It has long been known that fatty acids can either adversely or positively affect insulin signaling in skeletal muscle, depending on chain length or saturation, and can therefore be primary drivers of systemic insulin sensitivity. However, the detailed mechanisms linking fatty acids to insulin signaling in skeletal muscle have been elusive. In this issue of the JCI, Ferrara et al. suggest a model whereby membrane lipid remodeling mediates skeletal muscle insulin sensitivity. The authors demonstrate that membrane glycerophospholipid fatty acid remodeling by lysophosphatidylcholine acyltransferase 3 (LPCAT3) in skeletal muscle from subjects with obesity was induced, suppressing insulin signaling and glucose tolerance. Loss or gain of LPCAT3 function in mouse models showed that Lpcat3 was both required and sufficient for high-fat diet–induced muscle insulin resistance. These results suggest that the physiochemical properties of muscle cell membranes may drive insulin sensitivity and, therefore, systemic glucose intolerance.
Michael J. Wolfgang
Loss-of-function mutations of SCN1A encoding the pore-forming α subunit of the NaV1.1 neuronal sodium channel cause a severe developmental epileptic encephalopathy, Dravet syndrome (DS). In this issue of the JCI, Chen, Luo, Gao, et al. describe a phenocopy for DS in mice deficient for posttranslational conjugation with neural precursor cell expressed, developmentally downregulated 8 (NEDD8) (neddylation), selectively engineered in inhibitory interneurons. Pursuing the possibility that this phenotype is also caused by loss of NaV1.1, Chen, Luo, Gao, and colleagues show that interneuron excitability and GABA release are impaired, NaV1.1 degradation rate is increased with a commensurate decrease of NaV1.1 protein, and NaV1.1 is a substrate for neddylation. These findings establish neddylation as a mechanism for stabilizing NaV1.1 subunits and suggest another pathomechanism for epileptic sodium channelopathy.
Stephen C. Cannon
Artificial intelligence has been applied to histopathology for decades, but the recent increase in interest is attributable to well-publicized successes in the application of deep-learning techniques, such as convolutional neural networks, for image analysis. Recently, generative adversarial networks (GANs) have provided a method for performing image-to-image translation tasks on histopathology images, including image segmentation. In this issue of the JCI, Koyuncu et al. applied GANs to whole-slide images of p16-positive oropharyngeal squamous cell carcinoma (OPSCC) to automate the calculation of a multinucleation index (MuNI) for prognostication in p16-positive OPSCC. Multivariable analysis showed that the MuNI was prognostic for disease-free survival, overall survival, and metastasis-free survival. These results are promising, as they present a prognostic method for p16-positive OPSCC and highlight methods for using deep learning to measure image biomarkers from histopathologic samples in an inherently explainable manner.
Toby C. Cornish
Bardet-Biedl syndrome (BBS) is a syndromic ciliopathy that has obesity as a cardinal feature. BBS is caused by mutations in BBS genes. BBS proteins control primary cilia function, and BBS mutations therefore lead to dysfunctional primary cilia. Obesity in patients with BBS is mainly caused by hyperphagia due to dysregulated neuronal function in the brain, in particular in the hypothalamus. However, the mechanism by which mutations in BBS genes result in dysfunction in hypothalamic neurons is not well understood. In this issue of the JCI, Wang et al. used BBS and non-BBS patient–derived induced pluripotent stem cells to generate neurons and hypothalamic neurons. Using this human model system, the authors demonstrated that mutations in BBS genes affected primary cilia function, neuronal morphology, and signaling pathways regulating the function of hypothalamic neurons, which control energy homeostasis. This study provides important insights into the mechanisms of BBS-induced obesity.
Sandra Blaess, Dagmar Wachten
Multisystem Inflammatory Syndrome in Children (MIS-C) is a rare but deadly new disease in children that rapidly progresses to hyperinflammation, shock, and can lead to multiple organ failure if unrecognized. It has been found to be temporally associated with the COVID-19 pandemic and is often associated with SARS-CoV-2 exposure in children. In this issue of the JCI, Porritt, Paschold, and Rivas et al. identify restricted T cell receptor (TCR) β-chain variable domain (Vβ) usage in patients with severe MIS-C indicating a potential role for SARS-CoV-2 as a superantigen. These findings suggest that a blood test that determines the presence of specific TCR beta variable gene segments (TRBV) may identify patients at risk for severe MIS-C.
Theodore Kouo, Worarat Chaisawangwong
Allergic asthma is a chronic inflammatory airway disease characterized by dysregulated type 2 immune responses, including degranulating airway eosinophils that induce tissue damage and airway hyperresponsiveness (AHR). The type 2 cytokines interleukin 5 (IL-5) and IL-13 and the eosinophil-specific chemokine CCL11/CCL24/CCL26 axis recruit, activate, and regulate eosinophils in the airways. In this issue of the JCI, Karcz et al. identified a mechanism involving the nucleotide sugar UDP-glucose (UDP-G) and the purinergic receptor P2Y14R in amplifying eosinophil accumulation in the lung. During type 2 inflammation, UDP-G activates P2Y14R on eosinophils, inducing the cells to move and migrate into the lung. Pharmacologically or genetically inhibiting P2Y14R on eosinophils attenuated eosinophil infiltration and AHR. Future experiments, including identifying additional type 2 factors regulating P2Y14R expression on lung eosinophils, are necessary to ascertain the impact of targeting P2Y14R as an alternative or adjunctive therapy to current type 2 biologics for the treatment of asthma.
Paul S. Foster, Hock L. Tay, Simon P. Hogan
Several COVID-19 studies have focused on neuropathology. In this issue of the JCI, Qin, Wu, and Chen, et al. focused specifically on people whose acute infection lacked obvious neurological involvement. Severely infected patients showed abnormal grey matter volumes, white matter diffusion, and cerebral blood flow compared with healthy controls and those with mild infection. The data remain associative rather than mechanistic, but correlations with systemic immune markers suggest effects of inflammation, hypercoagulation, or other aspects of disease severity. Mechanistic research is warranted. Given the lack of obvious neurological symptoms, neurocognitive assessments were not performed, but the findings suggest that such assessments may be warranted in severely affected patients, even without obvious symptoms. Further, studying CNS involvement of other disorders with overlapping pathophysiologies, such as inflammation, coagulation, hypoxia, or direct viral infection may reveal the causes for COVID-19 related neuropathology.
Amit Mahajan, Graeme F. Mason
Leber’s hereditary optic neuropathy (LHON) is the most common mitochondrial disease and in most cases is caused by mutations in mitochondrial DNA–encoded (mtDNA-encoded) respiratory complex I subunit ND1, ND4, or ND6. In this issue of the JCI, Stenton et al. describe biallelic mutations in a nuclear DNA–encoded gene, DNAJC30, establishing recessively inherited LHON (arLHON). Functional studies suggest that DNAJC30 is a protein chaperone required for exchange of damaged complex I subunits. Hallmark mtDNA LHON features were also found in arLHON, including incomplete penetrance, male predominance, and positive response to idebenone therapy. These results extend complex I–deficient phenotypes to include recessively inherited optic neuropathy, with important clinical implications for genetic counseling and therapeutic considerations.
Janey L. Wiggs
The enteric nervous system mediates reflexes independently of the brain and spinal cord and transmits signals bidirectionally between the gut and the brain. Hirschsprung disease and chronic intestinal pseudo-obstruction (CIPO) and pediatric CIPO are examples of congenital defects that impair gastrointestinal motility. In this issue of the JCI, Thuy-Linh Le et al. analyzed eight patients with defects in tissue that arose from the neural crest. The patients carried homozygous or heterozygous variants in ERBB3 or ERBB2, which encode transmembrane epidermal growth factor receptors that bind neuroregulin 1 (NRG1). Notably, the genetic variants resulted in loss of function with decreased expression or aberrant phosphorylation of the ERBB3/ERBB2 receptors. Experiments using mice revealed that Erbb3 and Erbb2 were expressed in enteric neuronal progenitor cells. This study is an outstanding example of descriptive observation that begs for mechanistic exploration to reveal precisely how the NRG1/ERBB3/ERBB2 pathway influences ENS development.
Michael D. Gershon
Interest in omega-3 fatty acids (colloquially known as fish oils) to lower residual cardiovascular risk in statin-treated patients has increased markedly in the wake of recent cardiovascular outcome trials. The triglyceride-lowering effects of omega-3 fatty acids are generally thought to occur by reduced hepatic VLDL production. In this issue of the JCI, Grevengoed et al. used mouse models and human plasma samples to reveal an additional mechanism whereby these polyunsaturated fatty acids can lower plasma triglycerides. Their findings indicate that omega-3 fatty acid–derived N-acyl taurines (NATs) greatly accumulate in bile and also in plasma following omega-3 supplementation. The authors further show that one of these NATs (C22:6 NAT) inhibited intestinal triglyceride hydrolysis and lipid absorption, which resulted in lower plasma triglycerides and protection against hepatic triacylglycerol accumulation in mice fed a high-fat diet. The findings open a potential avenue for triglyceride lowering by omega-3 fatty acids conjugated to taurine.
Karin E. Bornfeldt
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