Summary Fibroblast growth factor 21 (FGF21) is a hormone induced by various metabolic stresses, including ketogenic and high carbohydrate diets, that regulates energy homeostasis. In humans, SNPs in and around the FGF21 gene have been associated with macronutrient preference, including carbohydrate, fat and protein intake. Here we show that FGF21 administration markedly reduces sweet and alcohol preference in mice, and sweet preference in cynomolgus monkeys. In mice, these effects require the FGF21 co-receptor β-Klotho in the central nervous system and correlate with reductions in dopamine concentrations in the nucleus accumbens. Since analogs of FGF21 are currently undergoing clinical evaluation for the treatment of obesity and type 2 diabetes, our findings raise the possibility that FGF21 administration could affect nutrient preference and other reward behaviors in humans.

Autophagy-dependent mitochondrial turnover in response to cellular stress is necessary for maintaining cellular homeostasis. However, the mechanisms that govern the selective targeting of damaged mitochondria are poorly understood. Parkin, an E3 ubiquitin ligase, has been shown to be essential for the selective clearance of damaged mitochondria. Parkin is expressed in the heart, yet its function has not been investigated in the context of cardioprotection. We previously reported that autophagy is required for cardioprotection by ischemic preconditioning (IPC). In the present study, we used simulated ischemia (sI) in vitro and IPC of hearts to investigate the role of Parkin in mediating cardioprotection ex vivo and in vivo. In HL-1 cells, sI induced Parkin translocation to mitochondria and mitochondrial elimination. IPC induced Parkin translocation to mitochondria in Langendorff-perfused rat hearts and in vivo in mice subjected to regional IPC. Mitochondrial depolarization with an uncoupling agent similarly induced Parkin translocation to mitochondria in cells and Langendorff-perfused rat hearts. Mitochondrial loss was blunted in Atg5-deficient cells, revealing the requirement for autophagy in mitochondrial elimination. Consistent with previous reports indicating a role for p62/SQSTM1 in mitophagy, we found that depletion of p62 attenuated mitophagy and exacerbated cell death in HL-1 cardiomyocytes subjected to sI. While wild type mice showed p62 translocation to mitochondria and an increase in ubiquitination, Parkin knockout mice exhibited attenuated IPC-induced p62 translocation to the mitochondria. Importantly, ablation of Parkin in mice abolished the cardioprotective effects of IPC. These results reveal for the first time the crucial role of Parkin and mitophagy in cardioprotection.

Aims: We have shown that autophagy and mitophagy are required for preconditioning. While statin's cardioprotective effects are well known, the role of autophagy/mitophagy in statin-mediated cardioprotection is not. In this study, we used HL-1 cardiomyocytes and mice subjected to ischemia/reperfusion to elucidate the mechanism of statin-mediated cardioprotection. Results: HL-1 cardiomyocytes exposed to simvastatin for 24 h exhibited diminished protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling, increased activation of unc-51-like kinase 1, and upregulation of autophagy and mitophagy. Similar findings were obtained in hearts of mice given simvastatin. Mevalonate abolished simvastatin's effects on Akt/mTOR signaling and autophagy induction in HL-1 cells, indicating that the effects are mediated through inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. Simvastatin-treated HL-1 cells exhibited mitochondrial translocation of Parkin and p62/SQSTM1, fission, and mitophagy. Because Parkin is required for mitophagy and is expressed in heart, we investigated the effect of simvastatin on infarct size in Parkin knockout mice. Simvastatin reduced infarct size in wild-type mice but showed no benefit in Parkin knockout mice. Inhibition of HMG-CoA reductase limits mevalonate availability for both cholesterol and coenzyme Q 10 (CoQ) biosynthesis. CoQ supplementation had no effect on statin-induced Akt/mTOR dephosphorylation or macroautophagy in HL-1 cells, but it potently blocked mitophagy. Importantly, CoQ supplementation abolished statin-mediated cardioprotection in vivo. Innovation and Conclusion: Acute simvastatin treatment suppresses mTOR signaling and triggers Parkindependent mitophagy, the latter which is required for cardioprotection. Coadministration of CoQ with simvastatin impairs mitophagy and cardioprotection. These results raise the concern that CoQ may interfere with anti-ischemic benefits of statins mediated through stimulation of mitophagy.

The SARS-CoV-2 RNA genome contains a 5′-cap that facilitates translation of viral proteins, protection from exonucleases and evasion of the host immune response [1][2][3][4] . How this cap is made is not completely understood. Here, we reconstitute the SARS-CoV-2 7Me GpppA2′-O-Me-RNA cap using virally encoded non-structural proteins (nsps). We show that the kinase-like NiRAN domain 5 of nsp12 transfers RNA to the amino terminus of nsp9, forming a covalent RNA-protein intermediate (a process termed RNAylation). Subsequently, the NiRAN domain transfers RNA to GDP, forming the cap core structure GpppA-RNA. The nsp14 6 and nsp16 7 methyltransferases then add methyl groups to form functional cap structures. Structural analyses of the replicationtranscription complex bound to nsp9 identified key interactions that mediate the capping reaction. Furthermore, we demonstrate in a reverse genetics system 8 that the N-terminus of nsp9 and the kinase-like active site residues in the NiRAN domain are required for successful SARS-CoV-2 replication. Collectively, our results reveal an unconventional mechanism by which SARS-CoV-2 caps its RNA genome, thus exposing a new target in the development of antivirals to treat COVID-19. 3 Main TextCoronaviruses (CoVs) are a family of positive-sense, single-stranded RNA viruses that cause disease in humans, ranging from mild common colds to more severe respiratory infections 9 . The most topical of these is severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiological agent of the ongoing COVID-19 pandemic, which to date has resulted in over 5.7million deaths and almost 400-million cases globally 10 .The SARS-CoV-2 RNA genome contains two open reading frames (ORF1a and ORF1ab), which are translated by host ribosomes to form two large polyproteins 2 . These polyproteins are subsequently cleaved by viral proteases to form 16 non-structural proteins (nsp1-16), some of which make up the Replication-Transcription Complex (RTC) 2 . At the core of the RTC is the nsp12 RNA-dependent RNA polymerase (RdRp), which is the target of several promising antivirals used to treat COVID-19 including remdesivir 11 and molnupiravir 12 . In addition to the RdRp domain, nsp12 contains an N-terminal Nidovirus RdRp-Associated Nucleotidyltransferase (NiRAN) domain (Fig. 1a) 5 . The NiRAN domain shares sequence and structural similarity with the pseudokinase selenoprotein-O (SelO), which transfers AMP from ATP to protein substrates (a process termed AMPylation) [13][14][15] . Notably, the active site kinase-like residues of the NiRAN domain are highly conserved in Nidovirales (Extended Data Fig. 1) and are required for equine arteritis virus (EAV) and SARS-CoV-1 replication in cell culture 5 . Several hypotheses for the function of the NiRAN domain have been proposed, including roles in protein-primed RNA synthesis, RNA ligation, and mRNA capping 5,16 .The CoV RNA genome, like eukaryotic mRNAs, contains a methylated guanosine linked to the first nucleotide of the RNA via a reverse 5′ to 5′ triphosphat...

Summary The metabolic stress hormone FGF21 is highly expressed in exocrine pancreas, where its levels are increased by refeeding and chemically-induced pancreatitis. However, its function in the exocrine pancreas remains unknown. Here, we show that FGF21 stimulates digestive enzyme secretion from pancreatic acinar cells through an autocrine/paracrine mechanism that requires signaling through a tyrosine kinase receptor complex composed of an FGF receptor and β-Klotho. Mice lacking FGF21 accumulate zymogen granules and are susceptible to pancreatic ER stress, an effect that is reversed by administration of recombinant FGF21. Mice carrying an acinar cell-specific deletion of β-Klotho also accumulate zymogen granules, but are refractory to FGF21-stimulated secretion. Like the classical post-prandial secretagogue, cholecystokinin (CCK), FGF21 triggers intracellular calcium release via PLC-IP3R signaling. However, unlike CCK, FGF21 does not induce protein synthesis, thereby preventing protein accumulation. Thus, pancreatic FGF21 is a digestive enzyme secretagogue whose physiologic function is to maintain acinar cell proteostasis.