthesising enzymes, such as CTH, CBS, and MPST, in the physiology of adipose tissue and the differentiation of preadipocyte into adipocytes. Here, our objective was to investigate the combined role of CTH, CBS, and MPST in the preservation of adipocyte protein persulfidation and adipogenesis. Combined partial CTH, CBS, and MPST gene knockdown was achieved treating fully human adipocytes with siRNAs against these transcripts (siRNA_MIX). Adipocyte protein persulfidation was analyzed using label-free quantitative mass spectrometry coupled with a dimedone-switch method for protein labeling and purification. Proteomic analysis quantified 216 proteins with statistically different levels of persulfidation in KD cells compared to control adipocytes. In fully differentiated adipocytes, CBS and MPST mRNA and protein levels were abundant, while CTH expression was very low. It is noteworthy that siRNA_MIX administration resulted in a significant decrease in CBS and MPST expression, without impacting on CTH. The combined partial knockdown of the CBS and MPST genes resulted in reduced cellular sulfide levels in parallel to decreased expression of relevant genes for adipocyte biology, including adipogenesis, mitochondrial biogenesis, and lipogenesis, but increased proinflammatory- and senescence-related genes. It should be noted that the combined partial knockdown of CBS and MPST genes also led to a significant disruption in the persulfidation pattern of the adipocyte proteins. Although among the less persulfidated proteins, we identified several relevant proteins for adipocyte adipogenesis and function, among the most persulfidated, key mediators of adipocyte inflammation and dysfunction as well as some proteins that might play a positive role in adipogenesis were found. In conclusion, the current study indicates that the combined partial elimination of CBS and MPST (but not CTH) in adipocytes affects the expression of genes related to the maintenance of adipocyte function and promotes inflammation, possibly by altering the pattern of protein persulfidation in these cells, suggesting that these enzymes were required for the functional maintenance of adipocytes.

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

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.

Peptide Adjuvant to Invigorate Cytolytic Activity of NK Cells in an Obese Mouse Cancer Model

Cancer patients who are overweight compared to those with normal body weight have obesity-associated alterations of natural killer (NK) cells, characterized by poor cytotoxicity, slow proliferation, and inadequate anti-cancer activity. Concomitantly, prohibitin overexpressed by cancer cells elevates glucose metabolism, rendering the tumor microenvironment (TME) more tumor-favorable, and leading to malfunction of immune cells present in the TME. These changes cause vicious cycles of tumor growth. Adoptive immunotherapy has emerged as a promising option for cancer patients; however, obesity-related alterations in the TME allow the tumor to bypass immune surveillance and to down-regulate the activity of adoptively transferred NK cells. We hypothesized that inhibiting the prohibitin signaling pathway in an obese model would reduce glucose metabolism of cancer cells, thereby changing the TME to a pro-immune microenvironment and restoring the cytolytic activity of NK cells. Priming tumor cells with an inhibitory the prohibitin-binding peptide (PBP) enhances cytokine secretion and augments the cytolytic activity of adoptively transferred NK cells. NK cells harvested from the PBP-primed tumors exhibit multiple markers associated with the effector function of active NK cells. Our findings suggest that PBP has the potential as an adjuvant to enhance the cytolytic activity of adoptively transferred NK cells in cancer patients with obesity.

The Expanding Role of Mitochondria, Autophagy and Lipophagy in Steroidogenesis

The fundamental framework of steroidogenesis is similar across steroidogenic cells, especially in initial mitochondrial steps. For instance, the START domain containing protein-mediated cholesterol transport to the mitochondria, and its conversion to pregnenolone by the enzyme P450scc, is conserved across steroidogenic cells. The enzyme P450scc localizes to the inner mitochondrial membrane, which makes the mitochondria essential for steroidogenesis. Despite this commonality, mitochondrial structure, number, and dynamics vary substantially between different steroidogenic cell types, indicating implications beyond pregnenolone biosynthesis. This review aims to focus on the growing roles of mitochondria, autophagy and lipophagy in cholesterol uptake, trafficking and homeostasis in steroidogenic cells and consequently in steroidogenesis. We will focus on these aspects in the context of the physiological need for different steroid hormones and cell-intrinsic inherent features in different steroidogenic cell types beyond mitochondria as a mere site for the beginning of steroidogenesis. The overall goal is to provide an authentic and comprehensive review on the expanding role of steroidogenic cell-intrinsic processes in cholesterol homeostasis and steroidogenesis, and to bring attention to the scientific community working in this field on these promising advancements. Moreover, we will discuss a novel mitochondrial player, prohibitin, and its potential role in steroidogenic mitochondria and cells, and consequently, in steroidogenesis.

A novel dual-targeted rosiglitazone-loaded nanoparticle for the prevention of diet-induced obesity via the browning of white adipose tissue

Adipose tissue in the body is classified as white adipose tissue (WAT); a fat-accumulating tissue, or brown adipose tissue (BAT); an energy-dissipating tissue. Transforming WAT-to-BAT (browning) is a promising strategy for the treatment of obesity, since it would lead to an increase in energy expenditure. Rosiglitazone (Rosi), an agonist of the peroxisome proliferator-activated receptor γ (PPARγ), is known to be a potent browning inducer in subcutaneous WAT. However, the effectiveness of Rosi has been quite limited because of several off-target effects. The objective of this study was to develop locally administered Rosi-loaded nanoparticles (Rs-NPs) with the ability to target adipocytes to achieve the adipose tissue-specific activation of PPARγ, thus causing the browning of WAT. We prepared dual targeted Rs-NPs that were modified with a specific peptide that targets prohibitin that are expressed in adipocytes, and a cell penetrating peptide for enhancing cellular uptake and controlling intracellular trafficking. The Rs-NPs modified with a single ligand were internalized into mature adipocytes and induced browning activity in vitro but they failed to significantly affect the body weight of the diet-induced obese mice model. The dual-targeted Rs-NPs induced a strong browning activity, both in vitro and in vivo, and successfully inhibited the progression of obesity, as evidenced by the shrinkage of hypertrophied adipocytes without any detectable systemic adverse effects. Meanwhile, free Rosi aggravated hepatic steatosis and did not cause adipose tissue browning nor the inhibition of body weight gain. We conclude that the increased energy expenditure via adipose tissue browning using dual-targeted Rs-NP is a promising strategy for the treatment of obesity and its related metabolic syndrome.

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.

Cholix toxin, an eukaryotic elongation factor 2 ADP-ribosyltransferase, interacts with Prohibitins and induces apoptosis with mitochondrial dysfunction in human hepatocytes

Vibrio cholerae produced-Cholix toxin (Cholix) is a cytotoxin that ADP-ribosylates eukaryotic elongation factor 2, inhibiting protein synthesis, and inducing apoptosis. Here, we identified prohibitin (PHB) 1 and 2 as novel Cholix-interacting membrane proteins in immortalised human hepatocytes and HepG2 cells by Cholix immunoprecipitation assays. The expression level of PHB1 was decreased by Cholix after a 12hr incubation. Cholix-induced poly (ADP-ribose) polymerase (PARP) cleavage was significantly enhanced in PHB (PHB1 or PHB2) knockdown cells. In contrast, transiently overexpressed PHB in hepatocytes attenuated Cholix-induced Bax/Bak conformational changes and PARP cleavage. In addition, Cholix-induced reactive oxygen species production and accumulation of fragmented mitochondria were enhanced in PHB-knockdown cells. Furthermore, Cholix induced activation of Rho-associated coiled coil-containing protein kinase 1 (ROCK1), which was enhanced in PHB-knockdown cells, followed by actin filament depolymerisation and accumulation of tubulin in the blebbing cells. Inhibition of ROCK1 by siRNA or its inhibitor suppressed Cholix-induced PARP cleavage and reactive oxygen species generation. Our findings identify PHB as a new protein that interacts with Cholix and is involved in Cholix-induced mitochondrial dysfunction and cytoskeletal rearrangement by ROCK1 activation during apoptosis.

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.

The hypolipidemic effects of peptides prepared from Cicer arietinum in ovariectomized rats and HepG2 cells

BACKGROUND

The lack of estrogen in postmenopausal women is a key risk factor for disorders of lipid metabolism and for obesity. Except in cases where estrogen replacement therapy (ERT) is being used, chickpea peptides (ChPs) may be a potential candidate for treating hyperlipidemia.

RESULTS

In ovariectomized rats model, ChPs were found to decrease body weight, adipose tissue size, total cholesterol (TC), total triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and the atherogenic index (AI) in serum and liver TC and TG. Serum high-density lipoprotein cholesterol (HDL-C), bile acids in liver and feces, fecal TC and TG were observed to increase significantly (P < 0.05). ChPs play a role in inhibiting the activities of fatty acid synthetase (FAS) and HMG-CoA reductase (HMGR). The expression of peroxisome proliferator-activated receptors (PPAR)γ and sterol regulatory element-binding protein (SREBP)-1c were downregulated and the expression of liver X receptor (LXR) α, estrogen receptor(ER)α and ERβ were upregulated by ChPs. In HepG2 cell experiments, the cellular TC levels decreased and the uptake of NBD-cholesterol increased significantly after treatment with Mw < 1 kDa and Mw < 5 kDa ChPs fractions. Val-Phe-Val-Arg-Asn (VFVRN) could inhibit TC biosynthesis by decreasing the expression of HMGR.

CONCLUSION

We demonstrated that ChPs could effectively regulate lipid metabolism disorders and restrain obesity caused by estrogen deficiency. Val-Phe-Val-Arg-Asn identified from ChPs could reduce the expression of HMGR to inhibit cholesterol biosynthesis. © 2018 Society of Chemical Industry.

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.

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.

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 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.

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.

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

Adipocytes are the primary cells in the body that store excess energy as triglycerides. To perform this specialized function, adipocytes rely on their mitochondria; however, the role of adipocyte mitochondria in the regulation of adipose tissue homeostasis and its impact on metabolic regulation is not understood. We developed a transgenic mouse model, Mito-Ob, overexpressing prohibitin (PHB) in adipocytes. Mito-Ob mice developed obesity due to upregulation of mitochondrial biogenesis in adipocytes. Of note, Mito-Ob female mice developed more visceral fat than male mice. However, female mice exhibited no change in glucose homeostasis and had normal insulin and high adiponectin levels, whereas male mice had impaired glucose homeostasis, compromised brown adipose tissue structure, and high insulin and low adiponectin levels. Mechanistically, we found that PHB overexpression enhances the cross talk between the mitochondria and the nucleus and facilitates mitochondrial biogenesis. The data suggest a critical role of PHB and adipocyte mitochondria in adipose tissue homeostasis and reveal sex differences in the effect of PHB-induced adipocyte mitochondrial remodeling on whole-body metabolism. Targeting adipocyte mitochondria may provide new therapeutic opportunities for the treatment of obesity, a major risk factor for type 2 diabetes.

Mitochondria in metabolic disease: getting clues from proteomic studies

Mitochondria play a key role as major regulators of cellular energy homeostasis, but in the context of mitochondrial dysfunction, mitochondria may generate reactive oxidative species and induce cellular apoptosis. Indeed, altered mitochondrial status has been linked to the pathogenesis of several metabolic disorders and specially disorders related to insulin resistance, such as obesity, type 2 diabetes, and other comorbidities comprising the metabolic syndrome. In the present review, we summarize information from various mitochondrial proteomic studies of insulin-sensitive tissues under different metabolic states. To that end, we first focus our attention on the pancreas, as mitochondrial malfunction has been shown to contribute to beta cell failure and impaired insulin release. Furthermore, proteomic studies of mitochondria obtained from liver, muscle, and adipose tissue are summarized, as these tissues constitute the primary insulin target metabolic tissues. Since recent advances in proteomic techniques have exposed the importance of PTMs in the development of metabolic disease, we also present information on specific PTMs that may directly affect mitochondria during the pathogenesis of metabolic disease. Specifically, mitochondrial protein acetylation, phosphorylation, and other PTMs related to oxidative damage, such as nitrosylation and carbonylation, are discussed.

Characterization of PHB1 and its role in mitochondrial maturation and yolk platelet degradation during development of Artemia embryos

BACKGROUND

To cope with harsh environments, crustaceans such as Artemia produce diapause gastrula embryos (cysts) with suppressed metabolism. Metabolism and development resume during post-diapause development, but the mechanism behind these cellular events remains largely unknown.

PRINCIPAL FINDING

Our study investigated the role of prohibitin 1 (PHB1) in metabolic reinitiation during post-diapause development. We found that PHB1 was developmentally regulated via changes in phosphorylation status and localization. Results from RNA interference experiments demonstrated PHB1 to be critical for mitochondrial maturation and yolk degradation during development. In addition, PHB1 was present in yolk platelets, and it underwent ubiquitin-mediated degradation during the proteolysis of yolk protein.

CONCLUSIONS/SIGNIFICANCE

PHB1 has an indispensable role in coordinating mitochondrial maturation and yolk platelet degradation during development in Artemia. This novel function of PHB1 provides new clues to comprehend the roles of PHB1 in metabolism and development.

Regulation of Adipocyte Differentiation via MicroRNAs

Adipocyte differentiation, termed adipogenesis, is a complicated process in which pluripotent mesenchymal stem cells differentiate into mature adipocytes. The process of adipocyte differentiation is tightly regulated by a number of transcription factors, hormones and signaling pathway molecules. Recent studies have demonstrated that microRNAs, which belong to small noncoding RNA species, are also involved in adipocyte differentiation. In vivo and in vitro studies have revealed that various microRNAs affect adipogenesis by targeting several adipogenic transcription factors and key signaling molecules. In this review, we will summarize the roles of microRNAs in adipogenesis and their target genes associated with each stage of adipocyte differentiation.

MicroRNA-27 (miR-27) targets prohibitin and impairs adipocyte differentiation and mitochondrial function in human adipose-derived stem cells

Prohibitin (PHB) has been reported to play a crucial role in adipocyte differentiation and mitochondrial function. However, the regulative mechanism of PHB during adipogenesis remains unclear. In this study, we determined that the levels of both microRNA (miR)-27a and miR-27b were down-regulated following adipogenic induction of human adipose-derived stem cells, whereas the mRNA level of PHB was up-regulated. Overexpression of miR-27a or miR-27b inhibited PHB expression and adipocyte differentiation. Using PHB 3'-UTR luciferase reporter assay, we observed that miR-27a and miR-27b directly targeted PHB in human adipose-derived stem cells. A compensation of PHB partially restored the adipogenesis inhibited by miR-27. Moreover, we demonstrated the novel finding that ectopic expression of miR-27a or miR-27b impaired mitochondrial biogenesis, structure integrity, and complex I activity accompanied by excessive reactive oxygen species production. Our data suggest that miR-27 is an anti-adipogenic microRNA partly by targeting PHB and impairing mitochondrial function. Pharmacological modulation of miR-27 function may provide a new therapeutic strategy for the treatment of obesity.

Investigation of adipocyte proteome during the differentiation of brown preadipocytes

Brown adipocytes oxidize fatty acids to produce heat in response to cold or caloric overfeeding. The motivation and function of the development of brown fat may thus counteract obesity, though this remains uncertain. We investigated the brown adipocyte proteome by two-dimensional gel electrophoresis followed by mass spectrometry. Comparative analyses of proteins focused on total protein spots to filter differentially expressed proteins during the differentiation of mouse primary brown preadipocytes. A Western blot analysis was performed to verify the target proteins. The results indicated that 10 protein spots were differentially expressed with significant changes, including the three up-regulated proteins of prohibitin, hypoxanthine-guanine phosphoribosyltransferase, and enoyl-CoA hydratase protein; the 5 down-regulated proteins of triosephosphate isomerase, elongation factor 2, α-tropomyosin slow, endophilin-B1, and cofilin-1 (CFL1); and the two unequivocally expressed proteins of peroxiredoxin-1 and collagen α-1(i) chain precursor. We found that during brown adipogenesis, CFL1 has an inhibitory effect on brown adipocyte differentiation. The overexpression of CFL1 inhibited the brown fat deposition and repressed the brown marker genes UCP1, PRDM16, PGC-1α and PPARγ via actin dynamics and polymerization. These observations may be novel findings that bring new insight into the detailed mechanisms of brown adipogenesis and identify possible therapeutic targets for anti-obesity.

BIOLOGICAL SIGNIFICANCE

We use 2-DE to compare the proteomes of adipocytes during the brown adipogenesis of primary mouse preadipocytes. We identified 10 proteins that are differentially expressed. Among these, we found that the actin binding protein CFL1 inhibits the differentiation of brown preadipocytes. CFL1 overexpressing cells showed lower deposition of brown fat droplets, and the brown marker genes of UCP1, PRDM16, PGC-1α and PPARγ were decreased through actin dynamics and polymerization.

Prohibitin ligands in cell death and survival: mode of action and therapeutic potential

Prohibitins (PHBs) are scaffold proteins that modulate many signaling pathways controlling cell survival, metabolism, and inflammation. Several drugs that target PHBs have been identified and evaluated for various clinical applications. Preclinical and clinical studies indicate that these PHB ligands may be useful in oncology, cardiology, and neurology, as well as against obesity. This review covers the physiological role of PHBs in health and diseases and current developments concerning PHB ligands.

Prohibitin-2 binding modulates insulin-like growth factor-binding protein-6 (IGFBP-6)-induced rhabdomyosarcoma cell migration

Insulin-like growth factor (IGF)-binding protein (IGFBP)-6 decreases cancer cell proliferation and survival by inhibiting the effects of IGF-II. More recently, IGFBP-6 was found to promote the migration of rhabdomyosarcoma (RMS) cells in an IGF-independent manner, and MAPK pathways were involved in this process. However, the precise molecular mechanisms of these IGF-independent migratory actions of IGFBP-6 are largely unknown. Here, we report that prohibitin-2 (PHB2), a single-span membrane protein, is a key regulator of IGFBP-6-induced RMS cell migration. PHB2 and IGFBP-6 co-localize on the RMS cell surface, and they specifically interact, as demonstrated by affinity chromatography, co-immunoprecipitation, biosensor analysis, and confocal microscopy. Binding affinities for PHB2 are 9.0 ± 1.0 nM for IGFBP-6 and 10.2 ± 0.5 nM for mIGFBP-6, a non-IGF-binding mutant of IGFBP-6. The C-domain but not the N-domain of IGFBP-6 is involved in PHB2 binding. In addition, IGFBP-6 indirectly increases PHB2 tyrosine phosphorylation on RMS membranes. Importantly, PHB2 knockdown completely abolished IGFBP-6-mediated RMS cell migration. In contrast, IGFBP-6-induced MAPK pathway activation was not affected, suggesting that PHB2 may act as a downstream effector of these pathways. These results indicate that PHB2 plays a key role in this IGF-independent action of IGFBP-6 and suggest a possible therapeutic target for RMS.

Follicular stage-dependent regulation of apoptosis and steroidogenesis by prohibitin in rat granulosa cells

BACKGROUND

Follicular growth and atresia are tightly regulated processes, which involve the participation of endocrine, autocrine and paracrine factors at the cellular level. Prohibitin (PHB) is a multifunctional intracellular protein playing an important role in the regulation of proliferation, apoptosis and differentiation. Here we examined the expression of PHB and its regulation by FSH in vitro and studied the role of PHB in the regulation of apoptosis and steroidogenesis in response to the apoptosis inducer staurosporine (STS) and to FSH, respectively.

METHODS

Undifferentiated and differentiated granulosa cells were collected from diethylstilbestrol (DES)- and equine chronic gonadotropin (eCG)-primed immature rats, respectively and then cultured with various treatments (FSH, adenovirus infection, STS) according to experimental design. The apoptosis rate, the production of estradiol and progesterone, and the expression of distinct proteins (PHB, caspase-3, phospho- and total Akt) were assessed.

RESULTS

PHB is anti-apoptotic and its action is dependent on the differentiated state of the granulosa cells. Data from gain- and loss-of-function experiments demonstrate that PHB inhibited STS-induced caspase-3 cleavage and apoptosis in undifferentiated granulosa cells, but was ineffective in differentiated cells. In contrast, PHB suppresses FSH-induced steroidogenesis and this response is evident irrespective of the differentiated state of granulosa cells.

CONCLUSION

These findings suggest that PHB regulates granulosa cell apoptosis and steroidogenesis in a follicular stage-dependent manner and that the dysregulation of PHB expression and action may be relevant to ovarian dysfunction.

Inhibitory roles of prohibitin and chemerin in FSH-induced rat granulosa cell steroidogenesis

Follicular differentiation is a tightly regulated process involving various endocrine, autocrine, and paracrine factors. The biosynthesis of progesterone and estradiol in response to FSH involves the regulation of multiple steroidogenic enzymes, such as p450 cholesterol side-chain cleavage enzyme and aromatase. Here we demonstrated that prohibitin (PHB), a multifunctional protein, inhibits FSH-induced progesterone and estradiol secretion in rat granulosa cells. The mRNA abundances of cyp11a (coding p450 cholesterol side-chain cleavage enzyme) and cyp19 (coding aromatase) were also suppressed by PHB in a time-dependent manner. It is known that a novel adipokine chemerin suppresses FSH-induced steroidogenesis in granulosa cells. Chemerin up-regulates the content of PHB, and PHB knockdown attenuates the suppressive role of chemerin on steroidogenesis. In addition, inhibition of phosphatidylinositol 3-kinase/Akt pathway enhances the suppressive action of PHB, whereas expression of constitutively active Akt attenuates this response. These findings suggest that PHB is a novel negative regulator of FSH-induced steroidogenesis, and its action with chemerin may contribute to the dysregulation of steroidogenesis in the pathogenesis of polycystic ovarian syndrome.

Signaling pathways of prohibitin and its role in diseases

Prohibitin (PHB), appearing to be a negative regulator of cell proliferation and to be a tumor suppressor, has been connected to diverse cellular functions including cell cycle control, senescence, apoptosis and the regulation of mitochondrial activities. It is a growth regulatory gene that has pleiotropic functions in the nucleus, mitochondria and cytoplasmic compartments. However, in different tissues/cells, the expression of PHB was different, such as that it was increased in most of the cancers, but its expression was reduced in kidney diseases. Signaling pathways might be very important in the pathogenesis of diseases. This review was performed to provide a relatively complete signaling pathways flowchart for PHB to the investigators who were interested in the roles of PHB in the pathogenesis of diseases. Here, we review the signal transduction pathways of PHB and its role in the pathogenesis of diseases.

Temporal analysis of protein lysine acetylation during adipocyte differentiation

The post-translational modification of protein by acetylation has been emerging as a prevalent modification in enzymes that catalyze intermediary metabolism. However, the dynamics of protein acetylation during adipocyte differentiation that involves a major shift in cellular metabolism is not known. In this study, we investigated the temporal changes in acetylation during adipocyte differentiation. Almost all acetylated proteins identified showed a sequential change in acetylation during the differentiation process. While the majority of the acetylated proteins showed a sequential upregulation during adipocyte differentiation, in a few proteins a sequential downregulation of protein acetylation was also observed. Our findings suggest that a wide-ranging temporal change in protein acetylation occurs during adipocyte differentiation including differentially expressed proteins signifying an important role in adipocyte differentiation.

Explore the Molecular Mechanism of Apoptosis Induced by Tanshinone IIA on Activated Rat Hepatic Stellate Cells

Since the activated hepatic stellate cell (HSC) is the predominant event in the progression of liver fibrosis, selective clearance of HSC should be a potential strategy in therapy. Salvia miltiorrhiza roots ethanol extract (SMEE) remarkably ameliorates liver fibrogenesis in DMN-administrated rat model. Next, tanshinone IIA (Tan IIA), the major compound of SMEE, significantly inhibited rat HSC viability and led to cell apoptosis. Proteome tools elucidated that increased prohibitin is involved in cell cycle arrest under Tan IIA is the treatment while knockdown of prohibitin could attenuate Tan IIA-induced apoptosis. In addition, Tan IIA mediated translocation of C-Raf which interacted with prohibitin activating MAPK and inhibiting AKT signaling in HSC. MAPK antagonist suppressed ERK phosphorylation which was necessary for Tan IIA-induced expression of Bax and cytochrome c. PD98059 also abolished Tan IIA-modulated cleavage of PARP. Our findings suggested that Tan IIA could contribute to apoptosis of HSC by promoting ERK-Bax-caspase pathways through C-Raf/prohibitin complex.

Lentiviral vector-mediated RNA interference targeted against prohibitin inhibits apoptosis of the retinoic acid-resistant acute promyelocytic leukemia cell line NB4-R1

To investigate the possibility of prohibitin (PHB) inhibition by lentiviral vector-mediated RNA interference (RNAi) and its influence on cell apoptosis in the retinoic acid-resistant acute promyelocytic leukemia cell line NB4-R1, a lentiviral vector encoding a short hairpin RNA (shRNA) targeted against PHB (pGCSIL-GFP-PHB) was constructed and transfected into the packaging cells 293T, and the viral supernatant was collected to transfect NB4-R1 cells. Quantitative real-time fluorescent PCR and western blotting were used to detect the expression levels of PHB. Flow cytometry and detection of enzymatic activity of caspase-3 by western blotting were employed to examine cell apoptosis. Our results provide evidence that the lentiviral vector pGCSIL-GFP-PHB was constructed successfully, and the PHB mRNA and the protein expression inhibitory rates were 90.3 and 95.8%, respectively. When compared to the control group, the activity of caspase-3 decreased significantly, which showed a 57.3% downregulation, and the apoptosis rate was reduced by 44.6% (P<0.05). In conclusion, downregulation of the PHB gene may inhibit apoptosis of NB4-R1 cells, and it is speculated that this was at least partly due to the downregulation of caspase-3, and PHB may be a novel target for gene therapy for retinoic acid-resistant acute promyelocytic leukemia.

Phosphorylation of transglutaminase 2 (TG2) at serine-216 has a role in TG2 mediated activation of nuclear factor-kappa B and in the downregulation of PTEN

Background

Transglutaminase 2 (TG2) and its phosphorylation have been consistently found to be upregulated in a number of cancer cell types. At the molecular level, TG2 has been associated with the activation of nuclear factor-kappa B (NF-κB), protein kinase B (PKB/Akt) and in the downregulation of phosphatase and tensin homologue deleted on chromosome 10 (PTEN). However, the underlying mechanism involved is not known. We have reported that protein kinase A (PKA) induced phosphorylation of TG2 at serine-216 (Ser²¹⁶) regulates TG2 function and facilitates protein-protein interaction. However, the role of TG2 phosphorylation in the modulation of NF-κB, Akt and PTEN is not explored.

Methods

In this study we have investigated the effect of TG2 phosphorylation on NF-κB, Akt and PTEN using embryonic fibroblasts derived from TG2 null mice (MEF^tg2-/-) overexpressing native TG2 or mutant-TG2 (m-TG2) lacking Ser²¹⁶ phosphorylation site with and without dibutyryl cyclic-AMP (db-cAMP) stimulation. Functional consequences on cell cycle and cell motility were determined by fluorescence activated cell sorting (FACS) analysis and cell migration assay respectively.

Results

PKA activation in TG2 overexpressing MEF^tg2-/- cells resulted in an increased activation of NF-κB and Akt phosphorylation in comparison to empty vector transfected control cells as determined by the reporter-gene assay and immunoblot analysis respectively. These effects were not observed in MEF^tg2-/- cells overexpressing m-TG2. Similarly, a significant downregulation of PTEN at both, the mRNA and protein levels were found in cells overexpressing TG2 in comparison to empty vector control and m-TG2 transfected cells. Furthermore, Akt activation correlated with the simultaneous activation of NF-κB and a decrease in PTEN suggesting that the facilitatory effect of TG2 on Akt activation occurs in a PTEN-dependent manner. Similar results were found with MCF-7 and T-47D breast cancer cells overexpressing TG2 and m-TG2 further supporting the role of TG2 phosphorylation in NF-κB activation and in the downregulation of PTEN.

Conclusions

Collectively, these data suggest that phosphorylation of TG2 at Ser²¹⁶ plays a role in TG2 mediated activation of NF-κB, Akt and in the downregulation of PTEN. Blocking TG2 phosphorylation may provide a novel strategy to attenuate NF-κB activation and downregulation of PTEN in TG2 overexpressing cancers.