Silicon dioxide nanoparticles inhibit the effects of cold exposure on metabolism and inflammatory responses in brown adipocytes

Objective:Nanoparticles(NPs)in haze are potentially hazardous to health,which is more severe in the winter.Brown adipose tissue(BAT)plays important roles in obesity,insulin resistance,and diabetes.Though the toxicology of NPs has been intensively studied,few studies have been reported on the antagonistic effects between Silicon dioxide(SiO_(2))NPs and cold exposure in brown adipocytes.Materials and methods:We evaluated changes by quantitative real-time reverse-transcriptase polymerase chain reaction(qRT-PCR)on metabolism genes,plasticity genes and the inflammatory responses genes in brown adipocytes in vitro.Results:The expression of adipogenic genes PRDM16,Dio2,PGC-1αand UCP1 was upregulated upon cold exposure(P<0.05),but downregulated by SiO_(2) NPs(P<0.05).The results demonstrated that there was antagonistic effect between SiO_(2) NPs and cold exposure on the plasticity genes and metabolism genes in brown adipocytes,where the main effects of SiO_(2) NPs or cold exposure on the plasticity genes and metabolism genes were significant(P<0.05).Moreover,the levels of interleukin(IL)-1β,IL-6 and tumor necrosis factor(TNF)-αwere upregulated by SiO_(2) NPs or cold exposure(P<0.05).The factorial analysis indicated that there was also antagonistic effect between SiO_(2) NPs and cold exposure on the toxic effects in brown adipocytes,in which the main effects of cold exposure and/or SiO_(2) NPs on the toxic effects were significant(P<0.05).Conclusion:SiO_(2) NPs inhibit the effect of cold exposure on metabolic genes and inflammatory responses genes in brown adipocytes.

Mitochondrial flashes are interlinked with adaptive thermogenesis in brown adipocytes

Mitochondrial flash(mitoflash)is the electrochemical excitation of a single mitochondrion and plays diverse signaling roles in a variety of cells.From the viewpoint of bioenergetics,it represents the transient uncoupling of mitochondrial respiration from ATP synthesis.Brown adipose tissue(BAT)produces heat,primarily via mitochondrial uncoupled respiration.Here,we aim to illustrate the mitoflash activity in BAT thermogenesis.We show that BAT mitochondria undergo stochastic and intermittent mitoflashes at the levels of isolated mitochondria,cultured brown adipocytes,and even intact BAT.A BAT mitoflash contains multiple signals,including transient depolarization of mitochondrial membrane potential,transient matrix alkalization,and bursting production of reactive oxygen species.Importantly,thermogenic activation by b3-adrenergic stimulation dramatically augments mitoflash incidence,with mild effects on its unitary characteristics.Ablation of the thermogenic uncoupling protein 1(UCP1)showed little effect on mitoflash biogenesis during heat production.Collectively,our results suggest that mitoflash might constitute an elemental signaling activity of mitochondria to regulate BAT thermogenesis.

NF-κB regulates brown adipocyte function through suppression of ANT2

The transcription factor nuclear factor of kappa-light-chain-enhancer of activated B cells(NF-κB)is expressed in brown adipocytes,but its role remains largely unknown in the cells.This issue was addressed in current study by examining NF-κB in brown adipocytes in vitro and in vivo.NF-κB activity was increased by differentiation of brown adipocytes through elevation of p65(RelA)expression.The transcriptional activity of NF-κB was induced by the cold stimulation with an elevation in S276 phosphorylation of p65 protein.Inactivation of NF-κB in brown adipocytes made the knockout mice[uncoupling protein 1(Ucp1)-CreER-p65^(f/f),U-p65-KO]intolerant to the cold environment.The brown adipocytes exhibited an increase in apoptosis,a decrease in cristae density and uncoupling activity in the interscapular brown adipose tissue(iBAT)of p65-KO mice.The alterations became severer after cold exposure of the KO mice.The brown adipocytes of mice with NF-κB activation(p65 overexpression,p65-OE)exhibited a set of opposite alterations with a reduction in apoptosis,an increase in cristae density and uncoupling activity.In mechanism,NF-κB inhibited expression of the adenine nucleotide translocase 2(ANT2)in the control of apoptosis.Data suggest that NF-κB activity is increased in brown adipocytes by differentiation and cold stimulation to protect the cells from apoptosis through down-regulation of ANT2 expression.

Brown and beige fat： the metabolic function, induction, and therapeutic potential

Adipose tissue is an important organ for energy homeostasis. White adipose tissue stores energy in the form of triglycerides, whereas brown adipocytes and recently identified beige adipocytes are specialized in dissipating energy by thermogenesis or contribution to dispose glucose and clear triglycerides in blood. The inverse correlation between the brown adipose tissue activity and body mass suggests its protective role against body fat accumulation. Thus, recruitment and activation of brown or beige adipose tissue become particularly appealing targets for increasing energy expenditure. Angiogenesis and sympathetic nerve signals are the fundamental determinants for brown and beige adipose tissue development, as well as for their metabolic functions. Secretary factors including BMPs can induce the development, the activation of brown or beige adipose tissue, which seem to be promising for therapeutic development.

Fabricating 3-dimensional human brown adipose microtissues for transplantation studies

Transplanting cell cultured brown adipocytes(BAs)represents a promising approach to prevent and treat obesity(OB)and its associated metabolic disorders,including type 2 diabetes mellitus(T2DM).However,transplanted BAs have a very low survival rate in vivo.The enzymatic dissociation during the harvest of fully differentiated BAs also loses significant cells.There is a critical need for novel methods that can avoid cell death during cell preparation,transplantation,and in vivo.Here,we reported that preparing BAs as injectable microtissues could overcome the problem.We found that 3D culture promoted BA differentiation and UCP-1 expression,and the optimal initial cell aggregate size was 100μm.The microtissues could be produced at large scales via 3D suspension assisted with a PEG hydrogel and could be cryopreserved.Fabricated microtissues could survive in vivo for long term.They alleviated body weight and fat gain and improved glucose tolerance and insulin sensitivity in high-fat diet(HFD)-induced OB and T2DM mice.Transplanted microtissues impacted multiple organs,secreted protein factors,and influenced the secretion of endogenous adipokines.To our best knowledge,this is the first report on fabricating human BA microtissues and showing their safety and efficacy in T2DM mice.The proposal of transplanting fabricated BA microtissues,the microtissue fabrication method,and the demonstration of efficacy in T2DM mice are all new.Our results show that engineered 3D human BA microtissues have considerable advantages in product scalability,storage,purity,safety,dosage,survival,and efficacy.

In Situ Saturating Mutagenesis Screening Identifies a Functional Genomic Locus that Regulates Ucp1 Expression

A better understanding of the molecular mechanisms that control the UCP1 expression in brown and beige adipocytes is essential for us to modulate adipose cell fate and promote thermogenesis,which may provide a therapeutic view for the treatment of obesity and obesity-related diseases.To systematically identify cis-element(s)that transcriptionally regulates Ucp1,we here took advantage of the high-throughput CRIPSR-Cas9 screening system,and performed an in situ saturating mutagenesis screen,by using a customized sgRNA library targeting the~20 kb genomic region near Ucp1.Through the screening,we have identified several genomic loci that may contain key regulatory element for Ucp1 expression in cultured brown and white adipocytes in vitro,and in inguinal white adipose tissue in vivo.Our study highlights a broadly useful approach for studying cis-regulatory elements in a high-throughput manner.

Peptidoglycan inhibits beigeing of adipose tissue

To the Editor:Obesity, an epidemic metabolic disease characterized by excessive fat accumulation, causes a significant economic burden on families and the society. The discovery of beige adipocytes has provided us with a brand new approach for the intervention of obesity^(1). Beige adipocytes increase energy expenditure and improve the balance of glucose and lipid metabolism. Reduction of beige adipocytes is a hallmark of obesity. Mechanism underlying the decrement of beigeing remains largely unknown.