Nicotinamide mononucleotide alters body composition and ameliorates metabolic disorders induced by a high-fat diet.

Obesity is caused by an imbalance between calorie intake and energy expenditure, leading to excessive adipose tissue accumulation. Nicotinamide adenine dinucleotide (NAD+ ) is an important molecule in energy and signal transduction, and NAD+ supplementation therapy is a new treatment for obesity in recent years. Liver kinase B1 (LKB1) is an energy metabolism regulator. The relationship between NAD+ and LKB1 has only been studied in the heart and has not yet been reported in obesity. Nicotinamide mononucleotide (NMN), as a direct precursor of NAD+ , can effectively enhance the level of NAD+ . In the current study, we showed that NMN intervention altered body composition in obese mice, characterized by a reduction in fat mass and an increase in lean mass. NMN reversed high-fat diet-induced blood lipid levels then contributed to reducing hepatic steatosis. NMN also improved glucose tolerance and alleviated adipose tissue inflammation. Moreover, our data suggested that NMN supplementation may be depends on the NAD+ /SIRT6/LKB1 pathway to regulate brown adipose metabolism. These results provided new evidence for NMN in obesity treatment.

Ginsenoside Rb1 Facilitates Browning by Repressing Wnt/ß-Catenin Signaling in 3T3-L1 Adipocytes.

BACKGROUND The discovery of browning in white adipose tissue has provided new ideas for treating obesity. Many studies have reported that ginsenoside Rb1 (G-Rb1) has activity against diabetes, inflammation, and obesity, but further investigation is needed on the effect and mechanism of G-Rb1 on browning. MATERIAL AND METHODS We treated 3T3-L1 adipocytes with 0-200 µM G-Rb1, and 0.5 µM Compound 3f and 30 µM SKL2001 were used to activate Wnt/b-catenin signaling. Adipocyte activity was evaluated by Cell Counting Kit-8. Oil Red O staining was used to detect the lipid droplets. Quantitative real-time polymerase chain reaction was used to measure the expression of Cd-137, Cited-1, Txb-1, Prdm-16, and Ucp-1 mRNA. Western blotting was used to measure the expression of Ucp-1, pGSK-3ß (Ser 9), GSK- 3ß, and ß-catenin proteins. The expression of Ucp-1 was also detected with immunofluorescence. RESULTS Adipocyte activity was not affected by 0-100 µM G-Rb1. However, G-Rb1 dose-dependently reduced the accumulation of lipid droplets; increased the expression of Cd-137, Cited-1, Txb-1, Prdm-16, and Ucp-1 mRNA; and increased the expression of Ucp-1, pGSK-3ß (Ser 9), GSK-3ß, and ß-catenin proteins. The accumulation of lipid droplets and the expression of Ucp-1 protein decreased as b-catenin increased. CONCLUSIONS G-Rb1 at various concentrations (0-100 µM) promoted the browning of adipocytes in a dose-dependent manner. Further, we confirmed that activation of Wnt/ß-catenin signaling could inhibit browning. Therefore, the browning promoted by G-Rb1 may be associated with the inhibition of Wnt/ß-catenin signaling.

Intraventricular Injection of LKB1 Inhibits the Formation of Diet-Induced Obesity in Rats by Activating the AMPK-POMC Neurons-Sympathetic Nervous System Axis.

BACKGROUND/AIMS: Obesity is increasingly becoming a major public health problem worldwide. Peripheral LKB1 inhibits white fat generation, but the effect of central LKB1 on diet-induced obesity (DIO) is unknown. Therefore, we examined whether LKB1 over-expression in the hypothalamus can inhibit the development of obesity. METHODS: Adult male Sprague-Dawley rats were anesthetized and placed in a stereotaxic apparatus. LKB1-AAV-EGFP (2.0 × 108 or 2.0 × 1010 vector genomes) or Control-AAV-EGFP (2.0 × 108 vector genomes) was injected into the third ventricle. After administration, the rats were fed a high-fat diet (HFD) for 9 weeks to induce obesity. Rats fed a chow fat diet were used as normal controls. RESULTS: LKB1 delivery decreased body weight, energy intake, fat mass, and serum lipid levels. LKB1 also improved HFD-induced hepatic fatty degeneration. Interestingly, LKB1 over-expression in the hypothalamus activated the AMPK-POMC neurons-sympathetic nervous system (SNS) axis, which can release epinephrine to promote white fat browning. Conversely, the elevated expression of MC3R/MC4R inhibited food intake. These two factors worked together to inhibit the development of obesity. CONCLUSIONS: LKB1 in the hypothalamus may have therapeutic potential for DIO through the activation of the AMPK-POMC neurons-SNS axis.

mTOR remains unchanged in diet-resistant (DR) rats despite impaired LKB1/AMPK cascade in adipose tissue.

Liver kinase B1 (LKB1) plays an important role in adipogenesis, but the underlying molecular mechanism is poorly understood. Here, we explored the functional relationship between LKB1 and the mammalian target of rapamycin (mTOR) in regulating adipogenesis in rats and preadipocytes. We found that LKB1 and the adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) cascade are impaired in the white adipose tissue (WAT) of diet-induced obesity (DIO) and diet-resistant (DR) rats when compared with chow-fed (CF) rats. While DIO activated the mTOR pathway in WAT and led to a more fat mass gain, DR maintained the normal activity of the mTOR pathway and normal weight and percentage of fat mass. We further constructed overexpressed LKB1 (OE) and silenced LKB1 (Si) 3T3-L1 preadipocytes monoclonal cell lines. In the OE cell line, the mTOR pathway was inactivated, and intracellular lipid content was reduced during differentiation. This effect could be reversed by AMPK inhibition. Conversely, in the Si cell line, the mTOR pathway was activated and intracellular lipid content increased. This effect could be reversed by rapamycin, an inhibitor of mTOR. Our results suggest that mTOR mediates the effect of LKB1 on adipogenesis, and normal activity of mTOR in DR rats interferes with the effect of LKB1 in WAT.

TRPV4 in adipose tissue ameliorates diet-induced obesity by promoting white adipocyte browning.

The induction of adipocyte browning to increase energy expenditure is a promising strategy to combat obesity. Transient receptor potential channel V4 (TRPV4) functions as a nonselective cation channel in various cells and plays physiological roles in osmotic and thermal sensations. However, the function of TRPV4 in energy metabolism remains controversial. This study revealed the role of TRPV4 in adipose tissue in the development of obesity. Adipose-specific TRPV4 overexpression protected mice against diet-induced obesity (DIO) and promoted white fat browning. TRPV4 overexpression was also associated with decreased adipose inflammation and improved insulin sensitivity. Mechanistically, TRPV4 could directly promote white adipocyte browning via the AKT pathway. Consistently, adipose-specific TRPV4 knockout exacerbated DIO with impaired thermogenesis and activated inflammation. Corroborating our findings in mice, TRPV4 expression was low in the white adipose tissue of obese people. Our results positioned TRPV4 as a potential regulator of obesity and energy expenditure in mice and humans.

LKB1 on POMC neurons affect the formation of diet-induced obesity by regulating the expression of HDAC1.

BACKGROUND: Obesity is considered a major public health issue worldwide. Liver Kinase B1 (LKB1) is a serine/threonine kinase, peripheral LKB1 is involved in obesity by regulating adipogenesis, but the role of central LKB1 in the development of obesity remains unclear. OBJECTIVE: This study aims to explore the main role of LKB1 in POMC neurons on obesity, and reveal the underlying mechanism of central LKB1 affecting obesity through quantitative proteomics. METHODS: We constructed POMC neuron specific LKB1 knockout mice (PomcLkb1 KO) and exposed them to high fat diet intervention for three months. The effect of LKB1 knockout on obesity was evaluated by monitoring body weight, food intake and measuring fat content. The hypothalamus tissues were collected for proteomic analysis and validated by RT-PCR. RESULTS: The degree of obesity was aggravated in PomcLkb1 KO mice fed with high fat diet. Proteomic results showed that only Histone deacetylase 1 (HDAC1) was down-regulated in the hypothalamus of PomcLkb1 KO mice. Our research also found that LKB1 knockout on POMC neurons led to reduction of Peroxisome proliferator-activated receptor γ (PPARγ). Meanwhile, the software predicted that the transcription factor PPARγ binds to the HDAC1 promoter. Therefore, we speculated that central LKB1 may regulate diet-induced obesity development by influencing HDAC1/PPARγ expression. CONCLUSION: We firstly found that central LKB1 may affect the development of obesity by regulating the expression of HDAC1, which provides a new idea for the central regulatory mechanism of obesity.

LKB1 up-regulation inhibits hypothalamic inflammation and attenuates diet-induced obesity in mice.

BACKGROUND: Diet-induced obesity (DIO) is associated with chronic, low-grade inflammation in the hypothalamus. The inflammatory pathway of the hypothalamus is activated during obesity, and inhibition of activation of the inflammatory pathway can partially reverse obesity. Therefore, exploring new targets for inhibiting hypothalamic inflammation will provide new ideas for the prevention and treatment of obesity. Liver kinase B1 (LKB1), a serine/threonine kinase, is a tumor suppressor and metabolic regulator. Recent studies have shown that LKB1 has a certain anti-inflammatory effect. However, a role of LKB1 in the regulation of hypothalamic inflammation remains unclear. Therefore, we examined whether LKB1 overexpression in the hypothalamus could weaken the hypothalamic inflammation and inhibit the development of obesity. METHODS: LKB1 overexpressing adeno-associated virus (AAV) particles were injected stereotactically into the third ventricle (3 V) of C57BL/6 mice fed with HFD. We assessed changes in body mass and adiposity, food intake, hypothalamic inflammatory markers, and energy and glucose metabolism. RESULTS: LKB1 up-regulation in hypothalamus attenuated diet-induced hypothalamic inflammation, reduced food intake and body weight gain. In addition, the overexpression of hypothalamic LKB1 increased the insulin sensitivity and improved whole-body lipid metabolism, which attenuated hepatic fat accumulation and serum lipid levels. CONCLUSION: Hypothalamic LKB1 up-regulation attenuates hypothalamic inflammation, and protects against hypothalamic inflammation induced damage to melanocortin system, resulting in lower food intake and lower fat mass accumulation, which consequently protects mice from the development of obesity. Our data suggest LKB1 as a novel negative regulator of hypothalamic inflammation, and also a potentially important target for treating other inflammatory diseases.

Deletion of liver kinase B1 in POMC neurons predisposes to diet-induced obesity.

AIMS: Liver kinase B1 (LKB1) is a serine/threonine kinase. Although many biological functions of LKB1 have been identified, the role of hypothalamic LKB1 in the regulation of central energy metabolism and susceptibility to obesity is unknown. Therefore, we constructed POMC neuron-specific LKB1 knockout mice (PomcLkb1 KO) and studied it at the physiological, morphological, and molecular biology levels. MAIN METHODS: Eight-week-old male PomcLkb1 KO mice and their littermates were fed a standard chow fat diet (CFD) or a high-fat diet (HFD) for 3 months. Body weight and food intake were monitored. Dual-energy X-ray absorptiometry was used to measure the fat mass and lean mass. Glucose and insulin tolerance tests and serum biochemical markers were evaluated in the experimental mice. In addition, the levels of peripheral lipogenesis genes and central energy metabolism were measured. KEY FINDINGS: PomcLkb1 KO mice did not exhibit impairments under normal physiological conditions. After HFD intervention, the metabolic phenotype of the PomcLkb1 KO mice changed, manifesting as increased food intake and an enhanced obesity phenotype. More seriously, PomcLkb1 KO mice showed increased leptin resistance, worsened hypothalamic inflammation and reduced POMC neuronal expression. SIGNIFICANCE: We provide evidence that LKB1 in POMC neurons plays a significant role in regulating energy homeostasis. LKB1 in POMC neurons emerges as a target for therapeutic intervention against HFD-induced obesity and metabolic diseases.

Liver kinase B1 induces browning phenotype in 3 T3-L1 adipocytes.

Induction of brown adipocytes in white adipose tissue is a promising therapy for combating human obesity and its associated disorders. Liver kinase B1 (LKB1) is a tumor inhibitor and metabolic modulator. Recent data suggest that LKB1 is necessary for adipogenesis, but its role in the browning of white adipocytes remains unknown. The objective of this study was to reveal the effect of LKB1 on browning. In our study, we showed that overexpression of LKB1 in 3 T3-L1 adipocytes up-regulated the expression of brown adipocyte markers, including UCP1, PGC-1α, Cidea, and PRDM16, and beige-cell-specific genes, such as CD137 and Tmem26. It was possible that the expression of UCP1 and other beige markers was increased by activation of PPARγ, resulting in the browning of 3 T3-L1 preadipocytes. The browning effect was abolished by a PPARγ inhibitor (GW9662). Moreover, these effects were dramatically abrogated by silencing of LKB1. Additionally, LKB1 decreased the expression levels of adipogenesis proteins (C/EBPα and SREBP1) and up-regulated lipid catabolism protein, perilipin (PLIN). In summary, the study suggested that LKB1 induces the browning of white adipocytes, in addition to promoting lipid metabolism. Therefore, LKB1 may be a helpful therapeutic candidate for treating obesity.