Substance P enhances the activation of AMPK and cellular lipid accumulation in 3T3‑L1 cells in response to high levels of glucose

The neuropeptide substance P/neurokinin-1 receptor system and diabetes: From mechanism to therapy

Diabetes is a significant public health issue known as the world's fastest-growing disease condition. It is characterized by persistent hyperglycemia and subsequent chronic complications leading to organ dysfunction and, ultimately, the failure of target organs. Substance P (SP) is an undecapeptide that belongs to the family of tachykinin (TK) peptides. The SP-mediated activation of the neurokinin 1 receptor (NK1R) regulates many pathophysiological processes in the body. There is also a relation between the SP/NK1R system and diabetic processes. Importantly, deregulated expression of SP has been reported in diabetes and diabetes-associated chronic complications. SP can induce both diabetogenic and antidiabetogenic effects and thus affect the pathology of diabetes destructively or protectively. Here, we review the current knowledge of the functional relevance of the SP/NK1R system in diabetes pathogenesis and its exploitation for diabetes therapy. A comprehensive understanding of the role of the SP/NK1R system in diabetes is expected to shed further light on developing new therapeutic possibilities for diabetes and its associated chronic conditions.

Dipeptidyl Peptidase 4 (DPP4) as A Novel Adipokine: Role in Metabolism and Fat Homeostasis

Dipeptidyl peptidase 4 (DPP4) is a molecule implicated in the regulation of metabolic homeostasis and inflammatory processes, and it exerts its main action through its enzymatic activity. DPP4 represents the enzyme most involved in the catabolism of incretin hormones; thus, its activity impacts appetite, energy balance, and the fine regulation of glucose homeostasis. Indeed, DPP4 inhibitors represent a class of antidiabetic agents widely used for the treatment of Type 2 diabetes mellitus (T2DM). DPP4 also acts as an adipokine and is mainly secreted by the adipose tissue, mostly from mature adipocytes of the visceral compartment, where it exerts autocrine and paracrine activities. DPP4 can disrupt insulin signaling within the adipocyte and in other target cells and tissues, where it also favors the development of a proinflammatory environment. This is likely at the basis of the presence of elevated circulating DPP4 levels in several metabolic diseases. In this review, we summarize the most recent evidence of the role of the DPP4 as an adipokine-regulating glucose/insulin metabolism and fat homeostasis, with a particular focus on clinical outcomes associated with its increased secretion in the presence of adipose tissue accumulation and dysfunction.

Bone marrow fat: friend or foe in people with diabetes mellitus?

Global trends in the prevalence of overweight and obesity put the adipocyte in the focus of huge medical interest. This review highlights a new topic in adipose tissue biology, namely the emerging pathogenic role of fat accumulation in bone marrow (BM). Specifically, we summarize current knowledge about the origin and function of BM adipose tissue (BMAT), provide evidence for the association of excess BMAT with diabetes and related cardiovascular complications, and discuss potential therapeutic approaches to correct BMAT dysfunction. There is still a significant uncertainty about the origins and function of BMAT, although several subpopulations of stromal cells have been suggested to have an adipogenic propensity. BM adipocytes are higly plastic and have a distinctive capacity to secrete adipokines that exert local and endocrine functions. BM adiposity is abundant in elderly people and has therefore been interpreted as a component of the whole-body ageing process. BM senescence and BMAT accumulation has been also reported in patients and animal models with Type 2 diabetes, being more pronounced in those with ischaemic complications. Understanding the mechanisms responsible for excess and altered function of BMAT could lead to new treatments able to preserve whole-body homeostasis.

Lipopolysaccharide promoted proliferation and adipogenesis of preadipocytes through JAK/STAT and AMPK-regulated cPLA2 expression

The proliferation and adipogenesis of preadipocytes played important roles in the development of adipose tissue and contributed much to the processes of obesity. On the other hand, lipopolysaccharide (LPS), also known as endotoxin, is a key outer membrane component of gram-negative bacteria in the gut microbiota, and has a dominant role in linking inflammation to high-fat diet-induced metabolic syndrome. Studies suggested the potential roles of LPS in hepatic steatosis and in obese mice models. However, the molecular mechanisms underlying LPS-regulated obesity remained largely unknown. Here we reported that LPS stimulated expression of cyosolic phospholipase A2 (cPLA2), one of inflammation regulators of obesity, in the preadipocytes. Pretreatment the inhibitors of JAK2, STAT3, STAT5 or AMPK significantly reduced LPS-increased mRNA and protein expression of cPLA2 together with phosphorylation of JAK2, STAT3, STAT5 and AMPK, separately. Similarly, transfection of siRNA against JAK2 or AMPK abolished expression of cPLA2 and phosphorylation of JAK2 or AMPK together with downregulated expression of JAK2 and AMPK protein. LPS enhanced activation of STAT3 and STAT5 via JAK2-dependent manner in the preadipocytes. Transfection of JAK2 or AMPK siRNA further proofed the independence of JAK2 and AMPK in LPS-treated preadipocytes. In addition, LPS-increased DNA synthesis, cell numbers and cell viability of preadipocytes were attenuated by AACOCF3, AG490, BML-275, cPLA2 siRNA, JAK2 siRNA or AMPK siRNA. Attenuation JAK2/STAT or AMPK-dependent cPLA2 expression reduced LPS-mediated adipogenesis of preadipocytes. Stimulation of arachidonic acid or AMPK activator, A-769662, increased cell numbers and cell viability and promoted differentiation of preadipocytes. Collectively, these results indicated that LPS increased preadipocytes proliferation and adipogenesis via JAK/STAT and AMPK-dependent cPLA2 expression. The mechanisms of LPS-stimulated cPLA2 expression may be a link between bacteria and obesity and provides the molecular basis for preventing metabolic syndrome or hyperplasic obesity.

Dual targeting of Nur77 and AMPKα by isoalantolactone inhibits adipogenesis in vitro and decreases body fat mass in vivo

BACKGROUND

Suppression of adipogenesis has been considered as a potential target for the prevention and treatment of obesity and associated metabolic disorders, and the nuclear receptor 4A1 (NR4A1/Nur77) and AMPKα are known to play important roles during early and intermediate stages of adipogenesis. Therefore, we hypothesized that dual targeting Nur77 and AMPKα would show strong inhibitory effect on adipogenesis.

METHODS

We screened a herbal medicine-based small molecule library to identify novel natural compounds dual targeting Nur77 and AMPKα, and the antiadipogenic effects and mechanisms of action of a "hit" compound were studied in 3T3-L1 cells. In vivo antiobesity effects of the compound were also investigated in high-fat diet (HFD)-induced obese mice.

RESULTS

We identified isoalantolactone (ISO) as a new NR4A1 inactivator that also activates AMPKα in 3T3-L1 cells. ISO, as expected, inhibited adipogenic differentiation of 3T3-L1 preadipocytes, accompanied by reduced mitotic clonal expansion (MCE) which occurs in the early stage of adipogenesis and decreased expression of genes required for MCE and cell cycle markers including cyclin A, cyclin D1. Furthermore, ISO reduced body weight gain and fat mass (epididymal, subcutaneous, perirenal, and inguinal white adipose tissues) in the high-fat diet-fed C57BL/6 N mice. Serum levels of triglycerides, aspartate transaminase, and alanine transaminase and hepatic steatosis were also significantly improved in the ISO-treated group compared to the high-fat diet control group.

CONCLUSIONS

These results suggest that ISO dual targeting Nur77 and AMPKα during adipogenesis represents a novel class of mechanism-based antiadipogenic agents for treatment of obesity and associated metabolic disorders, including hyperlipidemia and fatty liver.

The inflammasome as a target for pain therapy

The interleukin-1 family of cytokines are potent inducers of inflammation and pain. Proteolytic activation of this family of cytokines is under the control of several innate immune receptors that coordinate to form large multiprotein signalling platforms, termed inflammasomes. Recent evidence suggests that a wide range of inflammatory diseases, cancers, and metabolic and autoimmune disorders, in which pain is a common complaint, may be coordinated by inflammasomes. Activation of inflammasomes results in cleavage of caspase-1, which subsequently induces downstream initiation of several potent pro-inflammatory cascades. Therefore, it has been proposed that targeting inflammasome activity may be a novel and effective therapeutic strategy for these pain-related diseases. The purpose of this narrative review article is to provide the reader with an overview of the activation and regulation of inflammasomes and to investigate the potential therapeutic role of inflammasome inhibition in the treatment of diseases characterized by pain, including the following: complex regional pain syndrome, gout, rheumatoid arthritis, inflammatory pain, neuropathic pain, chronic prostatitis, chronic pelvic pain syndrome, and fibromyalgia. We conclude that the role of the inflammasome in pain-associated diseases is likely to be inflammasome subtype and disease specific. The currently available evidence suggests that disease-specific targeting of the assembly and activity of the inflammasome complex may be a novel therapeutic opportunity for the treatment of refractory pain in many settings.

Cross-talk between the transcription factor Sp1 and C/EBPβ modulates TGFβ1 production to negatively regulate the expression of chemokine RANTES

RANTES is a key chemokine for atherosclerosis, and obesity is associated with progression of atherosclerosis. Substance P (SP) increases glucose uptake and accumulation of lipids in adipocytes, and SP may upregulate RANTES expression. This study investigated the mechanism of RANTES expression by human M1 macrophages stimulated with SP.

SP upregulated RANTES protein expression, whereas aprepitant (an NK1R antagonist) blunted this response. Pretreatment of macrophages with BIRB796 (a combined p38γ/p38δ inhibitor) led to a significant decrease of RANTES expression. Next, we investigated the effect of several NK1R internalization factors on RANTES expression, including GRK2, β-arrestin 2, dynamin, ROCK, and TGFβ1. Exposure of macrophages to SP upregulated TGFβ1 expression. Silencing of β-arrestin 2 or GRK2 significantly enhanced the RANTES protein level after stimulation by SP, whereas TGFβ1/2/3 siRNA or dynasore (a dynamin inhibitor) decreased RANTES and Y-27632 (a ROCK inhibitor) had no effect. Surprisingly, silencing of transcription factor specificity protein 1 (Sp1) or inhibition of Sp1 activity by mithramycin led to significant upregulation of TGFβ1 protein and corresponding enhancement of RANTES expression (by ELISA or western blotting), whereas siRNA for C/EBPβ attenuated expression of both TGFβ1 and RANTES. Next, we investigated transcriptional cross-talk among Sp1 and C/EBPβ, TIF1β, or Fli-1 in relation to RANTES expression. Compared with TIF1β or Fli-1 siRNA, C/EBPβ siRNA showed significantly stronger inhibition of RANTES production by Sp1 siRNA-transfected macrophages after stimulation with SP.

In conclusion, transcription factor Sp1 engages in cross-talk with C/EBPβ and modulates TGFβ1 production to negatively regulate RANTES expression in macrophages stimulated with SP.

In conclusion, cross-talk between the transcription factor Sp1 and C/EBPβ modulates TGFβ1 production to negatively regulate expression of the atherogenic chemokine RANTES in SP-stimulated macrophages, while RANTES is upregulated by SP via the p38γδMAPK/C/EBPβ/TGFβ1 signaling pathway.

Gastrointestinal factors regulating lipid droplet formation in the intestine

Cytoplasmic lipid droplets (CLD) are considered as neutral lipid reservoirs, which protect cells from lipotoxicity. It became clear that these fascinating dynamic organelles play a role not only in energy storage and metabolism, but also in cellular lipid and protein handling, inter-organelle communication, and signaling among diverse functions. Their dysregulation is associated with multiple disorders, including obesity, liver steatosis and cardiovascular diseases. The central aim of this review is to highlight the link between intra-enterocyte CLD dynamics and the formation of chylomicrons, the main intestinal dietary lipid vehicle, after overviewing the morphology, molecular composition, biogenesis and functions of CLD.

Altered circadian feeding behavior and improvement of metabolic syndrome in obese Tac1-deficient mice

BACKGROUND

Metabolic function is regulated by the interplay of central and peripheral factors that ultimately regulate food intake and energy expenditure. The tachykinin substance P (SP) has been identified as a novel regulator of energy balance, however, the mechanisms underlying this effect are ill-defined and conflicting data regarding the role of SP on food intake have been reported by different groups.

OBJECTIVE

To further characterize the metabolic role of the Tac1 gene products (SP and neurokinin A (NKA)) in mice through a series of genetic, metabolic and behavioral studies in Tac1 deficient mice.

RESULTS

Tac1^−/− mice are leaner than controls and display reduced food intake and altered feeding circadian rhythm, supported by disrupted expression of the clock genes Cry1/2, Per1/2 in the suprachiasmatic nucleus (SCN), medio-basal hypothalamus (MBH) and liver, as well as increased Pomc expression in the MBH. Tac1 ablation induced resistance to obesity, improved glucose tolerance, prevented insulin resistance under high-fat-diet, increased activation of brown adipose tissue and improved hepatic steatosis. Moreover, deletion of Tac1 in ob/ob mice ameliorated BW gain in females only but was sufficient to decrease fat and triglyceride content in the liver of males.

CONCLUSIONS

These results provide further evidence that Tac1 controls circadian feeding behavior and metabolism in mice through mechanisms that involve the regulation of the melanocortin system. In addition, these studies suggest that the blockade of SP may offer a new method to treat metabolic syndrome.