National Institutes of Health social and behavioral research in response to the SARS-CoV2 Pandemic.

The COVID-19 pandemic has been mitigated primarily using social and behavioral intervention strategies, and these strategies have social and economic impacts, as well as potential downstream health impacts that require further study. Digital and community-based interventions are being increasingly relied upon to address these health impacts and bridge the gap in health care access despite insufficient research of these interventions as a replacement for, not an adjunct to, in-person clinical care. As SARS-CoV-2 testing expands, research on encouraging uptake and appropriate interpretation of these test results is needed. All of these issues are disproportionately impacting underserved, vulnerable, and health disparities populations. This commentary describes the various initiatives of the National Institutes of Health to address these social, behavioral, economic, and health disparities impacts of the pandemic, the findings from which can improve our response to the current pandemic and prepare us better for future infectious disease outbreaks.

Opioids and Infectious Diseases: A Converging Public Health Crisis.

A converging public health crisis is emerging because the opioid epidemic is fueling a surge in infectious diseases, such as human immunodeficiency virus infection with or without AIDS, the viral hepatitides, infective endocarditis, and skin and soft-tissue infections. An integrated strategy is needed to tailor preventive and therapeutic approaches toward infectious diseases in people who misuse and/or are addicted to opioids and to concurrently address the underlying predisposing factor for the infections-opioid use disorder. This commentary highlights the unique and complementary roles that the infectious diseases and substance use disorder communities can play in addressing this crisis of dual public health concerns.

The Extended Impact of Human Immunodeficiency Virus/AIDS Research.

Human immunodeficiency virus (HIV) is one of the most extensively studied viruses in history, and numerous extraordinary scientific advances, including an in-depth understanding of viral biology, pathogenesis, and life-saving antiretroviral therapies, have resulted from investments in HIV/AIDS research. While the substantial investments in HIV/AIDS research are validated solely on these advances, the collateral broader scientific progress resulting from the support of HIV/AIDS research over the past 30 years is extraordinary as well. The positive impact has ranged from innovations in basic immunology and structural biology to treatments for immune-mediated diseases and cancer and has had an enormous effect on the research and public and global health communities well beyond the field of HIV/AIDS. This article highlights a few select examples of the unanticipated and substantial positive spin-offs of HIV/AIDS research on other scientific areas.

Differential stimulation of insulin secretion by GLP-1 and Kisspeptin-10.

ß-cells in the pancreatic islet respond to elevated plasma glucose by secreting insulin to maintain glucose homeostasis. In addition to glucose stimulation, insulin secretion is modulated by numerous G-protein coupled receptors (GPCRs). The GPCR ligands Kisspeptin-10 (KP) and glucagon-like peptide-1 (GLP-1) potentiate insulin secretion through Gq and Gs-coupled receptors, respectively. Despite many studies, the signaling mechanisms by which KP and GLP-1 potentiate insulin release are not thoroughly understood. We investigated the downstream signaling pathways of these ligands and their affects on cellular redox potential, intracellular calcium activity ([Ca(2+)]i), and insulin secretion from ß-cells within intact murine islets. In contrast to previous studies performed on single ß-cells, neither KP nor GLP-1 affect [Ca(2+)]i upon stimulation with glucose. KP significantly increases the cellular redox potential, while no effect is observed with GLP-1, suggesting that KP and GLP-1 potentiate insulin secretion through different mechanisms. Co-treatment with KP and the Gßγ-subunit inhibitor gallein inhibits insulin secretion similar to that observed with gallein alone, while co-treatment with gallein and GLP-1 does not differ from GLP-1 alone. In contrast, co-treatment with the Gßγ activator mSIRK and either KP or GLP-1 stimulates insulin release similar to mSIRK alone. Neither gallein nor mSIRK alter [Ca(2+)]i activity in the presence of KP or GLP-1. These data suggest that KP likely alters insulin secretion through a Gßγ-dependent process that stimulates glucose metabolism without altering Ca(2+) activity, while GLP-1 does so, at least partly, through a Gα-dependent pathway that is independent of both metabolism and Ca(2+).

Channel sialic acids limit hERG channel activity during the ventricular action potential.

Activity of human ether-a-go-go-related gene (hERG) 1 voltage-gated K(+) channels is responsible for portions of phase 2 and phase 3 repolarization of the human ventricular action potential. Here, we questioned whether and how physiologically and pathophysiologically relevant changes in surface N-glycosylation modified hERG channel function. Voltage-dependent hERG channel gating and activity were evaluated as expressed in a set of Chinese hamster ovary (CHO) cell lines under conditions of full glycosylation, no sialylation, no complex N-glycans, and following enzymatic deglycosylation of surface N-glycans. For each condition of reduced glycosylation, hERG channel steady-state activation and inactivation relationships were shifted linearly by significant depolarizing ∼9 and ∼18 mV, respectively. The hERG window current increased significantly by 50-150%, and the peak shifted by a depolarizing ∼10 mV. There was no significant change in maximum hERG current density. Deglycosylated channels were significantly more active (20-80%) than glycosylated controls during phases 2 and 3 of action potential clamp protocols. Simulations of hERG current and ventricular action potentials corroborated experimental data and predicted reduced sialylation leads to a 50-70-ms decrease in action potential duration. The data describe a novel mechanism by which hERG channel gating is modulated through physiologically and pathophysiologically relevant changes in N-glycosylation; reduced channel sialylation increases hERG channel activity during the action potential, thereby increasing the rate of action potential repolarization.

Neuropeptide Y and somatostatin inhibit insulin secretion through different mechanisms.

Pancreatic ß-cells regulate glucose homeostasis by secreting insulin in response to glucose elevation and G protein-coupled receptor (GPCR) activation. Neuropeptide Y (NPY) and somatostatin (SST) attenuate insulin secretion through G(i) activation of Y(1) and SSTR(1&5) receptors, respectively. The downstream pathways altered by NPY and SST are poorly understood. Thus, we investigated these underlying mechanisms. NPY and SST increase cellular redox potential, suggesting that their inhibitory effect may not be mediated through metabolic inhibition. NPY does not affect intracellular calcium ([Ca(2+)](i)) activity upon glucose stimulation, whereas SST alters this response. G(ßγ)-subunit inhibition by gallein attenuates insulin secretion but does not alter metabolism or [Ca(2+)](i). mSIRK-induced G(ßγ) activation does not modulate glucose metabolism but increases [Ca(2+)](i) activity and potentiates insulin release. Cotreatment with gallein and NPY or SST reduces insulin secretion to levels similar to that of gallein alone. mSIRK and NPY cotreatment potentiates insulin secretion similarly to mSIRK alone, whereas mSIRK and SST treatment decreases insulin release. The data support a model where SST attenuates secretion through G(ßγ) inhibition of Ca(2+) activity, while NPY activates a Ca(2+)-independent pathway mediated by G(α). GPCR ligands signal through multiple pathways to inhibit insulin secretion, and determining these mechanisms could lead to novel diabetic therapies.

Sialic acids attached to O-glycans modulate voltage-gated potassium channel gating.

Neuronal, cardiac, and skeletal muscle action potentials are produced and conducted through the highly regulated activity of several types of voltage-gated ion channels. Voltage-gated potassium (K(v)) channels are responsible for action potential repolarization. Glycans can be attached to glycoproteins through N- and O-linkages. Previous reports described the impact of N-glycans on voltage-gated ion channel function. Here, we show that sialic acids attached through O-linkages modulate gating of K(v)2.1, K(v)4.2, and K(v)4.3. The conductance-voltage (G-V) relationships for each isoform were shifted uniquely by a depolarizing 8-16 mV under conditions of reduced sialylation. The data indicate that sialic acids modulate K(v) channel activation through apparent electrostatic mechanisms that promote channel activity. Voltage-dependent steady-state inactivation was unaffected by changes in sialylation. N-Linked sialic acids cannot be responsible for the G-V shifts because K(v)4.2 and K(v)4.3 cannot be N-glycosylated, and immunoblot analysis confirmed K(v)2.1 is not N-glycosylated. Glycosidase gel shift analysis suggested that K(v)2.1, K(v)4.2, and K(v)4.3 were O-glycosylated and sialylated. To confirm this, azide-modified sugar residues involved specifically in O-glycan and sialic acid biosynthesis were shown to incorporate into all three K(v) channel isoforms using Cu(I)-catalyzed cycloaddition chemistry. Together, the data indicate that sialic acids attached to O-glycans uniquely modulate gating of three K(v) channel isoforms that are not N-glycosylated. These data provide the first evidence that external O-glycans, with core structures distinct from N-glycans in type and number of sugar residues, can modulate K(v) channel function and thereby contribute to changes in electrical signaling that result from regulated ion channel expression and/or O-glycosylation.

N-glycans modulate K(v)1.5 gating but have no effect on K(v)1.4 gating.

Nerve and muscle action potential repolarization are produced and modulated by the regulated expression and activity of several types of voltage-gated K(+) (K(v)) channels. Here, we show that sialylated N-glycans uniquely impact gating of a mammalian Shaker family K(v) channel isoform, K(v)1.5, but have no effect on gating of a second Shaker isoform, K(v)1.4. Each isoform contains one potential N-glycosylation site located along the S1-S2 linker; immunoblot analyses verified that K(v)1.4 and K(v)1.5 were N-glycosylated. The conductance-voltage (G-V) relationships and channel activation rates for two glycosylation-site deficient K(v)1.5 mutants, K(v)1.5(N290Q) and K(v)1.5(S292A), and for wild-type K(v)1.5 expressed under conditions of reduced sialylation, were each shifted linearly by a depolarizing approximately 18 mV compared to wild-type K(v)1.5 activation. External divalent cation screening experiments suggested that K(v)1.5 sialic acids contribute to an external surface potential that modulates K(v)1.5 activation. Channel availability was unaffected by changes in K(v)1.5 glycosylation or sialylation. The data indicate that sialic acid residues attached to N-glycans act through electrostatic mechanisms to modulate K(v)1.5 activation. The sialic acids fully account for effects of N-glycans on K(v)1.5 gating. Conversely, K(v)1.4 gating was unaffected by changes in channel sialylation or following mutagenesis to remove the N-glycosylation site. Each phenomenon is unique for K(v)1 channel isoforms, indicating that sialylated N-glycans modulate gating of homologous K(v)1 channels through isoform-specific mechanisms. Such modulation is relevant to changes in action potential repolarization that occur as ion channel expression and glycosylation are regulated.

Regulated and aberrant glycosylation modulate cardiac electrical signaling.

Millions afflicted with Chagas disease and other disorders of aberrant glycosylation suffer symptoms consistent with altered electrical signaling such as arrhythmias, decreased neuronal conduction velocity, and hyporeflexia. Cardiac, neuronal, and muscle electrical signaling is controlled and modulated by changes in voltage-gated ion channel activity that occur through physiological and pathological processes such as development, epilepsy, and cardiomyopathy. Glycans attached to ion channels alter channel activity through isoform-specific mechanisms. Here we show that regulated and aberrant glycosylation modulate cardiac ion channel activity and electrical signaling through a cell-specific mechanism. Data show that nearly half of 239 glycosylation-associated genes (glycogenes) were significantly differentially expressed among neonatal and adult atrial and ventricular myocytes. The N-glycan structures produced among cardiomyocyte types were markedly variable. Thus, the cardiac glycome, defined as the complete set of glycan structures produced in the heart, is remodeled. One glycogene, ST8sia2, a polysialyltransferase, is expressed only in the neonatal atrium. Cardiomyocyte electrical signaling was compared in control and ST8sia2((-/-)) neonatal atrial and ventricular myocytes. Action potential waveforms and gating of less sialylated voltage-gated Na+ channels were altered consistently in ST8sia2((-/-)) atrial myocytes. ST8sia2 expression had no effect on ventricular myocyte excitability. Thus, the regulated (between atrium and ventricle) and aberrant (knockout in the neonatal atrium) expression of a single glycogene was sufficient to modulate cardiomyocyte excitability. A mechanism is described by which cardiac function is controlled and modulated through physiological and pathological processes that involve regulated and aberrant glycosylation.