Zebrafish cardiac repolarization does not functionally depend on the expression of the hERG1b-like transcript.

Zebrafish provide a translational model of human cardiac function. Their similar cardiac electrophysiology enables screening of human cardiac repolarization disorders, drug arrhythmogenicity, and novel antiarrhythmic therapeutics. However, while zebrafish cardiac repolarization is driven by delayed rectifier potassium channel current (IKr), the relative role of alternate channel transcripts is uncertain. While human ether-a-go-go-related-gene-1a (hERG1a) is the dominant transcript in humans, expression of the functionally distinct alternate transcript, hERG1b, modifies the electrophysiological and pharmacologic IKr phenotype. Studies of zebrafish IKr are frequently translated without consideration for the presence and impact of hERG1b in humans. Here, we performed phylogenetic analyses of all available KCNH genes from Actinopterygii (ray-finned fishes). Our findings confirmed zebrafish cardiac zkcnh6a as the paralog of human hERG1a (hKCNH2a), but also revealed evidence of a hERG1b (hKCNH2b)-like N-terminally truncated gene, zkcnh6b, in zebrafish. zkcnh6b is a teleost-specific variant that resulted from the 3R genome duplication. qRT-PCR showed dominant expression of zkcnh6a in zebrafish atrial and ventricular tissue, with low levels of zkcnh6b. Functional evaluation of zkcnh6b in a heterologous system showed no discernable function under the conditions tested, and no influence on zkcnh6a function during the zebrafish ventricular action potential. Our findings provide the first descriptions of the zkcnh6b gene, and show that, unlike in humans, zebrafish cardiac repolarization does not rely upon co-assembly of zERG1a/zERG1b. Given that hERG1b modifies IKr function and drug binding in humans, our findings highlight the need for consideration when translating hERG variant effects and toxicological screens in zebrafish, which lack a functional hERG1b-equivalent gene.

Targeted activation of human ether-à-go-go-related gene channels rescues electrical instability induced by the R56Q+/- long QT syndrome variant.

AIMS: Long QT syndrome type 2 (LQTS2) is associated with inherited variants in the cardiac human ether-à-go-go-related gene (hERG) K+ channel. However, the pathogenicity of hERG channel gene variants is often uncertain. Using CRISPR-Cas9 gene-edited hiPSC-derived cardiomyocytes (hiPSC-CMs), we investigated the pathogenic mechanism underlying the LQTS-associated hERG R56Q variant and its phenotypic rescue by using the Type 1 hERG activator, RPR260243. METHODS AND RESULTS: The above approaches enable characterization of the unclear causative mechanism of arrhythmia in the R56Q variant (an N-terminal PAS domain mutation that primarily accelerates channel deactivation) and translational investigation of the potential for targeted pharmacologic manipulation of hERG deactivation. Using perforated patch clamp electrophysiology of single hiPSC-CMs, programmed electrical stimulation showed that the hERG R56Q variant does not significantly alter the mean action potential duration (APD90). However, the R56Q variant increases the beat-to-beat variability in APD90 during pacing at constant cycle lengths, enhances the variance of APD90 during rate transitions, and increases the incidence of 2:1 block. During paired S1-S2 stimulations measuring electrical restitution properties, the R56Q variant was also found to increase the variability in rise time and duration of the response to premature stimulations. Application of the hERG channel activator, RPR260243, reduces the APD variance in hERG R56Q hiPSC-CMs, reduces the variability in responses to premature stimulations, and increases the post-repolarization refractoriness. CONCLUSION: Based on our findings, we propose that the hERG R56Q variant leads to heterogeneous APD dynamics, which could result in spatial dispersion of repolarization and increased risk for re-entry without significantly affecting the average APD90. Furthermore, our data highlight the antiarrhythmic potential of targeted slowing of hERG deactivation gating, which we demonstrate increases protection against premature action potentials and reduces electrical heterogeneity in hiPSC-CMs.

Spinal cord injury impairs cardiac function due to impaired bulbospinal sympathetic control.

Spinal cord injury chronically alters cardiac structure and function and is associated with increased odds for cardiovascular disease. Here, we investigate the cardiac consequences of spinal cord injury on the acute-to-chronic continuum, and the contribution of altered bulbospinal sympathetic control to the decline in cardiac function following spinal cord injury. By combining experimental rat models of spinal cord injury with prospective clinical studies, we demonstrate that spinal cord injury causes a rapid and sustained reduction in left ventricular contractile function that precedes structural changes. In rodents, we experimentally demonstrate that this decline in left ventricular contractile function following spinal cord injury is underpinned by interrupted bulbospinal sympathetic control. In humans, we find that activation of the sympathetic circuitry below the level of spinal cord injury causes an immediate increase in systolic function. Our findings highlight the importance for early interventions to mitigate the cardiac functional decline following spinal cord injury.

Preserved Adrenal Function After Lumbar Spinal Cord Transection Augments Low Pressure Bladder Activity in the Rat.

Spinal cord injury (SCI) disconnects supraspinal micturition centers from the lower urinary tract resulting in immediate and long-term changes in bladder structure and function. While cervical and high thoracic SCI have a greater range of systemic effects, clinical data suggest that those with lower (suprasacral) injuries develop poorer bladder outcomes. Here we assess the impact of SCI level on acute changes in bladder activity. We used two SCI models, T3 and L2 complete transections in male Wistar rats, and compared bladder pressure fluctuations to those of naïve and bladder-denervated animals. By 2 days after L2 transection, but not T3 transection or bladder denervation, small amplitude rhythmic contractions (1 mmHg, 0.06 Hz) were present at low intravesical pressures (<6 mmHg); these were still present 1 month following injury, and at 3 months, bladders from L2 SCI animals were significantly larger than those from T3 SCI or naïve animals. Low-pressure contractions were unaffected by blocking ganglionic signaling or bladder denervation at the time of measurements. L2 (and sham surgery) but not T3 transection preserves supraspinal adrenal control, and by ELISA we show lower plasma adrenal catecholamine concentration in the latter. When an adrenalectomy preceded the L2 transection, the aberrant low-pressure contractions more closely resembled those after T3 transection, indicating that the increased bladder activity after lumbar SCI is mediated by preserved adrenal function. Since ongoing low-pressure contractions may condition the detrusor and exacerbate detrusor-sphincter dyssynergia, moderating bladder catecholamine signaling may be a clinically viable intervention strategy.

Advillin Is Expressed in All Adult Neural Crest-Derived Neurons.

Promoter-based genetic recombination (via, e.g., Cre-lox) is most useful when all cells of interest express a particular gene. The discovery that the actin-binding protein advillin is expressed in all somatic sensory neurons has been exploited repeatedly to drive DNA recombination therein, yet specificity of expression has not been well demonstrated. Here, we characterize advillin expression amongst sensory neurons and in several other neural and non-neural tissues. We first validate an advillin antibody against advillin knock-out tissue, advillin promoter-driven EGFP, and advillin mRNA expression. In the dorsal root ganglion (DRG), advillin is enriched in non-peptidergic nociceptors. We also show that advillin expression, and advillin promotor-driven EGFP and Cre-recombinase expression, occurs in multiple tissues including the dorsal habenula of the epithalamus, endocrine cells of the gut, Merkel cells in the skin, and most strikingly, throughout the autonomic nervous system (sympathetic, parasympathetic, and enteric neurons) in mice, rats, and non-human primates. In the mouse pelvic ganglion, advillin immunoreactivity is most intense in pairs of small neurons, and concentrated in spine-like structures on the axon initial segment contacted by sympathetic preganglionic axons. In autonomic targets (iris and blood vessels), advillin is distributed along cholinergic parasympathetic axons and in sympathetic varicosities. Developmentally, advillin expression is absent from sympathetics at postnatal day 4 but begins to emerge by day 7, accounting for previous reports (based on embryonic expression) of advillin's specificity to sensory neurons. These results indicate that caution is warranted in interpreting previous studies in which advillin-driven genomic editing is either constitutive or performed after postnatal day 4.

Loukoumasomes Are Distinct Subcellular Structures from Rods and Rings and Are Structurally Associated with MAP2 and the Nuclear Envelope in Retinal Cells.

"Rods and rings" (RR) and loukoumasomes are similarly shaped, subcellular macromolecular structures with as yet unknown function. RR, so named because of their shape, are formed in response to inhibition in the GTP or CTP synthetic pathways and are highly enriched in the two key enzymes of the nucleotide synthetic pathway. Loukoumasomes also occur as linear and toroidal bodies and were initially inferred to be the same as RR, largely due to their shared shape and size and the fact that it was unclear if they shared the same subcomponents. In human retinoblastoma tissue and cells we have observed toroidal, perinuclear, macromolecular structures of similar size and antigenicity to those previously reported in neurons (neuronal-loukoumasomes). To further characterize the subcomponents of the retinal-loukoumasomes, confocal analysis following immunocytochemical staining for alpha-tubulin, beta-III tubulin and detyrosinated tubulin was performed. These studies indicate that retinal-loukoumasomes are enriched for beta-III tubulin and other tubulins associated with microtubules. Immunofluorescence together with the in situ proximity ligation assay (PLA), confirmed that beta-III tubulin colocalized with detyrosinated tubulin within loukoumasomes. Our results indicate that these tissues contain only loukoumasomes because these macromolecular structures are immunoreactive with an anti-tubulin antibody but are not recognized by the prototype anti-RR/inosine monophosphate dehydrogenase (IMPDH) antibody (It2006). To further compare the RR and retinal-loukoumasomes, retinoblastoma cells were exposed to the IMPDH-inhibitor ribavirin, a drug known to induce the formation of RR. In contrast to RR, the production of retinal-loukoumasomes was unaffected. Coimmunostaining of Y79 cells for beta-III tubulin and IMPDH indicate that these cells, when treated with ribavirin, can contain both retinal-loukoumasomes and RR and that these structures are antigenically distinct. Subcellular fractionation studies indicate that ribavirin increased the RR subcomponent, IMPDH, in the nuclear fraction of Y79 cells from 21.3 ± 5.8% (0 mM ribavirin) to 122.8 ± 7.9% (1 mM ribavirin) while the subcellular localization of the retinal-loukoumasome subcomponent tubulin went unaltered. Further characterization of retinal-loukoumasomes in retinoblastoma cells reveals that they are intimately associated with lamin folds within the nuclear envelope. Using immunofluorescence and the in situ PLA in this cell type, we have observed colocalization of beta-III tubulin with MAP2. As MAP2 is a microtubule-associated protein implicated in microtubule crosslinking, this supports a role for microtubule crosslinkers in the formation of retinal-loukoumasomes. Together, these results suggest that loukoumasomes and RR are distinct subcellular macromolecular structures, formed by different cellular processes and that there are other loukoumasome-like structures within retinal tissues and cells.

LINE-1 retrotransposable element DNA accumulates in HIV-1-infected cells.

Type 1 long-interspersed nuclear elements (L1s) are autonomous retrotransposable elements that retain the potential for activity in the human genome but are suppressed by host factors. Retrotransposition of L1s into chromosomal DNA can lead to genomic instability, whereas reverse transcription of L1 in the cytosol has the potential to activate innate immune sensors. We hypothesized that HIV-1 infection would compromise cellular control of L1 elements, resulting in the induction of retrotransposition events. Here, we show that HIV-1 infection enhances L1 retrotransposition in Jurkat cells in a Vif- and Vpr-dependent manner. In primary CD4(+) cells, HIV-1 infection results in the accumulation of L1 DNA, at least the majority of which is extrachromosomal. These data expose an unrecognized interaction between HIV-1 and endogenous retrotransposable elements, which may have implications for the innate immune response to HIV-1 infection, as well as for HIV-1-induced genomic instability and cytopathicity.

HERV-K-specific T cells eliminate diverse HIV-1/2 and SIV primary isolates.

The genetic diversity of HIV-1 represents a major challenge in vaccine development. In this study, we establish a rationale for eliminating HIV-1-infected cells by targeting cellular immune responses against stable human endogenous retroviral (HERV) antigens. HERV DNA sequences in the human genome represent the remnants of ancient infectious retroviruses. We show that the infection of CD4+ T cells with HIV-1 resulted in transcription of the HML-2 lineage of HERV type K [HERV-K(HML-2)] and the expression of Gag and Env proteins. HERV-K(HML-2)-specific CD8+ T cells obtained from HIV-1-infected human subjects responded to HIV-1-infected cells in a Vif-dependent manner in vitro. Consistent with the proposed mode of action, a HERV-K(HML-2)-specific CD8+ T cell clone exhibited comprehensive elimination of cells infected with a panel of globally diverse HIV-1, HIV-2, and SIV isolates in vitro. We identified a second T cell response that exhibited cross-reactivity between homologous HIV-1-Pol and HERV-K(HML-2)-Pol determinants, raising the possibility that homology between HIV-1 and HERVs plays a role in shaping, and perhaps enhancing, the T cell response to HIV-1. This justifies the consideration of HERV-K(HML-2)-specific and cross-reactive T cell responses in the natural control of HIV-1 infection and for exploring HERV-K(HML-2)-targeted HIV-1 vaccines and immunotherapeutics.

Human endogenous retrovirus K(HML-2) Gag- and Env-specific T-cell responses are infrequently detected in HIV-1-infected subjects using standard peptide matrix-based screening.

T-cell responses to human endogenous retrovirus (HERV) K(HML-2) Gag and Env were mapped in HIV-1-infected subjects using 15 mer peptides. Small peptide pools and high concentrations were used to maximize sensitivity. In the 23 subjects studied, only three bona fide HERV-K(HML-2)-specific responses were detected. At these high peptide concentrations, we detected false-positive responses, three of which were mapped to an HIV-1 Gag peptide contaminant. Thus, HERV-K(HML-2) Gag- and Env-specific T-cell responses are infrequently detected by 15 mer peptide mapping.

Human immunodeficiency virus type 1 escapes from interleukin-2-producing CD4+ T-cell responses without high-frequency fixation of mutations.

The presence of interleukin-2 (IL-2)-producing human immunodeficiency virus type 1 (HIV-1)-specific CD4(+) T-cell responses has been associated with the immunological control of HIV-1 replication; however, the causal relationship between these factors remains unclear. Here we show that IL-2-producing HIV-1-specific CD4(+) T cells can be cloned from acutely HIV-1-infected individuals. Despite the early presence of these cells, each of the individuals in the present study exhibited progressive disease, with one individual showing rapid progression. In this rapid progressor, three IL-2-producing HIV-1 Gag-specific CD4(+) T-cell responses were identified and mapped to the following optimal epitopes: HIVWASRELER, REPRGSDIAGT, and FRDYVDRFYKT. Responses to these epitopes in peripheral blood mononuclear cells were monitored longitudinally to >1 year postinfection, and contemporaneous circulating plasma viruses were sequenced. A variant of the FRDYVDRFYKT epitope sequence, FRDYVDQFYKT, was observed in 1/21 plasma viruses sequenced at 5 months postinfection and 1/10 viruses at 7 months postinfection. This variant failed to stimulate the corresponding CD4(+) T-cell clone and thus constitutes an escape mutant. Responses to each of the three Gag epitopes were rapidly lost, and this loss was accompanied by a loss of antigen-specific cells in the periphery as measured by using an FRDYVDRFYKT-presenting major histocompatibility complex class II tetramer. Highly active antiretroviral therapy was associated with the reemergence of FRDYVDRFYKT-specific cells by tetramer. Thus, our data support that IL-2-producing HIV-1-specific CD4(+) T-cell responses can exert immune pressure during early HIV-1 infection but that the inability of these responses to enforce enduring control of viral replication is related to the deletion and/or dysfunction of HIV-1-specific CD4(+) T cells rather than to the fixation of escape mutations at high frequencies.