Combined inhibition of PI3Kβ and PI3Kγ reduces fat mass by enhancing α-MSH-dependent sympathetic drive

The metabolically protective energy expenditure increase of Pik3r1-related insulin resistance is not explained by Ucp1-mediated thermogenesis

Human SHORT syndrome is caused by dominant negative human PIK3R1 mutations that impair insulin-stimulated phosphoinositide 3-kinase (PI3K) activity. This produces severe insulin resistance (IR) and often reduced adiposity, commonly described as lipodystrophy. However, unlike human primary lipodystrophies, SHORT syndrome does not feature fatty liver or dyslipidemia. Pik3r1Y657*/WT (Pik3r1Y657*) mice metabolically phenocopy humans, moreover exhibiting increased energy expenditure on high-fat feeding. We have hypothesized that this increased energy expenditure explains protection from lipotoxicity and suggested that understanding its mechanism may offer novel approaches to mitigating the metabolic syndrome. We set out to determine whether increased Ucp1-dependent thermogenesis explains the increased energy expenditure in Pik3r1-related IR. Male and female Pik3r1Y657* mice challenged with a 45% fat diet for 3 wk at 21°C showed reduced metabolic efficiency not explained by changes in food intake or physical activity. No changes were seen in thermoregulation, assessed by thermal imaging and a modified Scholander protocol. Ucp1-dependent thermogenesis, assessed by norepinephrine-induced oxygen consumption, was also unaltered. Housing at 30°C did not alter the metabolic phenotype of male Pik3r1Y657* mice but led to lowered physical activity in female Pik3r1Y657* mice compared with controls. Nevertheless, these mice still exhibited increased energy expenditure. Ucp1-dependent thermogenic capacity at 30°C was similar in Pik3r1Y657* and WT mice. We conclude that the likely metabolically protective "energy leak" in Pik3r1-related IR is not caused by Ucp1-mediated brown adipose tissue (BAT) hyperactivation, nor impaired thermal insulation. Further metabolic studies are required to seek alternative explanations such as non-Ucp1-mediated futile cycling.NEW & NOTEWORTHY Understanding how Pik3r1Y657* mice and humans are protected from lipotoxicity despite insulin resistance may suggest new ways to mitigate metabolic syndrome. We find reduced metabolic efficiency in Pik3r1Y657* mice but no differences in locomotion, thermoregulation, or Ucp1-dependent thermogenesis. The protective higher energy expenditure in Pik3r1-related insulin resistance has an alternative, likely metabolic, explanation.

Ablation of PI3Kγ in neurons protects mice from diet-induced obesity MASLD and insulin resistance

Mice with genetic ablation of PI3Kγ are protected from diet-induced obesity. However, the cell type responsible for PI3Kγ action in obesity remains unknown. We generated mice with conditional deletion of PI3Kγ in neurons using the nestin promoter to drive the expression of the Cre recombinase (PI3KγNest mice) and investigated their metabolic phenotype in a model of diet-induced obesity. On a chow diet, lean PI3KγNest mice display reduced linear growth and a normal metabolic phenotype. PI3KγNest mice were largely protected from diet-induced obesity and liver steatosis and showed improved glucose tolerance and insulin sensitivity. This phenotype was associated with increased phosphorylation of hormone-sensitive lipase (HSL) at protein kinase A (PKA) sites in white fat. It is concluded that PI3Kγ action in diet-induced obesity depends on its activity in neurons controlling adipose tissue lipolysis. Future clinical studies on PI3Kγ inhibitors capable of crossing the brain-blood barrier will reveal the relevance of these findings to humans.

Targeting PI3K/AKT signaling pathway in obesity

Obesity is a disorder with an increasing prevalence, which impairs the life quality of patients and intensifies societal health care costs. The development of safe and innovative prevention strategies and therapeutic approaches is thus of great importance. The complex pathophysiology of obesity involves multiple signaling pathways that influence energy metabolism in different tissues. The phosphatidylinositol 3-kinases (PI3K)/protein kinase B (AKT) pathway is critical for the metabolic homeostasis and its function in insulin-sensitive tissues is described in the context of health, obesity and obesity-related complications. The PI3K family participates in the regulation of diverse physiological processes including but not limited to cell growth, survival, differentiation, autophagy, chemotaxis, and metabolism depending on the cellular context. AKT is downstream of PI3K in the insulin signaling pathway, and promotes multiple cellular processes by targeting a plethora of regulatory proteins that control glucose and lipid metabolism. Natural products are essential for prevention and treatment of many human diseases, including obesity. Anti-obesity natural compounds effect multiple pathophysiological mechanisms involved in obesity development. Numerous recent preclinical studies reveal the advances in using plant secondary metabolites to target the PI3K/AKT signaling pathway for obesity management. In this paper the druggability of PI3K as a target for compounds with anti-obesity potential is evaluated. Perspectives on the strategies and limitations for clinical implementation of obesity management using natural compounds modulating the PI3K/AKT pathway are suggested.

PI3Kγ promotes obesity-associated hepatocellular carcinoma by regulating metabolism and inflammation

Background & Aims

Phosphatidylinositides-3 kinases (PI3Ks) are promising drug targets for cancer therapy, but blockage of PI3K-AKT signalling causes hyperglycaemia, hyperinsulinaemia, and liver damage in patients, and hepatocellular carcinoma (HCC) in mice. There are 4 PI3Ks: PI3Kα, PI3Kβ, PI3Kδ, and PI3Kγ. The role of PI3Kγ in HCC is unknown.

Methods

We performed histopathological, metabolic, and molecular phenotyping of mice with genetic ablation of PI3Kγ using models where HCC was initiated by the carcinogen diethylnitrosamine (DEN) and promoted by dietary or genetic obesity (ob/ob). The role of PI3Kγ in leucocytes was investigated in mice lacking PI3Kγ in haematopoietic and endothelial cells.

Results

Loss of PI3Kγ had no effects on the development of DEN-induced HCC in lean mice. However, in mice injected with DEN and placed on an obesogenic diet, PI3Kγ ablation reduced tumour growth, which was associated with reduced insulinaemia, steatosis, and expression of inflammatory cytokines. ob/ob mice lacking PI3Kγ, and mice with diet-induced obesity lacking PI3Kγ in leucocytes and endothelial cells did not display improved insulin sensitivity, steatosis, metabolic inflammation, or reduced tumour growth. However, these mice showed a reduced number of tumours, reduced liver infiltration by neutrophils, and reduced hepatocyte proliferation acutely induced by DEN.

Conclusions

Loss of PI3Kγ reduces tumour development in obesity-promoted HCC through multiple cell types and mechanisms that include improved insulinaemia, steatosis, and metabolic inflammation as well as the regulation of acute neutrophil infiltration and compensatory hepatocyte proliferation. PI3Kγ-selective inhibition may represent a novel therapeutic approach to reduce HCC initiation and slow HCC progression.

Lay summary

Class-1 phosphatidylinositides-3 kinases (PI3Ks) are critical targets in cancer therapy, but complete inhibition of all isoforms causes liver damage, hyperglycaemia, and insulinaemia. Here we show that selective ablation of the PI3Kγ isoform dampens tumour initiation and growth in a mouse model of carcinogen-initiated and obesity-promoted hepatocellular carcinoma (HCC). The effect of PI3Kγ ablation on reduced tumour growth was explained by reduced tumour cell proliferation, which was associated with reduced insulin levels, liver lipids, and reduced expression of tumour-promoting cytokines. PI3Kγ ablation in leucocytes of obese mice had no effects on tumour size. However, it reduced tumour number in association with reduced carcinogen-induced neutrophil infiltration and hepatocyte proliferation in livers of obese mice. Inhibition of PI3Kγ may thus reduce HCC initiation and growth in obese subjects by a mechanism involving reduced metabolic stress and insulinaemia and reduced carcinogen-induced neutrophil infiltration to the fatty liver.

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PI3Kγ ablation does not affect carcinogen-induced liver cancer in lean mice.

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PI3Kγ ablation reduces carcinogen-induced liver cancer in obese mice.

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Systemic PI3Kγ ablation reduces hyperinsulinaemia, steatosis, metabolic inflammation, and growth of liver tumours.

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PI3Kγ ablation in leucocytes and endothelial cells reduces neutrophil infiltration and hepatocyte proliferation acutely induced by carcinogen in the fatty liver.

Phytochemicals in cancer and their effect on the PI3K/AKT-mediated cellular signalling

Protein kinases belong to the largest family of enzymes controlling every aspect of cellular activity including gene expression, cell division, differentiation and metabolism. They are part of major intracellular signalling pathways. Hence, it is not surprising that they are involved in the development of major diseases such as cardiovascular disorders, diabetes, dementia and, most importantly, cancer when they undergo mutations, modifications and unbalanced expression. This review will explore the possibility to draw a connection between the application of natural phytochemicals and the treatment of cancer. We have chosen to focus on the PI3K/AKT cellular signalling pathway which has been shown to be a major target by natural compounds in cell cultures and animal models.

Impact of ambient temperature on inflammation-induced encephalopathy in endotoxemic mice-role of phosphoinositide 3-kinase gamma

BACKGROUND

Sepsis-associated encephalopathy (SAE) is an early and frequent event of infection-induced systemic inflammatory response syndrome. Phosphoinositide 3-kinase γ (PI3Kγ) is linked to neuroinflammation and inflammation-related microglial activity. In homeotherms, variations in ambient temperature (Ta) outside the thermoneutral zone lead to thermoregulatory responses, mainly driven by a gradually increasing sympathetic activity, and may affect disease severity. We hypothesized that thermoregulatory response to hypothermia (reduced Ta) aggravates SAE in PI3Kγ-dependent manner.

METHODS

Experiments were performed in wild-type, PI3Kγ knockout, and PI3Kγ kinase-dead mice, which were kept at neutral (30 ± 0.5 °C) or moderately lowered (26 ± 0.5 °C) Ta. Mice were exposed to lipopolysaccharide (LPS, 10 μg/g, from Escherichia coli serotype 055:B5, single intraperitoneal injection)-evoked systemic inflammatory response (SIR) and monitored 24 h for thermoregulatory response and blood-brain barrier integrity. Primary microglial cells and brain tissue derived from treated mice were analyzed for inflammatory responses and related cell functions. Comparisons between groups were made with one-way or two-way analysis of variance, as appropriate. Post hoc comparisons were made with the Holm-Sidak test or t tests with Bonferroni's correction for adjustments of multiple comparisons. Data not following normal distribution was tested with Kruskal-Wallis test followed by Dunn's multiple comparisons test.

RESULTS

We show that a moderate reduction of ambient temperature triggers enhanced hypothermia of mice undergoing LPS-induced systemic inflammation by aggravated SAE. PI3Kγ deficiency enhances blood-brain barrier injury and upregulation of matrix metalloproteinases (MMPs) as well as an impaired microglial phagocytic activity.

CONCLUSIONS

Thermoregulatory adaptation in response to ambient temperatures below the thermoneutral range exacerbates LPS-induced blood-brain barrier injury and neuroinflammation. PI3Kγ serves a protective role in suppressing release of MMPs, maintaining microglial motility and reinforcing phagocytosis leading to improved brain tissue integrity. Thus, preclinical research targeting severe brain inflammation responses is seriously biased when basic physiological prerequisites of mammal species such as preferred ambient temperature are ignored.

Function, Regulation and Biological Roles of PI3Kγ Variants

Phosphatidylinositide 3-kinase (PI3K) γ is the only class IB PI3K member playing significant roles in the G-protein-dependent regulation of cell signaling in health and disease. Originally found in the immune system, increasing evidence suggest a wide array of functions in the whole organism. PI3Kγ occur as two different heterodimeric variants: PI3Kγ (p87) and PI3Kγ (p101), which share the same p110γ catalytic subunit but differ in their associated non-catalytic subunit. Here we concentrate on specific PI3Kγ features including its regulation and biological functions. In particular, the roles of its non-catalytic subunits serving as the main regulators determining specificity of class IB PI3Kγ enzymes are highlighted.

Phosphoinositide 3-Kinase Is Integral for the Acute Activity of Leptin and Insulin in Male Arcuate NPY/AgRP Neurons

Neuropeptide Y (NPY)/Agouti-related protein (AgRP) neurons in the arcuate nucleus of the hypothalamus are part of a neuroendocrine feedback loop that regulates feeding behavior and glucose homeostasis. NPY/AgRP neurons sense peripheral signals (including the hormones leptin, insulin, and ghrelin) and integrate those signals with inputs from other brain regions. These inputs modify both long-term changes in gene transcription and acute changes in the electrical activity of these neurons, leading to a coordinated response to maintain energy and glucose homeostasis. However, the mechanisms by which the hormones insulin and leptin acutely modify the electrical activity of these neurons remain unclear. In this study, we show that loss of the phosphoinositide 3-kinase catalytic subunits p110α and p110β in AgRP neurons abrogates the leptin- and insulin-induced inhibition of AgRP neurons. Moreover, continual disruption of p110α and p110β in AgRP neurons results in increased weight gain. The increased adiposity was concomitant with a hypometabolic phenotype: decreased energy expenditure independent of changes in food intake. Deficiency of p110α and p110β in AgRP neurons also impaired glucose homeostasis and insulin sensitivity. In summary, these data highlight the requirement of both p110α and p110β in AgRP neurons for the proper regulation of energy balance and glucose homeostasis.

Metabolic Alterations in a Slow-Paced Model of Pancreatic Cancer-Induced Wasting

Cancer cachexia is a devastating syndrome occurring in the majority of terminally ill cancer patients. Notably, skeletal muscle atrophy is a consistent feature affecting the quality of life and prognosis. To date, limited therapeutic options are available, and research in the field is hampered by the lack of satisfactory models to study the complexity of wasting in cachexia-inducing tumors, such as pancreatic cancer. Moreover, currently used in vivo models are characterized by an explosive cachexia with a lethal wasting within few days, while pancreatic cancer patients might experience alterations long before the onset of overt wasting. In this work, we established and characterized a slow-paced model of pancreatic cancer-induced muscle wasting that promotes efficient muscular wasting in vitro and in vivo. Treatment with conditioned media from pancreatic cancer cells led to the induction of atrophy in vitro, while tumor-bearing mice presented a clear reduction in muscle mass and functionality. Intriguingly, several metabolic alterations in tumor-bearing mice were identified, paving the way for therapeutic interventions with drugs targeting metabolism.

Functions of PDE3 Isoforms in Cardiac Muscle

Isoforms in the PDE3 family of cyclic nucleotide phosphodiesterases have important roles in cyclic nucleotide-mediated signalling in cardiac myocytes. These enzymes are targeted by inhibitors used to increase contractility in patients with heart failure, with a combination of beneficial and adverse effects on clinical outcomes. This review covers relevant aspects of the molecular biology of the isoforms that have been identified in cardiac myocytes; the roles of these enzymes in modulating cAMP-mediated signalling and the processes mediated thereby; and the potential for targeting these enzymes to improve the profile of clinical responses.

Association of PIK3CG gene polymorphisms with attention-deficit/hyperactivity disorder: A case-control study

Attention-deficit/hyperactivity disorder (ADHD) is a complicated neurodevelopmental disorder with high heritability. This study explores the association of PIK3CG gene single nucleotide polymorphisms (rs1129293, rs12536620, rs12667819, rs17847825, rs2230460) with ADHD in children and the relation of interaction between SNPs and environmental factors, including blood lead levels (BLLs) and feeding style. A case-control study was conducted with children aged 6-18years old, consisting of 389 children newly diagnosed with ADHD via the DSM-IV at the Wuhan Women and Children Medical Care Center, and 393 control participants were healthy children for physical examination during the same period. All participants were tested using the Chinese Wechsler Intelligence Scale for Children and Parent Symptom Questionnaire (PSQ). Furthermore, a self-designed questionnaire was used to investigate the general situation and related environmental factors, and the BLLs were measured by atomic absorption spectrophotometry. The genotyping was performed using Sequenom MassArray. In our study, PIK3CG gene rs12667819 was consistently shown to be associated with ADHD risk in dominant model (OR=1.656, 95% CI=1.229-2.232), ADHD-I type (OR=2.278, 95% CI=1.666-4.632), and symptom scores. Moreover, rs12536620 has been observed to be related to ADHD-C type and symptom scores. Intriguingly, gene-environmental interactions analysis consistently revealed the potential interactions of rs12667819 collaborating with blood lead (P_mul=0.045) and feeding style (P_mul=0.041) to modify ADHD risk. Expression quantitative trait loci analysis suggested that rs12667819 may mediate PIK3CG gene expression. Therefore, our results suggest that selected PIK3CG gene variants may have a significant effect on ADHD risk.

Knockout of inositol-requiring enzyme 1α in pro-opiomelanocortin neurons decreases fat mass via increasing energy expenditure

Although numerous functions of inositol-requiring enzyme 1α (IRE1α) have been identified, a role of IRE1α in pro-opiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus is largely unknown. Here, we showed that mice lacking IRE1α specifically in POMC neurons (PIKO) are lean and resistant to high-fat diet-induced obesity and obesity-related insulin resistance, liver steatosis and leptin resistance. Furthermore, PIKO mice had higher energy expenditure, probably due to increased thermogenesis in brown adipose tissue. Additionally, α-melanocyte-stimulating hormone production was increased in the hypothalamus of PIKO mice. These results demonstrate that IRE1α in POMC neurons plays a critical role in the regulation of obesity and obesity-related metabolic disorders. Our results also suggest that IRE1α is not only an endoplasmic reticulum stress sensor, but also a new potential therapeutic target for obesity and obesity-related metabolic diseases.

PI3Kγ ablation does not promote diabetes in db/db mice, but improves insulin sensitivity and reduces pancreatic β-cell apoptosis

PI3Kγ has emerged as a promising target for the treatment of obesity and insulin resistance; however, previous studies have indicated that PI3Kγ activity in pancreatic β cells is required for normal insulin secretion in response to glucose. Hence, a possible deterioration of insulin secretion capacity in patients who are predisposed to the failure of pancreatic β-cell function is a major concern for the pharmacologic inhibition of PI3Kγ. To address this issue, we investigated the effects of PI3Kγ ablation in db/db diabetic mice, a genetic model of obesity-driven β-cell failure and diabetes. Mice that lacked PI3Kγ were backcrossed into db/+ mice C57BL/KS (>10 generations) to obtain db/db-PI3Kγ^-/- mice. db/db-PI3Kγ^-/- mice and control db/db mice were phenotyped for glucose homeostasis, insulin sensitivity, insulin secretion, steatosis, metabolic inflammation, pancreatic islet morphometry, islet cellular composition, and inflammation. Pancreatic β-cell apoptosis and proliferation were also evaluated. db/db-PI3Kγ ^-/- mice and control db/db mice developed similar body weight, steatosis, glycemia, and insulin levels after a glucose load; however, db/db-PI3Kγ^-/- mice displayed improved insulin tolerance, higher levels of fasting serum insulin, and lower pancreatic insulin content. In db/db-PI3Kγ^-/- mice, the number of adipose tissue macrophages was similar to control, but displayed reduced adipose tissue neutrophils and M2-polarized adipose tissue gene expression. Finally, db/db-PI3Kγ^-/- mice have more pancreatic β cells and larger islets than db/db mice, despite displaying similar islet inflammation. This phenotype could be explained by reduced β-cell apoptosis in db/db-PI3Kγ^-/- mice compared with control db/db mice. Our results are consistent with the concept that the beneficial action of PI3Kγ ablation in obesity-driven glucose intolerance is largely a result of its leptin-dependent effects on adiposity and, to a lesser extent, the promotion of adipose tissue neutrophil recruitment and M1 polarization of gene expression. Of importance, our data challenge the concept that PI3Kγ is required for insulin secretion in response to glucose in vivo, and indicate that PI3Kγ ablation protects db/db mice from β-cell apoptosis and improves fasting insulin levels. We conclude that PI3Kγ inhibition in obese patients who are predisposed to β-cell failure is not expected to produce adverse effects on insulin secretion.-Breasson, L., Sardi, C., Becattini, B., Zani, F., Solinas, G. PI3Kγ ablation does not promote diabetes in db/db mice, but improves insulin sensitivity and reduces pancreatic β-cell apoptosis.

PI3Kγ activity in leukocytes promotes adipose tissue inflammation and early-onset insulin resistance during obesity

The phosphoinositide 3-kinase γ (PI3Kγ) plays a major role in leukocyte recruitment during acute inflammation and has been proposed to inhibit classical macrophage activation by driving immunosuppressive gene expression. PI3Kγ plays an important role in diet-induced obesity and insulin resistance. In seeking to determine the underlying molecular mechanisms, we showed that PI3Kγ action in high-fat diet-induced inflammation and insulin resistance depended largely on its role in the control of adiposity, which was due to PI3Kγ activity in a nonhematopoietic cell type. However, PI3Kγ activity in leukocytes was required for efficient neutrophil recruitment to adipose tissue. Neutrophil recruitment was correlated with proinflammatory gene expression in macrophages in adipose tissue, which triggered insulin resistance early during the development of obesity. Our data challenge the concept that PI3Kγ is a general suppressor of classical macrophage activation and indicate that PI3Kγ controls macrophage gene expression by non-cell-autonomous mechanisms, the outcome of which is context-dependent.

ATF4/ATG5 Signaling in Hypothalamic Proopiomelanocortin Neurons Regulates Fat Mass via Affecting Energy Expenditure

Although many biological functions of activating transcription factor 4 (ATF4) have been identified, a role of hypothalamic ATF4 in the regulation of energy homeostasis is poorly understood. In this study, we showed that hypothalamic proopiomelanocortin (POMC) neuron-specific ATF4 knockout (PAKO) mice are lean and have higher energy expenditure. Furthermore, PAKO mice were resistant to high-fat diet-induced obesity, glucose intolerance, and leptin resistance. Moreover, the expression of autophagy protein 5 (ATG5) was increased or decreased by ATF4 knockdown or overexpression, respectively, and ATF4 inhibited the transcription of ATG5 by binding to the basic zipper-containing protein sites on its promoter. Importantly, mice with double knockout of ATF4 and ATG5 in POMC neurons gained more fat mass and reduced energy expenditure compared with PAKO mice under a high-fat diet. Finally, the effect of ATF4 deletion in POMC neurons was possibly mediated via enhanced ATG5-dependent autophagy and α-melanocyte-stimulating hormone production in the hypothalamus. Taken together, these results identify the beneficial role of hypothalamic ATF4/ATG5 axis in the regulation of energy expenditure, obesity, and obesity-related metabolic disorders, which suggests that ATF4/ATG5 axis in the hypothalamus may be a new potential therapeutic target for treating obesity and obesity-related metabolic diseases.

α-MSH and Foxc2 promote fatty acid oxidation through C/EBPβ negative transcription in mice adipose tissue

Alpha melanocyte stimulating hormone (α-MSH) and Forkhead box C2 protein (Foxc2) enhance lipolysis in multiple tissues. However, their relationship in adipose fatty acid oxidation (FAO) remains unclear. Here, we demonstrated that α-MSH and Foxc2 increased palmitate oxidation to CO₂ in white (WAT) and brown adipose tissue (BAT). C/EBPβ expression was reduced by α-MSH and Foxc2. FFA level was elevated by α-MSH and pc-Foxc2 treatment along with increased FAO in white and brown adipocytes. The expression of FAO key enzymes, medium-chain acyl-CoA dehydrogenase (MCAD) and long-chain acyl-CoA dehydrogenase (LCAD) were increased in α-MSH and pc-Foxc2 group. Combination of α-MSH and Foxc2 treatment synergistically promoted FAO through increasing the activity of CPT-1 and phosphorylation of ACC. We found C/EBPβ bind to MC5R and Foxc2 promoter regions and inhibited FAO. cAMP level was increased by α-MSH and Foxc2 individually treated or combined treatment. Furthermore, cAMP/PKA pathway-specific inhibitor (H89) blocked the FAO, despite in α-MSH and Foxc2 both added group. While forskolin, the cAMP agonist, promoted FAO and enhanced the effect of α-MSH and Foxc2. Collectively, α-MSH and Foxc2 mutual promote FAO in WAT and BAT via cAMP/PKA signal pathway. And C/EBPβ as a transcription suppressor inhibits α-MSH and Foxc2 expression and FAO.

αMSH promotes preadipocyte proliferation by alleviating ER stress-induced leptin resistance and by activating Notch1 signal in mice

Alpha-melanocyte stimulating hormone (αMSH) has an important role in the regulation of body weight and energy expenditure. Nevertheless, the molecular mechanisms of circulating αMSH on preadipocyte proliferation remain elusive. We found αMSH was reduced by high fat diet (HFD) while leptin was elevated in adipose tissue. Leptin resistance and endoplasmic reticulum (ER) stress of adipose tissue were increased in obese mice. αMSH increased leptin sensitivity and alleviated ER stress along with increased p-STAT3 level and reduced SOCS3, GRP78, CHOP, ATF4, p27 and p53 levels. αMSH and leptin co-treatment alleviated ER stress through decreasing the levels of GRP78 and CHOP. Tunicamycin (TM) or thapsigargin (Tg) induced ER stress blunted leptin sensitivity and inhibited preadipocyte proliferation. αMSH and leptin co-treatment increased the cell number, augmented G1-S transition, elevated leptin sensitivity, and reduced ER stress; it also activated Notch1 signal and stimulated preadipocyte proliferation, whereas ER stress marker genes were decreased during this process. However, the effects of αMSH and leptin were blocked by the specific inhibitor of Notch1 signal. In summary, our data revealed αMSH enhanced leptin sensitivity and preadipocyte proliferation, meanwhile inhibited ER stress of preadipocytes by activating Notch1 signal.

Fat tissues, the brite and the dark sides

Fat tissue is well known for its capacity to store energy and its detrimental role in obesity and metaflammation. However, humans possess different types of fat that have different functions in physiology and metabolic diseases. Apart from white adipose tissue (WAT), the body's main energy storage, there is also brown adipose tissue (BAT) that dissipates energy as a defense against cold and maintains energy balance for the whole body. BAT is present not only in newborns but also in adult humans and its mass correlates with leanness. Moreover, "brown-like" adipocytes have been detected in human WAT. These "brown-in-white" (brite) or beige cells can be induced by cold and a broad spectrum of pharmacological substances and, therefore, they are also known as "inducible brown adipocytes." Activation of brown and/or brite adipocytes reduces metabolic diseases, at least in murine models of obesity. Thus, brown/brite adipocytes represent the "brite" side of fat and are potential targets for novel therapeutic approaches for treatment of obesity and obesity-associated diseases.

Recent advances in the understanding of how neuropeptide Y and -melanocyte stimulating hormone function in adipose physiology

Communication between the brain and the adipose tissue has been the focus of many studies in recent years, with the "brain-fat axis" identified as a system that orchestrates the assimilation and usage of energy to maintain body mass and adequate fat stores. It is now well-known that appetite-regulating peptides that were studied as neurotransmitters in the central nervous system can act both on the hypothalamus to regulate feeding behavior and also on the adipose tissue to modulate the storage of energy. Energy balance is thus partly controlled by factors that can alter both energy intake and storage/expenditure. Two such factors involved in these processes are neuropeptide Y (NPY) and α-melanocyte stimulating hormone (α-MSH). NPY, an orexigenic factor, is associated with promoting adipogenesis in both mammals and chickens, while α-MSH, an anorexigenic factor, stimulates lipolysis in rodents. There is also evidence of interaction between the 2 peptides. This review aims to summarize recent advances in the study of NPY and α-MSH regarding their role in adipose tissue physiology, with an emphasis on the cellular and molecular mechanisms. A greater understanding of the brain-fat axis and regulation of adiposity by bioactive peptides may provide insights on strategies to prevent or treat obesity and also enhance nutrient utilization efficiency in agriculturally-important species.

Functional Coupling with Cardiac Muscle Promotes Maturation of hPSC-Derived Sympathetic Neurons

Neurons derived from human pluripotent stem cells (hPSCs) are powerful tools for studying human neural development and diseases. Robust functional coupling of hPSC-derived neurons with target tissues in vitro is essential for modeling intercellular physiology in a dish and to further translational studies, but it has proven difficult to achieve. Here, we derive sympathetic neurons from hPSCs and show that they can form physical and functional connections with cardiac muscle cells. Using multiple hPSC reporter lines, we recapitulated human autonomic neuron development in vitro and successfully isolated PHOX2B::eGFP+ neurons that exhibit sympathetic marker expression and electrophysiological properties and norepinephrine secretion. Upon pharmacologic and optogenetic manipulation, PHOX2B::eGFP+ neurons controlled beating rates of cardiomyocytes, and the physical interactions between these cells increased neuronal maturation. This study provides a foundation for human sympathetic neuron specification and for hPSC-based neuronal control of organs in a dish.

Biased signaling initiated by agouti-related peptide through human melanocortin-3 and -4 receptors

The neural melanocortin receptors (MCRs), melanocortin-3 and -4 receptors (MC3R and MC4R), have been increasingly recognized as important regulators of energy homeostasis. The orexigenic agouti-related peptide (AgRP), initially identified as an endogenous antagonist for both neural MCRs, has been suggested to be a biased agonist of MC4R independent of its antagonizing effects. In the present study, we sought to determine the potential of AgRP to regulate the activation of intracellular kinases, including extracellular signal-regulated kinase 1 and 2 (ERK1/2), AKT and AMP-activated protein kinase (AMPK), through neural MCRs. We showed that AgRP acted as a biased agonist in human MC3R (hMC3R), decreasing cAMP activity of constitutively active mutant (F347A) hMC3R but stimulating ERK1/2 activation in both wide type and F347A hMC3Rs. AgRP-stimulated ERK1/2 phosphorylation through MC3R was abolished by protein kinase A (PKA) inhibitor H-89 but not Rp-cAMPS, whereas AgRP-initiated ERK1/2 activation through MC4R was inhibited by phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002. Both NDP-MSH and AgRP treatment induced significant AKT phosphorylation in GT1-7 cells but not in MC3R- or MC4R-transfected HEK293T cells. The phosphorylated AMPK levels in both GT1-7 cells and HERK293T cells transfected with neural MCRs were significantly decreased upon stimulation with NDP-MSH but not with AgRP. In summary, we provided novel data for AgRP-initiated multiple intracellular signaling pathways, demonstrating biased agonism of AgRP in both neural MCRs, leading to a better understanding of neural MCR pharmacology.

Lack of kinase-independent activity of PI3Kγ in locus coeruleus induces ADHD symptoms through increased CREB signaling

Although PI3Kγ has been extensively investigated in inflammatory and cardiovascular diseases, the exploration of its functions in the brain is just at dawning. It is known that PI3Kγ is present in neurons and that the lack of PI3Kγ in mice leads to impaired synaptic plasticity, suggestive of a role in behavioral flexibility. Several neuropsychiatric disorders, such as attention-deficit/hyperactivity disorder (ADHD), involve an impairment of behavioral flexibility. Here, we found a previously unreported expression of PI3Kγ throughout the noradrenergic neurons of the locus coeruleus (LC) in the brainstem, serving as a mechanism that regulates its activity of control on attention, locomotion and sociality. In particular, we show an unprecedented phenotype of PI3Kγ KO mice resembling ADHD symptoms. PI3Kγ KO mice exhibit deficits in the attentive and mnemonic domains, typical hyperactivity, as well as social dysfunctions. Moreover, we demonstrate that the ADHD phenotype depends on a dysregulation of CREB signaling exerted by a kinase-independent PI3Kγ-PDE4D interaction in the noradrenergic neurons of the locus coeruleus, thus uncovering new tools for mechanistic and therapeutic research in ADHD.

Obesity-Driven Gut Microbiota Inflammatory Pathways to Metabolic Syndrome

The intimate interplay between immune system, metabolism, and gut microbiota plays an important role in controlling metabolic homeostasis and possible obesity development. Obesity involves impairment of immune response affecting both innate and adaptive immunity. The main factors involved in the relationship of obesity with inflammation have not been completely elucidated. On the other hand, gut microbiota, via innate immune receptors, has emerged as one of the key factors regulating events triggering acute inflammation associated with obesity and metabolic syndrome. Inflammatory disorders lead to several signaling transduction pathways activation, inflammatory cytokine, chemokine production and cell migration, which in turn cause metabolic dysfunction. Inflamed adipose tissue, with increased macrophages infiltration, is associated with impaired preadipocyte development and differentiation to mature adipose cells, leading to ectopic lipid accumulation and insulin resistance. This review focuses on the relationship between obesity and inflammation, which is essential to understand the pathological mechanisms governing metabolic syndrome.

Leptin receptor expressing neurons express phosphodiesterase-3B (PDE3B) and leptin induces STAT3 activation in PDE3B neurons in the mouse hypothalamus

Leptin signaling in the hypothalamus is critical for normal food intake and body weight regulation. Cumulative evidence suggests that besides the signal transducer and activator of transcription-3 (STAT3) pathway, several non-STAT3 pathways including the phosphodiesterase-3B (PDE3B) pathway mediate leptin signaling in the hypothalamus. We have shown that PDE3B is localized in various hypothalamic sites implicated in the regulation of energy homeostasis and that the anorectic and body weight reducing effects of leptin are mediated by the activation of PDE3B. It is still unknown if PDE3B is expressed in the long form of the leptin-receptor (ObRb)-expressing neurons in the hypothalamus and whether leptin induces STAT3 activation in PDE3B-expressing neurons. In this study, we examined co-localization of PDE3B with ObRb neurons in various hypothalamic nuclei in ObRb-GFP mice that were treated with leptin (5mg/kg, ip) for 2h. Results showed that most of the ObRb neurons in the arcuate nucleus (ARC, 93%), ventromedial nucleus (VMN, 94%), dorsomedial nucleus (DMN, 95%), ventral premammillary nucleus (PMv, 97%) and lateral hypothalamus (LH, 97%) co-expressed PDE3B. We next examined co-localization of p-STAT3 and PDE3B in the hypothalamus in C57BL6 mice that were treated with leptin (5mg/kg, ip) for 1h. The results showed that almost all p-STAT3 positive neurons in different hypothalamic nuclei including ARC, VMN, DMN, LH and PMv areas expressed PDE3B. These results suggest the possibility for a direct role for the PDE3B pathway in mediating leptin action in the hypothalamus.

Macrophage polarization in pathology

Macrophages are cells of the innate immunity constituting the mononuclear phagocyte system and endowed with remarkable different roles essential for defense mechanisms, development of tissues, and homeostasis. They derive from hematopoietic precursors and since the early steps of fetal life populate peripheral tissues, a process continuing throughout adult life. Although present essentially in every organ/tissue, macrophages are more abundant in the gastro-intestinal tract, liver, spleen, upper airways, and brain. They have phagocytic and bactericidal activity and produce inflammatory cytokines that are important to drive adaptive immune responses. Macrophage functions are settled in response to microenvironmental signals, which drive the acquisition of polarized programs, whose extremes are simplified in the M1 and M2 dichotomy. Functional skewing of monocyte/macrophage polarization occurs in physiological conditions (e.g., ontogenesis and pregnancy), as well as in pathology (allergic and chronic inflammation, tissue repair, infection, and cancer) and is now considered a key determinant of disease development and/or regression. Here, we will review evidence supporting a dynamic skewing of macrophage functions in disease, which may provide a basis for macrophage-centered therapeutic strategies.

Phosphoinositide 3-kinase: friend and foe in cardiovascular disease

Class I phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases activated by cell membrane receptors, either receptor tyrosine kinases (RTKs) or G protein–coupled receptors (GPCRs), to catalyze the production of the lipid second messenger phosphatidylinositol (3,4,5)-trisphosphate (PIP3). These enzymes engage multiple downstream intracellular signaling pathways controlling cell proliferation, survival and migration. In the cardiovascular system, the four class I PI3K isoforms, PI3Kα, PI3Kβ, PI3Kδ, and PI3Kγ are differentially expressed in distinct cell subsets which include cardiomyocytes, fibroblasts, endothelial, and vascular smooth muscle cells as well as leukocytes, suggesting specific functions for distinct PI3K isoenzymes. During the last decades, genetic disruption studies targeting different PI3K genes have elucidated the contribution of specific isoenzymes to cardiac and vascular function regulation, highlighting both beneficial and maladaptive roles. New layers of complexity in the function of PI3Ks have recently emerged, indicating that distinct PI3K isoforms are interconnected by various crosstalk events and can function not only as kinases, but also as scaffold proteins coordinating key signalosomes in cardiovascular health and disease. In this review, we will summarize major breakthroughs in the comprehension of detrimental and beneficial actions of PI3K signaling in cardiovascular homeostasis, and we will discuss recently unraveled cross-talk and scaffold mechanisms as well as the role of the less characterized class II and III PI3K isoforms.

PI3K signaling in the pathogenesis of obesity: The cause and the cure

With the steady rise in the incidence of obesity and its associated comorbidities, in the last decades research aimed at understanding molecular mechanisms that control body weight has gained new interest. Fat gain is frequently associated with chronic adipose tissue inflammation and with peripheral as well as central metabolic derangements, resulting in an impaired hypothalamic regulation of energy homeostasis. Recent attention has focused on the role of phosphatidylinositol 3-kinase (PI3K) in both immune and metabolic response pathways, being involved in the pathophysiology of obesity and its associated metabolic diseases. In this review, we focus on distinct PI3K isoforms, especially class I PI3Ks, mediating inflammatory cells recruitment to the enlarged fat as well as intracellular responses to key hormonal regulators of fat storage, both in adipocytes and in the central nervous system. This integrated view of PI3K functions may ultimately help to develop new therapeutic interventions for the treatment of obesity.

Pharmacological inhibition of PI3K reduces adiposity and metabolic syndrome in obese mice and rhesus monkeys

Genetic inhibition of PI3K signaling increases energy expenditure, protects from obesity and metabolic syndrome, and extends longevity. Here, we show that two pharmacological inhibitors of PI3K, CNIO-PI3Ki and GDC-0941, decrease the adiposity of obese mice without affecting their lean mass. Long-term treatment of obese mice with low doses of CNIO-PI3Ki reduces body weight until reaching a balance that is stable for months as long as the treatment continues. CNIO-PI3Ki treatment also ameliorates liver steatosis and decreases glucose serum levels. The above observations have been recapitulated in independent laboratories and using different oral formulations of CNIO-PI3Ki. Finally, daily oral treatment of obese rhesus monkeys for 3 months with low doses of CNIO-PI3Ki decreased their adiposity and lowered their serum glucose levels, in the absence of detectable toxicities. Therefore, pharmacological inhibition of PI3K is an effective and safe anti-obesity intervention that could reverse the negative effects of metabolic syndrome in humans.

De novo lipogenesis in metabolic homeostasis: More friend than foe?

Background

An acute surplus of carbohydrates, and other substrates, can be converted and safely stored as lipids in adipocytes via de novo lipogenesis (DNL). However, in obesity, a condition characterized by chronic positive energy balance, DNL in non-adipose tissues may lead to ectopic lipid accumulation leading to lipotoxicity and metabolic stress. Indeed, DNL is dynamically recruited in liver during the development of fatty liver disease, where DNL is an important source of lipids. Nonetheless, a number of evidences indicates that DNL is an inefficient road for calorie to lipid conversion and that DNL may play an important role in sustaining metabolic homeostasis.

Scope of review

In this manuscript, we discuss the role of DNL as source of lipids during obesity, the energetic efficiency of this pathway in converting extra calories to lipids, and the function of DNL as a pathway supporting metabolic homeostasis.

Major conclusion

We conclude that inhibition of DNL in obese subjects, unless coupled with a correction of the chronic positive energy balance, may further promote lipotoxicity and metabolic stress. On the contrary, strategies aimed at specifically activating DNL in adipose tissue could support metabolic homeostasis in obese subjects by a number of mechanisms, which are discussed in this manuscript.

Synergy in activating class I PI3Ks

The class I phosphoinositide 3-kinases (PI3Ks) are lipid kinases that transduce a host of cellular signals and regulate a broad range of essential functions including growth, proliferation, and migration. As such, PI3Ks have pivotal roles in diseases such as cancer, diabetes, primary immune disorders, and inflammation. These enzymes are activated downstream of numerous activating stimuli including receptor tyrosine kinases, G protein-coupled receptors (GPCRs), and the Ras superfamily of small G proteins. A major challenge is to decipher how each PI3K isoform is able to successfully synergize these inputs into their intended signaling function. This article highlights recent progress in characterizing the molecular mechanisms of PI3K isoform-specific activation pathways, as well as novel roles for PI3Ks in human diseases, specifically cancer and immune diseases.