Savary, J. | bioRxiv Science

bioRxiv2023

A NRF2/beta3-adrenoreceptor axis drives a sustained antioxidant and metabolic rewiring through the pentose-phosphate pathway to alleviate cardiac stress

BackgroundCardiac {beta}3-adrenergic receptors ({beta}3AR) are upregulated in diseased hearts and mediate antithetic effects to those of {beta}1AR and {beta}2AR. {beta}3AR agonists were recently shown to protect from myocardial remodeling in preclinical studies and to improve systolic function in patients with severe heart failure. The underlying mechanisms, however, remain elusive. MethodsTo dissect functional, transcriptional and metabolic effects, hearts and isolated ventricular myocytes from mice harboring a moderate, cardiac-specific expression of a human ADRB3 transgene ({beta}3AR-Tg) and subjected to transverse aortic constriction (TAC) were assessed using echocardiography, RNAseq, PET scan, metabolomics, seahorse and metabolic flux analysis. Subsequently, signaling and metabolic pathways were investigated further in vivo in {beta}3AR-Tg and in vitro in neonatal rat ventricular myocytes adenovirally infected to express {beta}3AR and subjected to neurohormonal stress. These results were completed with an analysis of single nucleus RNAseq data from human cardiac myocytes from heart failure patients. ResultsCompared with WT littermate, {beta}3AR-Tg mice were protected from hypertrophy after transaortic constriction (TAC), while systolic function was preserved. {beta}3AR-expressing hearts displayed enhanced myocardial glucose uptake under stress in absence of increased lactate levels. Instead, metabolomic and metabolic flux analyses in stressed hearts revealed an increase in intermediates of the Pentose-Phosphate Pathway (PPP) in {beta}3AR-Tg, an alternative route of glucose utilization, paralleled with increased transcript levels of NADPH-producing and rate-limiting enzymes of the PPP, without fueling the hexosamine metabolism. The ensuing increased content of NADPH and of reduced glutathione decreased myocyte oxidant stress, while downstream oxidative metabolism assessed by oxygen consumption was preserved with higher glucose oxidation in {beta}3AR-Tg post-TAC compared to WT, together with increased mitochondrial biogenesis. Unbiased transcriptomics and pathway analysis identified NRF2 (NFE2L2) as upstream transcription factor which was functionally verified in {beta}3AR-expressing cardiac myocytes where its translocation and nuclear activity was dependent on {beta}3AR activation of nitric-oxide synthase (NOS) NO production. ConclusionModerate expression of cardiac {beta}3AR, at levels observed in human cardiac myocardium, exerts antioxidant effects through activation of the PPP and NRF2 pathway, thereby preserving myocardial oxidative metabolism, function and integrity under pathophysiological stress.

physiology↗

bioRxiv2023

Crane fly semiochemical overrules coordinate cyanobiont differentiation in Azolla ferns

Semiochemicals from insects that restrict plant symbiont dinitrogen fixation had not been known. Here we report on a the glycosylated triketide {delta}-lactone only found in Nephrotoma cornicina crane flies, cornicinine, that causes chlorosis in the floating-fern symbioses from the genus Azolla. Cornicinine was chemically synthesized, as well as its aglycone and diastereoisomer. Only the glycosylated trans-A form was active: 500 nM cornicinine in the growth medium turned the dinitrogen-fixing cyanobacterial filaments from Nostoc azollae inside the host leaf cavities into akinete-like cells. Cornicinine further inhibited akinete germination in Azolla sporelings, precluding re-establishment of the symbiosis during sexual reproduction. It did not affect the plant Arabidopsis thaliana or several free-living cyanobacteria from the genera Anabaena or Nostoc. Chlorosis occurred in hosts on nitrogen with and devoid of cyanobiont. Cornicinine, therefore, targeted host mechanisms resulting in coordinate cyanobiont differentiation. Sequence profiling of messenger RNA from isolated leaf cavities confirmed high NH4-assimilation and proanthocyanidin biosynthesis in this trichome-rich tissue. Leaf-cavity transcripts in ferns grown on cornicinine reflected activation of Cullin-RING ubiquitin-ligase pathways, known to mediate metabolite signaling and plant elicitation consistent with the chlorosis phenotype. Transcripts accumulating when akinetes are induced, in leaf cavities of ferns on cornicinine and in megasporocarps, were consistent with increased JA-oxidase, sulfate transport and exosome formation. The work begins to uncover molecular mechanisms of cyanobiont differentiation in a seed-free plant symbiosis important for wetland ecology or circular crop-production today, that once caused massive CO2 draw-down during the Eocene geological past. SignificanceCoordinated differentiation of host and filamentous cyanobacteria underlies the development of ecologically important symbioses; this includes the floating ferns Azolla which share their wetland habitat with Nephrotoma cornicina craneflies containing the glycosylated triketide {delta}-lactone semiochemical, cornicinine. Cornicinine overrules cyanobiont differentiation thus inhibiting symbiosis N2-fixation and sexual reproduction; its mode of action resembles plant elicitation as suggested by transcriptional profiling of cells lining the cyanobiont cavities using a new release of the fern host genome.

plant biology↗