Induction of UCP1 and thermogenesis by a small molecule via AKAP1/PKA modulation

Gene Regulation and Mitochondrial Activity During White and Brown Adipogenesis Are Modulated by KDM5 Histone Demethylase

Body fat accumulation differs between males and females and is influenced by both gonadal sex (ovaries vs testes) and chromosomal sex (XX vs XY). We previously showed that an X chromosome gene, Kdm5c, is expressed at higher levels in females compared to males and correlates with adiposity in mice and humans. Kdm5c encodes a KDM5 histone demethylase that regulates gene expression by modulating histone methylation at gene promoters and enhancers. Here, we use chemical inhibition and genetic knockdown to identify a role for KDM5 activity during early stages of white and brown preadipocyte differentiation, with specific effects on white adipocyte clonal expansion, and white and brown adipocyte gene expression and mitochondrial activity. In white adipogenesis, KDM5 activity modulates H3K4 histone methylation at the Dlk1 gene promoter to repress gene expression and promote progression from preadipocytes to mature adipocytes. In brown adipogenesis, KDM5 activity modulates H3K4 methylation and gene expression of Ucp1, which is required for thermogenesis. Unbiased transcriptome analysis revealed that KDM5 activity regulates genes associated with cell cycle regulation and mitochondrial function, and this was confirmed by functional analyses of cell proliferation and cellular bioenergetics. Using genetic knockdown, we demonstrate that KDM5C is the likely KDM5 family member that is responsible for regulation of white and brown preadipocyte programming. Given that KDM5C levels are higher in females compared to males, our findings suggest that sex differences in white and brown preadipocyte gene regulation may contribute to sex differences in adipose tissue function.

Adipocyte retinoic acid receptor α prevents obesity and steatohepatitis by regulating energy expenditure and lipogenesis

OBJECTIVE

The adipose tissue-liver axis is a major regulator of the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Retinoic acid signaling plays an important role in development and metabolism. However, little is known about the role of adipose retinoic acid signaling in the development of obesity-associated NAFLD. In this work, the aim was to investigate whether and how retinoic acid receptor alpha (RARα) regulated the development of obesity and NAFLD.

METHODS

RARα expression in adipose tissue of db/db or ob/ob mice was determined. Rarαfl/fl mice and adipocyte-specific Rarα-/- (RarαAdi-/- ) mice were fed a chow diet for 1 year or high-fat diet (HFD) for 20 weeks. Primary adipocytes and primary hepatocytes were co-cultured. Metabolic regulation and inflammatory response were characterized.

RESULTS

RARα expression was reduced in adipose tissue of db/db or ob/ob mice. RarαAdi-/- mice had increased obesity and steatohepatitis (NASH) when fed a chow diet or HFD. Loss of adipocyte RARα induced lipogenesis and inflammation in adipose tissue and the liver and reduced thermogenesis. In the co-culture studies, loss of RARα in adipocytes induced inflammatory and lipogenic programs in hepatocytes.

CONCLUSIONS

The data demonstrate that RARα in adipocytes prevents obesity and NASH via inhibiting lipogenesis and inflammation and inducing energy expenditure.

ILC2s control obesity by regulating energy homeostasis and browning of white fat

Innate lymphoid cells (ILCs) have been a hot topic in recent research, they are widely distributed in vivo and play an important role in different tissues. The important role of group 2 innate lymphoid cells (ILC2s) in the conversion of white fat into beige fat has attracted widespread attention. Studies have shown that ILC2s regulate adipocyte differentiation and lipid metabolism. This article reviews the types and functions of ILCs, focusing on the relationship between differentiation, development and function of ILC2s, and elaborates on the relationship between peripheral ILC2s and browning of white fat and body energy homeostasis. This has important implications for the future treatment of obesity and related metabolic diseases.

Emerging therapies for autosomal dominant polycystic kidney disease with a focus on cAMP signaling

Autosomal dominant polycystic kidney disease (ADPKD), with an estimated genetic prevalence between 1:400 and 1:1,000 individuals, is the third most common cause of end stage kidney disease after diabetes mellitus and hypertension. Over the last 3 decades there has been great progress in understanding its pathogenesis. This allows the stratification of therapeutic targets into four levels, gene mutation and polycystin disruption, proximal mechanisms directly caused by disruption of polycystin function, downstream regulatory and signaling pathways, and non-specific pathophysiologic processes shared by many other diseases. Dysfunction of the polycystins, encoded by the PKD genes, is closely associated with disruption of calcium and upregulation of cyclic AMP and protein kinase A (PKA) signaling, affecting most downstream regulatory, signaling, and pathophysiologic pathways altered in this disease. Interventions acting on G protein coupled receptors to inhibit of 3′,5′-cyclic adenosine monophosphate (cAMP) production have been effective in preclinical trials and have led to the first approved treatment for ADPKD. However, completely blocking cAMP mediated PKA activation is not feasible and PKA activation independently from cAMP can also occur in ADPKD. Therefore, targeting the cAMP/PKA/CREB pathway beyond cAMP production makes sense. Redundancy of mechanisms, numerous positive and negative feedback loops, and possibly counteracting effects may limit the effectiveness of targeting downstream pathways. Nevertheless, interventions targeting important regulatory, signaling and pathophysiologic pathways downstream from cAMP/PKA activation may provide additive or synergistic value and build on a strategy that has already had success. The purpose of this manuscript is to review the role of cAMP and PKA signaling and their multiple downstream pathways as potential targets for emergent therapies for ADPKD.

Potato protease inhibitor II prevents obesity by inducing browning of white adipose tissue in mice via β3 adrenergic receptor signaling pathway

There are currently few effective and safe pharmacologic means for inducing beige adipogenesis in humans. This study highlights the role of potato protease inhibitor II (PPI II) in regulating the browning of adipose tissue. The in vitro results showed that PPI II increased the expression of the uncoupling protein 1 (UCP1) protein and gene and beige-specific genes, including Cd137, Cited1, Tbx1, and Tmem26 in vitro. PPI II treatment for three months in diet-induced obesity mice increased the levels of the UCP1 protein in white adipose tissue, causing elevated energy expenditure, thus preventing obesity and improving glucose tolerance. Mechanistic studies further revealed that PPI II regulated the abundance and activity of β₃ adrenergic receptor (β₃ -AR) in white adipocytes. Chemical-inhibition experiments revealed the crucial role of β₃ -AR-dependent protein kinase A (PKA)-p38 kinase (p38)/extracellular signal-related kinase1/2 (ERK1/2) signaling in PPI II-mediated browning program of white adipose tissues. In summary, our findings highlight the role of PPI II in beige adipocyte differentiation and thermogenesis and provide new insights into its use in preventing obesity.

Expression of Functional Cannabinoid Type-1 (CB1) Receptor in Mitochondria of White Adipocytes

Via activation of the cannabinoid type-1 (CB₁) receptor, endogenous and exogenous cannabinoids modulate important biochemical and cellular processes in adipocytes. Several pieces of evidence suggest that alterations of mitochondrial physiology might be a possible mechanism underlying cannabinoids' effects on adipocyte biology. Many reports suggest the presence of CB₁ receptor mRNA in both white and brown adipose tissue, but the detailed subcellular localization of CB₁ protein in adipose cells has so far been scarcely addressed. In this study, we show the presence of the functional CB₁ receptor at different subcellular locations of adipocytes from epididymal white adipose tissue (eWAT) depots. We observed that CB₁ is located at different subcellular levels, including the plasma membrane and in close association with mitochondria (mtCB₁). Functional analysis in tissue homogenates and isolated mitochondria allowed us to reveal that cannabinoids negatively regulate complex-I-dependent oxygen consumption in eWAT. This effect requires mtCB₁ activation and consequent regulation of the intramitochondrial cAMP-PKA pathway. Thus, CB₁ receptors are functionally present at the mitochondrial level in eWAT adipocytes, adding another possible mechanism for peripheral regulation of energy metabolism.

Phosphate Group-Derivated Bipyridine-Ruthenium Complex and Titanium Dioxide Nanoparticles for Electrochemical Sensing of Protein Kinase Activity

Monitoring of protein kinase activity is of significance for fundamentals of biochemistry, biomedical diagnose, and drug screening. To reduce the usage of a relatively complicated bio-labeled signal probe, the phosphate group-derivated bipyridine-ruthenium (Pbpy-Ru) complex and titanium dioxide nanoparticles (TiO₂ NPs) were employed as signal probes to develop an electrochemical sensor for evaluating the protein kinase A (PKA) activity. Through the specific interaction between the phosphate groups and TiO₂ NPs, the preparation of a Pbpy-Ru-TiO₂ NP signal probe and its linkage with the phosphorylated PKA substrate peptides could be performed in a simple and effective way. The tethering of Pbpy-Ru onto the TiO₂ NP surface does not degrade the electrochemical property of the complex. The Pbpy-Ru-TiO₂ NP probe exhibits well-defined redox signals at about 1.0 V versus Ag/AgCl reference and notably has about fivefold current response than that of the TiO₂ NPs with physically adsorbed tris-(bipyridine)-Ru. The PKA activity evaluation was realized by measuring the electrochemical response of the Pbpy-Ru-TiO₂ NPs at the phosphorylated peptide-assembled electrode. Operating at optimal conditions, the cathodic signals at the potential of 1.03 V exhibit a good linearity with the PKA concentrations of 0.5-40 U mL^-1. The electrochemical sensor shows good selectivity, low detection limit (0.2 U mL^-1, signal/noise = 3), qualified reproducibility, and satisfactory applicability for PKA determination in the cell lysate. The Pbpy-Ru-TiO₂ NPs/electrode system would be an excellent electrochemical platform for protein phosphorylation monitoring and sensing.

Geniposide suppresses thermogenesis via regulating PKA catalytic subunit in adipocytes

Geniposide has been widely found to ameliorate many metabolic diseases. The recruitment and activation of brown/beige adipocytes are effective and promising methods for counteracting obesity and related diseases. However, the effect of geniposide on thermogenesis of adipocytes and its underlying mechanism have not yet been investigated. Here, we demonstrate that geniposide (25 mg/kg) reduces body temperature and cold tolerance of mice via suppressing thermogenic genes in interscapular brown adipose tissue (iBAT) and inguinal white adipose tissue (iWAT). Consistently, geniposide (20 mg/mL) suppresses thermogenic capacity of adipocytes (brown adipocytes and 3T3L1 preadipocyte cells) in vitro. Mechanistically, geniposide reduces the level of protein kinase A (PKA) catalytic subunit and further suppresses transcription activity and protein stability of uncoupling protein 1 (UCP1), leading to reduction of thermogenic capacity in adipocytes. Moreover, pharmacological PKA activation reverses geniposide-induced UCP1 inhibition, which indicated that geniposide suppresses thermogenesis of adipocytes via regulating PKA signaling. Together, our findings suggest that geniposide is an inhibitor of fat thermogenesis, establishing a novel function characteristic of geniposide.

A bioactive fraction of Pterocarpus santalinus inhibits adipogenesis and inflammation in 3T3-L1 cells via modulation of PPAR-γ/SREBP-1c and TNF-α/IL-6

Pterocarpus santalinus has huge demand owing to its commercial and medicinal value. However, there are limited research studies on its therapeutic activity against obesity and obesity-induced inflammation and underlying mechanism of action. Therefore, in the present study, chloroform bioactive fraction of P. santalinus (CFP) was isolated and evaluated for its activity against adipogenesis and adipogenesis-induced inflammation in 3T3-L1 cell culture model. LC-MS/MS analysis of CFP was performed to identify the compounds present. CFP-treated 3T3-L1 cells (50, 100 and 200 μg/ml) have significantly (p < 0.01 or < 0.05) enhanced glycerol release and adiponectin level, but reduced lipid accumulation and leptin, and MTT assay demonstrated CFP was non-toxic till a dose of 300 µg/ml at 24 and 48 h. A considerable reduction in tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels was witnessed in lipopolysaccharide (LPS)-induced 3T3-L1 cells with CFP treatment in dose-dependent manner. Gene expression studies demonstrated down-regulation of mRNA expression of peroxisome proliferator-activated receptor-γ (PPAR-γ), sterol regulatory element-binding protein-1c (SREBP-1c), leptin, TNF-α and IL-6 but up-regulation of adiponectin and uncoupling protein-1 (UCP-1) and the same trend was observed in protein expression also. In conclusion, it is suggested that CFP could be beneficial to treat obesity and associated inflammation.