Spatial Regulation of Reactive Oxygen Species via G6PD in Brown Adipocytes Supports Thermogenic Function

Loss of FoxO1 activates an alternate mechanism of mitochondrial quality control for healthy adipose browning

Browning of white adipose tissue is hallmarked by increased mitochondrial density and metabolic improvements. However, it remains largely unknown how mitochondrial turnover and quality control are regulated during adipose browning. In the present study, we found that mice lacking adipocyte FoxO1, a transcription factor that regulates autophagy, adopted an alternate mechanism of mitophagy to maintain mitochondrial turnover and quality control during adipose browning. Post-developmental deletion of adipocyte FoxO1 (adO1KO) suppressed Bnip3 but activated Fundc1/Drp1/OPA1 cascade, concurrent with up-regulation of Atg7 and CTSL. In addition, mitochondrial biogenesis was stimulated via the Pgc1α/Tfam pathway in adO1KO mice. These changes were associated with enhanced mitochondrial homeostasis and metabolic health (e.g., improved glucose tolerance and insulin sensitivity). By contrast, silencing Fundc1 or Pgc1α reversed the changes induced by silencing FoxO1, which impaired mitochondrial quality control and function. Ablation of Atg7 suppressed mitochondrial turnover and function, causing metabolic disorder (e.g., impaired glucose tolerance and insulin sensitivity), regardless of elevated markers of adipose browning. Consistently, suppression of autophagy via CTSL by high-fat diet was associated with a reversal of adO1KO-induced benefits. Our data reveal a unique role of FoxO1 in coordinating mitophagy receptors (Bnip3 and Fundc1) for a fine-tuned mitochondrial turnover and quality control, underscoring autophagic clearance of mitochondria as a prerequisite for healthy browning of adipose tissue.

Au@16-pH-16/miR-21 mimic nanosystem: An efficient treatment for obesity through browning and thermogenesis induction

Despite the abundance of registered clinical trials worldwide, the availability of effective drugs for obesity treatment is limited due to their associated side effects. Thus, there is growing interest in therapies that stimulate energy expenditure in white adipose tissue. Recently, we demonstrated that the delivery of a miR-21 mimic using JetPEI effectively inhibits weight gain in an obese mouse model by promoting metabolism, browning, and thermogenesis, suggesting the potential of miR-21 mimic as a treatment for obesity. Despite these promising results, the implementation of more advanced delivery system techniques for miR-21 mimic would greatly enhance the advancement of safe and efficient treatment approaches for individuals with obesity in the future. Our objective is to explore whether a new delivery system based on gold nanoparticles and Gemini surfactants (Au@16-ph-16) can replicate the favorable effects of the miR-21 mimic on weight gain, browning, and thermogenesis. We found that dosages as low as 0.2 μg miR-21 mimic /animal significantly inhibited weight gain and induced browning and thermogenic parameters. This was evidenced by the upregulation of specific genes and proteins associated with these processes, as well as the biogenesis of beige adipocytes and mitochondria. Significant increases in miR-21 levels were observed in adipose tissue but not in other tissue types. Our data indicates that Au@16-ph-16 could serve as an effective delivery system for miRNA mimics, suggesting its potential suitability for the development of future clinical treatments against obesity.

Ubiquitin ligase RNF20 coordinates sequential adipose thermogenesis with brown and beige fat-specific substrates

In mammals, brown adipose tissue (BAT) and inguinal white adipose tissue (iWAT) execute sequential thermogenesis to maintain body temperature during cold stimuli. BAT rapidly generates heat through brown adipocyte activation, and further iWAT gradually stimulates beige fat cell differentiation upon prolonged cold challenges. However, fat depot-specific regulatory mechanisms for thermogenic activation of two fat depots are poorly understood. Here, we demonstrate that E3 ubiquitin ligase RNF20 orchestrates adipose thermogenesis with BAT- and iWAT-specific substrates. Upon cold stimuli, BAT RNF20 is rapidly downregulated, resulting in GABPα protein elevation by controlling protein stability, which stimulates thermogenic gene expression. Accordingly, BAT-specific Rnf20 suppression potentiates BAT thermogenic activity via GABPα upregulation. Moreover, upon prolonged cold stimuli, iWAT RNF20 is gradually upregulated to promote de novo beige adipogenesis. Mechanistically, iWAT RNF20 mediates NCoR1 protein degradation, rather than GABPα, to activate PPARγ. Together, current findings propose fat depot-specific regulatory mechanisms for temporal activation of adipose thermogenesis.

A fingerprint of 2-[18F]FDG radiometabolites - How tissue-specific metabolism beyond 2-[18F]FDG-6-P could affect tracer accumulation

Studies indicate that the radiotracer 2-[18F]fluoro-2-deoxy-D-glucose (2-[18F]FDG) can be metabolized beyond 2-[18F]FDG-6-phosphate (2-[18F]FDG-6-P), but its metabolism is incompletely understood. Most importantly, it remains unclear whether downstream metabolism affects tracer accumulation in vivo. Here we present a fingerprint of 2-[18F]FDG radiometabolites over time in cancer cells, corresponding tumor xenografts and murine organs. Strikingly, radiometabolites representing glycogen metabolism or the oxPPP correlated inversely with tracer accumulation across all examined tissues. Recent studies suggest that not only hexokinase, but also hexose-6-phosphate dehydrogenase (H6PD), an enzyme of the oxidative pentose phosphate pathway (oxPPP), determines 2-[18F]FDG accumulation. However, little is known about the corresponding enzyme glucose-6-phosphate dehydrogenase (G6PD). Our mechanistic in vitro experiments on the role of the oxPPP propose that 2-[18F]FDG can be metabolized via both G6PD and H6PD, but data from separate enzyme knockdown suggest diverging roles in downstream tracer metabolism. Overall, we propose that tissue-specific metabolism beyond 2-[18F]FDG-6-P could matter for imaging.

Pan-cancer analysis of G6PD carcinogenesis in human tumors

Glucose-6-phosphate dehydrogenase (G6PD) is involved in the catalytic pentose phosphate pathway (PPP), which is closely related to energy metabolism. G6PD plays a crucial role in many types of cancer, but the specific molecular mechanisms of G6PD in cancer remain unclear. Therefore, we investigated the potential oncogenic role of G6PD in various tumors based on The Cancer Genome Atlas (TCGA), the cBioPortal datasets, the University of California Santa Cruz (UCSC) Xena browser, and the UALCAN-based online tool. G6PD was highly expressed in several cancer tissues (hepatocellular carcinoma, glioma, and breast cancer) compared with normal tissues and was significantly associated with poor prognosis of hepatocellular carcinoma, clear cell renal cell carcinoma, and breast cancer. Promoter methylation levels of G6PD were lower in Bladder Urothelial Carcinoma (BLCA) (P = 2.77e-02), breast invasive carcinoma (BRCA) (P = 1.62e-12), kidney renal clear cell carcinoma (KIRC) (P = 4.23e-02), kidney renal papillary cell carcinoma (KIRP) (P = 2.64e-03), liver hepatocellular carcinoma (LIHC) (P = 1.76e-02), stomach adenocarcinoma (STAD) (P = 3.50e-02), testicular germ cell tumors (TGCT) (P = 1.62e-12), higher in prostate adenocarcinoma (PRAD) (P = 1.81e-09), and uterine corpus endometrial carcinoma (UCEC) (P = 2.96e-04) compared with corresponding normal tissue samples. G6PD expression was positively correlated with the infiltration level of immune cells in most tumors, suggesting that G6PD may be involved in tumor immune infiltration. In addition, the functional mechanism of G6PD also involves 'Carbon metabolism', 'Glycolysis/Gluconeogenesis', 'Pentose phosphate pathway', and 'Central carbon pathway metabolism in cancer signaling pathway'. This pan-cancer study provides a relatively broad understanding of the oncogenic role of G6PD in various tumors and presents a theoretical basis for the development of G6PD inhibitors as therapeutic drugs for multiple cancers.

A multifunctional peroxidase-based reaction for imaging, sensing and networking of spatial biology

Peroxidase is a heme-containing enzyme that reduces hydrogen peroxide to water by extracting electron(s) from aromatic compounds via a sequential turnover reaction. This reaction can generate various aromatic radicals in the form of short-lived "spray" molecules. These can be either covalently attached to proximal proteins or polymerized via radical-radical coupling. Recent studies have shown that these peroxidase-generated radicals can be utilized as effective tools for spatial research in biological systems, including imaging studies aimed at the spatial localization of proteins using electron microscopy, spatial proteome mapping, and spatial sensing of metabolites (e.g., heme and hydrogen peroxide). This review may facilitate the wider utilization of these peroxidase-based methods for spatial discovery in cellular biology.

Enzymatic Recording of Local Hydrogen Peroxide Generation Using Genetically Encodable Enzyme

Reactive oxygen species (ROS) are endogenously generated in live cells and essential for cell signaling. However, excess ROS generation can cause oxidative damage to biomolecules, which are implicated in various human diseases, including aging. Here, we developed an in vivo hydrogen peroxide monitoring method using a genetically encodable peroxidase (APEX2)-based system. We confirmed that APEX2 is activated by endogenous H₂O₂ and generates phenoxyl radicals to produce biotinylated signals (i.e., biotin-phenol) and fluorescent signals (i.e., AmplexRed), which can be detected using a fluorescence microscope. We observed that all subcellular targeted APEX2s were activated by local H₂O₂ generation by menadione treatment. Among them, the endoplasmic reticulum lumen and lysosome-targeted APEX2 showed the highest response upon addition of menadione which implies that local H₂O₂ levels in those spaces are highly increased by menadione treatment. Using APEX2, we also found that a minimum amount of menadione (>10 μM) is required to generate detectable levels of H₂O₂ in all subcellular compartments. We also checked the local H₂O₂-quenching effect of N-acetylcysteine using our system. As APEX2 can be genetically expressed in diverse live organisms (e.g., cancer cell lines, mice, fly, worm, and yeast), our method can be effectively used to detect local generation of endogenously produced H₂O₂ in diverse live models.

What puts the heat on thermogenic fat: metabolism of fuel substrates

Owing to its unique capacity to clear macronutrients from circulation and use them to produce heat, thermogenic fat is capable of regulating glucose, lipids, and branched-chain amino acids (BCAA) circulatory levels. At the same time, its activity yields a higher energy expenditure, thereby conferring protection against cardiometabolic diseases. Our knowledge on the mechanisms of uptake and intracellular metabolism of such energy substrates into thermogenic fat has meaningfully evolved in recent years. This has allowed us to better understand how the thermogenic machinery processes those molecules to utilize them as substrates for heating up the body. Here, we discuss recent advances in the molecular and cellular regulatory process that governs the uptake and metabolism of such substrates within thermogenic fat.