Human leptin activates PI3K and MAPK pathways in human peripheral blood mononuclear cells: possible role of Sam68

Leptin and Leptin Signaling in Multiple Sclerosis: A Narrative Review

Obesity, a pandemic health problem, is now considered as a chronic inflammatory state, related to many autoimmune diseases, such as multiple sclerosis. Thus, adipokines, inflammatory mediators secreted by adipose tissue, play an important role modulating the immune response. In this context, obesity, especially during adolescent age, seems to be a key factor for the development of multiple sclerosis. Leptin, the main pro-inflammatory adipokine secreted by the adipose tissue, has been found increased in patients with multiple sclerosis and is able to regulate the immune system promoting a pro-inflammatory response. Leptin signaling in both innate and adaptative immune cells might have immunomodulatory effects in the context of multiple sclerosis. In this way, leptin has been found to produce a Th1 and Th17 response, increasing M1 macrophages and decreasing regulatory T cells and Th2 response. Moreover, circulating inflammatory adipokines, such as leptin, have been found in people with multiple sclerosis. In the present work, we are reviewing literature to update the body of knowledge regarding the role of obesity and leptin in multiple sclerosis.

Leveraging altered lipid metabolism in treating B cell malignancies

B cell malignancies, comprising over 80 heterogeneous blood cancers, pose significant prognostic challenges due to intricate oncogenic signaling. Emerging evidence emphasizes the pivotal role of disrupted lipid metabolism in the development of these malignancies. Variations in lipid species, such as phospholipids, cholesterol, sphingolipids, and fatty acids, are widespread across B cell malignancies, contributing to uncontrolled cell proliferation and survival. Phospholipids play a crucial role in initial signaling cascades leading to B cell activation and malignant transformation through constitutive B cell receptor (BCR) signaling. Dysregulated cholesterol and sphingolipid homeostasis support lipid raft integrity, crucial for propagating oncogenic signals. Sphingolipids impact malignant B cell stemness, proliferation, and survival, while glycosphingolipids in lipid rafts modulate BCR activation. Additionally, cancer cells enhance fatty acid-related processes to meet heightened metabolic demands. In obese individuals, the obesity-derived lipids and adipokines surrounding adipocytes rewire lipid metabolism in malignant B cells, evading cytotoxic therapies. Genetic drivers such as MYC translocations also intrinsically alter lipid metabolism in malignant B cells. In summary, intrinsic and extrinsic factors converge to reprogram lipid metabolism, fostering aggressive phenotypes in B cell malignancies. Therefore, targeting altered lipid metabolism has translational potential for improving risk stratification and clinical management of diverse B cell malignancy subtypes.

SAM68 directs STING signaling to apoptosis in macrophages

DNA is a danger signal sensed by cGAS to engage signaling through STING to activate innate immune functions. The best-studied downstream responses to STING activation include expression of type I interferon and inflammatory genes, but STING also activates other pathways, including apoptosis. Here, we report that STING-dependent induction of apoptosis in macrophages occurs through the intrinsic mitochondrial pathway and is mediated via IRF3 but acts independently of gene transcription. By intersecting four mass spectrometry datasets, we identify SAM68 as crucial for the induction of apoptosis downstream of STING activation. SAM68 is essential for the full activation of apoptosis. Still, it is not required for STING-mediated activation of IFN expression or activation of NF-κB. Mechanistic studies reveal that protein trafficking is required and involves SAM68 recruitment to STING upon activation, with the two proteins associating at the Golgi or a post-Golgi compartment. Collectively, our work identifies SAM68 as a STING-interacting protein enabling induction of apoptosis through this DNA-activated innate immune pathway.

Sam68 is a druggable vulnerability point in cancer stem cells

Sam68 (Src associated in mitosis of 68 kDa) is an RNA-binding and multifunctional protein extensively characterized in numerous cellular functions, such as RNA processing, cell cycle regulation, kinase- and growth factor signaling. Recent investigations highlighted Sam68 as a primary target of a class of reverse-turn peptidomimetic drugs, initially developed as inhibitors of Wnt/β-catenin mediated transcription. Further investigations on such compounds revealed their capacity to selectively eliminate cancer stem cell (CSC) activity upon engaging Sam68. This work highlighted previously unappreciated roles for Sam68 in the maintenance of neoplastic self-renewal and tumor-initiating functions. Here, we discuss the implication of Sam68 in tumorigenesis, where central findings support its contribution to chromatin regulation processes essential to CSCs. We also review advances in CSC-targeting drug discovery aiming to modulate Sam68 cellular distribution and protein-protein interactions. Ultimately, Sam68 constitutes a vulnerability point of CSCs and an attractive therapeutic target to impede neoplastic stemness in human tumors.

Role of Leptin in Obesity, Cardiovascular Disease, and Type 2 Diabetes

Diabetes mellitus (DM) is a highly prevalent disease worldwide, estimated to affect 1 in every 11 adults; among them, 90-95% of cases are type 2 diabetes mellitus. This is partly attributed to the surge in the prevalence of obesity, which has reached epidemic proportions since 2008. In these patients, cardiovascular (CV) risk stands as the primary cause of morbidity and mortality, placing a substantial burden on healthcare systems due to the potential for macrovascular and microvascular complications. In this context, leptin, an adipocyte-derived hormone, plays a fundamental role. This hormone is essential for regulating the cellular metabolism and energy balance, controlling inflammatory responses, and maintaining CV system homeostasis. Thus, leptin resistance not only contributes to weight gain but may also lead to increased cardiac inflammation, greater fibrosis, hypertension, and impairment of the cardiac metabolism. Understanding the relationship between leptin resistance and CV risk in obese individuals with type 2 DM (T2DM) could improve the management and prevention of this complication. Therefore, in this narrative review, we will discuss the evidence linking leptin with the presence, severity, and/or prognosis of obesity and T2DM regarding CV disease, aiming to shed light on the potential implications for better management and preventive strategies.

Sam68 promotes osteogenic differentiation of aortic valvular interstitial cells by TNF-α/STAT3/autophagy axis

Calcified aortic valve disease (CAVD) is a major non-rheumatic heart valve disease in the world, with a high mortality rate and without suitable pharmaceutical therapy due to its complex mechanisms. Src-associated in mitosis 68-KD (Sam68), an RNA binding protein, has been reported as a signaling adaptor in numerous signaling pathways (Huot in Mol Cell Biol, 29(7), 1933-1943, 2009), particularly in inflammatory signaling pathways. The effects of Sam68 on the osteogenic differentiation process of hVICs and its regulation on signal transducer and activator of transcription 3 (STAT3) signaling pathway have been investigated in this study. Human aortic valve samples detection found that Sam68 expression was up-regulated in human calcific aortic valves. We used tumor necrosis factor α (TNF-α) as an activator for osteogenic differentiation in vitro and the result indicated that Sam68 was highly expressed after TNF-α stimulation. Overexpression of Sam68 promoted osteogenic differentiation of hVICs while Sam68 knockdown reversed this effect. Sam68 interaction with STAT3 was predicted by using String database and was verified in this study. Sam68 knockdown reduced phosphorylation of STAT3 activated by TNF-α and the downstream gene expression, which further influenced autophagy flux in hVICs. STAT3 knockdown alleviated the osteogenic differentiation and calcium deposition promoted by Sam68 overexpression. In conclusion, Sam68 interacts with STAT3 and participates in its phosphorylation to promote osteogenic differentiation of hVICs to induce valve calcification. Thus, Sam68 may be a new therapeutic target for CAVD. Regulatory of Sam68 in TNF-α/STAT3/Autophagy Axis in promoting osteogenesis of hVICs.

Obesity and Risk for Lymphoma: Possible Role of Leptin

Obesity, which is considered a pandemic due to its high prevalence, is a risk factor for many types of cancers, including lymphoma, through a variety of mechanisms by promoting an inflammatory state. Specifically, over the last few decades, obesity has been suggested not only to increase the risk of lymphoma but also to be associated with poor clinical outcomes and worse responses to different treatments for those diseases. Within the extensive range of proinflammatory mediators that adipose tissue releases, leptin has been demonstrated to be a key adipokine due to its pleotropic effects in many physiological systems and diseases. In this sense, different studies have analyzed leptin levels and leptin/leptin receptor expressions as a probable bridge between obesity and lymphomas. Since both obesity and lymphomas are prevalent pathophysiological conditions worldwide and their incidences have increased over the last few years, here we review the possible role of leptin as a promising proinflammatory mediator promoting lymphomas.

Leptin-mediated proinflammatory bone marrow environment in acquired aplastic anemia

Acquired aplastic anemia (AA), a paradigm of bone marrow failure syndrome, is mainly caused by abnormal immune activation. The enhanced adipogenesis of bone marrow-derived mesenchymal stem cell (BM-MSC) results in a fatty marrow of AA. Leptin, an adipokine mainly generated by adipocytes, has powerful proinflammatory effects on immune cells and is associated with various autoimmune diseases. However, the role of leptin in the hyperimmune status of AA remains unknown. In this study, we firstly discovered the higher leptin concentration in AA-BM than that in healthy donors (HD)-BM and myelodysplastic syndrome (MDS)-BM. Then, we found AA-MSC could express high amounts of leptin during the process of adipogenesis. Compared with HD, the leptin receptor was also highly expressed on T cells in AA-BM. Furthermore, leptin significantly accelerated the proliferation and activation of T cells in AA-BM. And, leptin promoted the production of interferon-γby T cells in AA-BM. However, leptin remarkably inhibited the conversion of CD4⁺CD25^- T cells into CD4⁺Foxp3⁺ T cells. Finally, we detected the cell signaling pathway in T cells from AA patients and found leptin could activate the STAT3 pathway. In summary, our data revealed the high expression of adipokine leptin in AA-BM which shaped a proinflammatory environment for T cells in AA-BM by activating the JAK2/STAT3 pathway.

Infection and Immunometabolism in the Central Nervous System: A Possible Mechanistic Link Between Metabolic Imbalance and Dementia

Metabolic syndromes are frequently associated with dementia, suggesting that the dysregulation of energy metabolism can increase the risk of neurodegeneration and cognitive impairment. In addition, growing evidence suggests the link between infections and brain disorders, including Alzheimer's disease. The immune system and energy metabolism are in an intricate relationship. Infection triggers immune responses, which are accompanied by imbalance in cellular and organismal energy metabolism, while metabolic disorders can lead to immune dysregulation and higher infection susceptibility. In the brain, the activities of brain-resident immune cells, including microglia, are associated with their metabolic signatures, which may be affected by central nervous system (CNS) infection. Conversely, metabolic dysregulation can compromise innate immunity in the brain, leading to enhanced CNS infection susceptibility. Thus, infection and metabolic imbalance can be intertwined to each other in the etiology of brain disorders, including dementia. Insulin and leptin play pivotal roles in the regulation of immunometabolism in the CNS and periphery, and dysfunction of these signaling pathways are associated with cognitive impairment. Meanwhile, infectious complications are often comorbid with diabetes and obesity, which are characterized by insulin resistance and leptin signaling deficiency. Examples include human immunodeficiency virus (HIV) infection and periodontal disease caused by an oral pathogen Porphyromonas gingivalis. This review explores potential interactions between infectious agents and insulin and leptin signaling pathways, and discuss possible mechanisms underlying the relationship between infection, metabolic dysregulation, and brain disorders, particularly focusing on the roles of insulin and leptin.

Leptin and the Blood-Brain Barrier: Curiosities and Controversies

Leptin for over 25 years has been a central theme in the study of appetite, obesity, and starvation. As the major site of leptin production is peripheral, and the site of action of greatest interest is the hypothalamus, how leptin accesses the central nervous system (CNS) and crosses the blood-brain barrier (BBB) has been of great interest. We review here the ongoing research that addresses fundamental questions such as the sites of leptin resistances in obesity and other conditions, the causes of resistances and their relations to one another, the three barrier sites of entry into the CNS, why recent studies using suprapharmacological doses cannot address these questions but give insight into nonsaturable entry of leptin into the CNS, and how that might be useful in using leptin therapeutically. The current status of the controversy of whether the short form of the leptin receptor acts as the BBB leptin transporter and how obesity may transform leptin transport is reviewed. Review of these and other topics summarizes in a new appreciation of what leptin may have actually evolved to do and what physiological role leptin resistance may play. © 2021 American Physiological Society. Compr Physiol 11:1-19, 2021.

Control of T Cell Metabolism by Cytokines and Hormones

Dynamic, coordinated changes in metabolic pathway activity underpin the protective and inflammatory activity of T cells, through provision of energy and biosynthetic precursors for effector functions, as well as direct effects of metabolic enzymes, intermediates and end-products on signaling pathways and transcriptional mechanisms. Consequently, it has become increasingly clear that the metabolic status of the tissue microenvironment directly influences T cell activity, with changes in nutrient and/or metabolite abundance leading to dysfunctional T cell metabolism and interlinked immune function. Emerging evidence now indicates that additional signals are integrated by T cells to determine their overall metabolic phenotype, including those arising from interaction with cytokines and hormones in their environment. The impact of these on T cell metabolism, the mechanisms involved and the pathological implications are discussed in this review article.

Nutritional modulation of leptin expression and leptin action in obesity and obesity-associated complications

In obesity, an elevated accumulation and dysregulation of adipose tissue, due to an imbalance between energy intake and energy expenditure, usually coexists with the loss of responsiveness to leptin in central nervous system, and subsequently with hyperleptinemia. Leptin, a peptide hormone mainly produced by white adipose tissue, regulates energy homeostasis by stimulating energy expenditure and inhibiting food intake. Human obesity is characterized by increased plasma leptin levels, which have been related with different obesity-associated complications, such as chronic inflammatory state (risk factor for diabetes, cardiovascular and autoimmune diseases), as well as infertility and different types of cancer. Besides, leptin is also produced by placenta, and high leptin levels during pregnancy may be related with some pathological conditions such as gestational diabetes. This review focuses on the current insights and emerging concepts on potentially valuable nutrients and food components that may modulate leptin metabolism. Notably, several dietary food components, such as phenols, peptides, and vitamins, are able to decrease inflammation and improve leptin sensitivity by up- or down-regulation of leptin signaling molecules. On the other hand, some food components, such as saturated fatty acids may worsen chronic inflammation increasing the risk for pathological complications. Future research into nutritional mechanisms that restore leptin metabolism and signals of energy homeostasis may inspire new treatment options for obesity-related disorders.

Leptin, Leptin Receptor, KHDRBS1 (KH RNA Binding Domain Containing, Signal Transduction Associated 1), and Adiponectin in Bone Metastasis from Breast Carcinoma: An Immunohistochemical Study

Breast cancer patients are at a high risk of complications from bone metastasis. Molecular characterization of bone metastases is essential for the discovery of new therapeutic targets. Here, we investigated the expression and the intracellular distribution of KH RNA binding domain containing, signal transduction associated 1 (KHDRBS1), leptin, leptin receptor (LEPR), and adiponectin in bone metastasis from breast carcinoma and looked for correlations between the data. The expression of these proteins is known in breast carcinoma, but it has not been investigated in bone metastatic tissue to date. Immunohistochemical analysis was carried out on bone metastasis specimens, then semiquantitative evaluation of the results and the Pearson test were performed to determine eventual correlations. KHDRBS1 expression was significantly higher in the nuclei than in the cytosol of metastatic cells; LEPR was prevalently observed in the cytosol and the nuclei; leptin and adiponectin were found in metastatic cells and stromal cells; the strongest positive correlation was between nuclear KHDRBS1 and nuclear LEPR expression. Taken together, our findings support the importance of the leptin/LEPR/KHDRBS1 axis and of adiponectin in the progression of bone metastasis and suggest their potential application in pharmacological interventions.

Prognosis prediction model based on competing endogenous RNAs for recurrence of colon adenocarcinoma

BACKGROUND

Colon adenocarcinoma (COAD) patients who develop recurrence have poor prognosis. Our study aimed to establish effective prognosis prediction model based on competing endogenous RNAs (ceRNAs) for recurrence of COAD.

METHODS

COAD expression profilings downloaded from The Cancer Genome Atlas (TCGA) were used as training dataset, and expression profilings of GSE29623 retrieved from Gene Expression Omnibus (GEO) were set as validation dataset. Differentially expressed RNAs (DERs) between non-recurrent and recurrent specimens in training dataset were screened, and optimum prognostic signature DERs were revealed to establish prognostic score (PS) model. Kaplan-Meier survival analysis was conducted for PS model, and GEO dataset was used for validation. Prognosis prediction efficiencies were evaluated by area under curve (AUC) and C-index. Meanwhile, ceRNA regulatory network was constructed by using signature mRNAs, lncRNAs and miRNAs.

RESULTS

We identified 562 DERs including 42 lncRNAs, 36 miRNAs, and 484 mRNAs. PS prediction model, consisting of 17 optimum prognostic signature DERs, showed that high risk group had significantly poorer prognosis (5-year AUC = 0.951, C-index = 0.788), which also validated in GSE29623. Prognosis prediction model incorporating multi-RNAs with pathologic distant metastasis (M) and pathologic primary tumor (T) (5-year AUC = 0.969, C-index = 0.812) had better efficiency than clinical prognosis prediction model (5-year AUC = 0.712, C-index = 0.680). In the constructed ceRNA regulatory network, lncRNA NCBP2-AS1 could interact with hsa-miR-34c and hsa-miR-363, and lncRNA LINC00115 could interact with hsa-miR-363 and hsa-miR-4709. SIX4, GRAP, NKAIN4, MMAA, and ERVMER34-1 are regulated by hsa-miR-4709.

CONCLUSION

Prognosis prediction model incorporating multi-RNAs with pathologic M and pathologic T may have great value in COAD prognosis prediction.

Leptin Upregulates the Expression of β3-Integrin, MMP9, HB-EGF, and IL-1β in Primary Porcine Endometrium Epithelial Cells In Vitro

Obesity has become a global health problem. Research suggests that leptin, a hormone that responds to fat deposition, may be involved in mammalian reproduction; however, its precise role in embryo implantation is poorly understood. Here, primary porcine endometrium epithelium cells (PEECs) were cultured in vitro and used to evaluate the regulatory role of different leptin levels on β3-integrin, MMP9, HB-EGF, and IL-1β, which are, respectively, involved in four critical steps of embryo implantation. Results showed that only 0.01 nM leptin significantly improved β3-integrin mRNA expression (p < 0.05). MMP9 and HB-EGF mRNA expressions were upregulated by 0.10–10.00 nM leptin (p < 0.05). The IL-1β expression level was only increased by 10.00 nM leptin (p < 0.05). β3-integrin, MMP9, HB-EGF, and IL-1β mRNA and protein have a similar fluctuant response to increased leptin. Leptin’s influence on β3-integrin, MMP9, HB-EGF, and IL-1β disappeared when the JAK2, PI(3)K, or MAPK signaling pathways were blocked, respectively. In conclusion, leptin affected porcine implantation by regulating the expression of β3-integrin, MMP9, HB-EGF, and IL-1β in a dose-dependent manner. The signaling pathways of JAK2, PI(3)K, and MAPK may participate in this regulatory process. These findings will contribute to further understanding the mechanisms of reproductive disorders in obesity.

Obesity, the most common comorbidity in SARS-CoV-2: is leptin the link?

Overweight and obesity are major risk factors for diabetes, cardiovascular disease, and lung disease. These diseases are the most commonly reported health conditions that predispose individuals with SARS-CoV-2 infection to require hospitalization including intensive care unit admissions. The innate immune response is the host’s first line of defense against a human coronavirus infection. However, most coronaviruses are armed with one strategy or another to overcome host antiviral defense, and the pathogenicity of the virus is related to its capacity to suppress host immunity. The multifaceted nature of obesity including its effects on immunity can fundamentally alter the pathogenesis of acute respiratory distress syndrome and pneumonia, which are the major causes of death due to SARS-CoV-2 infection. Elevated circulating leptin concentrations are a hallmark of obesity, which is associated with a leptin-resistant state. Leptin is secreted by adipocytes in proportion to body fat and regulates appetite and metabolism through signaling in the hypothalamus. However, leptin also signals through the Jak/STAT and Akt pathways, among others, to modulate T cell number and function. Thus, leptin connects metabolism with the immune response. Therefore, it seems appropriate that its dysregulation would have serious consequences during an infection. We propose that leptin may be the link between obesity and its high prevalence as a comorbidity of the SARS-CoV-2 infection. In this article, we present a synthesis of the mechanisms underpinning susceptibility to respiratory viral infections and the contribution of the immunomodulatory effects of obesity to the outcome.

Leptin in the regulation of the immunometabolism of adipose tissue-macrophages

Obesity is a pandemic disease affecting around 15% of the global population. Obesity is a major risk factor for other conditions, such as type 2 diabetes and cardiovascular diseases. The adipose tissue is the main secretor of leptin, an adipokine responsible for the regulation of food intake and energy expenditure. Obese individuals become hyperleptinemic due to increased adipogenesis. Leptin acts through the leptin receptor and induces several immunometabolic changes in different cell types, including adipocytes and Mϕs. Adipose tissue resident Mϕs (ATMs) are the largest leukocyte population in the adipose tissue and these ATMs are in constant contact with the excessive leptin levels secreted in obese conditions. Leptin activates both the JAK2-STAT3 and the PI3K-AKT-mTOR pathways. The activation of these pathways leads to intracellular metabolic changes, with increased glucose uptake, upregulation of glycolytic enzymes, and disruption of mitochondrial function, as well as immunologic alterations, such as increased phagocytic activity and proinflammatory cytokines secretion. Here, we discuss the immunometabolic effects of leptin in Mϕs and how hyperleptinemia can contribute to the low-grade systemic inflammation in obesity.

Emergence of Leptin in Infection and Immunity: Scope and Challenges in Vaccines Formulation

Deficiency of leptin (ob/ob) and/or desensitization of leptin signaling (db/db) and elevated expression of suppressor of cytokine signaling-3 (SOCS3) reported in obesity are also reported in a variety of pathologies including hypertriglyceridemia, insulin resistance, and malnutrition as the risk factors in host defense system. Viral infections cause the elevated SOCS3 expression, which inhibits leptin signaling. It results in immunosuppression by T-regulatory cells (Tregs). The host immunity becomes incompetent to manage pathogens' attack and invasion, which results in the accelerated infections and diminished vaccine-specific antibody response. Leptin was successfully used as mucosal vaccine adjuvant against Rhodococcus equi. Leptin induced the antibody response to Helicobacter pylori vaccination in mice. An integral leptin signaling in mucosal gut epithelial cells offered resistance against Clostridium difficile and Entameoba histolytica infections. We present in this review, the intervention of leptin in lethal diseases caused by microbial infections and propose the possible scope and challenges of leptin as an adjuvant tool in the development of effective vaccines.

Involvement of leptin in the molecular physiology of the placenta

Leptin is a homeostatic regulator in the placenta where it promotes proliferation, protein synthesis and the expression of tolerogenic maternal response molecules such as HLA-G. Leptin also exerts an anti-apoptotic action in placenta controlling the expression of p53 master cell cycle regulator under different stress conditions. On the other hand, leptin is an integrative target of different placental stimuli. The expression of leptin in placenta is regulated by hCG, insulin, steroids, hypoxia and many other growth hormones, suggesting that it might have an important endocrine function in the trophoblastic cells. The leptin expression is induced involving the cAMP/PKA or cAMP/Epac pathways which have profound actions upon human trophoblast function. The activation of PI3K and MAPK pathways also participates in the leptin expression. Estrogens play a central role during pregnancy, particularly 17β-estradiol upregulates the leptin expression in placental cells through genomic and non-genomic actions. The leptin promoter analysis reveals specific elements that are active in placental cells. The transcription factors CREB, AP1, Sp1, NFκB and the coactivator CBP are involved in the placental leptin expression. Moreover, placental leptin promoter is a target of epigenetic marks such as DNA methylation and histone acetylation that regulates not only the leptin expression in placenta during pregnancy but also determines the predisposition of acquiring adult metabolism diseases. Taken together, all these results allow a better understanding of leptin function and regulatory mechanisms of leptin expression in human placental trophoblasts, and support the importance of leptin during pregnancy and in programming adult health.

Role of leptin as a link between metabolism and the immune system

Leptin is an adipocyte-derived hormone not only with an important role in the central control of energy metabolism, but also with many pleiotropic effects in different physiological systems. One of these peripheral functions of leptin is a regulatory role in the interplay between energy metabolism and the immune system, being a cornerstone of the new field of immunometabolism. Leptin receptor is expressed throughout the immune system and the regulatory effects of leptin include cells from both the innate and adaptive immune system. Leptin is one of the adipokines responsible for the inflammatory state found in obesity that predisposes not only to type 2 diabetes, metabolic syndrome and cardiovascular disease, but also to autoimmune and allergic diseases. Leptin is an important mediator of the immunosuppressive state in undernutrition status. Placenta is the second source of leptin and it may play a role in the immunomodulation during pregnancy. Finally, recent work has pointed to the participation of leptin and leptin receptor in the pathophysiology of inflammation in oral biology. Therefore, leptin and leptin receptor should be considered for investigation as a marker of inflammation and immune activation in the frontier of innate-adaptive system, and as possible targets for intervention in the immunometabolic mediated pathophysiology.

Adipokine Contribution to the Pathogenesis of Osteoarthritis

Recent studies have shown that overweight and obesity play an important role in the development of osteoarthritis (OA). However, joint overload is not the only risk factor in this disease. For instance, the presence of OA in non-weight-bearing joints such as the hand suggests that metabolic factors may also contribute to its pathogenesis. Recently, white adipose tissue (WAT) has been recognized not only as an energy reservoir but also as an important secretory organ of adipokines. In this regard, adipokines have been closely associated with obesity and also play an important role in bone and cartilage homeostasis. Furthermore, drugs such as rosuvastatin or rosiglitazone have demonstrated chondroprotective and anti-inflammatory effects in cartilage explants from patients with OA. Thus, it seems that adipokines are important factors linking obesity, adiposity, and inflammation in OA. In this review, we are focused on establishing the physiological mechanisms of adipokines on cartilage homeostasis and evaluating their role in the pathophysiology of OA based on evidence derived from experimental research as well as from clinical-epidemiological studies.

The Role of the Immune System in Metabolic Health and Disease

In addition to the immune system's traditional roles of conferring anti-infectious and anti-neoplastic protection, it has been recently implicated in the regulation of systemic metabolic homeostasis. This cross-talk between the immune and the metabolic systems is pivotal in promoting "metabolic health" throughout the life of an organism and plays fundamental roles in its adaptation to ever-changing environmental makeups and nutritional availability. Perturbations in this intricate immune-metabolic cross-talk contribute to the tendency to develop altered metabolic states that may culminate in metabolic disorders such as malnutrition, obesity, type 2 diabetes mellitus (T2DM), and other features of the metabolic syndrome. Regulators of immune-metabolic interactions include host genetics, nutritional status, and the intestinal microbiome. In this Perspective, we highlight current understanding of immune-metabolism interactions, illustrate differences among individuals and between populations in this respect, and point toward future avenues of research possibly enabling immune harnessing as means of personalized treatment for common metabolic disorders.

Sam68 Mediates the Activation of Insulin and Leptin Signalling in Breast Cancer Cells

Obesity is a well-known risk factor for breast cancer development in postmenopausal women. High insulin and leptin levels seem to have a role modulating the growth of these tumours. Sam68 is an RNA-binding protein with signalling functions that has been found to be overexpressed in breast cancer. Moreover, Sam68 may be recruited to insulin and leptin signalling pathways, mediating its effects on survival, growth and proliferation in different cellular types. We aimed to study the expression of Sam68 and its phosphorylation level upon insulin and leptin stimulation, and the role of Sam68 in the proliferative effect and signalling pathways that are activated by insulin or leptin in human breast adenocarcinoma cells. In the human breast adenocarcinoma cell lines MCF7, MDA-MB-231 and BT-474, Sam68 protein quantity and gene expression were increased upon leptin or insulin stimulation, as it was checked by qPCR and immunoblot. Moreover, both insulin and leptin stimulation promoted an increase in Sam68 tyrosine phosphorylation and negatively regulated its RNA binding capacity. siRNA was used to downregulate Sam68 expression, which resulted in lower proliferative effects of both insulin and leptin, as well as a lower activation of MAPK and PI3K pathways promoted by both hormones. These effects may be partly explained by the decrease in IRS-1 expression by down-regulation of Sam68. These results suggest the participation of Sam68 in both leptin and insulin receptor signaling in human breast cancer cells, mediating the trophic effects of these hormones in proliferation and cellular growth.

Leptin induces the generation of procoagulant, tissue factor bearing microparticles by human peripheral blood mononuclear cells

BACKGROUND

Obesity is linked to increased thrombotic risk. Circulating leptin concentration correlates with body mass index. Microparticles are small (.05-1 μm) vesicles shed by activated and apoptotic cells, involved in numerous pathophysiologically relevant phenomena including blood coagulation and thrombosis. We tested the hypothesis that leptin induces the shedding of procoagulant, tissue factor bearing microparticles by human peripheral blood mononuclear cells, and investigated the intracellular mechanisms leading to microparticle release upon incubation with leptin.

METHODS

Peripheral blood mononuclear cells were isolated from healthy donors. Cells were incubated with leptin in the presence or in the absence of a phospholipase C inhibitor, U73122, a calmodulin inhibitor, W-7, and three inhibitors of mitogen activated protein kinases. Microparticle generation was assessed as phosphatidylserine concentration with a prothrombinase assay and by cytofluorimetric analysis. Tissue factor expression on microparticles was measured with a one-stage clotting assay. Intracellular calcium concentration was assessed by a fluorescent probe.

RESULTS

Leptin increased intracellular calcium mobilization and stimulated the generation of tissue factor-bearing MP by peripheral blood mononuclear cells, as assessed by phosphatidylserine quantification, clotting tests and flow-cytometry. U73122, PD98059 (an extracellular signal-regulated kinase1/2 inhibitor), and W-7, significantly inhibited leptin-induced MP release. SB203580 (a p38 inhibitor), and SP600125 (a c-Jun N-terminal kinase inhibitor) had no effect.

CONCLUSION

Leptin-induced generation of procoagulant microparticles might represent a link between obesity and atherothrombotic risk. Inhibition of leptin-induced microparticle generation might prove a viable strategy for the reduction of such risk in obese individuals.

Regulation of energy balance by inflammation: common theme in physiology and pathology

Inflammation regulates energy metabolism in both physiological and pathological conditions. Pro-inflammatory cytokines involves in energy regulation in several conditions, such as obesity, aging (calorie restriction), sports (exercise), and cancer (cachexia). Here, we introduce a view of integrative physiology to understand pro-inflammatory cytokines in the control of energy expenditure. In obesity, chronic inflammation is derived from energy surplus that induces adipose tissue expansion and adipose tissue hypoxia. In addition to the detrimental effect on insulin sensitivity, pro-inflammatory cytokines also stimulate energy expenditure and facilitate adipose tissue remodeling. In caloric restriction (CR), inflammatory status is decreased by low energy intake that results in less energy supply to immune cells to favor energy saving under caloric restriction. During physical exercise, inflammatory status is elevated due to muscle production of pro-inflammatory cytokines, which promote fatty acid mobilization from adipose tissue to meet the muscle energy demand. In cancer cachexia, chronic inflammation is elevated by the immune response in the fight against cancer. The energy expenditure from chronic inflammation contributes to weight loss. Immune tolerant cancer cells gains more nutrients during the inflammation. In these conditions, inflammation coordinates energy distribution and energy demand between tissues. If the body lacks response to the pro-inflammatory cytokines (Inflammation Resistance), the energy metabolism will be impaired leading to an increased risk for obesity. In contrast, super-induction of the inflammation activity leads to weight loss and malnutrition in cancer cachexia. In summary, inflammation is a critical component in the maintenance of energy balance in the body. Literature is reviewed in above fields to support this view.

Role of Sam68 in post-transcriptional gene regulation

The STAR family of proteins links signaling pathways to various aspects of post-transcriptional regulation and processing of RNAs. Sam68 belongs to this class of heteronuclear ribonucleoprotein particle K (hnRNP K) homology (KH) single domain-containing family of RNA-binding proteins that also contains some domains predicted to bind critical components in signal transduction pathways. In response to phosphorylation and other post-transcriptional modifications, Sam68 has been shown to have the ability to link signal transduction pathways to downstream effects regulating RNA metabolism, including transcription, alternative splicing or RNA transport. In addition to its function as a docking protein in some signaling pathways, this prototypic STAR protein has been identified to have a nuclear localization and to take part in the formation of both nuclear and cytosolic multi-molecular complexes such as Sam68 nuclear bodies and stress granules. Coupling with other proteins and RNA targets, Sam68 may play a role in the regulation of differential expression and mRNA processing and translation according to internal and external signals, thus mediating important physiological functions, such as cell death, proliferation or cell differentiation.

Leptin metabolically licenses T cells for activation to link nutrition and immunity

Immune responses are highly energy-dependent processes. Activated T cells increase glucose uptake and aerobic glycolysis to survive and function. Malnutrition and starvation limit nutrients and are associated with immune deficiency and increased susceptibility to infection. Although it is clear that immunity is suppressed in times of nutrient stress, mechanisms that link systemic nutrition to T cell function are poorly understood. We show in this study that fasting leads to persistent defects in T cell activation and metabolism, as T cells from fasted animals had low glucose uptake and decreased ability to produce inflammatory cytokines, even when stimulated in nutrient-rich media. To explore the mechanism of this long-lasting T cell metabolic defect, we examined leptin, an adipokine reduced in fasting that regulates systemic metabolism and promotes effector T cell function. We show that leptin is essential for activated T cells to upregulate glucose uptake and metabolism. This effect was cell intrinsic and specific to activated effector T cells, as naive T cells and regulatory T cells did not require leptin for metabolic regulation. Importantly, either leptin addition to cultured T cells from fasted animals or leptin injections to fasting animals was sufficient to rescue both T cell metabolic and functional defects. Leptin-mediated metabolic regulation was critical, as transgenic expression of the glucose transporter Glut1 rescued cytokine production of T cells from fasted mice. Together, these data demonstrate that induction of T cell metabolism upon activation is dependent on systemic nutritional status, and leptin links adipocytes to metabolically license activated T cells in states of nutritional sufficiency.

Role of adipokines signaling in the modulation of T cells function

The field that links immunity and metabolism is rapidly expanding. Apparently non-immunological disorders such as obesity and type 2 diabetes have been linked to immune dysregulation, suggesting that metabolic alterations can be induced by or be consequence of an altered self-immune tolerance. In this context, adipose tissue produces and releases a variety of pro-inflammatory and anti-inflammatory factors, termed "adipokines," which can be considered as the bridge between obesity-related exogenous factors, such as nutrition and lifestyle, and the molecular events leading to metabolic syndrome, inflammatory, and/or autoimmune conditions. In obesity, increased production of most adipokines impacts on multiple functions such as appetite and energy balance, modulation of immune responses, insulin sensitivity, angiogenesis, blood pressure, lipid metabolism, and so on. This report aims to discuss some of the recent topics of adipocytokine research and their related signaling pathways, that may be of particular importance as could lead to effective therapeutic strategies for obesity-associated diseases.

Effects of recombinant trout leptin in superoxide production and NF-κB/MAPK phosphorylation in blood leukocytes

Studies in mammals indicate that leptin is a multifunctional cytokine involved in regulation of energy metabolism and the modulation of the immune function. However, evidence for an immunomodulatory effect of leptin in fish is still missing. At least in part, this lack of knowledge is due to the absence of materials and models. In this study, we produced trout recombinant leptin (rt-lep) and tested its capacity to trigger cellular pathways, usually active in mammal immune system cells. STAT3, NF-κB, and the three major MAPK cascades (JNK, p38 and ERK), were activated by rt-lep in in vitro incubations with blood leucocytes of the rainbow trout Oncorhynchus mykiss. We also showed that rt-lep causes a decrease in superoxide anion production in trout blood leucocytes. Thus our data indicate that as in mammals also in teleosts leptin plays pleiotropic activities. Importantly, its actions in fishes do not always conform to the picture emerging for mammals.

High expression level and nuclear localization of Sam68 are associated with progression and poor prognosis in colorectal cancer

BACKGROUND

Src-associated in mitosis (Sam68; 68 kDa) has been implicated in the oncogenesis and progression of several human cancers. The aim of this study was to investigate the clinicopathologic significance of Sam68 expression and its subcellular localization in colorectal cancer (CRC).

METHODS

Sam68 expression was examined in CRC cell lines, nine matched CRC tissues and adjacent noncancerous tissues using reverse transcription (RT)-PCR, quantitative RT-PCR and Western blotting. Sam68 protein expression and localization were determined in 224 paraffin-embedded archived CRC samples using immunohistochemistry. Statistical analyses were applied to evaluate the clinicopathologic significance.

RESULTS

Sam68 was upregulated in CRC cell lines and CRC, as compared with normal tissues; high Sam68 expression was detected in 120/224 (53.6%) of the CRC tissues. High Sam68 expression correlated significantly with poor differentiation (P = 0.033), advanced T stage (P < 0.001), N stage (P = 0.023) and distant metastasis (P = 0.033). Sam68 nuclear localization correlated significantly with poor differentiation (P = 0.002) and T stage (P =0.021). Patients with high Sam68 expression or Sam68 nuclear localization had poorer overall survival than patients with low Sam68 expression or Sam68 cytoplasmic localization. Patients with high Sam68 expression had a higher risk of recurrence than those with low Sam68 expression.

CONCLUSIONS

Overexpression of Sam68 correlated highly with cancer progression and poor differentiation in CRC. High Sam68 expression and Sam68 nuclear localization were associated with poorer overall survival.

Inflammation during obesity is not all bad: evidence from animal and human studies

Chronic inflammation is a characteristic of obesity and is associated with accompanying insulin resistance, a hallmark of type 2 diabetes mellitus (T2DM). Although proinflammatory cytokines are known for their detrimental effects on adipose tissue function and insulin sensitivity, their beneficial effects in the regulation of metabolism have not drawn sufficient attention. In obesity, inflammation is initiated by a local hypoxia to augment angiogenesis and improve adipose tissue blood supply. A growing body of evidence suggests that macrophages and proinflammatory cytokines are essential for adipose remodeling and adipocyte differentiation. Phenotypes of multiple lines of transgenic mice consistently suggest that proinflammatory cytokines increase energy expenditure and act to prevent obesity. Removal of proinflammatory cytokines by gene knockout decreases energy expenditure and induces adult-onset obesity. In contrast, elevation of proinflammatory cytokines augments energy expenditure and decreases the risk for obesity. Anti-inflammatory therapies have been tested in more than a dozen clinical trials to improve insulin sensitivity and glucose homeostasis in patients with T2DM, and the results are not encouraging. One possible explanation is that anti-inflammatory therapies also attenuate the beneficial effects of inflammation in stimulating energy expenditure, which may have limited the efficacy of the treatment by promoting energy accumulation. Thus, the positive effects of proinflammatory events should be considered in evaluating the impact of inflammation in obesity and type 2 diabetes.

Leptin inhibits neutrophil apoptosis in children via ERK/NF-κB-dependent pathways

Introduction and Rationale

Previous studies have shown that delayed neutrophil apoptosis is associated with chronic airway diseases. Leptin is an adipocyte-derived hormone that acts as a regulator of energy homeostasis and food intake. Emerging evidence suggests that leptin can regulate immune responses including the release of proinflammatory cytokines and protection of inflammatory cells from apoptosis. Serum leptin is increased during allergic reactions in the airways. However, the expression and function of leptin receptor in neutrophils isolated from children is not known.

Methods

Flow cytometry was used to detect leptin receptor expression in neutrophils isolated from allergic asthmatic (n = 14), allergic non asthmatic (n = 21), non allergic asthmatic (n = 7) and healthy children (n = 23); confocal laser scanning microscopy combined with immunofluorescence was performed to detect intracellular pool of leptin receptor; Annexin-V/PI staining and caspase 3 activity was used to determine neutrophil survival. Pharmacological inhibitors were utilized to understand the role of MAPK and NF-κB pathway in leptin-induced neutrophil survival.

Results and Conclusion

A heterogeneous leptin receptor expression was observed on neutrophils isolated from children. Neutrophils isolated from healthy children expressed more leptin receptor than those from allergic asthmatic (P<0.05) but not allergic non-asthmatic (P>0.05) or non-allergic asthmatic children (n = 7, P>0.05). Neutrophils isolated from children express an intracellular pool of leptin receptor that was mobilized to the cell surface upon GM-CSF stimulation. Finally, leptin exhibited anti-apoptotic properties on neutrophils via NF-κB and MEK1/2 MAPK pathway. Collectively, our data suggest that leptin may enhance airway inflammation by promoting neutrophil survival.

Metabolic regulation of T lymphocytes

T cell activation leads to dramatic shifts in cell metabolism to protect against pathogens and to orchestrate the action of other immune cells. Quiescent T cells require predominantly ATP-generating processes, whereas proliferating effector T cells require high metabolic flux through growth-promoting pathways. Further, functionally distinct T cell subsets require distinct energetic and biosynthetic pathways to support their specific functional needs. Pathways that control immune cell function and metabolism are intimately linked, and changes in cell metabolism at both the cell and system levels have been shown to enhance or suppress specific T cell functions. As a result of these findings, cell metabolism is now appreciated as a key regulator of T cell function specification and fate. This review discusses the role of cellular metabolism in T cell development, activation, differentiation, and function to highlight the clinical relevance and opportunities for therapeutic interventions that may be used to disrupt immune pathogenesis.

Immunomodulation at epithelial sites by obesity and metabolic disease

Obesity and related type 2 diabetes are increasing at epidemic proportions globally. It is now recognized that inflammatory responses mediated within the adipose tissue in obesity are central to the development of disease. Once initiated, chronic inflammation associated with obesity leads to the modulation of immune cell function. This review will focus specifically on the impact of obesity on γδ T cells, a T-cell subset that is found in high concentrations in epithelial tissues such as the skin, intestine, and lung. Epithelial γδ T cell function is of particular concern in obesity as they are the guardians of the epithelial barrier and mediate repair. A breakdown in their function, and subsequently the deterioration of the epithelium can result in dire consequences for the host. Obese patients are more prone to non-healing injuries, infection, and disease. The resulting inflammation from these pathologies further perpetuates the disease condition already present in obese hosts. Here we will provide insight into the immunomodulation of γδ T cells that occurs in the epithelial barrier during obesity and discuss current therapeutic options.

Immunological functions of leptin and adiponectin

Recent years have seen several advances in our understanding of the functions of adipose tissue regarding not only the energy storage, but also the regulation of complex metabolic and endocrine functions. In this context, leptin and adiponectin, the two most abundant adipocyte products, represent one of the best example of adipocytokines involved in the control of energy expenditure, lipid and carbohydrate metabolism as well as in the regulation of immune responses. Leptin and adiponectin secretion is counter-regulated in vivo, in relation to degree of adiposity, since plasma leptin concentrations are significantly elevated in obese subjects in proportion to body mass index while adiponectin secretion decreases in relation to the amount of adipose tissue. In this review we focus on the main biological activities of leptin and adiponectin on the lipid and carbohydrate metabolism and on their contribute in regulation of innate and adaptive immune responses.

Leptin promotes glioblastoma

The hormone leptin has a variety of functions. Originally known for its role in satiety and weight loss, leptin more recently has been shown to augment tumor growth in a variety of cancers. Within gliomas, there is a correlation between tumor grade and tumor expression of leptin and its receptor. This suggests that autocrine signaling within the tumor microenvironment may promote the growth of high-grade gliomas. Leptin does this through stimulation of cellular pathways that are also advantageous for tumor growth and recurrence: antiapoptosis, proliferation, angiogenesis, and migration. Conversely, a loss of leptin expression attenuates tumor growth. In animal models of colon cancer and melanoma, a decline in the expression and secretion of leptin resulted in a reduction of tumor growth. In these models, positive mental stimulation through environmental enrichment decreased leptin secretion and improved tumor outcome. This review explores the link between leptin and glioblastoma.

Toward an understanding of the protein interaction network of the human liver

An extensive interaction network of human liver-expressed proteins is described, composed of 3484 interactions among 2582 proteins. Proteins associated with liver disease tend to be central and highly connected in the network.

Proteome-scale protein interaction maps are available for many organisms, ranging from bacteria, yeast, worms and flies to humans. These maps provide substantial new insights into systems biology, disease research and drug discovery. However, only a small fraction of the total number of human protein–protein interactions has been identified. In this study, we map the interactions of an unbiased selection of 5026 human liver expression proteins by yeast two-hybrid technology and establish a human liver protein interaction network (HLPN) composed of 3484 interactions among 2582 proteins. The data set has a validation rate of over 72% as determined by three independent biochemical or cellular assays. The network includes metabolic enzymes and liver-specific, liver-phenotype and liver-disease proteins that are individually critical for the maintenance of liver functions. The liver enriched proteins had significantly different topological properties and increased our understanding of the functional relationships among proteins in a liver-specific manner. Our data represent the first comprehensive description of a HLPN, which could be a valuable tool for understanding the functioning of the protein interaction network of the human liver.

Inflammatory concepts of obesity

Obesity, long considered a condition characterized by the deposition of inert fat, is now recognized as a chronic and systemic inflammatory disease, where adipose tissue plays a crucial endocrine role through the production of numerous bioactive molecules, collectively known as adipokines. These molecules regulate carbohydrate and lipid metabolism, immune function and blood coagulability, and may serve as blood markers of cardiometabolic risk. Local inflammatory loops operate in adipose tissue as a consequence of nutrient overload, and crosstalk among its cellular constituents-adipocytes, endothelial and immune cells-results in the elaboration of inflammatory mediators. These mediators promote important systemic effects that can result in insulin resistance, dysmetabolism and cardiovascular disease. The understanding that inflammation plays a critical role in the pathogenesis of obesity-derived disorders has led to therapeutic approaches that target different points of the inflammatory network induced by obesity.

The RNA-binding protein Sam68 is a multifunctional player in human cancer

Src associated in mitosis, of 68 kDa (Sam68) is a KH domain RNA-binding protein that belongs to the signal transduction and activation of RNA family. Although ubiquitously expressed, Sam68 plays very specialized roles in different cellular environments. In most cells, Sam68 resides in the nucleus and is involved in several steps of mRNA processing, from transcription, to alternative splicing, to nuclear export. In addition, Sam68 translocates to the cytoplasm upon cell stimulation, cell cycle transitions or viral infections, where it takes part to signaling complexes and associates with the mRNA translation machinery. Recent evidence has linked Sam68 function to the onset and progression of endocrine tumors, such as prostate and breast carcinomas. Notably, all the biochemical activities reported for Sam68 seem to be implicated in carcinogenesis. Herein, we review the recent advancement in the knowledge of Sam68 function and regulation and discuss it in the frame of its participation to neoplastic transformation and tumor progression.

Sam68 mediates leptin-stimulated growth by modulating leptin receptor signaling in human trophoblastic JEG-3 cells

BACKGROUND

Sam68, a member of the signal transduction and activation of RNA metabolism (STAR) family of RNA-binding proteins, has been previously implicated as an adaptor molecule in different signaling systems, including leptin receptor (LEPR) signaling. LEPR activation is known to stimulate JAK-STAT, MAPK and PI3K signaling pathways, thus mediating the biological effects of leptin in different cell types, including trophoblastic cells. We have recently found that leptin stimulation also promotes the overexpression and tyrosine phosphorylation of Sam68 in human trophoblastic JEG-3 cells, suggesting a role for Sam68 in leptin signaling and action in these cells. In the present work, we have studied the participation of Sam68 in the main signaling pathways activated by LEPR to increase growth and proliferation in trophoblastic JEG-3 cells.

METHODS

We used an antisense strategy to down-regulate Sam68 expression in these cells, and we studied LEPR signaling by immunoprecipitation and poly-U affinity precipitation and by analyzing phosphorylation levels of signaling proteins by immunoblot. The effect of leptin on protein synthesis and proliferation was studied by ³[H]-leucine and ³[H]-thymidine incorporation.

RESULTS

Sam68 knockdown impaired leptin activation of JAK-STAT, PI3K and MAPK signaling pathways in JEG-3 cells. We have also found that leptin-stimulated Sam68 tyrosine phosphorylation is dependent on JAK-2 activity, since the pharmacological inhibitor AG490 prevents the phosphorylation of Sam68 in JEG-3 cells. Finally, the trophic and proliferative effect of leptin in trophoblastic cells is dependent on Sam68 expression, since its down-regulation impaired the leptin-stimulated DNA and protein synthesis.

CONCLUSIONS

These data demonstrate that Sam68 participates in the main signaling pathways of LEPR to mediate the trophic and proliferative effect of leptin in human trophoblastic cells.

Review: Leptin gene expression in the placenta--regulation of a key hormone in trophoblast proliferation and survival

Leptin is a 16000 MW protein originally described as an adipocyte-derived signaling molecule for the central control of metabolism. However, pleiotropic effects of leptin have been identified in reproduction and pregnancy. The leptin gene is expressed in placenta, where leptin promotes proliferation and survival of trophoblast cells. Study of the major signaling pathways known to be triggered by leptin receptor has revealed that leptin stimulates JAK/STAT, MAPK and PI3K pathways in placental cells. Leptin also exerts an antiapoptotic action in placenta and this effect is mediated by the MAPK pathway. Moreover, leptin stimulates protein synthesis by activating the translational machinery via both PI3K and MAPK pathways. Expression of leptin in placenta is highly regulated, suggesting that certain key pregnancy molecules participate in such regulation. An important hormone in reproduction, hCG, induces leptin expression in trophoblast cells and this effect involves the MAPK signal transduction pathway. Moreover, the cyclic nucleotide cAMP, which has profound actions upon human trophoblast function, also stimulates leptin expression and this effect seems to be mediated by crosstalk between the PKA and MAPK signaling pathways. Estrogens play a central role in reproduction. 17β-estradiol upregulates leptin expression in placental cells through genomic and non-genomic actions, probably via crosstalk between estrogen receptor-α and the MAPK and PI3K signal transduction pathways. Taken together these findings give a better understanding of the function of leptin and the regulatory mechanisms of leptin expression in human placental trophoblast and further support the importance of leptin in the biology of reproduction.

Airway and plasma leptin and adiponectin in lean and obese asthmatics and controls

INTRODUCTION

Obesity-mediated changes in plasma adipokines have been associated with increased systemic inflammation and oxidative stress. However, it is unknown whether obesity induces similar changes in airway levels of these adipokines and whether these changes are associated with increased airway biomarkers of inflammation and oxidative stress.

METHODS

Lean and obese asthmatics and controls underwent bronchoscopy with bronchoalveolar lavage (BAL), spirometry, and provided fasting plasma leptin and adiponectin. Biomarkers of oxidation and inflammation in the BAL included exhaled nitric oxide (NO), 8-isoprostanes, pH, and nitrogen oxide products (NOx).

RESULTS

Out of a total of 48 subjects, 44% had asthma and 56% were healthy controls. Among subjects with asthma, 66% were obese, 10% overweight, and 24% lean; in the controls these proportions were 63%, 11%, and 26%, respectively. After adjusting for age, sex, smoking history, ethnicity, and prebronchodilator forced exhalation in 1 second (FEV(1)), obesity was associated with higher BAL and plasma leptin levels in asthmatics and controls. Increasing BMI was associated with increased BAL leptin and was marginally and inversely associated with BAL adiponectin. Significant associations between BAL and plasma levels were only observed for leptin. No significant associations were observed between BAL and plasma adipokines with the airway biomarkers of oxidation and inflammation.

CONCLUSION

Increasing BMI is associated with changes in the concentrations of airway adipokines in asthmatics and healthy controls; however, these associations are not related with biomarkers of airway oxidation or inflammation.

Leptin-mediated cytoskeletal remodeling in chondrocytes occurs via the RhoA/ROCK pathway

Leptin affects a number of cell signaling pathways, at present, the mechanism(s) by which leptin affects the cartilage cells in OA patient is not well understood. The current study seeks to elucidate whether leptin induces cytoskeletal remodeling in chondrocytes and the possible involvement of the RhoA/ROCK pathway and its downstream mediators in this process. Fluorescent resonance energy transfer (FRET) and western analysis were used to determine the activations of the key proteins in the RhoA/LIMK1/Cofilin pathway. Accompanying cytoskeletal remodeling was elucidated. Upon leptin stimulation, a substantial increase of RhoA activity localized at one end of the cell was observed from 2 to 30 min post-stimulation. The results of Western blot showed leptin significantly increased LIMK1 and cofilin-2 phosphorylation in a time-dependent manner with maximal stimulation attained 60 min and 24 h post-stimulation, respectively. Chondrocytes stimulated with leptin exhibited an epithelioid morphology with increased cellular spreading. F-actin in leptin-stimulated chondrocytes also showed more intense cytoplasmic staining with occasional localization along filamentous structures. The results indicate that leptin activates the RhoA/ROCK/LIMK/cofilin pathway, which results in cytoskeletal reorganization in chondrocytes. These findings provide novel evidence supporting the possible involvement of leptin and the RhoA pathway in the pathogenesis of OA.

Leptin receptors

Leptin or obesity receptor (Ob-R) is a member of class I cytokine receptor family. Ob-R, expressed in six isoforms, is the product of alternative RNA splicing of db gene. According to its structural differences, the receptor's isoforms are divided into three classes: long, short, and secretory isoforms. A long, fully active isoform of Ob-Rb is expressed mainly in the hypothalamus, where it takes part in energy homeostasis and in the regulation of secretory organs' activity. Ob-Rb is also present on all types of immune cells, involved in innate and adaptive immunity. Short leptin isoforms (Ob-Ra, Ob-Rc, Ob-Rd, and Ob-Re) that contain box 1 motif are able to bind JAK kinases (Janus kinases) as well as to activate some other signal transduction cascades. A soluble isoform (Ob-Re) can regulate serum leptin concentration and serve as a carrier protein delivering the hormone to its membrane receptors and is able to transduce the signal into the cell. JAK/STAT pathway plays the major role in leptin signal transduction through membrane receptors. Among all Ob-R isoforms, only full-length isoform (Ob-Rb) is able to fully transduce activation signal into the cell.