(2016) FGF13 modulates the gating properties of the cardiac sodium channel Na v 1.5 in an isoform-specific manner, Channels, 10:5, 410-420, DOI: 10.1080/19336950.2016 To link to this article: https://doi.org/10. 1080/19336950.2016 ABSTRACT FGF13 (FHF2), the major fibroblast growth factor homologous factor (FHF) in rodent heart, directly binds to the C-terminus of the main cardiac sodium channel, Na V 1.5. Knockdown of FGF13 in cardiomyocytes induces slowed ventricular conduction by altering Na V 1.5 function. FGF13 has five splice variants, each of which possess the same core region and C terminus but differing in their respective N termini. Whether and how these alternatively spliced N termini impart isoform-specific regulation of Na V 1.5, however, has not been reported. Here, we exploited a heterologous expression to explore the specific modulatory effects of FGF13 splice variants FGF13S, FGF13U and FGF13YV on Na V 1.5 function. We found these three splice variants differentially modulated Na V 1.5 current density. Although steady-state activation was unaltered by any of the FGF13 isoforms (compared to control cells expressing Nav1.5 but not expressing FGF13), open-state fast inactivation and closedstate fast inactivation were markedly slowed, steady-state availability was significantly shifted toward the depolarizing direction, and the window current was increased by each of FGF13 isoforms. Most strikingly, FGF13S hastened the rate of Na V 1.5 entry into the slow inactivation state and induced a dramatic slowing of recovery from inactivation, which caused a large decrease in current after either low or high frequency stimulation. Overall, these data showed the diversity of the roles of the FGF13 N-termini in Na V 1.5 channel modulation and suggested the importance of isoform-specific regulation.

The fibroblast growth factor (FGF) homologous factor FGF13, a noncanonical FGF, has been best characterized as a voltage-gated Na + channel auxiliary subunit. Other cellular functions have been suggested, but not explored. In inducible, cardiac-specific Fgf13 knockout mice, we found-even in the context of the expected reduction in Na + channel current-an unanticipated protection from the maladaptive hypertrophic response to pressure overload. To uncover the underlying mechanisms, we searched for components of the FGF13 interactome in cardiomyocytes and discovered the complete set of the cavin family of caveolar coat proteins. Detailed biochemical investigations showed that FGF13 acts as a negative regulator of caveolae abundance in cardiomyocytes by controlling the relative distribution of cavin 1 between the sarcolemma and cytosol. In cardiac-specific Fgf13 knockout mice, cavin 1 redistribution to the sarcolemma stabilized the caveolar structural protein caveolin 3. The consequent increase in caveolae density afforded protection against pressure overload-induced cardiac dysfunction by two mechanisms: (i) enhancing cardioprotective signaling pathways enriched in caveolae, and (ii) increasing the caveolar membrane reserve available to buffer membrane tension. Thus, our results uncover unexpected roles for a FGF homologous factor and establish FGF13 as a regulator of caveolae-mediated mechanoprotection and adaptive hypertrophic signaling. (1), share a core domain with homology to canonical FGFs, but FHFs are not secreted, do not bind or activate FGF receptors, and do not function as growth factors (2). Instead, FHFs bind directly to voltage-gated Na + channels, modulating channel gating and trafficking (3, 4). Widely expressed in the brain (1), FHFs have been implicated in neurologic diseases such as spinocerebellar ataxia 27, caused by missense mutations in FGF14 that diminish Na + channel current, disrupt channel localization, and impair neuronal excitability (5-7).In addition to their broad distribution in the central nervous system, FHFs are expressed in the mammalian heart (1). Their roles in regulating cardiac function, however, have only been recently investigated. We showed that FGF13, the predominant FHF in rodent heart and a common transcript in human heart (8), directly binds to the C terminus of cardiac Na V 1.5 Na + channels, and thereby regulates current density and conduction velocity by affecting channel gating and surface expression (9). Similarly, mutations that disrupt interaction between Na V 1.5 and FGF12, the major human cardiac FHF, have been linked to lifethreatening arrhythmia syndromes (8, 10). In addition to regulating Na + channels, FHFs can modulate voltage-gated Ca 2+ channels (11, 12). Fgf13 knockdown in adult rodent ventricular cardiomyocytes decreased Ca V 1.2 current density, perturbed Ca V 1.2 localization at the dyad, and thereby affected Ca 2+ -induced Ca 2+ release (11). Because previous studies were conducted in cultured cardiomyocytes, however, the in vivo roles for FHFs in ...

Cyclosporine A (CSA, calcineurin inhibitor) has been shown to block both vascular smooth muscle cell (VSMC) proliferation in cell culture and vessel neointimal formation following injury in vivo. The purpose of this study was to determine molecular and pathological effects of CSA on VSMCs. Using real-time reverse transcription-polymerase chain reaction, Western blot analysis, and immunofluorescence microscopy, we show that CSA upregulated the expression of Krü ppel-like factor-4 (KLF4) in VSMCs. KLF4 plays a key role in regulating VSMC phenotypic modulation. KLF4 antagonizes proliferation, facilitates migration, and down-regulates VSMC differentiation marker gene expression. We show that the VSMC differentiation marker genes smooth muscle ␣-actin (ACTA2), transgelin (TAGLN), smoothelin (SMTN), and myocardin (MYOCD) are all downregulated by CSA in VSMC monoculture, whereas cyclindependent kinase inhibitor-1A (CDKN1A) and matrix metalloproteinase-3 (MMP3) are up-regulated. CSA did not affect the abundance of the VSMC microRNA (MIR) markers MIR143 and MIR145. Administration of CSA to rat carotid artery in vivo resulted in acute and transient suppression of ACTA2, TAGLN, SMTN, MYOCD, and smooth muscle myosin heavy chain (MYH11) mRNA levels. The tumor suppressor genes KLF4, p53, and CDKN1A, however, were up-regulated, as well as MMP3, MMP9, and collagen-VIII. CSA-treated arteries showed remarkable remodeling, including breakdown of the internal elastic lamina and reorientation of VSMCs, as well as increased KLF4 immunostaining in VSMCs and endothelial cells. Altogether, these data show that cyclosporin up-regulates KLF4 expression and promotes phenotypic modulation of VSMCs.Cyclosporine A (CSA) is a fungus-derived immunosuppressant used clinically to combat organ graft rejection in transplant subjects. CSA suppresses the immune system by inhibiting proliferation of lymphocytes. Lymphocyte proliferation is facilitated by the cytokine interleukin-2 (IL-2), whose secretion is blocked by CSA. The transcriptional activation of IL-2 is dependent on the nuclear factor of activated T cells (NFAT) family of transcription factors (Shaw et al., 1988). NFAT nuclear translocation from the cytoplasm and subsequent transcriptional activity is facilitated through its dephosphorylation by the calcineurin (Cn) phosphatase (Flanagan et al., 1991). Cn activity can be inhibited by interaction with a complex of CSA and the endogenous cellular protein cyclophilin A (CYPA). In a similar fashion, the bacteriumderived immunosuppressant FK506 (tacrolimus, Prograf) binds to the cellular protein FK506-binding protein 1A, 12 kDa (FKBP12) to inhibit Cn activity. CSA and FK506 are thus powerful immunosuppressants used to combat organ

Objective.To define the risks and consequences of cardiac abnormalities in ATP1A3-related syndromes.Methods.Patients meeting clinical diagnostic criteria for Rapid-onset Dystonia-Parkinsonism (RDP), Alternating Hemiplegia of Childhood (AHC), and Cerebellar ataxia, Areflexia, Pes cavus, Optic atrophy, and Sensorineural hearing loss (CAPOS), with ATP1A3 genetic analysis, and had at least one cardiac assessment, were included. We evaluated the cardiac phenotype in an Atp1a3 knock-in mouse (Mashl+/-) to determine the sequence of events in seizure-related cardiac death.Results.98 AHC, nine RDP, and three CAPOS patients (63 females, mean age 17 years) were included. Resting EKG abnormalities were found in 52/87 (60%) AHC, 2/3 (67%) CAPOS, and 6/9 (67%) RDP patients. Serial EKGs showed dynamic changes in 10/18 AHC patients. The first Holter EKG was abnormal in 24/65 (37%) AHC and RDP cases, with either repolarization or conduction abnormalities. Echocardiography was normal. Cardiac intervention was required in 3/98 (∼3%) AHC patients. In the mouse model, resting EKGs showed intra-cardiac conduction delay; during induced seizures, heart block or complete sinus arrest led to death.Conclusions.We found increased prevalence of EKG dynamic abnormalities in all ATP1A3-related syndromes, with a risk of life-threatening cardiac rhythm abnormalities equivalent to that in established cardiac channelopathies (∼3%). Sudden cardiac death due to conduction abnormality emerged as a seizure-related outcome in murine Atp1a3-related disease. ATP1A3-related syndromes are cardiac diseases as well as neurological diseases. We provide guidance to identify patients potentially at higher risk of sudden cardiac death who may benefit from insertion of a pacemaker or implantable cardioverter-defibrillator.

Fibroblast growth factor (FGF)13, a nonsecreted, X‐linked, FGF homologous factor, is differentially expressed in adipocytes in response to diet, yet Fgf13′s role in metabolism has not been explored. Heterozygous Fgf13 knockouts fed normal chow and housed at 22°C showed hyperactivity accompanying reduced core temperature and obesity when housed at 30°C. Those heterozygous knockouts showed defects in thermogenesis even at 30°C and an inability to protect core temperature. Surprisingly, we detected trivial FGF13 in adipose of wild‐type mice fed normal chow and no obesity in adipose‐specific heterozygous knockouts housed at 30°C, and we detected an intact brown fat response through exogenous β3 agonist stimulation, suggesting a defect in sympathetic drive to brown adipose tissue. In contrast, hypothalamic‐specific ablation of Fgf13 recapitulated weight gain at 30°C. Norepinephrine turnover in brown fat was reduced at both housing temperatures. Thus, our data suggest that impaired CNS regulation of sympathetic activation of brown fat underlies obesity and thermogenesis in Fgf13 heterozygous knockouts fed normal chow.—Sinden, D. S., Holman, C. D., Bare, C. J., Sun, X., Gade, A. R., Cohen, D. E., Pitt, G. S. Knockout of the X‐linked Fgf13 in the hypothalamic paraventricular nucleus impairs sympathetic output to brown fat and causes obesity. FASEB J. 33, 11579–11594 (2019). http://www.fasebj.org

Background Hydroxychloroquine (HCQ) poisoning is a life-threatening but treatable toxic ingestion. The scale of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (COVID-19) and the controversial suggestion that HCQ is a treatment option have led to a significant increase in HCQ use. 1 Hence, HCQ poisoning should be at the top-of-mind for emergency providers in cases of toxic ingestion. Treatment for HCQ poisoning includes sodium bicarbonate, epinephrine, and aggressive electrolyte repletion. 2–5 Here, we highlight the use of hypertonic saline and diazepam. Case Report We describe the case of a 37-year-old man who presented to the emergency department (ED) after the ingestion of approximately 16 grams of HCQ tablets (initial serum concentration 4,270 ng/mL). He was treated with an epinephrine infusion, hypertonic sodium chloride, high-dose diazepam, sodium bicarbonate, and aggressive potassium repletion. Persistent altered mental status necessitated intubation, and he was managed in the medical intensive care unit until his QRS widening and QTc prolongation resolved. After his mental status improved and it was confirmed that his ingestion was not with the intent to self-harm, he was discharged home with outpatient follow-up. Why should an emergency physician be aware of this? For patients presenting with HCQ overdose and an unknown initial serum potassium level, high-dose diazepam and hypertonic sodium chloride should be started immediately for the patient with widened QRS. The choice of hypertonic sodium chloride instead of sodium bicarbonate is to avoid exacerbating underlying hypokalemia which may in turn potentiate unstable dysrhythmia. In addition, early intubation should be a priority in vomiting patients as both HCQ toxicity and high-dose diazepam cause profound sedation.

Introduction: E-cigarette, or vaping, product use associated lung injury (EVALI) is a newly recognized form of toxic lung injury largely associated with cannabinoid-containing products. Increasing recognition of EVALI cases demonstrate heterogeneous manifestations of respiratory injury that may represent distinct clinical syndromes. We present a probable case of EVALI in a patient with recurrent small-volume hemoptysis and pulmonary vascular abnormalities. Case: A 64-year-old male with history of allergic rhinitis, osteoarthritis, and anxiety presented with recurrent small-volume hemoptysis. His symptoms began two weeks prior during a coughing episode that led to expectoration of blood and dark clot for which he was first admitted. He reported no tobacco smoking history. Three years prior he started vaping cannabis cartridges and later switched to vaping marijuana for anxiety. Contrasted computed tomography (CT) of the chest was without evidence of pulmonary embolism, extravasation, pulmonary arteriovenous malformations, bronchiectasis, or consolidation. Flexible bronchoscopy showed fresh clot and bleeding in the right lower lobe (RLL). Bronchial alveolar lavage gram stain and cultures, including acid-fast bacilli smear and culture, were unrevealing. Serologic evaluation included negative anti-neutrophil cytoplasmic antibody (ANCA), antinuclear antibody (ANA), anti-glomerular basement membrane antibody, and cryoglobulins. C-reactive protein was measured at 1.6mg/L and erythrocyte sedimentation rate (ESR) was 2mm/h. Urine toxicology was positive for cannabinoids. His hemoptysis resolved spontaneously, and he was discharged. Two days later he was re-admitted with small-volume hemoptysis. Contrasted CT chest demonstrated bilateral bronchial wall thickening and RLL opacities. Repeat sputum culture grew moderate E. coli for which levofloxacin was initiated. Bronchial arteriography displayed tortuous and beaded-appearing hypertrophied bronchial arteries with diffuse vascular shunting between bronchial arteries and both pulmonary arteries and pulmonary veins, greatest in the RLL. No embolization was performed due to concern for systemic distribution of embolic material through vascular shunts. His hemoptysis resolved, and he was discharged with instructions to discontinue vaping. In the four-week outpatient follow-up visit, he reported abstinence from vaping and no recurrent hemoptysis. Discussion: EVALI is a poorly understood clinical syndrome with a range of symptoms and severity. Initial reports have suggested an increased association of adverse outcomes with vaping cannabinoids. To the best of our knowledge, this is the first reported case to suggest recurrent hemoptysis with vaping cannabinoids. The history, arteriography findings, and temporal proximity of symptom resolution to vaping termination led us to this diagnosis. It remains unclear whether vaping induced pulmonary vascular abnormalities or if pre-existent abnormalities predisposed the patient to EVALI.

Cyclosporine‐A (CSA, a calcineurin inhibitor) is a fungus‐derived immunosuppressant that blocks proliferation of lymphocytes. CSA has also been shown to block both vascular smooth muscle cell (SMC) proliferation in culture and vessel neointimal formation following injury in vivo. The molecular and pathological effects of CSA on SMCs are not fully understood. We show here that CSA increased SMC expression of Krüppel like factor 4 (KLF4) mRNA and protein. KLF4 is a transcription factor that regulates SMC phenotype. KLF4 inhibits proliferation, promotes migration, and suppresses SMC differentiation marker genes. We show that CSA suppressed SMC differentiation markers SM α‐actin (ACTA2), transgelin (TAGLN), smoothelin (SMTN), and myocardin (MYOCD), but increased cyclin‐dependent kinase inhibitor‐1A (CDKN1A) & matrix metalloproteinase‐3 (MMP3). CSA treatment of rat carotid arteries in vivo resulted in acute and transient suppression of ACTA2, TAGLN, SMTN, MYOCD, & SM myosin heavy chain (MYH11) mRNA. Conversely, tumor suppressor genes KLF4, p53, & CDKN1A were increased, as well as MMP3, MMP9, & collagen‐VIII (COL8). CSA‐treated arteries showed breakdown of the internal elastic lamina and pathological reorientation of SMCs. KLF4 immunostaining in SMCs and endothelial cells was increased. In conclusion, CSA increases KLF4 expression and promotes SMC phenotypic modulation in vivo. Sources of support: APS UGSRF, APS post‐doc, NIH HL81682, AHA SDG.