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Summary: Respiration in leaves and the continued elevation in the atmospheric CO2 concentration cause CO2‐mediated reduction in stomatal pore apertures. Several mutants have been isolated for which stomatal responses to both abscisic acid (ABA) and CO2 are simultaneously defective. However, there are only few mutations that impair the stomatal response to elevated CO2, but not to ABA. Such mutants are invaluable in unraveling the molecular mechanisms of early CO2 signal transduction in guard cells. Recently, mutations in the mitogen‐activated protein (MAP) kinase, MPK12, have been shown to partially impair CO2‐induced stomatal closure. Here, we show that mpk12 plants, in which MPK4 is stably silenced specifically in guard cells (mpk12 mpk4GC homozygous double‐mutants), completely lack CO2‐induced stomatal responses and have impaired activation of guard cell S‐type anion channels in response to elevated CO2/bicarbonate. However, ABA‐induced stomatal closure, S‐type anion channel activation and ABA‐induced marker gene expression remain intact in the mpk12 mpk4GC double‐mutants. These findings suggest that MPK12 and MPK4 act very early in CO2 signaling, upstream of, or parallel to the convergence of CO2 and ABA signal transduction. The activities of MPK4 and MPK12 protein kinases were not directly modulated by CO2/bicarbonate in vitro, suggesting that they are not direct CO2/bicarbonate sensors. Further data indicate that MPK4 and MPK12 have distinguishable roles in Arabidopsis and that the previously suggested role of RHC1 in stomatal CO2 signaling is minor, whereas MPK4 and MPK12 act as key components of early stomatal CO2 signal transduction. Significance statement: We show that MPK4 and MPK12 are required for CO2‐triggered stomatal responses but not for ABA‐induced stomatal closure. These results suggest that these two MAP kinases function upstream of the convergence of CO2 and ABA signaling. However, activities of MPK4 and MPK12 were not modulated by CO2/bicarbonate and, thus, direct HCO3−/CO2 sensing mechanisms remain to be identified. [ABSTRACT FROM AUTHOR]

Summary: Drought is a major environmental stress that threatens crop production. Therefore, identification of genes involved in drought stress response is of vital importance to decipher the molecular mechanism of stress signal transduction and breed drought tolerance crops, especially for maize.Clade A PP2C phosphatases are core abscisic acid (ABA) signaling components, regulating ABA signal transduction and drought response. However, the roles of other clade PP2Cs in drought resistance remain largely unknown. Here, we discovered a clade F PP2C, ZmPP84, that negatively regulates drought tolerance by screening a transgenic overexpression maize library.Quantitative RT‐PCR indicates that the transcription of ZmPP84 is suppressed by drought stress. We identified that ZmMEK1, a member of the MAPKK family, interacts with ZmPP84 by immunoprecipitation and mass spectrometry analysis. Additionally, we found that ZmPP84 can dephosphorylate ZmMEK1 and repress its kinase activity on the downstream substrate kinase ZmSIMK1, while ZmSIMK1 is able to phosphorylate S‐type anion channel ZmSLAC1 at S146 and T520 in vitro. Mutations of S146 and T520 to phosphomimetic aspartate could activate ZmSLAC1 currents in Xenopus oocytes.Taken together, our study suggests that ZmPP84 is a negative regulator of drought stress response that inhibits stomatal closure through dephosphorylating ZmMEK1, thereby repressing ZmMEK1–ZmSIMK1 signaling pathway. [ABSTRACT FROM AUTHOR]

Objective. The aims of this study were to investigate the impact of TAK-242 on the Toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (MyD88)/nuclear transcription factor-κB (NF-κB) signal transduction pathway in rats with hepatic fibrosis (HF) using the liver gut axis and to investigate the molecular mechanism of its intervention on HF. Methods. SPF grade SD male rats were randomly allocated to the control, model, and TAK-242 groups. For 8 weeks, the model and TAK-242 groups received 3 mL·kg-1 (the initial dose 5 mL·kg-1) intraperitoneal injections of 40% CCL4 olive oil solution. TAK-242 (5 mg·kg-1) was administered once a day for 5 days after modeling. The pathological alterations of liver and small intestine tissues in each group were observed using H&E and Masson staining. ELISA was used to measure serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), direct bilirubin (DBIL), total bilirubin (TBIL), interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α). RT-qPCR was utilized to identify the mRNA expression level of IL-1β, IL-6, TNF-α, TLR4, MyD88, and NF-κB in rat liver and small intestine tissues. The protein level of IL-1β, IL-6, TNF-α, TLR4, MyD88, and NF-κB protein in rat liver and small intestine tissues was determined utilizing Western blot and IHC. Results. TAK-242 significantly reduced AST, ALT, TBIL, and DBIL expression in HF rats' serum (P < 0.01) and alleviated liver tissue injury. Hematoxylin-eosin (H&E) and Masson staining revealed inflammatory cell infiltration and fibrous proliferation in the liver and small intestine tissue in the model group and partial cell swelling in the TAK-242 group, which indicated a considerable improvement compared to the model group. RT-qPCR, Western blot, and IHC data indicated that TAK-242 reduced the IL-1β, IL-6, TNF-α, TLR4, MyD88, and NF-κB expression in the liver and small intestine tissues of HF rats. Conclusion. TAK-242 might downregulate the TLR4/MyD88/NF-κB signal pathway through the liver-gut axis, suppress the inflammatory response, and eventually alleviate HF in rats. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) is a common neurodegenerative disease characterized by a disorder of the dopaminergic system in the midbrain, causing classical PD motor symptoms. The therapeutic effect of cannabidiol (CBD) on PD has been a research frontier in recent years. However, the pathogenesis of PD and the therapeutic mechanism of cannabinoid remain unclear. To further study the causes of PD and the effect of CBD on PD, we exposed the PD transgenic mouse model to CBD and then estimated the motorial and postural coordination through a modified swim test. Afterwards, the mechanism was investigated via the histopathology of substantia nigra and the gut-brain metabolic analysis in the approach of UHPLC-TOF-MS. The results showed that CBD significantly improved motor deficits of PD model and protected the substantia nigra area. The metabolic function of fatty acid biosynthesis, arginine biosynthesis/metabolism, butanoate (ketone body) metabolism, β-alanine metabolism, and pantothenate/CoA biosynthesis was highlighted in the pathological and therapeutic process along the gut-brain axis. In conclusion, CBD could attenuate PD via the neuroprotective effect on the midbrain. The attenuation of the central nervous system in turn improved motor performance of PD, which might be partially induced by the metabolic interaction between the gut-brain. In view of gut-brain metabolomics, the mechanism of PD pathogenesis and the effect of CBD on PD are highly related to the biosynthesis and metabolism of energy and essential substance. [ABSTRACT FROM AUTHOR]

NRT1.1, a nitrate transceptor, plays an important role in nitrate binding, sensing, and nitrate-dependent lateral root (LR) morphology. However, little is known about NRT1.1-mediated nitrate signaling transduction through plasma membrane (PM)-localized proteins. Through in-depth phosphoproteome profiling using membranes of Arabidopsis roots, we identified receptor kinase QSK1 and plasma membrane H+-ATPase AHA2 as potential downstream components of NRT1.1 signaling in a mild low-nitrate (LN)-dependent manner. QSK1, as a functional kinase and molecular link, physically interacts with NRT1.1 and AHA2 at LN and specifically phosphorylates AHA2 at S899. Importantly, we found that LN, not high nitrate (HN), induces formation of the NRT1.1-QSK1-AHA2 complex in order to repress the proton efflux into the apoplast by increased phosphorylation of AHA2 at S899. Loss of either NRT1.1 or QSK1 thus results in a higher T947/S899 phosphorylation ratio on AHA2, leading to enhanced pump activity and longer LRs under LN. Our results uncover a regulatory mechanism in which NRT1.1, under LN conditions, promotes coreceptor QSK1 phosphorylation and enhances the NRT1.1-QSK1 complex formation to transduce LN sensing to the PM H+-ATPase AHA2, controlling the phosphorylation ratio of activating and inhibitory phosphorylation sites on AHA2. This then results in altered proton pump activity, apoplast acidification, and regulation of NRT1.1-mediated LR growth. • Transceptor NRT1.1 is critical for plasma membrane ATPase AHA2 activity under LN • Upon nitrate binding, NRT1.1 promotes coreceptor QSK1 phosphorylation • QSK1 physically links NRT1.1 and AHA2, specifically phosphorylating AHA2 on S899 • NRT1.1-QSK1 transduces LN sensing to AHA2, repressing proton efflux and LR growth Zhu and Krall et al. uncover a mechanism in which NRT1.1, in LN, increases the phosphorylation of QSK1. This forms a complex to transduce LN sensing to the PM H+-ATPase AHA2, regulating the phosphorylation ratio of AHA2 activation and inhibitory phosphorylation sites, resulting in altered apoplast acidification and regulation of LR growth. [ABSTRACT FROM AUTHOR]

Renal interstitial fibrosis is a major pathologic feature of diabetic nephropathy, while the pathogenesis and therapeutic interventions of diabetic renal interstitial fibrosis are not well established. In this study, we first demonstrated that high glucose could induce renal fibroblast (NRK-49F) cell proliferation and activation to myofibroblasts, accompanied by a significant increase in the intracellular levels of reactive oxygen species (ROS) derived from nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4). ROS-mediated ERK1/2 activation was found to play a crucial role in high glucose-induced fibroblast proliferation and activation. Resveratrol, like the NOX4-targeting small interfering RNA (siRNA), markedly inhibited high glucose-induced fibroblast proliferation and activation by reducing NOX4-derived ROS production. It was then revealed that the increase in the expression of NOX4 induced by high glucose was due to the inactivation of AMP-activated protein kinase (AMPK), which could be reversed by resveratrol. Further in vivo investigation demonstrated that resveratrol treatment significantly attenuated renal fibrosis in db/db mice, accompanied by an evident increase in phospho-AMPK and decrease in NOX4. In summary, our results suggest that high glucose can directly promote renal fibroblasts proliferation and activation in a ROS-dependent manner, and resveratrol is a potential therapeutic agent against diabetic renal fibrosis via regulation of AMPK/NOX4/ROS signaling. Key message: [ABSTRACT FROM AUTHOR]

As a typical protein-bound uremic toxin, indoxyl sulfate is considered to be able to induce cardiomyocytes hypertrophy by promoting oxidative stress in chronic kidney disease (CKD). Uncoupling protein 2 (UCP2), a member of the uncoupling protein family, may protect cardiomyocytes from oxidative stress by suppressing mitochondrial reactive oxygen species (ROS). In the present study, we aimed to determine whether UCP2 was involved in indoxyl sulfate-induced cardiomyocytes hypertrophy. We demonstrated that indoxyl sulfate could increase the ROS levels in a time and dose-dependent manner in cultured neonatal rat cardiomyocytes. Significant increases in [ 3 H]-leucine incorporation, cell volume, and the mRNA expression levels of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), and beta myosin heavy chain (β-MHC) were detected in cardiomyocytes after treatement with indoxyl sulfate at the concentration of 500 μM for 48 h, accompanied by a decreased expression of UCP2. In contrast, cardiomyocytes transfected with the lentiviral vector carrying UCP2 gene were resistant to indoxyl sulfate-induced ROS production and cell hypertrophy. Additionally, indoxyl sulfate-induced UCP2 reduction was correlated with the inhibition of AMP-activated protein kinase (AMPK) activity, while pretreatment with AICAR, an AMPK activator, effectively attenuated indoxyl sulfate-induced UCP2 down-regulation and hypertrophy in cardiomyocytes. Taken together, these results suggest that indoxyl sulfate-induced cardiomyocytes hypertrophy was partly due to the inhibition of AMPK/UCP2 signaling and the enhancement of oxidative stress. [ABSTRACT FROM AUTHOR]