GGPP Depletion Triggers Metaflammation Through Disequilibrating CYB5R3-Dependent Eicosanoids Metabolism

Metabolic syndromes(Mets)is becoming popular all over the world along with life improvement.At least 30 percent of population in USA suffer from Mets,and the incidence in China is also increasing with years.The Mets refers to the co-occurrence of several known type 2 diabetes mellitus(T2DM)and cardiovascular risk factors,including insulin resistance,obesity,atherogenic dyslipidemia and hypertension.Mets not only seriously affect the life quality of patients,follow-up severe cardiovascular attacks could even cause death.Mets has become a major health concern worldwide due to the large patient population.So,studying the pathogenesis and searching new therapeutic methods to control Mets have a great social significance.These risk factors of Mets include smoking,hypertension,hyperlipidemia,inflammation and oxidative stress.Recently,the lifestyle modifications of dietary change and increased physical activity are the most common treatment.But it can't stop the disease from getting worse even treatment with medicine.Inflammation has been discovered to be implicated in several metabolic disorders for decades(the chronic metabolic inflammation was called metaflammation).Considerable research shows that the integration of metabolic and inflammatory signalling network occurs at multiple levels,but how the metabolic disorders start with inflammation have long been unclear.The clinical therapeutic effect of inflammation blockade or anti-inflammatory molecules is variable.Based on the complicated metaflammation network in obesity and several metabolic disorders,further research on the trigger mechanism of metaflammation in metabolic diseases will contribute to the development of better and more precise drugs for the treatment of metabolic diseases.Mevalonic acid(MVA)pathway is responsible for cholesterol synthesis and isoprenoids synthesis.Isoprenoids are composed of farnesyl pyrophosphate(FPP)and geranylgeranyl pyrophosphate(GGPP),who can modify targets proteins by prenylation.The prenylated proteins acquire the ability of membrane binding through increased lipophicity.Emerging evidence demonstrates that MVA pathway can regulate inflammation/immunity and can be regulated by glucose or lipid metabolism.So we hypothesized that MVA pathway might be a metabolic pathway triggering metaflammation.Although,it is already know that vascular smooth muscle cells are sensitive to MVA pathway impairment or GGPP depletion,but the mechanisms underlying are still not clear.Our previous results showed that MVA pathway is very important compared with glucose and lipid metabolism during vascular smooth muscle cells development.So in our study,we generated neonatal smooth muscle specific GGPPS(GGPP synthetase)knockout mice lines and adult smooth muscle specific GGPPS(GGPP synthetase)knockout mice lines by breeding Ggps1-floxed mice with SMA-Cre or SM22-Cre mice,to systematically study the mechanism of metaflammation trigger by MVA pathway in metabolic diseases,as well as role of MVA pathway in vascular smooth muscle.The expression of GGPPS reduced markedly in multiple smooth muscle types in GGPPSSMKO mice.GGPPSSMKO mice showed a series of phenotypic change including weight loss,significantly reduced blood pressure,significantly abolished mesentery contraction and slightly impacted cardiac function.Based on in vivo and in vitro studies,we further found that vascular smooth muscle cells in GGPPSSMKO mice start apoptosis along with mitophagy from 3 weeks old,and the apoptosis can be partially inhibited by adding of exogenous GGPP.However,there were no obvious phenotypes in GGPPSSM22 mice.Thus,we think that GGPPS/GGPP is essentially required for neonatal vascular smooth muscle cells(VSMCs)development and survival.Its deprivation led to the apoptosis of vascular smooth muscle,resulting in low blood pressure and cardiovascular complications,which eventually led to the death of the mice.By transcriptome analysis of aorta from 3-week old mice,we found that GGPP depletion caused an apparent metaflammation as evidenced by increased expression of proinflammatory cytokines and activated immune responses,which were resulted from metabolic imbalances of eicosanoids metabolism in microsome.In addition,metabonomics analysis showed that eicosanoids metabolites altered as a pro-inflammatory tendency.Mechanistically,the alteration of eicosanoids metabolism was due to the impaired ER anchor of cytochrome b5 reductase 3(CYB5R3).Deficient prenylation by GGPP impaired CYB5R3 to translocate from mitochondrial to endoplasmic reticulum(ER)pool.Therefore,we propose that GGPP deficiency mediated anchor failure of CYB5R3 in ER destroy eicosanoids metabolism homeostasis and redox homeostasis in ER,then lead to severe inflammation,which may be the cause of apoptosis and mitophagy in vascular smooth muscle.In summary,our research shows the mechanistic regulation of GGPP on metaflammation via eicosanoids metabolism.Mechanistically,GGPP can prenylate CYB5R3 and thereby translocating it from mitochondrial pool to ER,which is necessary for ER redox homeostasis as well as eicosanoids metabolism.In addition,this is the first model for a coupled regulation of MVA pathway and microsomal metabolism.Our mechanism explains the physiological function of GGPP in vascular smooth muscle and the immune clinical symptoms of patients with mevalonate kinase deficiency(MKD).We also suggest a potential therapeutic strategy for treatment of metabolic disorders by targeting MVA pathway or GGPP.