Adaptor protein APPL1 coordinates HDAC3 to modulate brown adipose tissue thermogenesis in mice

Huanglian-Jiedu decoction promotes adipose thermogenesis in obese mice by suppressing the expression of HDAC3

ETHNOPHARMACOLOGICAL RELEVANCE

Huanglian Jiedu Decoction (HLJDD) is an ancient formula of traditional Chinese medicine that is commonly utilized in a range of disorders, and it has been shown to have pharmacological effects on glucose and lipid metabolism. However, the specific mechanism of HLJDD for the treatment of obesity and related metabolic disorders remains to be further investigated.

AIM OF THE STUDY

It has been thought that encouraging adipose thermogenesis to raise the body's energy expenditure is a useful tactic for improving metabolic abnormalities and losing weight. In this study, we investigated the ability and underlying mechanisms of HLJDD to regulate fat cell thermogenesis to improve energy expenditure in obesity.

METHODS

The obese mouse model was established on a high-fat diet for 12 weeks. All mice were divided into NC, HFD, HFD with HLJDD of a low dose (2.25 g/kg/d), and HFD with HLJDD of a high dose (4.5 g/kg/d) groups and kept for 4 weeks. In vitro experiments were conducted to evaluate the effects of 5% and 10% HLJDD-containing serum on differentiated 3T3-L1 cells and HDAC3-knocking-down 3T3-L1 cells.

RESULTS

The results showed that HLJDD treatment significantly improved glucose and insulin tolerance and decreased the adipocyte radius of WATs, as well as increased energy consumption in obese mice. Besides, HLJDD treatment dramatically increased the levels of thermogenic genes UCP-1 and PGC-1α while suppressing HDAC3 levels in WATs and 3T3-L1 adipocytes. Importantly, the effects of HLJDD on PGC-1α and UCP-1 were blocked in HDAC3 knockdown adipocytes.

CONCLUSIONS

Therefore, these results suggest that HLJDD enhanced adipose thermogenesis and improved energy expenditure by inhibiting HDAC3, thereby increasing UCP-1 and PGC-1α expression. These findings amplified the mechanisms of HLJDD and its potential to treat obesity and related metabolic disorders.

Proteomic insights into circadian transcription regulation: novel E-box interactors revealed by proximity labeling

Circadian clocks (∼24 h) are responsible for daily physiological, metabolic, and behavioral changes. Central to these oscillations is the regulation of gene transcription. Previous research has identified clock protein complexes that interact with the transcriptional machinery to orchestrate circadian transcription, but technological constraints have limited the identification of de novo proteins. Here we use a novel genomic locus-specific quantitative proteomics approach to provide a new perspective on time of day-dependent protein binding at a critical chromatin locus involved in circadian transcription: the E-box. Using proximity labeling proteomics at the E-box of the clock-controlled Dbp gene in mouse fibroblasts, we identified 69 proteins at this locus at the time of BMAL1 binding. This method successfully enriched BMAL1 as well as HDAC3 and HISTONE H2A.V/Z, known circadian regulators. New E-box proteins include the MINK1 kinase and the transporters XPO7 and APPL1, whose depletion in human U-2 OS cells results in disrupted circadian rhythms, suggesting a role in the circadian transcriptional machinery. Overall, our approach uncovers novel circadian modulators and provides a new strategy to obtain a complete temporal picture of circadian transcriptional regulation.

NMDAR-dependent synaptic potentiation via APPL1 signaling is required for the accessibility of a prefrontal neuronal assembly in retrieving fear extinction

BACKGROUND

The ventromedial prefrontal cortex (vmPFC) has been viewed as a locus to store and recall extinction memory. However, the synaptic and cellular mechanisms underlying this process remain elusive.

METHODS

We combined transgenic mice, electrophysiological recording, activity-dependent cell labeling, and chemogenetic manipulation to analyze the role of adaptor protein APPL1 in the vmPFC for fear extinction retrieval.

RESULTS

We found that both constitutive and conditional APPL1 knockout decreases NMDA receptor (NMDAR) function in the vmPFC and impairs fear extinction retrieval. Moreover, APPL1 undergoes nuclear translocation during extinction retrieval. Blocking APPL1 nucleocytoplasmic translocation reduces NMDAR currents and disrupts extinction retrieval. We further identified a prefrontal neuronal ensemble that is both necessary and sufficient for the storage of extinction memory. Inducible APPL1 knockout in this ensemble abolishes NMDAR-dependent synaptic potentiation and disrupts extinction retrieval, while simultaneously chemogenetic activation of this ensemble rescues the impaired behaviors.

CONCLUSIONS

Therefore, our results indicate that a prefrontal neuronal ensemble stores extinction memory, and APPL1 signaling supports these neurons to retrieve extinction memory via controlling NMDAR-dependent potentiation.

Imipramine activates FAM3A-FOXA2-CPT2 pathway to ameliorate hepatic steatosis

Mitochondrial FAM3A has been revealed to be a viable target for treating diabetes and nonalcoholic fatty liver disease (NAFLD). However, its distinct mechanism in ameliorating hepatic steatosis remained unrevealed. High-throughput RNA sequencing revealed that carnitine palmityl transferase 2 (CPT2), one of the key enzymes for lipid oxidation, is the downstream molecule of FAM3A signaling pathway in hepatocytes. Intensive study demonstrated that FAM3A-induced ATP release activated P2 receptor to promote the translocation of calmodulin (CaM) from cytoplasm into nucleus, where it functioned as a co-activator of forkhead box protein A2 (FOXA2) to promote the transcription of CPT2, increasing free fatty acid oxidation and reducing lipid deposition in hepatocytes. Furthermore, antidepressant imipramine activated FAM3A-ATP-P2 receptor-CaM-FOXA2-CPT2 pathway to reduce lipid deposition in hepatocytes. In FAM3A-deficient hepatocytes, imipramine failed to activate CaM-FOXA2-CPT2 axis to increase lipid oxidation. Imipramine administration significantly ameliorated hepatic steatosis, hyperglycemia and obesity of obese mice mainly by activating FAM3A-ATP-CaM-FOXA2-CPT2 pathway in liver and thermogenesis in brown adipose tissue (BAT). In FAM3A-deficient mice fed on high-fat-diet, imipramine treatment failed to correct the dysregulated lipid and glucose metabolism, and activate thermogenesis in BAT. In conclusion, imipramine activates FAM3A-ATP-CaM-FOXA2-CPT2 pathway to ameliorate steatosis. For depressive patients complicated with metabolic disorders, imipramine may be recommended in priority as antidepressive drug.

Non-shivering Thermogenesis Signalling Regulation and Potential Therapeutic Applications of Brown Adipose Tissue

In mammals, thermogenic organs exist in the body that increase heat production and enhance energy regulation. Because brown adipose tissue (BAT) consumes energy and generates heat, increasing energy expenditure via BAT might be a potential strategy for new treatments for obesity and obesity-related diseases. Thermogenic differentiation affects normal adipose tissue generation, emphasizing the critical role that common transcriptional regulation factors might play in common characteristics and sources. An understanding of thermogenic differentiation and related factors could help in developing ways to improve obesity indirectly or directly through targeting of specific signalling pathways. Many studies have shown that the active components of various natural products promote thermogenesis through various signalling pathways. This article reviews recent major advances in this field, including those in the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA), cyclic guanosine monophosphate-GMP-dependent protein kinase G (cGMP-AKT), AMP-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), transforming growth factor-β/bone morphogenic protein (TGF-β/BMP), transient receptor potential (TRP), Wnt, nuclear factor-κ-light-chain-enhancer of activated B cells (NF-κΒ), Notch and Hedgehog (Hh) signalling pathways in brown and brown-like adipose tissue. To provide effective information for future research on weight-loss nutraceuticals or drugs, this review also highlights the natural products and their active ingredients that have been reported in recent years to affect thermogenesis and thus contribute to weight loss via the above signalling pathways.

AP2-microRNA-26a overexpression reduces visceral fat mass and blood lipids

BACKGROUND

MicroRNA-26a (miR-26a) is a key player in tumor suppression and plays important roles in glucose and lipid metabolism. However, its function in adipose tissue is not well defined.

OBJECTIVE

The study aimed to examine the effect on fat expansion and function of miR-26a in adipose tissue.

METHODS

Adipose-specific miR-26a transgenic mice (Ap2-miR-26a) were firstly generated by breeding miR-26a floxed (Mir26a^loxP/^loxP) mice with Ap2-Cre recombinase transgenic mice. The effects of miR-26a adipose-specific overexpression on body weight, body fat composition, fat pad weight, adipocyte size, blood lipid levels, glucose metabolism, and adipogenesis were investigated in mice on a chow diet and a high fat diet. White adipose tissue browning was evaluated by energy expenditure, adipocyte morphology and browning related genes expression levels both at room temperature and after cold exposure. Gene expression was determined by Real-Time quantitative PCR and western blotting.

RESULTS

MiR-26a was specifically overexpressed in adipose by ~4 folds. Ap2-miR-26a mice had a moderate decrease in body weight, body fat composition, epididymal white adipose (eWAT) weight and blood lipid levels, along with smaller adipocytes in eWAT. The favorable phenotype was not due to white adipose tissue browning (even after cold exposure) or adipogenesis or lipolysis. Ap2-miR-26a mice exhibited no significant metabolic phenotype under high-fat-diet feeding.

CONCLUSION

This study suggests that adipose-specific overexpression of miR-26a could moderately reduce visceral fat pad mass and lipid levels independent of white adipose tissue browning, adipogenesis and adipose lipolysis based on the gene expression level.

Analysis of APPL1 Gene Polymorphisms in Patients with a Phenotype of Maturity Onset Diabetes of the Young

The APPL1 gene encodes a protein mediating the cross-talk between adiponectin and insulin signaling. Recently, it was found that APPL1 mutations can cause maturity onset diabetes of the young, type 14. Here, an analysis of APPL1 was performed in patients with a maturity-onset diabetes of the young (MODY) phenotype, and prevalence of these mutations was estimated in a Russian population, among type 2 diabetes mellitus (T2DM) and MODY patients. Whole-exome sequencing or targeted sequencing was performed on 151 probands with a MODY phenotype, with subsequent association analysis of one of identified variants, rs11544593, in a white population of Western Siberia (276 control subjects and 169 T2DM patients). Thirteen variants were found in APPL1, three of which (rs79282761, rs138485817, and rs11544593) are located in exons. There were no statistically significant differences in the frequencies of rs11544593 alleles and genotypes between T2DM patients and the general population. In the MODY group, AG rs11544593 genotype carriers were significantly more frequent (AG vs. AA + GG: odds ratio 1.83, confidence interval 1.15-2.90, p = 0.011) compared with the control group. An association of rs11544593 with blood glucose concentration was revealed in the MODY group. The genotyping data suggest that rs11544593 may contribute to carbohydrate metabolism disturbances.

APPL1 knockdown blocks adipogenic differentiation and promotes adipocyte lipolysis

Adipocyte dysfunction is closely associated with the development of obesity, insulin resistance, and type 2 diabetes. In addition to having a positive effect on adiponectin pathway and insulin signaling through direct and/or indirect mechanisms, adapter protein APPL1 has also been reported to regulate body weight, brown fat tissues thermogenesis, and body fat distribution in diabetic individuals. However, there is dearth of data on the specific role of APPL1 on adipogenic differentiation and adipocyte lipolysis. In this study, APPL1's function in adipocyte differentiation and adipocyte lipolysis was evaluated, and the possible mechanisms were investigated. We found that APPL1 knockdown (KD) impeded differentiation of 3T3-L1 preadipocytes into mature 3T3-L1 adipocytes and enhanced basal and insulin-suppressed lipolysis in mature 3T3-L1 adipocytes. APPL1 KD cells presented a reduced autophagic activity in 3T3-L1 preadipocytes and mature 3T3-L1 adipocytes. In 3T3-L1 preadipocytes, APPL1 KD reduced PPARγ protein levels, which was prevented by administration with proteasome inhibitor MG132. Furthermore, APPL1 KD-reduced autophagic activity in mature 3T3-L1 adipocytes was markedly restored by inhibition of PKA, accompanied with prevention of APPL1-induced lipolysis. In addition, APPL1 KD caused insulin resistance in mature 3T3-L1 adipocytes. Unexpectedly, we found that APPL1 overexpression did not appear to play a role in adipogenic differentiation and adipocyte lipolysis. Our results confirmed that APPL1 KD inhibits adipogenic differentiation by suppressing autophagy and enhances adipocyte lipolysis through activating PKA respectively. These findings may deepen our understanding of APPL1 function, especially its regulation on adipocyte biology.