An ERK/Cdk5 axis controls the diabetogenic actions of PPARγ

RAF1 in AgRP neurons involved in the regulation of energy metabolism via the MAPK signaling pathway

V-raf-leukemia viral oncogene 1(RAF1), a serine/threonine protein kinase, is universally acknowledged to play a crucial role in tumorigenesis and cell development. However, the specific role of hypothalamic RAF1 in regulating energy metabolism remains unknown. In this study, we found that the expression of RAF1 was significantly increased in hypothalamic AgRP neurons of diet induced obesity (DIO) mice. Under normal chow diet (NCD) feeding, over-expression of Raf1 in AgRP neurons leads to obesity in mice characterized by increased body weight, fat mass, and impaired glucose tolerance. Conversely, knock-out of the Raf1 gene in AgRP neurons protects against DIO, reducing fat mass and improving glucose tolerance. Mechanistically, Raf1 activates the MAPK signaling pathway, culminating in cAMP response element-binding protein (CREB) phosphorylation, which enhances transcription of Agrp and Npy. Insulin stimulation further potentiates the RAF1-MEK1/2-ERK1/2-CREB axis, highlighting RAF1's role in integrating hormonal and nutritional signals to regulate energy balance. Collectively, these findings underscore the important role of RAF1 in AgRP neurons in maintaining the energy homeostasis and obesity pathogenesis, positioning it and its downstream pathways as potential therapeutic targets for innovative strategies to combat obesity and related metabolic diseases.

A tethering mechanism underlies Pin1-catalyzed proline cis-trans isomerization at a noncanonical site

The prolyl isomerase Pin1 catalyzes the cis-trans isomerization of proline peptide bonds, a noncovalent posttranslational modification that influences cellular and molecular processes, including protein-protein interactions. Pin1 is a two-domain enzyme containing a WW domain that recognizes phosphorylated serine/threonine-proline (pS/pT-P) canonical motifs and an enzymatic PPIase domain that catalyzes proline cis-trans isomerization of pS/pT-P motifs. Here, we show that Pin1 uses a tethering mechanism to bind and catalyze proline cis-trans isomerization of a noncanonical motif in the disordered N-terminal activation function-1 (AF-1) domain of the human nuclear receptor PPARγ. NMR reveals multiple Pin1 binding regions within the PPARγ AF-1, including a canonical motif (pS112-P113) that when phosphorylated by the kinase ERK2 binds the Pin1 WW domain with high affinity. NMR methods reveal that Pin1 also binds and accelerates cis-trans isomerization of a noncanonical motif containing a tryptophan-proline motif (W39-P40) previously shown to be involved in an interdomain interaction with the C-terminal ligand-binding domain (LBD) of PPARγ. Cellular transcription studies combined with mutagenesis and Pin1 inhibitor treatment reveal a functional role for Pin1-mediated acceleration of cis-trans isomerization of the PPARγ W39-P40 motif. Our data inform a refined model of the Pin1 catalytic mechanism where the WW domain can bind a canonical pS/T-P motif and tether Pin1 to a target, which enables the PPIase domain to exert catalytic cis-trans isomerization at a distal noncanonical site.

Acute regulation of murine adipose tissue lipolysis and insulin resistance by the TGFβ superfamily protein GDF3

TGFβ superfamily proteins can affect cellular differentiation, thermogenesis, and fibrosis in mammalian adipose tissue. Here we describe a role for Growth Differentiation Factor 3 (GDF3) on mature adipocyte biology. We find inducible GDF3 loss of function in obese adult mice leads to reduced lipolysis, improved glucose tolerance, and reduced glycemic variability. The effects on lipolysis are driven by lower levels of β3-adrenergic receptor, decreased cAMP and PKA signaling. GDF3 is an ALK5, ALK7, ACVR2A and ACVR2B agonist and also a BMPR2 antagonist. Unlike ALK7 or activin E knockouts, acute GDF3 loss of function does not affect body weight or energy balance but significantly improves metabolic health. These results suggest that blocking GDF3 can improve metabolic health independent of body weight and food intake, an intriguing new model for developing anti-diabetic therapies. Together these results provide much-needed clarity to both the molecular pathways involved in GDF3 signaling and its physiological effects.

Network toxicology and molecular docking techniques to explore the mechanism of bisphenol A on obesity

The study investigates how bisphenol A (BPA) exposure may lead to obesity (OB) by identifying molecular mechanisms and suggests a new research approach for examining the health effects of chemical toxins. Researchers identified 237 potential targets associated with BPA exposure and OB using CTD, STITCH, DrugBank, GeneCards, and OMIM databases. Analysis with STRING and Cytoscape revealed 10 key targets, including INS, IL-6, AKT1, and PPARG. Enrichment analysis via the DAVID database indicated that these targets are primarily involved in PI3K-Akt and Insulin signaling pathways. These findings indicate that BPA may contribute to the occurrence and development of OB by influencing apoptosis, proliferation, inflammatory signaling, and insulin resistance. Molecular docking showed strong binding of BPA to INS, IL-6, AKT1, and PPARG, with molecular dynamics simulations revealing a stable complex of BPA and PPARG. This study offers insights into BPA's role in OB and supports efforts to prevent and treat OB diseases linked to exposure to BPA-containing plastic products and certain BPA-inundated environments.

A tethering mechanism underlies Pin1-catalyzed proline cis-trans isomerization at a noncanonical site

The prolyl isomerase Pin1 catalyzes the cis-trans isomerization of proline peptide bonds, a noncovalent post-translational modification that influences cellular and molecular processes, including protein-protein interactions. Pin1 is a two-domain enzyme containing a WW domain that recognizes phosphorylated serine/threonine-proline (pS/pT-P) canonical motifs and an enzymatic PPIase domain that catalyzes proline cis-trans isomerization of pS/pT-P motifs. Here, we show that Pin1 uses a tethering mechanism to bind and catalyze proline cis-trans isomerization of a noncanonical motif in the disordered N-terminal activation function-1 (AF-1) domain of the human nuclear receptor PPARγ. NMR reveals multiple Pin1 binding regions within the PPARγ AF-1, including a canonical motif (pS112-P113) that when phosphorylated by the kinase ERK2 binds the Pin1 WW domain with high affinity. NMR methods reveal that Pin1 also binds and accelerates cis-trans isomerization of a noncanonical motif containing a tryptophan-proline motif (W39-P40) previously shown to be involved in an interdomain interaction with the C-terminal ligand-binding domain (LBD) of PPARγ. Cellular transcription studies combined with mutagenesis and Pin1 inhibitor treatment reveal a functional role for Pin1-mediated acceleration of cis-trans isomerization of the PPARγ W39-P40 motif. Our data inform a refined model of the Pin1 catalytic mechanism where the WW domain can bind a canonical pS/T-P motif and tether Pin1 to a target, which enables the PPIase domain to exert catalytic cis-trans isomerization at a distal noncanonical site.

Diverse Physiological Roles of Kynurenine Pathway Metabolites: Updated Implications for Health and Disease

Tryptophan is an essential amino acid critical for human health. It plays a pivotal role in numerous physiological and biochemical processes through its metabolism. The kynurenine (KYN) pathway serves as the principal metabolic route for tryptophan, producing bioactive metabolites, including KYN, quinolinic acid, and 3-hydroxykynurenine. Numerous studies are actively investigating the relationship between tryptophan metabolism and physiological functions. These studies are highlighting the interactions among metabolites that may exert synergistic or antagonistic effects, such as neuroprotective or neurotoxic, and pro-oxidative or antioxidant activities. Minor disruptions in the homeostasis of these metabolites can result in immune dysregulation, contributing to a spectrum of diseases. These diseases include neurological disorders, mental illnesses, cardiovascular conditions, autoimmune diseases, and chronic kidney disease. Therefore, understanding the physiological roles of the KYN pathway metabolites is essential for elucidating the contribution of tryptophan metabolism to health regulation. The present review emphasizes the physiological roles of KYN pathway metabolites and their mechanisms in disease development, aiming to establish a theoretical basis for leveraging dietary nutrients to enhance human health.

Drugs targeting peroxisome proliferator-activated receptors

The year 2024 witnessed the accelerated approvals of two peroxisome proliferator-activated receptor (PPAR) agonists for the treatment of primary biliary cholangitis (PBC). PPARs, including three isoforms (PPARα, PPARγ, and PPARδ), are therapeutic targets generating considerable debate yet also seeing significant advances in their successful targeting. Currently, selective PPAR agonists are used to manage hyperlipidemia, type 2 diabetes mellitus (T2DM), and PBC, and dual/pan-PPAR agonists have been developed to address various disorders. In this review, we summarize the PPAR agonists approved globally, and their pros and cons as therapeutic agents for various diseases, with a particular focus on those agonists marketed since 2010.

Recent advances and therapeutic applications of PPARγ-targeted ligands based on the inhibition mechanism of Ser273 phosphorylation

PPARγ functions as a master ligand-dependent transcription factor that regulates the expressions of a variety of key genes related to metabolic homeostasis and inflammatory immunity. It has been recognized as a popular and druggable target in modern drug discovery. Similar to other nuclear receptors, PPARγ is a phosphoprotein, and its biological functions are regulated by phosphorylation, especially at Ser273 site which is mediated by CDK5 or ERK. In the past decade, the excessive level of PPARγ-Ser273 phosphorylation has been confirmed to be a crucial factor in promoting the occurrence and development of some major diseases. Ligands capable of inhibiting PPARγ-Ser273 phosphorylation have shown great potentials for treatment. Despite these achievements, to our knowledge, no related review focusing on this topic has been conducted so far. Therefore, we herein summarize the basic knowledge of PPARγ and CDK5/ERK-mediated PPARγ-Ser273 phosphorylation as well as its physiopathological role in representative diseases. We also review the developments and therapeutic applications of PPARγ-targeted ligands based on this mechanism. Finally, we suggest several directions for future investigations. We expect that this review can evoke more inspiration of scientific communities, ultimately facilitating the promotion of the PPARγ-Ser273 phosphorylation-involved mechanism as a promising breakthrough point for addressing the clinical treatment of human diseases.

CDK5: Insights into its roles in diseases

Cyclin-dependent kinase 5 (CDK5), a unique member of the CDK family, is a proline-directed serine/threonine protein kinase with critical roles in various physiological and pathological processes. Widely expressed in the central nervous system, CDK5 is strongly implicated in neurological diseases. Beyond its neurological roles, CDK5 is involved in metabolic disorders, psychiatric conditions, and tumor progression, contributing to processes such as proliferation, migration, immune evasion, genomic stability, and angiogenesis. This review explores the structure and biological functions of CDK5, highlighting its regulatory roles in disease development through the phosphorylation of diverse substrate proteins. Additionally, we examine the therapeutic potential of CDK5 inhibition, offering novel perspectives for disease diagnosis and treatment.

Cyclin-dependent protein kinases and cell cycle regulation in biology and disease

Cyclin Dependent Kinases (CDKs) are closely connected to the regulation of cell cycle progression, having been first identified as the kinases able to drive cell division. In reality, the human genome contains 20 different CDKs, which can be divided in at least three different sub-family with different functions, mechanisms of regulation, expression patterns and subcellular localization. Most of these kinases play fundamental roles the normal physiology of eucaryotic cells; therefore, their deregulation is associated with the onset and/or progression of multiple human disease including but not limited to neoplastic and neurodegenerative conditions. Here, we describe the functions of CDKs, categorized into the three main functional groups in which they are classified, highlighting the most relevant pathways that drive their expression and functions. We then discuss the potential roles and deregulation of CDKs in human pathologies, with a particular focus on cancer, the human disease in which CDKs have been most extensively studied and explored as therapeutic targets. Finally, we discuss how CDKs inhibitors have become standard therapies in selected human cancers and propose novel ways of investigation to export their targeting from cancer to other relevant chronic diseases. We hope that the effort we made in collecting all available information on both the prominent and lesser-known CDK family members will help in identify and develop novel areas of research to improve the lives of patients affected by debilitating chronic diseases.

Macrophage MST1 protects against schistosomiasis-induced liver fibrosis by promoting the PPARγ-CD36 pathway and suppressing NF-κB signaling

Schistosomiasis is characterized by egg-induced hepatic granulomas and subsequent fibrosis. Monocyte-derived macrophages play critical and plastic roles in the progression and regression of liver fibrosis, adopting different polarization phenotypes. Mammalian STE20-like protein kinase 1 (MST1), a serine/threonine kinase, has been established to act as a negative regulator of macrophage-associated inflammation. However, the specific role of MST1 in Schistosoma-induced liver fibrosis has not been fully understood. In this study, we demonstrate that macrophage MST1 functions as an inhibitor of inflammation and fibrosis following infection with Schistosoma japonicum (S. japonicum). Mice with macrophages-specific Mst1 knockout (termed Mst1△M/△M) mice developed exacerbated liver pathology, characterized by larger egg-induced granulomas, and increased fibrosis post infection. This was accompanied by enhanced production of proinflammatory cytokines (IL1B, IL6, IL23, TNFA and TGFB) and a shift in macrophage phenotype towards Ly6Chigh. Mechanistically, MST1 activation by soluble egg antigen (SEA) promoted PPARγ-mediated CD36 expression, enhancing phagocytosis and consequently upregulation of fibrolytic genes such as Arg1 and Mmps. Conversely, MST1 deletion leads to up-regulation of pro-inflammatory genes instead of fibrolytic genes in macrophages, accompanied by decreased expression of CD36 and impaired phagocytosis. Furthermore, the ablation of MST1 enhances NF-κB activation in S. japonicum-infected and SEA-stimulated macrophages, resulting in increased production of proinflammatory cytokines. Overall, our data identified MST1 as a novel regulator for egg-induced liver fibrosis via modulation of macrophage function and phenotype by CD36-mediated phagocytosis and suppression of NF-κB pathway.

Phosphoproteomic analysis reveals CDK5-Mediated phosphorylation of MTDH inhibits protein synthesis in microglia

CDK5 plays a crucial role in maintaining normal central nervous system (CNS) development and synaptic function, while microglia are the primary immune cells present in the CNS and play vital physiological roles in CNS development, immune surveillance, and regulation of synaptic plasticity. Despite this, our understanding of both the substrate proteins and functional mechanisms of CDK5 in microglia remains limited. To address this, we utilized CRISPR-Cas9 knockout of Cdk5 in BV2 cells and conducted quantitative phosphoproteomics analysis to systematically screen potential CDK5 substrates in microglia. Our findings identified 335 phosphorylation sites on 234 proteins as potential CDK5 substrates in microglia based on the reported sequence motif. Through in vitro kinase assay and intracellular inhibition and knockout of CDK5 experiments, we confirmed that ER proteins MTDH (protein LYRIC) and Calnexin are novel substrate proteins of CDK5. Moreover, we demonstrated for the first time a critical mechanism for regulating protein synthesis in microglia, that the phosphorylation of S565 site on MTDH, a key protein mediating cell growth, by CDK5 inhibits protein synthesis. Our data provide valuable insights for the discovery of new substrate proteins of CDK5 and the in-depth investigation of the function and mechanism of CDK5 in microglia.

Insights into the chirality-dependent recognition of Danshensu Bingpian Zhi stereoisomers with PPARγ

Peroxisome proliferator-activated receptor γ (PPARγ), a nuclear receptor involved in metabolic processes, inflammation, and energy balance, represents a promising therapeutic target for cardiovascular diseases. Danshensu Bingpian Zhi (DBZ), a chiral compound derived from traditional Chinese medicine, exhibits potential as a PPARγ agonist. Using an ensemble-based docking approach, molecular dynamics (MD) simulations, and the molecular mechanics generalized born surface area (MM/GBSA) methods, we explored the binding modes and energetics of DBZ stereoisomers with the PPARγ ligand-binding domain (LBD). The results indicated that the right-handed stereoisomer (DBZR) binds like a full agonist, while the left-handed stereoisomer (DBZS) binds as a partial agonist with stronger binding energies (ΔGbind), indicating a robust interaction with PPARγ. Both the stereoisomers stabilize the β-sheet region of PPARγ-LBD, potentially protecting Ser245 from phosphorylation by Cdk5, a process implicated in atherosclerosis. Principal component analysis (PCA) and dynamic cross-correlation matrices (DCCM) revealed the complex structural dynamics within the Ω loop, β-sheet, and AF-2 region of PPARγ-LBD upon ligand binding, which may contribute to the unique binding mode and efficacy of DBZS. These findings provide insights into the molecular recognition of PPARγ-LBD by DBZ stereoisomers and their impact on the conformational dynamics of PPARγ, highlighting the therapeutic potential of DBZ and the significance of chirality in drug design.

SPA Promotes Atherosclerosis Through Mediating Macrophage Foam Cell Formation-Brief Report

BACKGROUND

Atherosclerosis is a progressive inflammatory disease in which macrophage foam cells play a central role in disease pathogenesis. SPA (surfactant protein A) is a lipid-associating protein involved with regulating macrophage function in various inflammatory diseases. However, the role of SPA in atherosclerosis and macrophage foam cell formation has not been investigated.

METHODS

SPA expression was assessed in healthy and atherosclerotic human coronary arteries and the brachiocephalic arteries of wild-type or ApoE-deficient mice fed high-fat diets for 4 weeks. Hypercholesteremic wild-type and SPA-deficient mice fed a high-fat diet for 6 weeks were investigated for atherosclerotic lesions in vivo. In vitro experiments using RAW264.7 macrophages, primary resident peritoneal macrophages extracted from wild-type or SPA-deficient mice, and human monocyte-derived macrophages from the peripheral blood of healthy donors determined the functional effects of SPA in macrophage foam cell formation.

RESULTS

SPA expression was increased in atherosclerotic lesions in humans and ApoE-deficient mice and in response to a proatherosclerotic stimulus in vitro. SPA deficiency reduced the lipid profiles induced by hypercholesterolemia, attenuated atherosclerosis, and reduced the number of lesion-associated macrophage foam cells. In vitro studies revealed that SPA deficiency reduced intracellular cholesterol accumulation and macrophage foam cell formation. Mechanistically, SPA deficiency dramatically downregulated the expression of scavenger receptor CD36 (cluster of differentiation antigen 36) cellular and lesional expression. Importantly, SPA also increased CD36 expression in human monocyte-derived macrophages.

CONCLUSIONS

Our results elucidate that SPA is a novel factor promoting atherosclerosis development. SPA enhances macrophage foam cell formation and atherosclerosis by increasing scavenger receptor CD36 expression, leading to increasing cellular OxLDL influx.

The anti-obesity effects of polyphenols: a comprehensive review of molecular mechanisms and signal pathways in regulating adipocytes

Excess weight gain is a growing concern worldwide, fueled by increased consumption of calorie-dense foods and more sedentary lifestyles. Obesity in China is also becoming increasingly problematic, developing into a major public health concern. Obesity not only increases the risk of associated disease but also imposes a burden on health care systems, and it is thus imperative that an effective intervention approach be identified. Recent studies have demonstrated that the polyphenol-rich Mediterranean diet has considerable potential in this regard. Polyphenols can inhibit the production of adipocytes and reduce adverse reactions, such as inflammation, insulin resistance, and gut microflora imbalance. In this review, we examine four polyphenols (curcumin, ellagic acid, ferulic acid, and quercetin) in terms of their potential as interventions targeting obesity. The mechanisms that help promote adipocyte browning, increase thermogenic factors, increase thermogenesis, and regulate adipocyte differentiation are summarized, and key signaling pathways, including PPARγ, C/EBP-, and others, are reviewed.

Structure-based screening, optimization and biological evaluation of novel chrysin-based derivatives as selective PPARγ modulators for the treatment of T2DM and hepatic steatosis

In consideration of several serious side effects induced by the classical AF-2 involved "lock" mechanism, recently disclosed PPARγ-Ser273 phosphorylation mode of action has become an alternative and mainstream mechanism for currently PPARγ-based drug discovery and development with an improved therapeutic index. In this study, by virtue of structure-based virtual high throughput screening (SB-VHTS), structurally chemical optimization by targeting the inhibition of the PPARγ-Ser273 phosphorylation as well as in vitro biological evaluation, which led to the final identification of a chrysin-based potential hit (YGT-31) as a novel selective PPARγ modulator with potent binding affinity and partial agonism. Further in vivo evaluation demonstrated that YGT-31 possessed potent glucose-lowering and relieved hepatic steatosis effects without involving the TZD-associated side effects. Mechanistically, YGT-31 presented such desired therapeutic index, mainly because it effectively inhibited the CDK5-mediated PPARγ-Ser273 phosphorylation, selectively elevated the level of insulin sensitivity-related Glut4 and adiponectin but decreased the expression of insulin-resistance-associated genes PTP1B and SOCS3 as well as inflammation-linked genes IL-6, IL-1β and TNFα. Finally, the molecular docking study was also conducted to uncover an interesting hydrogen-bonding network of YGT-31 with PPARγ-Ser273 phosphorylation-related key residues Ser342 and Glu343, which not only gave a clear verification for our targeting modification but also provided a proof of concept for the abovementioned molecular mechanism.

Mechanisms of the NAD+ salvage pathway in enhancing skeletal muscle function

Nicotinamide adenine dinucleotide (NAD+) is crucial for cellular energy production, serving as a coenzyme in oxidation-reduction reactions. It also supports enzymes involved in processes such as DNA repair, aging, and immune responses. Lower NAD+ levels have been associated with various diseases, highlighting the importance of replenishing NAD+. Nicotinamide phosphoribosyltransferase (NAMPT) plays a critical role in the NAD+ salvage pathway, which helps sustain NAD+ levels, particularly in high-energy tissues like skeletal muscle.This review explores how the NAMPT-driven NAD+ salvage pathway influences skeletal muscle health and functionality in aging, type 2 diabetes mellitus (T2DM), and skeletal muscle injury. The review offers insights into enhancing the salvage pathway through exercise and NAD+ boosters as strategies to improve muscle performance. The findings suggest significant potential for using this pathway in the diagnosis, monitoring, and treatment of skeletal muscle conditions.

Pharmacology of Aging: Drosophila as a Tool to Validate Drug Targets for Healthy Lifespan

Finding effective therapies to manage age-related conditions is an emerging public health challenge. Although disease-targeted treatments are important, a preventive approach focused on aging can be more efficient. Pharmacological targeting of aging-related processes can extend lifespan and improve health in animal models. However, drug development and translation are particularly challenging in geroscience. Preclinical studies have survival as a major endpoint for drug screening, which requires years of research in mammalian models. Shorter-lived invertebrates can be exploited to accelerate this process. In particular, the fruit fly Drosophila melanogaster allows the validation of new drug targets using precise genetic tools and proof-of-concept experiments on drugs impacting conserved aging processes. Screening for clinically approved drugs that act on aging-related targets may further accelerate translation and create new tools for aging research. To date, 31 drugs used in clinical practice have been shown to extend the lifespan of flies. Here, we describe recent advances in the pharmacology of aging, focusing on Drosophila as a tool to repurpose these drugs and study age-related processes.

Class Effect Unveiled: PPARγ Agonists and MEK Inhibitors in Cancer Cell Differentiation

Epithelial-to-mesenchymal transition (EMT) plays a major role in breast cancer progression and the development of drug resistance. We have previously demonstrated a trans-differentiation therapeutic approach targeting invasive dedifferentiated cancer cells. Using a combination of PPARγ agonists and MEK inhibitors, we forced the differentiation of disseminating breast cancer cells into post-mitotic adipocytes. Utilizing murine breast cancer cells, we demonstrated a broad class effect of PPARγ agonists and MEK inhibitors in inducing cancer cell trans-differentiation into adipocytes. Both Rosiglitazone and Pioglitazone effectively induced adipogenesis in cancer cells, marked by PPARγ and C/EBPα upregulation, cytoskeleton rearrangement, and lipid droplet accumulation. All tested MEK inhibitors promoted adipogenesis in the presence of TGFβ, with Cobimetinib showing the most prominent effects. A metastasis ex vivo culture from a patient diagnosed with triple-negative breast cancer demonstrated a synergistic upregulation of PPARγ with the combination of Pioglitazone and Cobimetinib. Our results highlight the potential for new therapeutic strategies targeting cancer cell plasticity and the dedifferentiation phenotype in aggressive breast cancer subtypes. Combining differentiation treatments with standard therapeutic approaches may offer a strategy to overcome drug resistance.

Diet-Induced Obesity Induces Transcriptomic Changes in Neuroimmunometabolic-Related Genes in the Striatum and Olfactory Bulb

The incidence of obesity has markedly increased globally over the last several decades and is believed to be associated with the easier availability of energy-dense foods, including high-fat foods. The reinforcing hedonic properties of high-fat foods, including olfactory cues, activate reward centers in the brain, motivating eating behavior. Thus, there is a growing interest in the understanding of the genetic changes that occur in the brain that are associated with obesity and eating behavior. This growing interest has paralleled advances in genomic methods that enable transcriptomic-wide analyses. Here, we examined the transcriptomic-level differences in the olfactory bulb and striatum, regions of the brain associated with olfaction and hedonic food-seeking, respectively, in high-fat-diet (HFD)-fed obese mice. To isolate the dietary effects from obesity, we also examined transcriptomic changes in normal-chow-fed and limited-HFD-fed groups, with the latter being pair-fed with an HFD isocaloric to the consumption of the normal-chow-fed mice. Using RNA sequencing, we identified 274 differentially expressed genes (DEGs) in the striatum and 11 in the olfactory bulb of ad libitum HFD-fed mice compared to the chow-fed group, and thirty-eight DEGs in the striatum between the ad libitum HFD and limited-HFD-fed groups. The DEGs in both tissues were associated with inflammation and immune-related pathways, including oxidative stress and immune function, and with mitochondrial dysfunction and reward pathways in the striatum. These results shed light on potential obesity-associated genes in these regions of the brain.

Lipid synthesis, triggered by PPARγ T166 dephosphorylation, sustains reparative function of macrophages during tissue repair

Macrophages may acquire a reparative phenotype that supports tissue repair and remodeling in response to tissue injury. However, the metabolic requirements underpinning this process are incompletely understood. Here, we show that posttranslational modification (PTM) of PPARγ regulates lipid synthesis in response to wound microenvironmental cues and that metabolic rewiring orchestrates function of reparative macrophages. In injured tissues, repair signaling leads to decreased macrophage PPARγ threonine 166 (T166) phosphorylation, which results in a partially active PPARγ transcriptional program comprised of increased binding activity to the regulator regions of lipid synthesis-associated genes, thereby increased lipogenesis. The accumulated lipids serve as signaling molecules, triggering STAT3-mediated growth factor expression, and supporting the synthesis of phospholipids for the expansion of the endoplasmic reticulum (ER), which is required for protein secretion. Genetic or pharmacological inhibition of PPARγ T166 phosphorylation promotes the reparative function of macrophages and facilitates tissue regeneration. In summary, our work identifies PPARγ T166-regulated lipid biosynthesis as an essential pathway for meeting the anabolic demands of the activation and function of macrophages and provides a rationale for potential therapeutic targeting of tissue repair.

Endothelin 3/EDNRB signaling induces thermogenic differentiation of white adipose tissue

Thermogenic adipose tissue, consisting of brown and beige fat, regulates nutrient utilization and energy metabolism. Human brown fat is relatively scarce and decreases with obesity and aging. Hence, inducing thermogenic differentiation of white fat offers an attractive way to enhance whole-body metabolic capacity. Here, we show the role of endothelin 3 (EDN3) and endothelin receptor type B (EDNRB) in promoting the browning of white adipose tissue (WAT). EDNRB overexpression stimulates thermogenic differentiation of human white preadipocytes through cAMP-EPAC1-ERK activation. In mice, cold induces the expression of EDN3 and EDNRB in WAT. Deletion of EDNRB in adipose progenitor cells impairs cold-induced beige adipocyte formation in WAT, leading to excessive weight gain, glucose intolerance, and insulin resistance upon high-fat feeding. Injection of EDN3 into WAT promotes browning and improved whole-body glucose metabolism. The findings shed light on the mechanism of WAT browning and offer potential therapeutics for obesity and metabolic disorders.

Rosiglitazone and trametinib exhibit potent anti-tumor activity in a mouse model of muscle invasive bladder cancer

Muscle invasive bladder cancers (BCs) can be divided into 2 major subgroups-basal/squamous (BASQ) tumors and luminal tumors. Since Pparg has low or undetectable expression in BASQ tumors, we tested the effects of rosiglitazone, Pparg agonist, in a mouse model of BASQ BC. We find that rosiglitazone reduces proliferation while treatment with rosiglitazone plus trametinib, a MEK inhibitor, induces apoptosis and reduces tumor volume by 91% after 1 month. Rosiglitazone and trametinib also induce a shift from BASQ to luminal differentiation in tumors, which our analysis suggests is mediated by retinoid signaling, a pathway known to drive the luminal differentiation program. Our data suggest that rosiglitazone, trametinib, and retinoids, which are all FDA approved, may be clinically active in BASQ tumors in patients.

Sulfonylureas exert antidiabetic action on adipocytes by inhibition of PPARγ serine 273 phosphorylation

OBJECTIVE

Sulfonylureas (SUs) are still among the mostly prescribed antidiabetic drugs with an established mode of action: release of insulin from pancreatic β-cells. In addition, effects of SUs on adipocytes by activation of the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) have been described, which might explain their insulin-sensitizing potential observed in patients. However, there is a discrepancy between the impact of SUs on antidiabetic action and their rather moderate in vitro effect on PPARγ transcriptional activity. Recent studies have shown that some PPARγ ligands can improve insulin sensitivity by blocking PPARγ Ser-273 phosphorylation without having full agonist activity. It is unknown if SUs elicit their antidiabetic effects on adipocytes by inhibition of PPARγ phosphorylation. Here, we investigated if binding of SUs to PPARγ can interfere with PPARγ Ser-273 phosphorylation and determined their antidiabetic actions in vitro in primary human white adipocytes and in vivo in high-fat diet (HFD) obese mice.

METHODS

Primary human white preadipocytes were differentiated in the presence of glibenclamide, glimepiride and PPARγ ligands rosiglitazone and SR1664 to compare PPARγ Ser-273 phosphorylation, glucose uptake and adipokine expression. Transcriptional activity at PPARγ was determined by luciferase assays, quantification of PPARγ Ser-273 phosphorylation was determined by Western blotting and CDK5 kinase assays. In silico modelling was performed to gain insight into the binding characteristics of SUs to PPARγ. HFD mice were administered SUs and rosiglitazone for 6 days. PPARγ Ser-273 phosphorylation in white adipose tissue (WAT), body composition, glucose tolerance, adipocyte morphology and expression levels of genes involved in PPARγ activity in WAT and brown adipose tissue (BAT) were evaluated.

RESULTS

SUs inhibit phosphorylation of PPARγ at Ser-273 in primary human white adipocytes and exhibit a positive antidiabetic expression profile, which is characterized by up regulation of insulin-sensitizing and down regulation of insulin resistance-inducing adipokines. We demonstrate that SUs directly bind to PPARγ by in silico modelling and inhibit phosphorylation in kinase assays to a similar extend as rosiglitazone and SR1664. In HFD mice SUs reduce PPARγ phosphorylation in WAT and have comparable effects on gene expression to rosiglitazone. In BAT SUs increase UCP1 expression and reduce lipid droplets sizes.

CONCLUSIONS

Our findings indicate that a part of SUs extra-pancreatic effects on adipocytes in vitro and in vivo is probably mediated via their interference with PPARγ phosphorylation rather than via classical agonistic activity at clinical concentrations.

Enhanced detection of ligand-PPARγ binding based on surface plasmon resonance through complexation with SRC1- or NCOR2-related polypeptide

A previous study reported the use of a biosensing technique based on surface plasmon resonance (SPR) for the ligand binding detection of peroxisome proliferator activator receptor gamma (PPARγ). This detection was designed based on the structural properties of PPARγ. Because of cross-linked protein inactivation and the low molecular weight of conventional ligands, direct ligand binding detection based on SPR has low stability and repeatability. In this study, we report an indirect response methodology based on SPR technology in which anti-His CM5 chip binds fresh PPARγ every cycle, resulting in more stable detection. We developed a remarkable improvement in ligand-protein binding detectability in vitro by introducing two coregulator-related polypeptides into this system. In parallel, a systematic indirect response methodology can reflect the interaction relationship between ligands and proteins to some extent by detecting the changes in SA-SRC1 and GST-NCOR2 binding to PPARγ. Rosiglitazone, a PPARγ agonist with strong affinity, is a potent insulin-sensitizing agent. Some ligands may be competitively exerted at the same sites of PPARγ (binding rosiglitazone). We demonstrated using indirect response methodology that selective PPARγ modulator (SPPARM) candidates of PPARγ can be found by competing for the binding of the rosiglitazone site on PPARγ, although they may have no effect on polypeptides and PPARγ binding.

Raloxifene-driven benzothiophene derivatives: Discovery, structural refinement, and biological evaluation as potent PPARγ modulators based on drug repurposing

By virtue of the drug repurposing strategy, the anti-osteoporosis drug raloxifene was identified as a novel PPARγ ligand through structure-based virtual high throughput screening (SB-VHTS) of FDA-approved drugs and TR-FRET competitive binding assay. Subsequent structural refinement of raloxifene led to the synthesis of a benzothiophene derivative, YGL-12. This compound exhibited potent PPARγ modulation with partial agonism, uniquely promoting adiponectin expression and inhibiting PPARγ Ser273 phosphorylation by CDK5 without inducing the expression of adipongenesis associated genes, including PPARγ, aP2, CD36, FASN and C/EBPα. This specific activity profile resulted in effective hypoglycemic properties, avoiding major TZD-related adverse effects like weight gain and hepatomegaly, which were demonstrated in db/db mice. Molecular docking studies showed that YGL-12 established additional hydrogen bonds with Ile281 and enhanced hydrogen-bond interaction with Ser289 as well as PPARγ Ser273 phosphorylation-related residues Ser342 and Glu343. These findings suggested YGL-12 as a promising T2DM therapeutic candidate, thereby providing a molecular framework for the development of novel PPARγ modulators with an enhanced therapeutic index.

Recent advances of myotubularin-related (MTMR) protein family in cardiovascular diseases

Belonging to a lipid phosphatase family containing 16 members, myotubularin-related proteins (MTMRs) are widely expressed in a variety of tissues and organs. MTMRs preferentially hydrolyzes phosphatidylinositol 3-monophosphate and phosphatidylinositol (3,5) bis-phosphate to generate phosphatidylinositol and phosphatidylinositol 5-monophosphate, respectively. These phosphoinositides (PIPs) promote membrane degradation during autophagosome-lysosomal fusion and are also involved in various regulatory signal transduction. Based on the ability of modulating the levels of these PIPs, MTMRs exert physiological functions such as vesicle trafficking, cell proliferation, differentiation, necrosis, cytoskeleton, and cell migration. It has recently been found that MTMRs are also involved in the occurrence and development of several cardiovascular diseases, including cardiomyocyte hypertrophy, proliferation of vascular smooth muscle cell, LQT1, aortic aneurysm, etc. This review summarizes the functions of MTMRs and highlights their pathophysiological roles in cardiovascular diseases.

Large-scale comparison of machine learning methods for profiling prediction of kinase inhibitors

Conventional machine learning (ML) and deep learning (DL) play a key role in the selectivity prediction of kinase inhibitors. A number of models based on available datasets can be used to predict the kinase profile of compounds, but there is still controversy about the advantages and disadvantages of ML and DL for such tasks. In this study, we constructed a comprehensive benchmark dataset of kinase inhibitors, involving in 141,086 unique compounds and 216,823 well-defined bioassay data points for 354 kinases. We then systematically compared the performance of 12 ML and DL methods on the kinase profiling prediction task. Extensive experimental results reveal that (1) Descriptor-based ML models generally slightly outperform fingerprint-based ML models in terms of predictive performance. RF as an ensemble learning approach displays the overall best predictive performance. (2) Single-task graph-based DL models are generally inferior to conventional descriptor- and fingerprint-based ML models, however, the corresponding multi-task models generally improves the average accuracy of kinase profile prediction. For example, the multi-task FP-GNN model outperforms the conventional descriptor- and fingerprint-based ML models with an average AUC of 0.807. (3) Fusion models based on voting and stacking methods can further improve the performance of the kinase profiling prediction task, specifically, RF::AtomPairs + FP2 + RDKitDes fusion model performs best with the highest average AUC value of 0.825 on the test sets. These findings provide useful information for guiding choices of the ML and DL methods for the kinase profiling prediction tasks. Finally, an online platform called KIPP ( https://kipp.idruglab.cn ) and python software are developed based on the best models to support the kinase profiling prediction, as well as various kinase inhibitor identification tasks including virtual screening, compound repositioning and target fishing.

CABLES1 expression is reduced in human subcutaneous adipose tissue in obesity and type 2 diabetes but may not directly impact adipocyte glucose and lipid metabolism

Cdk5 and Abl enzyme substrate 1 (CABLES1) is a cell cycle regulator that has previously been identified as a candidate gene for obesity-related phenotypes, but little is known about its role in adipose tissue metabolism. In this study, we explore the role of CABLES1 in obesity and type 2 diabetes (T2D) in human subcutaneous adipose tissue (SAT). We performed gene expression analysis of SAT obtained from subjects with and without T2D, and from a second validation cohort consisting of subjects without T2D. We used CRISPR/Cas9 genome editing to perform CABLES1 loss-of-function studies in human primary preadipocytes and assessed them functionally after differentiation. CABLES1 gene expression in SAT was decreased in T2D by almost 25%, and inversely associated with insulin resistance markers and hyperglycaemia. mRNA levels were reduced with increasing BMI and negatively correlated with obesity markers. We found that adipocytes are likely the main CABLES1-expressing cell type in SAT, but CABLES1 depletion in adipocytes caused no phenotypical changes in regards to differentiation, glucose uptake, or expression of key genes of adipocyte function. These findings suggest that CABLES1 gene expression in SAT might be altered in obesity and T2D as a consequence of metabolic dysregulation rather than being a causal factor.

IL-27 increases energy storage in white adipocytes by enhancing glucose uptake and fatty acid esterification

The cytokine interleukin (IL)-27 has been reported to induce thermogenesis in white adipocytes. However, it remains unknown whether IL-27-mediated adipocyte energy dissipation is paralleled by an elevated energy supply from lipids and/or carbohydrates. We hypothesized that IL-27 increases lipolysis and glucose uptake in white adipocytes, thereby providing substrates for thermogenesis. Unexpectedly, we found that treatment of 3T3-L1 adipocytes with IL-27 reduced intra- and extracellular free fatty acid (FFA) concentrations and that phosphorylation of hormone-sensitive lipase (HSL) was not affected by IL-27. These results were confirmed in subcutaneous white adipocytes. Further, application of IL-27 to 3T3-L1 adipocytes increased intracellular triglyceride (TG) content but not mitochondrial ATP production nor expression of enzymes involved in beta-oxidation indicating that elevated esterification rather than oxidation causes FFA disappearance. In addition, IL-27 significantly increased GLUT1 protein levels, basal glucose uptake as well as glycolytic ATP production, suggesting that increased glycolytic flux due to IL-27 provides the glycerol backbone for TG synthesis. In conclusion, our findings suggest IL-27 increases glucose uptake and TG deposition in white adipocytes.

Sphingolipids in mitochondria-from function to disease

Sphingolipids are not only structural components of cellular membranes but also play vital roles in cell signaling and modulation of cellular processes. Within mitochondria, sphingolipids exert diverse effects on mitochondrial dynamics, energy metabolism, oxidative stress, and cell death pathways. In this review, we summarize literature addressing the crucial role of sphingolipids in mitochondria, highlighting their impact on mitochondrial dynamics, cellular bioenergetics, and important cell processes including apoptosis and mitophagy.

Genistein enhances NAD+ biosynthesis by upregulating nicotinamide phosphoribosyltransferase in adipocytes

A decrease in the NAD+ level in adipocytes causes adipose-tissue dysfunction, leading to systemic glucose, and lipid metabolism failure. Therefore, it is necessary to develop small molecules and nutraceuticals that can increase NAD+ levels in adipocytes. Genistein, a nutraceutical derived from soybeans, has various physiological activities and improves glucose and lipid metabolism. In this study, we aimed to unravel the effects of genistein on the NAD+ level in adipocytes and the underlying molecular mechanisms. Genistein enhanced NAD+ biosynthesis by increasing the expression of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in NAD+ biosynthesis. A pull-down assay using genistein-immobilized beads revealed prohibitin 1 (PHB1) as a target protein of genistein. The knockdown of Phb1 suppressed the genistein-induced increase in NAMPT expression and NAD+ level in adipocytes. Genistein-bound PHB1 contributed to the stabilization of the transcription factor CCAAT/enhancer-binding protein β through the activation of extracellular signal-regulated kinase, resulting in increased NAMPT expression at the transcriptional level. Genistein induced the dephosphorylation of peroxisome proliferator-activated receptor at serine 273 and increased the level of the insulin-sensitizing adipokine adiponectin in adipocytes, whereas the knockdown of Nampt and Phb1 abolished these genistein-mediated effects. Our results proved the potential efficacy of genistein in increasing the NAD+ level and restoring metabolic function in adipocytes. Furthermore, we identified PHB1, localized to the plasma membrane, as a novel candidate target protein for increased expression of NAMPT in adipocytes. Overall, these findings will assist in developing NAD+-boosting nutraceuticals to alleviate metabolic dysfunctions in adipose tissues.

International Union of Basic and Clinical Pharmacology CXIII: Nuclear Receptor Superfamily-Update 2023

The NR superfamily comprises 48 transcription factors in humans that control a plethora of gene network programs involved in a wide range of physiologic processes. This review will summarize and discuss recent progress in NR biology and drug development derived from integrating various approaches, including biophysical techniques, structural studies, and translational investigation. We also highlight how defective NR signaling results in various diseases and disorders and how NRs can be targeted for therapeutic intervention via modulation via binding to synthetic lipophilic ligands. Furthermore, we also review recent studies that improved our understanding of NR structure and signaling. SIGNIFICANCE STATEMENT: Nuclear receptors (NRs) are ligand-regulated transcription factors that are critical regulators of myriad physiological processes. NRs serve as receptors for an array of drugs, and in this review, we provide an update on recent research into the roles of these drug targets.

Peroxisomal ERK mediates Akh/glucagon action and glycemic control

The enhanced response of glucagon and its Drosophila homolog, adipokinetic hormone (Akh), leads to high-caloric-diet-induced hyperglycemia across species. While previous studies have characterized regulatory components transducing linear Akh signaling promoting carbohydrate production, the spatial elucidation of Akh action at the organelle level still remains largely unclear. In this study, we find that Akh phosphorylates extracellular signal-regulated kinase (ERK) and translocates it to peroxisome via calcium/calmodulin-dependent protein kinase II (CaMKII) cascade to increase carbohydrate production in the fat body, leading to hyperglycemia. The mechanisms include that ERK mediates fat body peroxisomal conversion of amino acids into carbohydrates for gluconeogenesis in response to Akh. Importantly, Akh receptor (AkhR) or ERK deficiency, importin-associated ERK retention from peroxisome, or peroxisome inactivation in the fat body sufficiently alleviates high-sugar-diet-induced hyperglycemia. We also observe mammalian glucagon-induced hepatic ERK peroxisomal translocation in diabetic subjects. Therefore, our results conclude that the Akh/glucagon-peroxisomal-ERK axis is a key spatial regulator of glycemic control.

Bavachinin selectively modulates PPAR γ and maintains bone homeostasis in Type 2 Diabetes

Full peroxisome proliferator-activated receptor (PPAR) γ agonists, Thiazolidinediones (TZDs), effectively prevent the process of Type 2 Diabetes Mellitus (T2DM), but their side effects have curtailed use in the clinic, including weight gain and bone loss. Here, we identified that a selective PPAR γ modulator, Bavachinin (BVC), isolated from the seeds of Psoralea Corylifolia L., could potently regulate bone homeostasis. MC3T3-E1 pre-osteoblast cells and C3H10T1/2 mesenchymal stem cells were assessed for osteogenic differentiation activities, and receptor activator of NF-κB ligand (RANKL)-induced RAW 264.7 cells were assessed osteoclasts formation. Leptin receptor-deficient mice and diet-induced obesity mice were applied to evaluate the effect of BVC on bone homeostasis in vivo. Compared to full PPAR γ agonist rosiglitazone, BVC significantly increased the osteogenesis differentiation activities under normal and high glucose conditions in MC3T3-E1 cells. Moreover, BVC could alleviate osteoclast differentiation in RANKL-induced RAW 264.7 cells. In vivo, synthesized BVC prodrug (BN) has been applied to improve water solubility, increase the extent of oral absorption of BVC and prolong its residence time in blood circulation. BN could prevent weight gain, ameliorate lipid metabolism disorders, improve insulin sensitivity, and maintain bone mass and bone biomechanical properties. BVC, a unique PPAR γ selective modulator, could maintain bone homeostasis, and its prodrug (BN) exhibits insulin sensitizer activity while circumventing the side effects of the TZDs, including bone loss and undesirable weight gain.

PPARγ in Atherosclerotic Endothelial Dysfunction: Regulatory Compounds and PTMs

The formation of atherosclerotic plaques is one of the main sources of cardiovascular disease. In addition to known risk factors such as dyslipidemia, diabetes, obesity, and hypertension, endothelial dysfunction has been shown to play a key role in the formation and progression of atherosclerosis. Peroxisome proliferator-activated receptor-gamma (PPARγ), a transcription factor belonging to the steroid superfamily, is expressed in the aorta and plays a critical role in protecting endothelial function. It thereby serves as a target for treating both diabetes and atherosclerosis. Although many studies have examined endothelial cell disorders in atherosclerosis, the role of PPARγ in endothelial dysfunction is still not well understood. In this review, we summarize the possible mechanisms of action behind PPARγ regulatory compounds and post-translational modifications (PTMs) of PPARγ in the control of endothelial function. We also explore the potential use of endothelial PPARγ-targeted agents in the prevention and treatment of atherosclerosis.

Combined Mek inhibition and Pparg activation Eradicates Muscle Invasive Bladder cancer in a Mouse Model of BBN-induced Carcinogenesis

Bladder cancers (BCs) can be divided into 2 major subgroups displaying distinct clinical behaviors and mutational profiles: basal/squamous (BASQ) tumors that tend to be muscle invasive, and luminal/papillary (LP) tumors that are exophytic and tend to be non-invasive. Pparg is a likely driver of LP BC and has been suggested to act as a tumor suppressor in BASQ tumors, where it is likely suppressed by MEK-dependent phosphorylation. Here we tested the effects of rosiglitazone, a Pparg agonist, in a mouse model of BBN-induced muscle invasive BC. Rosiglitazone activated Pparg signaling in suprabasal epithelial layers of tumors but not in basal-most layers containing highly proliferative invasive cells, reducing proliferation but not affecting tumor survival. Addition of trametinib, a MEK inhibitor, induced Pparg signaling throughout all tumor layers, and eradicated 91% of tumors within 7-days of treatment. The 2-drug combination also activated a luminal differentiation program, reversing squamous metaplasia in the urothelium of tumor-bearing mice. Paired ATAC-RNA-seq analysis revealed that tumor apoptosis was most likely linked to down-regulation of Bcl-2 and other pro-survival genes, while the shift from BASQ to luminal differentiation was associated with activation of the retinoic acid pathway and upregulation of Kdm6a, a lysine demethylase that facilitates retinoid-signaling. Our data suggest that rosiglitazone, trametinib, and retinoids, which are all FDA approved, may be clinically active in BASQ tumors in patients. That muscle invasive tumors are populated by basal and suprabasal cell types with different responsiveness to PPARG agonists will be an important consideration when designing new treatments.

FAM3D: A gut secreted protein and its potential in the regulation of glucose metabolism

The number of diabetic patients is rising globally and concomitantly so do the diabetes associated complications. The gut secretes a variety of proteins to control blood glucose levels and/or food intake. As the drug class of GLP-1 agonists is based on a gut secreted peptide and the positive metabolic effects of bariatric surgery are at least partially mediated by gut peptides, we were interested in other gut secreted proteins which have yet to be explored. In this respect we identified the gut secreted protein FAM3D by analyzing sequencing data from L- and epithelial cells of VSG and sham operated as well as chow and HFD fed mice. FAM3D was overexpressed in diet induced obese mice via an adeno-associated virus (AAV), which resulted in a significant improvement of fasting blood glucose levels, glucose tolerance and insulin sensitivity. The liver lipid deposition was reduced, and the steatosis morphology was improved. Hyperinsulinemic clamps indicated that FAM3D is a global insulin sensitizer and increases glucose uptake into various tissues. In conclusion, the current study demonstrated that FAM3D controls blood glucose levels by acting as an insulin sensitizing protein and improves hepatic lipid deposition.

3-Hydroxybutyrate ameliorates insulin resistance by inhibiting PPARγ Ser273 phosphorylation in type 2 diabetic mice

3-Hydroxybutyrate (3HB) is a small ketone body molecule produced endogenously by the body in the liver. Previous studies have shown that 3HB can reduce blood glucose level in type 2 diabetic (T2D) patients. However, there is no systematic study and clear mechanism to evaluate and explain the hypoglycemic effect of 3HB. Here we demonstrate that 3HB reduces fasting blood glucose level, improves glucose tolerance, and ameliorates insulin resistance in type 2 diabetic mice through hydroxycarboxylic acid receptor 2 (HCAR2). Mechanistically, 3HB increases intracellular calcium ion (Ca²⁺) levels by activating HCAR2, thereby stimulating adenylate cyclase (AC) to increase cyclic adenosine monophosphate (cAMP) concentration, and then activating protein kinase A (PKA). Activated PKA inhibits Raf1 proto-oncogene serine/threonine-protein kinase (Raf1) activity, resulting in a decrease in extracellular signal-regulated kinases 1/2 (ERK1/2) activity and ultimately inhibiting peroxisome proliferator-activated receptor γ (PPARγ) Ser273 phosphorylation in adipocytes. Inhibition of PPARγ Ser273 phosphorylation by 3HB altered the expression of PPARγ regulated genes and reduced insulin resistance. Collectively, 3HB ameliorates insulin resistance in type 2 diabetic mice through a pathway of HCAR2/Ca²⁺/cAMP/PKA/Raf1/ERK1/2/PPARγ.

AZD5438 a GSK-3a/b and CDK inhibitor is antiapoptotic modulates mitochondrial activity and protects human neurons from mitochondrial toxins

We previously reported that kenpaullone, which inhibits GSK-3a/b and CDKs inhibited CCCP mediated mitochondrial depolarisation and augments the mitochondrial network. To investigate the actions of this class of drug further, we compared the ability of kenpaullone, alsterpaullone, 1-azakenapaullone, AZD5438, AT7519 (CDK and GSK-3a/b inhibitors) and dexpramipexole and olesoxime (mitochondrial permeability transition pore inhibitors) to prevent CCCP mediated mitochondrial depolarisation and found that AZD5438 and AT7519, were the most effective. Furthermore, treatment with AZD5438 alone increased the complexity of the mitochondrial network. We also found that AZD5438 prevented the rotenone induced decrease in PGC-1alpha and TOM20 levels and that it mediated powerful anti-apoptotic effects and promoted glycolytic respiration. Importantly, experiments in human iPSC derived cortical and midbrain neurons showed AZD5438 mediated significant protective effects, preventing the neuronal cell death, and collapse in the neurite and mitochondrial network associated with rotenone treatment. These results suggest drugs that target GSK-3a/b and CDKs should be developed and assessed further as they may have significant therapeutic potential.

Impaired PPARγ activation by cadmium exacerbates infection-induced lung injury

Emerging data indicate an association between environmental heavy metal exposure and lung disease, including lower respiratory tract infections (LRTIs). Here, we show by single-cell RNA sequencing an increase in Pparg gene expression in lung macrophages from mice exposed to cadmium and/or infected with Streptococcus pneumoniae. However, the heavy metal cadmium or infection mediated an inhibitory posttranslational modification of peroxisome proliferator-activated receptor γ (PPARγ) to exacerbate LRTIs. Cadmium and infection increased ERK activation to regulate PPARγ degradation in monocyte-derived macrophages. Mice harboring a conditional deletion of Pparg in monocyte-derived macrophages had more severe S. pneumoniae infection after cadmium exposure, showed greater lung injury, and had increased mortality. Inhibition of ERK activation with BVD-523 protected mice from lung injury after cadmium exposure or infection. Moreover, individuals residing in areas of high air cadmium levels had increased cadmium concentration in their bronchoalveolar lavage (BAL) fluid, increased barrier dysfunction, and showed PPARγ inhibition that was mediated, at least in part, by ERK activation in isolated BAL cells. These observations suggest that impaired activation of PPARγ in monocyte-derived macrophages exacerbates lung injury and the severity of LRTIs.

Adipose Tissue Macrophage-Mediated Inflammation in Obesity: A Link to Posttranslational Modification

Adipose tissue macrophages (ATM) are an essential type of immune cells in adipose tissue. Obesity induces the inflammation of adipose tissues, as expressed by ATM accumulation, that is more likely to become a source of systemic metabolic diseases, including insulin resistance. The process is characterized by the transcriptional regulation of inflammatory pathways by virtue of signaling molecules such as cytokines and free fatty acids. Notably, posttranslational modification (PTM) is a key link for these signaling molecules to trigger the proinflammatory or anti-inflammatory phenotype of ATMs. This review focuses on summarizing the functions and molecular mechanisms of ATMs regulating inflammation in obese adipose tissue. Furthermore, the role of PTM is elaborated, hoping to identify new horizons of treatment and prevention for obesity-mediated metabolic disease.

U0126 Compound Triggers Thermogenic Differentiation in Preadipocytes via ERK-AMPK Signaling Axis

In recent years, thermogenic differentiation and activation in brown and white adipose tissues have been regarded as one of the major innovative and promising strategies for the treatment and amelioration of obesity. However, the pharmacological approach towards this process has had limited and insufficient commitments, which presents a greater challenge for obesity treatment. This research evaluates the effects of U0126 compound on the activation of thermogenic differentiation during adipogenesis. The results show that U0126 pretreatment primes both white and brown preadipocytes to upregulate thermogenic and mitochondrial genes as well as enhance functions during the differentiation process. We establish that U0126-mediated thermogenic differentiation induction occurs partially via AMPK activation signaling. The findings of this research suggest U0126 as a promising alternative ligand in pursuit of a pharmacological option to increase thermogenic adipocyte formation and improve energy expenditure. Thus it could pave the way for the discovery of therapeutic drugs for the treatment of obesity and its related complications.

Med25 Limits Master Regulators That Govern Adipogenesis

Mediator 25 (Med25) is a member of the mediator complex that relays signals from transcription factors to the RNA polymerase II machinery. Multiple transcription factors, particularly those involved in lipid metabolism, utilize the mediator complex, but how Med25 is involved in this context is unclear. We previously identified Med25 in a translatome screen of adult cardiomyocytes (CMs) in a novel cell type-specific model of LMNA cardiomyopathy. In this study, we show that Med25 upregulation is coincident with myocardial lipid accumulation. To ascertain the role of Med25 in lipid accumulation, we utilized iPSC-derived and neonatal CMs to recapitulate the in vivo phenotype by depleting lamins A and C (lamin A/C) in vitro. Although lamin A/C depletion elicits lipid accumulation, this effect appears to be mediated by divergent mechanisms dependent on the CM developmental state. To directly investigate Med25 in lipid accumulation, we induced adipogenesis in Med25-silenced 3T3-L1 preadipocytes and detected enhanced lipid accumulation. Assessment of pertinent mediators driving adipogenesis revealed that C/EBPα and PPARγ are super-induced by Med25 silencing. Our results indicate that Med25 limits adipogenic potential by suppressing the levels of master regulators that govern adipogenesis. Furthermore, we caution the use of early-developmental-stage cardiomyocytes to model adult-stage cells, particularly for dissecting metabolic perturbations emanating from LMNA mutations.

PPAR-γ signaling in nonalcoholic fatty liver disease: Pathogenesis and therapeutic targets

Non-alcoholic fatty liver disease (NAFLD), currently the leading cause of global chronic liver disease, has emerged as a major public health problem, more efficient therapeutics of which are thus urgently needed. Peroxisome proliferator-activated receptor γ (PPAR-γ), ligand-activated transcription factors of the nuclear hormone receptor superfamily, is considered a crucial metabolic regulator of hepatic lipid metabolism and inflammation. The role of PPAR-γ in the pathogenesis of NAFLD is gradually being recognized. Here, we outline the involvement of PPAR-γ in the pathogenesis of NAFLD through adipogenesis, insulin resistance, inflammation, oxidative stress, endoplasmic reticulum stress, and fibrosis. In addition, the evidence for PPAR-γ- targeted therapy for NAFLD are summarized. Altogether, PPAR-γ is a promising therapeutic target for NAFLD, and the development of drugs that can balance the beneficial and undesirable effects of PPAR-γ will bring new light to NAFLD patients.

Recent Developments in Islet Biology: A Review With Patient Perspectives

Navigating the coronavirus disease-2019 (COVID-19, now COVID) pandemic has required resilience and creativity worldwide. Despite early challenges to productivity, more than 2,000 peer-reviewed articles on islet biology were published in 2021. Herein, we highlight noteworthy advances in islet research between January 2021 and April 2022, focussing on 5 areas. First, we discuss new insights into the role of glucokinase, mitogen-activated protein kinase-kinase/extracellular signal-regulated kinase and mitochondrial function on insulin secretion from the pancreatic β cell, provided by new genetically modified mouse models and live imaging. We then discuss a new connection between lipid handling and improved insulin secretion in the context of glucotoxicity, focussing on fatty acid-binding protein 4 and fetuin-A. Advances in high-throughput "omic" analysis evolved to where one can generate more finely tuned genetic and molecular profiles within broad classifications of type 1 diabetes and type 2 diabetes. Next, we highlight breakthroughs in diabetes treatment using stem cell-derived β cells and innovative strategies to improve islet survival posttransplantation. Last, we update our understanding of the impact of severe acute respiratory syndrome-coronavirus-2 infection on pancreatic islet function and discuss current evidence regarding proposed links between COVID and new-onset diabetes. We address these breakthroughs in 2 settings: one for a scientific audience and the other for the public, particularly those living with or affected by diabetes. Bridging biomedical research in diabetes to the community living with or affected by diabetes, our partners living with type 1 diabetes or type 2 diabetes also provide their perspectives on these latest advances in islet biology.

Heterogeneous effects of individual high-fat diet compositions on phenotype, metabolic outcome, and hepatic proteome signature in BL/6 male mice

The multitude of obesogenic diets used in rodent studies can hardly be overviewed. Since standardization is missing and assuming that individual compositions provoke individual effects, the choice of quality, quantity and combination of diet ingredients seems to be crucial for the outcome and interpretation of obesity studies. Therefore, the present study was conducted to compare the individual effects of three commonly used obesogenic diets, mainly differing in sugar and fat content. Besides basic phenotypic and metabolic characterization, one main aspect was a comparative liver proteome analysis. As expected, the obtained results picture differentiated consequences mainly depending on fat source and/or fat- and sugar quantity. By confirming the general presumption that the choice of nutritional composition is a pivotal factor, the present findings demonstrate that a conscious selection is indispensable for obtaining reliable and sound results in obesity research. In conclusion, we strongly recommend a careful selection of the appropriate diet in advance of a new experiment, taking into account the specific research question.

Deletion of Spinophilin Promotes White Adipocyte Browning

Browning of white adipose tissue (WAT) is suggested as a promising therapeutic approach to induce energy expenditure and counteract obesity and its associated complications. Systemic depletion of spinophilin (SPL) increases metabolism and improves energy balance in mice. In this study, we explored the mechanistic insight of SPL action in WAT browning. Gene expression and mitochondria tracker staining showed that visceral white adipose tissue (vWAT) harvested from SPL KO mice had a higher expression of classic browning-related genes, including uncoupling protein 1 (UCP1), Cell death inducing DFFA like effector A (CIDEA) and PR domain containing 16 (PRDM16), as well as a higher mtDNA level compared to vWAT from wild type (WT) control mice. When adipogenesis was induced in pre-adipocytes harvested from KO and WT mice ex vivo using the PPAR-γ agonist rosiglitazone (Rosi), SPL KO cells showed increased browning marker gene expression and mitochondria function compared to cells from WT mice. Increased PPAR-γ protein expression and nucleus retention in vWAT from SPL KO mice after Rosi treatment were also observed. The effect of SPL on vWAT browning was further confirmed in vivo when WT and KO mice were treated with Rosi. As a result, SPL KO mice lost body weight, which was associated with increased expression of browning maker genes in vWAT. In summary, our data demonstrate the critical role of SPL in the regulation of WAT browning.

Citrus nutraceutical eriocitrin and its metabolites are partial agonists of peroxisome proliferator-activated receptor gamma (PPARγ): a molecular docking and molecular dynamics study

Peroxisome proliferator-activated receptor gamma (PPARγ) agonists are potent insulin sensitizers in treating type 2 diabetes. Despite being very effective in the fight against diabetes-mediated complications, PPARγ agonists are accompanied by severe side effects leading to complicated health problems, making the discovery of novel safe ligands highly pertinent. A significant intense research effort is in progress to explore the PPARγ activating potential of a wide range of natural compounds. Lemon (Citrus limon) contains various bioactive flavonoids, and eriocitrin is the major flavonoid. It possesses substantial antioxidant and anticancer, lipid-lowering activities and prevents obesity-associated metabolic diseases. Eriocitrin is metabolized to eriodictyol in the intestine, and the absorbed eriodictyol undergoes conversion to numerous metabolites in vivo. It is unclear if eriocitrin or its metabolites are responsible for their beneficial effects. We have used molecular docking, ADMET properties, drug-likeness score and molecular dynamics simulation study to find if eriocitrin and its metabolites are potent binders for PPARγ. Docking studies revealed that eriocitrin binds to PPARγ with the highest binding energy, but ADMET properties and in vivo studies show that the bioavailability of eriocitrin is very poor. Molecular dynamics studies were carried out to validate the docking results, and multiple parameters like RMSD, RMSF, Radius of gyration, SASA, hydrogen bond analysis, interaction energy, principal component analysis, Gibbs free energy and MM-PBSA were calculated. Based on our studies, eriodictyol, eriodictyol 7-O-glucuronide, eriodictyol 3'-O-glucuronide, homoeriodictyol and homoeriodictyol 7-O-glucuronide which are metabolites of eriocitrin appear to be potent partial agonists of PPARγ under physiological conditions.Communicated by Ramaswamy H. Sarma.

Metabolites of endophytic fungi isolated from leaves of Bauhinia variegata exhibit antioxidant activity and agonist activity on peroxisome proliferator-activated receptors α, β/δ and γ

Diabetes mellitus is a metabolic disorder that affects millions of people worldwide and is linked to oxidative stress and inflammation. Thiazolidinediones (TZD) improve insulin sensitization and glucose homeostasis mediated by the activation of peroxisome proliferator-activated receptors γ (PPARγ) in patients with type 2 diabetes. However, their use is associated with severe adverse effects such as loss of bone mass, retention of body fluids, liver and heart problems, and increased risk of bladder cancer. Partial PPARγ agonists can promote the beneficial effects of thiazolidinediones with fewer adverse effects. Endophytic fungi colonize plant tissues and have a particularly active metabolism caused by the interaction with them, which leads to the production of natural products with significant biological effects that may be like that of the colonized plant. Here, we identify seven endophytic fungi isolated from Bauhinia variegata leaves that have antioxidant activities. Also, one of the extracts presented pan-agonist activity on PPAR, and another showed activity in PPARα and PPARβ/δ. A better understanding of this relationship could help to comprehend the mechanism of action of antioxidants in treating diabetes and its complications. Moreover, compounds with these capabilities to reduce oxidative stress and activate the receptor that promotes glucose homeostasis are promising candidates in treatment of diabetes.