Out-of-hospital cardiac arrest is associated with a dismal mortality rate and low long-term survival. A large pharmacological knowledge gap exists in identifying drugs that preserve neurological function and increase long-term survival after cardiac arrest. In this issue of the JCI, Li, Zhu, and colleagues report on their engineering of a 20–amino acid cell-permeable peptide (TAT-PHLPP9c) that antagonized the phosphatase PHLPP1 and prevented PHLPP1-mediated dephosphorylation and AKT inactivation. TAT-PHLPP9c administration maintained activated AKT after arrest and led to AKT-mediated beneficial effects on the heart, brain, and metabolism, resulting in increased cardiac output and cerebral blood flow and rescue of ATP levels in affected tissues. TAT-PHLPP9c improved neurological outcomes and increased survival after cardiac arrest in murine and porcine models of cardiac arrest. These findings provide proof of concept that pharmacological targeting of PHLPP1 may be a promising approach to augmenting long-term survival after cardiac arrest.
The proximal tubule is the high-capacity reabsorptive powerhouse of the kidney. Two papers in recent issues of the JCI highlight mechanisms of more delicate effects of the proximal tubule. Yoon et al. demonstrated the intracellular mechanism by which parathyroid hormone (PTH) increases production of 1,25-vitamin D. Activation of PTH receptor 1/cAMP/PKA signaling inhibited salt-inducible kinase 2 (SIK2) and SIK3, which increased CYB27B1 transcription and 1,25-vitamin D production. Replication of these effects with small-molecule SIK inhibitors suggests possible therapeutic applications for patients with disorders characterized by 1,25-vitamin D deficiency. Zhou et al. discovered that proximal tubule glycolysis acts as a phosphate sensor that regulates fibroblast growth factor 23 production in bone. They described several kidney-specific metabolic modifications that enabled glycolysis to be deployed as a phosphate sensor. The provocative results raise intriguing questions with implications for patients with disorders of phosphate homeostasis, including chronic kidney disease.
Michaela A.A. Fuchs, Myles Wolf
Multiple sclerosis (MS) is an inflammatory disease of the CNS. In this issue of the JCI, Ma and Sannino et al. show that two strains of intestinal Clostridium perfringens, known to produce epsilon toxin (ETX), were frequently found in patients with MS. Tiny amounts of this toxin added to immunization with myelin antigens provoked MS-like brain lesions in mice. The distribution of these lesions was diffuse, as in MS, in contrast to the spinal cord–restricted lesions of most animal models. ETX bound to endothelial cells of the CNS to enhance immune cell trafficking through the blood-brain barrier into inflammatory brain lessons. ETX also binds to human, but not murine, white blood cells, perhaps altering immune responses. Barrier disruption and changes in immunity due to the toxin could alter the benefits of immune-modulatory MS therapies and are likely to interact with the complex genetics and environmental influences seen in MS.
Anthony T. Reder
Cancer cells rely on lysosome-dependent degradation to recycle nutrients that serve their energetic and biosynthetic needs. Despite great interest in repurposing the antimalarial hydroxychloroquine as a lysosomal inhibitor in clinical oncology trials, the mechanisms by which hydroxychloroquine and other lysosomal inhibitors induce tumor-cell cytotoxicity remain unclear. In this issue of the JCI, Bhardwaj et al. demonstrate that DC661, a dimeric form of chloroquine that inhibits palmitoyl-protein thioesterase 1 (PPT1), promoted lysosomal lipid peroxidation, resulting in lysosomal membrane permeabilization and tumor cell death. Remarkably, this lysosomal cell death pathway elicited cell-intrinsic immunogenicity and promoted T lymphocyte–mediated tumor cell clearance. The findings provide the mechanistic foundation for the potential combined use of immunotherapy and lysosomal inhibition in clinical trials.
Pravin Phadatare, Jayanta Debnath
Optimal management of lower respiratory tract infection relies on distinguishing infectious from noninfectious etiologies and identifying the microbiologic cause if applicable. This process is complicated by overlapping clinical symptoms and the colonizing lung microbiota. In a recent issue of the JCI, Mick, Tsitsiklis, and colleagues apply RNA-Seq to tracheal aspirates from critically ill children and demonstrate how integration of the host response with microbial identification results in a harmonious and accurate diagnostic classifier. Though promising, there are numerous barriers to realizing a combined host and pathogen diagnostic.
Fiona R. Strouts, Linda B. McAllister, Ephraim L. Tsalik
Osteocytes are specialized bone cells that orchestrate skeletal remodeling. Senescent osteocytes are characterized by an activation of cyclin-dependent kinase inhibitor p16Ink4a and have been implicated in the pathogenesis of several bone loss disorders. In this issue of the JCI, Farr et al. have now shown that systemic removal of senescent cells (termed senolysis) prevented age-related bone loss at the spine and femur and mitigated bone marrow adiposity through a robust effect on osteoblasts and osteoclasts, whereas cell-specific senolysis in osteocytes alone was only partially effective. Surprisingly, transplantation of senescent fibroblasts into the peritoneum of young mice caused host osteocyte senescence associated with bone loss. This refined concept of osteocyte senescence and the effects of remote senolysis may help to develop improved senolytic strategies against multisystem aging in bone and beyond.
Lorenz C. Hofbauer, Franziska Lademann, Martina Rauner
Immune cells play an important functional role in bone fracture healing. Fracture repair is a well-choreographed process that takes approximately 21 days in healthy mice. While the process is complex, conceptually it can be divided into four overlapping stages: inflammation, cartilaginous callus formation, bony callus formation, and remodeling. T cells play a key role in both the cartilaginous and bony callus phases by producing IL-17A. In this issue of the JCI, Dar et al. showed that T cells were recruited from the gut, where the gut microbiota determined the pool of T cells that expressed IL-17A. Treatment with antibiotics and dysbiosis reduced the expansion of IL-17–expressing CD4+ T cells (Th17) and impaired callus formation. These findings demonstrate crosstalk among the gut microbiota, the adaptive immune system, and bone that has clinical implications for fracture healing.
Rajeev Aurora, Matthew J. Silva
The continued emergence of SARS-CoV-2 variants and waning vaccine immunity are some of the factors that drive the continuing search for more effective treatment and prevention options for COVID-19. In this issue of the JCI, Changrob, et al. describe an anti-SARS-CoV-2 spike antibody, isolated from a patient, that targets a vulnerable site on the spike protein receptor binding domain when it adopts a configuration called the “up” conformation. This antibody cross-neutralized all variants studied, including recent Omicron subvariants, and was protective against multiple variants in a hamster model. These results are of interest when considering the next generation of prophylactic and therapeutic antibodies for COVID-19, but they may also shape future approaches to vaccination against SARS-CoV-2.
Insulin secretion by pancreatic β cells is a dynamic and highly regulated process due to the central importance of insulin in enabling efficient utilization and storage of glucose. Multiple regulatory layers enable β cells to adapt to acute changes in nutrient availability as well as chronic changes in metabolic demand. While epigenetic factors have been well established as regulators of chronic β cell adaptations to insulin resistance, their role in acute adaptations in response to nutrient stimulation has been relatively unexplored. In this issue of the JCI, Wortham et al. report that short-term dynamic changes in histone modifications regulated insulin secretion and acute β cell adaptations in response to fasting and feeding cycles. These findings highlight the importance of investigating whether other epigenetic mechanisms may contribute to acute physiologic adaptations in β cells.
Kristie I. Aamodt, Alvin C. Powers
Major depressive disorder, characterized by aberrant glutamatergic signaling in the prefrontal cortex (PFC), is a leading cause of disability worldwide. Depression is highly comorbid with metabolic disorders, but a mechanistic link is elusive. In this issue of the JCI, Fan and coauthors report that elevated posttranslational modification with the glucose metabolite N-acetylglucosamine (GlcNAc) by O-GlcNAc transferase (OGT) contributed to stress-induced establishment of depression-like behaviors in mice. This effect was specific to medial PFC (mPFC) astrocytes, with glutamate transporter-1 (GLT-1) identified as an OGT target. Specifically, O-GlcNAcylation of GLT-1 resulted in diminished glutamate clearance from excitatory synapses. Further, astrocytic OGT knockdown restored stress-induced deficits in glutamatergic signaling, promoting resilience. These findings provide a mechanistic link between metabolism and depression and have relevance for antidepressant targets.
Sam E.J. Paton, Caroline Menard
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