MAPK Erk5 in Leptin Receptor‒Expressing Neurons Controls Body Weight and Systemic Energy Homeostasis in Female Mice

Pharmacological function of melanocortin-3 receptor in goldfish (Carassius auratus)

The melanocortin-3 receptor (MC3R) was recognized for its critical role in energy metabolism and inflammatory responses in mammals; however, its functions in fish remain poorly understood. This study characterized the mc3r gene in goldfish, investigating its sequence, tissue distribution, and pharmacological responses. The coding sequence of goldfish mc3r was 975 bp, translating to a 325-amino-acid protein typical of G protein-coupled receptors, with notable conservation across cyprinids. Quantitative PCR analysis revealed high expression levels in the brain. Luciferase assays demonstrated that various agonists, particularly NDP-MSH and ACTH (1-24), effectively activated the cAMP and MAPK/ERK signaling pathways. Furthermore, all agonists tested (α-MSH, β-MSH, ACTH (1-24), and NDP-MSH) significantly inhibited NF-κB signaling, correlating with their activation of cAMP. These findings enhanced our understanding of the melanocortin system's role in regulating energy metabolism and inflammatory processes in teleost fish.

Role of Mitogen-Activated Protein (MAP) Kinase Pathways in Metabolic Diseases

Physiological processes that govern the normal functioning of mammalian cells are regulated by a myriad of signalling pathways. Mammalian mitogen-activated protein (MAP) kinases constitute one of the major signalling arms and have been broadly classified into four groups that include extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), p38, and ERK5. Each signalling cascade is governed by a wide array of external and cellular stimuli, which play a critical part in mammalian cells in the regulation of various key responses, such as mitogenic growth, differentiation, stress responses, as well as inflammation. This evolutionarily conserved MAP kinase signalling arm is also important for metabolic maintenance, which is tightly coordinated via complicated mechanisms that include the intricate interaction of scaffold proteins, recognition through cognate motifs, action of phosphatases, distinct subcellular localisation, and even post-translational modifications. Aberration in the signalling pathway itself or their regulation has been implicated in the disruption of metabolic homeostasis, which provides a pathophysiological foundation in the development of metabolic syndrome. Metabolic syndrome is an umbrella term that usually includes a group of closely associated metabolic diseases such as hyperglycaemia, hyperlipidaemia, and hypertension. These risk factors exacerbate the development of obesity, diabetes, atherosclerosis, cardiovascular diseases, and hepatic diseases, which have accounted for an increase in the worldwide morbidity and mortality rate. This review aims to summarise recent findings that have implicated MAP kinase signalling in the development of metabolic diseases, highlighting the potential therapeutic targets of this pathway to be investigated further for the attenuation of these diseases.

Mechanisms of Cardiorenal Protection With SGLT2 Inhibitors in Patients With T2DM Based on Network Pharmacology

Purpose

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have cardiorenal protective effects regardless of whether they are combined with type 2 diabetes mellitus, but their specific pharmacological mechanisms remain undetermined.

Materials and Methods

We used databases to obtain information on the disease targets of “Chronic Kidney Disease,” “Heart Failure,” and “Type 2 Diabetes Mellitus” as well as the targets of SGLT2 inhibitors. After screening the common targets, we used Cytoscape 3.8.2 software to construct SGLT2 inhibitors' regulatory network and protein-protein interaction network. The clusterProfiler R package was used to perform gene ontology functional analysis and Kyoto encyclopedia of genes and genomes pathway enrichment analyses on the target genes. Molecular docking was utilized to verify the relationship between SGLT2 inhibitors and core targets.

Results

Seven different SGLT2 inhibitors were found to have cardiorenal protective effects on 146 targets. The main mechanisms of action may be associated with lipid and atherosclerosis, MAPK signaling pathway, Rap1 signaling pathway, endocrine resistance, fluid shear stress, atherosclerosis, TNF signaling pathway, relaxin signaling pathway, neurotrophin signaling pathway, and AGEs-RAGE signaling pathway in diabetic complications were related. Docking of SGLT2 inhibitors with key targets such as GAPDH, MAPK3, MMP9, MAPK1, and NRAS revealed that these compounds bind to proteins spontaneously.

Conclusion

Based on pharmacological networks, this study elucidates the potential mechanisms of action of SGLT2 inhibitors from a systemic and holistic perspective. These key targets and pathways will provide new ideas for future studies on the pharmacological mechanisms of cardiorenal protection by SGLT2 inhibitors.

Anxiety-like behavior in female mice is modulated by STAT3 signaling in midbrain dopamine neurons

The central signaling actions of cytokines are mediated by signal transducer and activator of transcription (STAT3). STAT3 activation plays a pivotal role in the behavioral responses to the adiposity hormone leptin, including in midbrain dopamine (DA) neurons where it mediates the influence of leptin to diminish physical activity and running reward in male mice. Leptin also has anxiolytic effects which have been tied to the mesolimbic DA system. To assess the contribution of STAT3 signaling in mesolimbic DA neurons on feeding, mesolimbic DA tone and anxiodepressive behaviors in female mice, we generated DA-specific STAT3 knockout mice by crossing mice expressing Cre under the control of the dopamine transporter with STAT3-LoxP mice. Feeding, locomotion, wheel running, conditioned place preference for palatable food and amphetamine locomotor sensitization were unaffected by DA-specific STAT3 deletion. Conversely, knockout mice exhibited heightened anxiety-like behavior (open field test and elevated plus maze) along with increased basal and stress-induced plasma corticosterone, whereas indices of behavioral despair (forced swim and tail-suspension tasks) were unchanged. In accordance with biochemical evidence of increased D1 receptor signaling (phospho-DARPP32_Thr34) in the central nucleus of the amygdala (CeA) of knockout mice, local microinjections of a D1 receptor antagonist reversed the anxiogenic phenotype of knockout mice. In addition to alluding to sex differences in the signaling mechanisms mediating anxiety-like behavior, our findings suggest that activation of STAT3 in midbrain dopamine neurons projecting to the CeA dampens anxiety in a D1R-dependent manner in female mice.

Peripheral leptin signaling persists in innate immune cells during diet-induced obesity

Leptin is a pleiotropic adipokine that regulates immunometabolism centrally and peripherally. Obese individuals present increased levels of leptin in the blood and develop hypothalamic resistance to this adipokine. Here we investigated whether leptin effects on the periphery are maintained despite the hypothalamic resistance. We previously reported that leptin injection induces in vivo neutrophil migration and peritoneal macrophage activation in lean mice through TNF-α- and CXCL1-dependent mechanisms. However, leptin effects on leukocyte biology during obesity remain unclear. In this study, we investigated the in vivo responsiveness of leukocytes to i.p. injected leptin in mice with diet-induced obesity (DIO). After 14-16 wk, high-sucrose, high-fat diet (HFD)-fed mice showed hyperglycemia, hyperleptinemia, and dyslipidemia compared to normal-sucrose, normal-fat diet (ND). Exogenous leptin did not reduce food intake in DIO mice in contrast to control mice, indicating that DIO mice were centrally resistant to leptin. Regardless of the diet, we found increased levels of TNF-α and CXCL1 in the animals injected with leptin, alongside a pronounced neutrophil migration to the peritoneal cavity and enhanced biogenesis of lipid droplets in peritoneal macrophages. Supporting our in vivo results, data from ex vivo leptin stimulation experiments confirmed hypothalamic resistance in DIO mice, whereas bone marrow cells responded to leptin stimulation through mTOR signaling despite obesity. Altogether, our results show that leukocytes responded equally to leptin in ND- or HFD-fed mice. These results support a role for leptin in the innate immune response also in obesity, contributing to the inflammatory status that leads to the development of metabolic disease.

[Fuxinfang improves hypoxia-induced injury of human aortic endothelial cells by regulating c-Fos-NR4A1-p38 pathway]

OBJECTIVE

To explore the molecular mechanism of Fuxinfang for improving injury of human aortic endothelial progenitor cells (HAECs).

OBJECTIVE

Serum samples were collected from male SD rats treated with Fuxinfang (n=8) or saline (n= 5). HAECs cultured in normoxia or hypoxic condition (2% O₂) were treated with serum from normal rats or with diluted serum (1% and 10%) from rats treated with Fuxinfang. The differentially expressed genes (DEGs) between Fuxinfang-treated and control cells were detected using high-throughput sequencing to screen the target DEGs that participated in arterial endothelial cell injury and underwent changes in response to both hypoxia and Fuxinfang treatment. AmiGo and String databases were used to infer the interactions among the target genes, and the expressions of the genes were analyzed in HAECs with different treatments using enzyme-linked immunosorbent assay (ELISA) and Western blotting.

OBJECTIVE

HAECs cultured in hypoxia did not show obvious changes in cell morphology or expressions of hypoxia-related factors in response to treatment with 1% or 10% serum from Fuxinfang-treated rats. The results of high-throughput sequencing showed a total of 7134 DEGs (4205 up-regulated and 2929 down-regulated genes) in HAECs in hypoxia model group and 762 DEGs (305 upregulated and 457 down-regulated genes) in Fuxinfang-treated HAECs. Analysis of AmiGo and String databases and the constructed protein-protein interaction network identified c-Fos, NR4A1, and p38MAPK as the target genes. The results of ELISA and Western blotting showed that the expressions of c-Fos, NR4A1, p38MAPK and pp38MAPK increased significantly in cells with hypoxic exposure (P < 0.05); treatment with the serum containing Fuxinfang significantly reduced the expression levels of c-Fos, NR4A1 and p-p38MAPK in hypoxic HAECs in a concentration-dependent manner (P < 0.05).

OBJECTIVE

The serum from Fuxinfang-treated rats can concentration-dependently inhibit the expressions of the DEGs occurring in hypoxia. Fuxinfang improves hypoxic injuries of HAECs possibly by down-regulating the expression of c-Fos to inhibit NR4A1 expression and suppressing hypoxia-induced p38 phosphorylation.

mTORC1 Overactivation Leads to Abnormalities in Skeletal Development

The mechanistic/mammalian target of rapamycin complex-1 (mTORC1) integrates multiple signaling pathways and regulates various cellular processes. Tuberous sclerosis complex 1 (Tsc1) and complex 2 (Tsc2) are critical negative regulators of mTORC1. Mouse genetic studies, including ours, have revealed that inactivation of mTORC1 in undifferentiated mesenchymal cells and chondrocytes leads to severe skeletal abnormalities, indicating a pivotal role for mTORC1 in skeletogenesis. Here, we show that hyperactivation of mTORC1 influences skeletal development through its expression in undifferentiated mesenchymal cells at the embryonic stage. Inactivation of Tsc1 in undifferentiated mesenchymal cells by paired-related homeobox 1 (Prx1)-Cre-mediated recombination led to skeletal abnormalities in appendicular skeletons. In contrast, Tsc1 deletion in chondrocytes using collagen type II α1 (Col2a1)-Cre or in osteoprogenitors using Osterix (Osx)-Cre did not result in skeletal defects in either appendicular or axial skeletons. These findings indicate that Tsc complex-mediated chronic overactivation of mTORC1 influences skeletal development at the embryonic stage through its expression in undifferentiated mesenchymal cells but not in chondrocytes or osteoprogenitors.

Impact of Conventional and Atypical MAPKs on the Development of Metabolic Diseases

The family of mitogen-activated protein kinases (MAPKs) consists of fourteen members and has been implicated in regulation of virtually all cellular processes. MAPKs are divided into two groups, conventional and atypical MAPKs. Conventional MAPKs are further classified into four sub-families: extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK1, 2 and 3), p38 (α, β, γ, δ), and extracellular signal-regulated kinase 5 (ERK5). Four kinases, extracellular signal-regulated kinase 3, 4, and 7 (ERK3, 4 and 7) as well as Nemo-like kinase (NLK) build a group of atypical MAPKs, which are activated by different upstream mechanisms than conventional MAPKs. Early studies identified JNK1/2 and ERK1/2 as well as p38α as a central mediators of inflammation-evoked insulin resistance. These kinases have been also implicated in the development of obesity and diabetes. Recently, other members of conventional MAPKs emerged as important mediators of liver, skeletal muscle, adipose tissue, and pancreatic β-cell metabolism. Moreover, latest studies indicate that atypical members of MAPK family play a central role in the regulation of adipose tissue function. In this review, we summarize early studies on conventional MAPKs as well as recent findings implicating previously ignored members of the MAPK family. Finally, we discuss the therapeutic potential of drugs targeting specific members of the MAPK family.