Concomitant Polyoma BK Virus and West Nile Virus in Renal Allografts

Surveillance of the renal allograft recipient is essential when monitoring renal function to detect the early onset of rejection and alter therapeutic treatments to treat acute rejection or other causes and improve long-term graft function. If renal function begins to deteriorate, a renal biopsy is often indicated to assess the Banff grade of potential rejection or other causes, especially in the setting of polyoma BK viral load elevation. Although BK infection in the allograft is asymptomatic, reactivation of the virus is known to be associated with the acceleration of pathologic change and a poor outcome in the allograft. BK reactivation in a transplant kidney is not uncommon, and determining inflammation related to the virus versus acute rejection is paramount for appropriate immunosuppressive therapy management. We identified a concomitant polyoma BK virus and West Nile Virus (WNV) infection in two renal transplant patients which, to our knowledge, has not previously been reported. However, other concomitant infections have been reported in renal allografts including BK virus and cytomegalovirus (CMV), CMV and hepatitis C (HCV), and HCV and human immunodeficiency virus (HIV). As WNV has become endemic in many regions of the United States, and since the transmission of the virus via transplanted organs is associated with significant morbidity and mortality, it may be prudent to consider serologic screening for WNV in living donors prior to organ procurement. Regardless, the observation we made and report here should underscore the potential for concomitant viral infections that may be masked when a renal allograft has a significant inflammatory response to BK virus.

BK channels sustain neuronal Ca2+ oscillations to support hippocampal long-term potentiation and memory formation

Mutations of large conductance Ca2+- and voltage-activated K+ channels (BK) are associated with cognitive impairment. Here we report that CA1 pyramidal neuron-specific conditional BK knock-out (cKO) mice display normal locomotor and anxiety behavior. They do, however, exhibit impaired memory acquisition and retrieval in the Morris Water Maze (MWM) when compared to littermate controls (CTRL). In line with cognitive impairment in vivo, electrical and chemical long-term potentiation (LTP) in cKO brain slices were impaired in vitro. We further used a genetically encoded fluorescent K+ biosensor and a Ca2+-sensitive probe to observe cultured hippocampal neurons during chemical LTP (cLTP) induction. cLTP massively reduced intracellular K+ concentration ([K+]i) while elevating L-Type Ca2+ channel- and NMDA receptor-dependent Ca2+ oscillation frequencies. Both, [K+]i decrease and Ca2+ oscillation frequency increase were absent after pharmacological BK inhibition or in cells lacking BK. Our data suggest that L-Type- and NMDAR-dependent BK-mediated K+ outflow significantly contributes to hippocampal LTP, as well as learning and memory.

Risk Factors for CMV and BK Infections in an Elderly Veteran Population Following Kidney Transplantation: Implications for Immunosuppression Induction and Management

Cytomegalovirus (CMV) and BK Polyomavirus (BKPyV) are the most common opportunistic pathogens following kidney transplantation. We evaluated 102 patients with a median age of 63 at Edward Hines VA Hospital from November 2020 to December 2022. Our primary interest was the incidence of CMV and BKPyV infections, as well as CMV and BKPyV coinfection. Secondary interests included time to infection, rejection, and graft and patient survival. There were no statistically significant differences in patient age, donor age, race, transplant type, incidence of delayed graft function, or induction in both cohorts (any infection (N = 46) vs. those without (N = 56)). There was a 36% (37/102) incidence of CMV, a 17.6% (18/102) of BKPyV and an 8.8% (9/102) incidence of coinfection. There was a decreased incidence of CMV infection in Basiliximab induction versus antithymocyte globulin (21% and 43%). CMV risk status had no effect on the incidence of CMV infection following transplant. African American recipients had a lower incidence of BKPyV infection (12% vs. 39%), yet a higher incidence was observed in those with high cPRA (50% vs. 14%). Most CMV and/or BKPyV infections occurred within the first six months post-transplant (54%). Immunosuppression management of the elderly should continually be evaluated to reduce opportunistic infections post-transplant.

Longitudinal Evaluation of Donor-Derived Cellfree DNA in Pediatric Kidney Transplantation

BACKGROUND AND OBJECTIVES

Donor-derived cellfree DNA (cfDNA) is a less-invasive marker of allograft injury compared with kidney biopsy. However, donor-derived cfDNA has not yet been extensively tested in children, where the test may have different characteristics.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We assayed donor-derived cfDNA (AlloSure; CareDx) from 290 stored plasma samples from a prospective biobank at our center, collected from 57 children monthly in the first year postkidney transplant between January 2013 and December 2019. We assessed the kinetic changes in donor-derived cfDNA levels within the first year post-transplant. We analyzed donor-derived cfDNA levels for associations with biopsy-proven acute rejection using area under the receiver operating characteristic curve to longitudinal plasma and urine BK viral loads using linear mixed models. We analyzed the prognostic effect of an elevated donor-derived cfDNA level on the eGFR 30 days after the assay via Kolmogorov-Smirnov two-sample tests or on measured GFR or interstitial fibrosis at 12 months post-transplant.

RESULTS

The donor-derived cfDNA levels in children remained persistently elevated for at least 4 months post-transplant, more so if there is greater disparity in size between the donor and the recipient, before reaching a steady low level. A donor-derived cfDNA level of >1% discriminated between biopsy-proven acute rejection with a receiver operating characteristic area under the curve of 0.82 (95% confidence interval, 0.71 to 0.93). During BK viruria or viremia, patients had a significantly higher median donor-derived cfDNA than before or after and a significant rise within the same patient. A donor-derived cfDNA of >0.5% predicted a wider spread in the eGFR over the next 30 days but not the 12-month outcomes.

CONCLUSIONS

In children, donor-derived cfDNA is a valuable, less invasive biomarker for assessment of allograft rejection and injury.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2022_10_27_CJN03840322.mp3.

Neurodegenerative Lysosomal Storage Disorders: TPC2 Comes to the Rescue!

Lysosomal storage diseases (LSDs) resulting from inherited gene mutations constitute a family of disorders that disturb lysosomal degradative function leading to abnormal storage of macromolecular substrates. In most LSDs, central nervous system (CNS) involvement is common and leads to the progressive appearance of neurodegeneration and early death. A growing amount of evidence suggests that ion channels in the endolysosomal system play a crucial role in the pathology of neurodegenerative LSDs. One of the main basic mechanisms through which the endolysosomal ion channels regulate the function of the endolysosomal system is Ca²⁺ release, which is thought to be essential for intracellular compartment fusion, fission, trafficking and lysosomal exocytosis. The intracellular TRPML (transient receptor potential mucolipin) and TPC (two-pore channel) ion channel families constitute the main essential Ca²⁺-permeable channels expressed on endolysosomal membranes, and they are considered potential drug targets for the prevention and treatment of LSDs. Although TRPML1 activation has shown rescue effects on LSD phenotypes, its activity is pH dependent, and it is blocked by sphingomyelin accumulation, which is characteristic of some LSDs. In contrast, TPC2 activation is pH-independent and not blocked by sphingomyelin, potentially representing an advantage over TRPML1. Here, we discuss the rescue of cellular phenotypes associated with LSDs such as cholesterol and lactosylceramide (LacCer) accumulation or ultrastructural changes seen by electron microscopy, mediated by the small molecule agonist of TPC2, TPC2-A1-P, which promotes lysosomal exocytosis and autophagy. In summary, new data suggest that TPC2 is a promising target for the treatment of different types of LSDs such as MLIV, NPC1, and Batten disease, both in vitro and in vivo.

Steroid-free maintenance immunosuppression using alemtuzumab in pediatric kidney transplantation: Long-term longitudinal follow-up

BACKGROUND

There is a scarcity of long-term data on steroid-free immunosuppression using alemtuzumab in pediatric kidney transplantation (KTx). This study examines long-term outcomes with alemtuzumab without steroid maintenance therapy in pediatric KTx.

METHODS

From July 2005 to June 2015, 71 pediatric KTx recipients received alemtuzumab without steroid maintenance. They were followed from 4.1 to 14.1 years post KTx.

RESULTS

Patient survival: One child expired with a functioning graft from post-transplant lymphoproliferative disorder (PTLD). Patient survival was 98.6%. Graft survival: Eighteen grafts were lost (16 from chronic rejection). Graft survival at 5 and 10 years was 92.3% and 61.3%, respectively. Rejection: Twenty-three (32.4%) patients were free from T-cell-mediated rejection (TCMR), 16 (22.5%) had >3 episodes. Sixteen (22.5%) were treated for antibody-mediated rejection (AMR). Infection: Twenty-three children developed Epstein-Barr virus (EBV), 5 developed cytomegalovirus (CMV), and 20 developed BK virus infection. Four (5.6%) developed PTLD. Twenty-two (31.0%) required treatment for neutropenia. Growth parameters: Mean height and weight increased by 0.56 and 0.69 SDS (standard deviation score), respectively. Body mass index increased by 5.1 kg/m² at 10 years. Less than 40% required antihypertensive medications at all-time points.

CONCLUSION

Alemtuzumab, without corticosteroid maintenance, offers 98.6% patient survival at 14 years with five and 10-year graft survival of 92.3% and 61.3%, respectively. TCMR and AMR requiring treatment were 67.4% and 22.5%, respectively. CMV, EBV, and BK viremia rates were 7.0%, 32.4%, and 28.2%, respectively. Thirty-one percent were treated for neutropenia; 5.6% developed PTLD. There were improvements in growth parameters and blood pressure.

Endolysosomal Cation Channels and Lung Disease

Endolysosomal cation channels are emerging as key players of endolysosomal function such as endolysosomal trafficking, fusion/fission, lysosomal pH regulation, autophagy, lysosomal exocytosis, and endocytosis. Diseases comprise lysosomal storage disorders (LSDs) and neurodegenerative diseases, metabolic diseases, pigmentation defects, cancer, immune disorders, autophagy related diseases, infectious diseases and many more. Involvement in lung diseases has not been a focus of attention so far but recent developments in the field suggest critical functions in lung physiology and pathophysiology. Thus, loss of TRPML3 was discovered to exacerbate emphysema formation and cigarette smoke induced COPD due to dysregulated matrix metalloproteinase 12 (MMP-12) levels in the extracellular matrix of the lung, a known risk factor for emphysema/COPD. While direct lung function measurements with the exception of TRPML3 are missing for other endolysosomal cation channels or channels expressed in lysosome related organelles (LRO) in the lung, links between those channels and important roles in lung physiology have been established such as the role of P2X4 in surfactant release from alveolar epithelial Type II cells. Other channels with demonstrated functions and disease relevance in the lung such as TRPM2, TRPV2, or TRPA1 may mediate their effects due to plasma membrane expression but evidence accumulates that these channels might also be expressed in endolysosomes, suggesting additional and/or dual roles of these channels in cell and intracellular membranes. We will discuss here the current knowledge on cation channels residing in endolysosomes or LROs with respect to their emerging roles in lung disease.

Anti-Inflammatory Effects of Rhamnetin on Bradykinin-Induced Matrix Metalloproteinase-9 Expression and Cell Migration in Rat Brain Astrocytes

Bradykinin (BK) has been shown to induce matrix metalloproteinase (MMP)-9 expression and participate in neuroinflammation. The BK/MMP-9 axis can be a target for managing neuroinflammation. Our previous reports have indicated that reactive oxygen species (ROS)-mediated nuclear factor-kappaB (NF-κB) activity is involved in BK-induced MMP-9 expression in rat brain astrocytes (RBA-1). Rhamnetin (RNT), a flavonoid compound, possesses antioxidant and anti-inflammatory effects. Thus, we proposed RNT could attenuate BK-induced response in RBA-1. This study aims to approach mechanisms underlying RNT regulating BK-stimulated MMP-9 expression, especially ROS and NF-κB. We used pharmacological inhibitors and siRNAs to dissect molecular mechanisms. Western blotting and gelatin zymography were used to evaluate protein and MMP-9 expression. Real-time PCR was used for gene expression. Wound healing assay was applied for cell migration. 2',7'-dichlorodihydrofluorescein diacetate (H2DCF-DA) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) were used for ROS generation and NOX activity, respectively. Promoter luciferase assay and chromatin immunoprecipitation (ChIP) assay were applied to detect gene transcription. Our results showed that RNT inhibits BK-induced MMP-9 protein and mRNA expression, promoter activity, and cell migration in RBA-1 cells. Besides, the levels of phospho-PKCδ, NOX activity, ROS, phospho-ERK1/2, phospho-p65, and NF-κB p65 binding to MMP-9 promoter were attenuated by RNT. In summary, RNT attenuates BK-enhanced MMP-9 upregulation through inhibiting PKCδ/NOX/ROS/ERK1/2-dependent NF-κB activity in RBA-1.

The role of lysosomal ion channels in lysosome dysfunction

Lysosomes offer a unique arrangement of degradative, exocytic, and signaling capabilities that make their continued function critical to cellular homeostasis. Lysosomes owe their function to the activity of lysosomal ion channels and transporters, which maintain concentration gradients of H⁺, K⁺, Ca²⁺, Na⁺, and Cl^- across the lysosomal membrane. This review examines the contributions of lysosomal ion channels to lysosome function, showing how ion channel function is integral to degradation and autophagy, maintaining lysosomal membrane potential, controlling Ca²⁺ signaling, and facilitating exocytosis. Evidence of lysosome dysfunction in a variety of disease pathologies creates a need to understand how lysosomal ion channels contribute to lysosome dysfunction. For example, the loss of function of the TRPML1 Ca²⁺ lysosome channel in multiple lysosome storage diseases leads to lysosome dysfunction and disease pathogenesis while neurodegenerative diseases are marked by lysosome dysfunction caused by changes in ion channel activity through the TRPML1, TPC, and TMEM175 ion channels. Autoimmune disease is marked by dysregulated autophagy, which is dependent on the function of multiple lysosomal ion channels. Understanding the role of lysosomal ion channel activity in lysosome membrane permeability and NLRP3 inflammasome activation could provide valuable mechanistic insight into NLRP3 inflammasome-mediated diseases. Finally, this review seeks to show that understanding the role of lysosomal ion channels in lysosome dysfunction could give mechanistic insight into the efficacy of certain drug classes, specifically those that target the lysosome, such as cationic amphiphilic drugs.

Age-related hearing loss pertaining to potassium ion channels in the cochlea and auditory pathway

Age-related hearing loss (ARHL) is the most prevalent sensory deficit in the elderly and constitutes the third highest risk factor for dementia. Lifetime noise exposure, genetic predispositions for degeneration, and metabolic stress are assumed to be the major causes of ARHL. Both noise-induced and hereditary progressive hearing have been linked to decreased cell surface expression and impaired conductance of the potassium ion channel K_V7.4 (KCNQ4) in outer hair cells, inspiring future therapies to maintain or prevent the decline of potassium ion channel surface expression to reduce ARHL. In concert with K_V7.4 in outer hair cells, K_V7.1 (KCNQ1) in the stria vascularis, calcium-activated potassium channels BK (KCNMA1) and SK2 (KCNN2) in hair cells and efferent fiber synapses, and K_V3.1 (KCNC1) in the spiral ganglia and ascending auditory circuits share an upregulated expression or subcellular targeting during final differentiation at hearing onset. They also share a distinctive fragility for noise exposure and age-dependent shortfalls in energy supply required for sustained surface expression. Here, we review and discuss the possible contribution of select potassium ion channels in the cochlea and auditory pathway to ARHL. We postulate genes, proteins, or modulators that contribute to sustained ion currents or proper surface expressions of potassium channels under challenging conditions as key for future therapies of ARHL.

Stimulatory Role of SPAK Signaling in the Regulation of Large Conductance Ca2+-Activated Potassium (BK) Channel Protein Expression in Kidney

SPS1-related proline/alanine-rich kinase (SPAK) plays important roles in regulating the function of numerous ion channels and transporters. With-no-lysine (WNK) kinase phosphorylates SPAK kinase to active the SPAK signaling pathway. Our previous studies indicated that WNK kinases regulate the activity of the large-conductance Ca²⁺-activated K⁺ (BK) channel and its protein expression via the ERK1/2 signaling pathway. It remains largely unknown whether SPAK kinase directly modulates the BK protein expression in kidney. In this study, we investigated the effect of SPAK on renal BK protein expression in both HEK293 cells and mouse kidney. In HEK293 cells, siRNA-mediated knockdown of SPAK expression significantly reduced BK protein expression and increased ERK1/2 phosphorylation, whereas overexpression of SPAK significantly enhanced BK expression and decreased ERK1/2 phosphorylation in a dose-dependent manner. Knockdown of ERK1/2 prevented SPAK siRNA-mediated inhibition of BK expression. Similarly, pretreatment of HEK293 cells with either the lysosomal inhibitor bafilomycin A1 or the proteasomal inhibitor MG132 reversed the inhibitory effects of SPAK knockdown on BK expression. We also found that there is no BK channel activity in PCs of CCD in SPAK KO mice using the isolated split-open tubule single-cell patching. In addition, we found that BK protein abundance in the kidney of SPAK knockout mice was significantly decreased and ERK1/2 phosphorylation was significantly enhanced. A high-potassium diet significantly increased BK protein abundance and SPAK phosphorylation levels, while reducing ERK1/2 phosphorylation levels. These findings suggest that SPAK enhances BK protein expression by reducing ERK1/2 signaling-mediated lysosomal and proteasomal degradations of the BK channel.

Activation of BK Channels Prevents Hepatic Stellate Cell Activation and Liver Fibrosis Through the Suppression of TGFβ1/SMAD3 and JAK/STAT3 Profibrotic Signaling Pathways

Large-conductance and Ca²⁺-activated K⁺ (BK) channels are expressed in human hepatic stellate cells (HSCs), where they have roles in normal hepatic microcirculation, as well as in portal hypertension in liver cirrhosis through the regulation of contractility in activated HSCs. Nevertheless, whether BK channel activity exerts protective effects against aberrant HSC activation and hepatic fibrosis is unknown. Here, we report that BK channels are expressed in activated primary rat HSCs as well as in a human HSC line. Moreover, whole-cell K⁺ currents recorded from activated HSCs were markedly increased by exposure to rottlerin, a BK channel-specific activator, but were inhibited by treatment with the BK channel-specific inhibitor, paxilline, suggesting that BK channels are functional in activated HSCs. Overexpression but not downregulation of the BK channel pore-forming alpha subunit, KCNMA1, led to reduced migration and collagen expression in activated HSCs. Consistently, rottlerin treatment suppressed the fibrogenic cell function both in vitro and in CCl₄-induced liver fibrosis in vivo. Microarray and pathway analysis, combined with a luciferase reporter assay and western blotting, further showed that rottlerin treatment led to a significant downregulation of the profibrotic TGFβ1/SMAD3 and JAK/STAT3 signaling pathways, both in vitro and in vivo. Our findings not only link BK channel function to profibrotic signaling pathways, but also provide evidence that BK channel activation represents a promising therapeutic strategy for the treatment of liver fibrosis.

Dynamic- and Frequency-Specific Regulation of Sleep Oscillations by Cortical Potassium Channels

Primary electroencephalographic (EEG) features of sleep arise in part from thalamocortical neural assemblies, and cortical potassium channels have long been thought to play a critical role. We have exploited the regionally dynamic nature of sleep EEG to develop a novel screening strategy and used it to conduct an adeno-associated virus (AAV)-mediated RNAi screen for cellular roles of 31 different voltage-gated potassium channels in modulating cortical EEG features across the circadian sleep-wake cycle. Surprisingly, a majority of channels modified only electroencephalographic frequency bands characteristic of sleep, sometimes diurnally or even in specific vigilance states. Confirming our screen for one channel, we show that depletion of the KCa1.1 (or "BK") channel reduces EEG power in slow-wave sleep by slowing neuronal repolarization. Strikingly, this reduction completely abolishes transcriptomic changes between sleep and wake. Thus, our data establish an unexpected connection between transcription and EEG power controlled by specific potassium channels. We postulate that additive dynamic roles of individual potassium channels could integrate different influences upon sleep and wake within single neurons.

Cochlea-Specific Deletion of Cav1.3 Calcium Channels Arrests Inner Hair Cell Differentiation and Unravels Pitfalls of Conditional Mouse Models

Inner hair cell (IHC) Ca_v1.3 Ca²⁺ channels are multifunctional channels mediating Ca²⁺ influx for exocytosis at ribbon synapses, the generation of Ca²⁺ action potentials in pre-hearing IHCs and gene expression. IHCs of deaf systemic Ca_v1.3-deficient (Ca_v1.3^-/-) mice stay immature because they fail to up-regulate voltage- and Ca²⁺-activated K⁺ (BK) channels but persistently express small conductance Ca²⁺-activated K⁺ (SK2) channels. In pre-hearing wildtype mice, cholinergic neurons from the superior olivary complex (SOC) exert efferent inhibition onto spontaneously active immature IHCs by activating their SK2 channels. Because Ca_v1.3 plays an important role for survival, health and function of SOC neurons, SK2 channel persistence and lack of BK channels in systemic Ca_v1.3^-/- IHCs may result from malfunctioning neurons of the SOC. Here we analyze cochlea-specific Ca_v1.3 knockout mice with green fluorescent protein (GFP) switch reporter function, Pax2::cre;Cacna1d-eGFP^flex/flexand Pax2::cre;Cacna1d-eGFP^flex/-. Profound hearing loss, lack of BK channels and persistence of SK2 channels in Pax2::cre;Cacna1d-eGFP^flex/- mice recapitulated the phenotype of systemic Ca_v1.3^-/- mice, indicating that in wildtype mice, regulation of SK2 and BK channel expression is independent of Ca_v1.3 expression in SOC neurons. In addition, we noticed dose-dependent GFP toxicity leading to death of basal coil IHCs of Pax2::cre;Cacna1d-eGFP^flex/flex mice, likely because of high GFP concentration and small repair capacity. This and the slower time course of Pax2-driven Cre recombinase in switching two rather than one Cacna1d-eGFP^flex allele lead us to study Pax2::cre;Cacna1d-eGFP^flex/- mice. Notably, control Cacna1d-eGFP^flex/- IHCs showed a significant reduction in Ca_v1.3 channel cluster sizes and currents, suggesting that the intronic construct interfered with gene translation or splicing. These pitfalls are likely to be a frequent problem of many genetically modified mice with complex or multiple gene-targeting constructs or fluorescent proteins. Great caution and appropriate controls are therefore required.

Potassium-sparing effects of furosemide in mice on high-potassium diets

In individuals on a regular "Western" diet, furosemide induces a kaliuresis and reduction in plasma K concentration by inhibiting Na reabsorption in the thick ascending limb of Henle's loop, enhancing delivery of Na to the aldosterone-sensitive distal nephron. In the aldosterone-sensitive distal nephron, the increased Na delivery stimulates K wasting due to an exaggerated exchange of epithelial Na channel-mediated Na reabsorption of secreted K. The effects of furosemide are different in mice fed a high-K, alkaline (HK) diet: the large-conductance Ca-activated K (BK) channel, in conjunction with the BK β₄-subunit (BK-α/β₄), mediates K secretion from intercalated cells (IC) of the connecting tubule and collecting ducts. The urinary alkaline load is necessary for BK-α/β₄-mediated K secretion in HK diet-fed mice. However, furosemide acidifies the urine by increasing vacuolar ATPase expression and acid secretion from IC, thereby inhibiting BK-α/β₄-mediated K secretion and sparing K. In mice fed a low-Na, high-K (LNaHK) diet, furosemide causes a greater increase in plasma K concentration and reduction in K excretion than in HK diet-fed mice. Micropuncture of the early distal tubule of mice fed a LNaHK diet, but not a regular or a HK diet, reveals K secretion in the thick ascending limb of Henle's loop. The sites of action of K secretion in individuals consuming a high-K diet should be taken into account when diuretic agents known to waste K with low or moderate K intakes are prescribed.

Large-conductance Ca2+- and voltage-gated K+ channels form and break interactions with membrane lipids during each gating cycle

Membrane depolarization and intracellular Ca²⁺ promote activation of the large-conductance Ca²⁺- and voltage-gated (Slo1) big potassium (BK) channel. We examined the physical interactions that stabilize the closed and open conformations of the ion conduction gate of the human Slo1 channel using electrophysiological and computational approaches. The results show that the closed conformation is stabilized by intersubunit ion-ion interactions involving negative residues (E321 and E324) and positive residues (³²⁹RKK³³¹) at the cytoplasmic ends of the transmembrane S6 segments ("RKK ring"). When the channel gate is open, the RKK ring is broken and the positive residues instead make electrostatic interactions with nearby membrane lipid oxygen atoms. E321 and E324 are stabilized by water. When the ³²⁹RKK³³¹ residues are mutated to hydrophobic amino acids, these residues form even stronger hydrophobic interactions with the lipid tails to promote the open conformation, shifting the voltage dependence of activation to the negative direction by up to 400 mV and stabilizing the selectivity filter region. Thus, the RKK segment forms electrostatic interactions with oxygen atoms from two sources, other amino acid residues (E321/E324), and membrane lipids, depending on the gate status. Each time the channel opens and closes, the aforementioned interactions are formed and broken. This lipid-dependent Slo1 gating may explain how amphipathic signaling molecules and pharmacologically active agents influence the channel activity, and a similar mechanism may be operative in other ion channels.

Functional Coupling of Cav2.3 and BK Potassium Channels Regulates Action Potential Repolarization and Short-Term Plasticity in the Mouse Hippocampus

Voltage-gated ion channels are essential for signal generation and propagation in neurons and other excitable cells. The high-voltage activated calcium-channel Cav2.3 is expressed throughout the central and peripheral nervous system, and within CA1 hippocampal pyramidal neurons it is localized throughout the somato-dendritic region and dendritic spines. Cav2.3 has been shown to provide calcium for other calcium-dependent potassium channels including small-conductance calcium-activated potassium channels (SK), but big-conductance calcium-activated potassium channels (BK) have been thought to be activated by calcium from all known voltage-gated calcium channels, except Cav2.3. Here we show for the first time that CA1 pyramidal cells which lack Cav2.3 show altered action potential (AP) waveforms, which can be traced back to reduced SK- and BK-channel function. This change in AP waveform leads to strengthened synaptic transmission between CA1 and the subiculum, resulting in increased short-term plasticity. Our results demonstrate that Cav2.3 impacts cellular excitability through functional interaction with BK channels, impacting communication between hippocampal subregions.

Lipid⁻Protein Interactions in Niemann⁻Pick Type C Disease: Insights from Molecular Modeling

The accumulation of lipids in the late endosomes and lysosomes of Niemann⁻Pick type C disease (NPCD) cells is a consequence of the dysfunction of one protein (usually NPC1) but induces dysfunction in many proteins. We used molecular docking to propose (a) that NPC1 exports not just cholesterol, but also sphingosine, (b) that the cholesterol sensitivity of big potassium channel (BK) can be traced to a previously unappreciated site on the channel's voltage sensor, (c) that transient receptor potential mucolipin 1 (TRPML1) inhibition by sphingomyelin is likely an indirect effect, and (d) that phosphoinositides are responsible for both the mislocalization of annexin A2 (AnxA2) and a soluble NSF (N-ethylmaleimide Sensitive Fusion) protein attachment receptor (SNARE) recycling defect. These results are set in the context of existing knowledge of NPCD to sketch an account of the endolysosomal pathology key to this disease.

Oligopeptidases activity in bipolar disorder: Ndel1 and angiotensin I converting enzyme

BACKGROUND

Abnormal activity of two enzymes relevant to neurodevelopment, namely nuclear-distribution element-like 1 (Ndel1) and angiotensin I-converting enzyme (ACE), was reported in individuals with schizophrenia; to our knowledge, these oligopeptidases were never measured in bipolar disorder (BD).

AIMS

Evaluate the enzyme activity of Ndel1 and ACE in euthymic individuals with BD type 1 which was compare to healthy control (HC) group.

METHODS

Ndel1 and ACE activities were assessed in the serum of individuals with BD type 1 according to DSM-IV criteria (n = 70) and a HC group (n = 34). The possible differences between BD type 1 and HC groups were evaluated using Analysis of Covariance (ANCOVA), and the results were adjusted for age, gender and body mass index.

RESULTS

We observed a positive correlation between Ndel1 activity and the total YMRS score in BD group (p = 0.030) and a positive correlation between ACE activity and Ham-D score (p = 0.047). ANCOVA analysis showed lower Ndel1 activity in BDs compared to HCs. Interestingly, we did not observe between-groups differences in ACE activity, despite the recognized correlation of ACE activity levels with cognitive functions, also described to be worsened in psychiatric patients.

CONCLUSION

Oligopeptidases, especially Ndel1, which has been strongly correlated with neurodevelopment and brain formation, are potentially a good new target in the study of the neurobiology of BD.

LIMITATIONS

The relatively small sample size did not permit to examine the cause-effect relationship of clinical dimensions of BD and the enzymatic activity.

Cancer-Associated Intermediate Conductance Ca2+-Activated K⁺ Channel KCa3.1

Several tumor entities have been reported to overexpress K_Ca3.1 potassium channels due to epigenetic, transcriptional, or post-translational modifications. By modulating membrane potential, cell volume, or Ca²⁺ signaling, K_Ca3.1 has been proposed to exert pivotal oncogenic functions in tumorigenesis, malignant progression, metastasis, and therapy resistance. Moreover, K_Ca3.1 is expressed by tumor-promoting stroma cells such as fibroblasts and the tumor vasculature suggesting a role of K_Ca3.1 in the adaptation of the tumor microenvironment. Combined, this features K_Ca3.1 as a candidate target for innovative anti-cancer therapy. However, immune cells also express K_Ca3.1 thereby contributing to T cell activation. Thus, any strategy targeting K_Ca3.1 in anti-cancer therapy may also modulate anti-tumor immune activity and/or immunosuppression. The present review article highlights the potential of K_Ca3.1 as an anti-tumor target providing an overview of the current knowledge on its function in tumor pathogenesis with emphasis on vasculo- and angiogenesis as well as anti-cancer immune responses.

Exploiting the Diversity of Ion Channels: Modulation of Ion Channels for Therapeutic Indications

Ion channels are macromolecular proteins that form water-filled pores in cell membranes and they are critical for a variety of physiological and pharmacological functions. Dysfunctional ion channels can cause diseases known as channelopathies. Ion channels are encoded by approximately 400 genes, representing the second largest class of proven drug targets for therapeutic areas including neuropsychiatric disorders, cardiovascular and metabolic diseases, immunological diseases, nephrological diseases, gastrointestinal diseases, pulmonary/respiratory diseases, and many cancers. With more ion channel structures are being solved and functional robust assays are being developed, there are tremendous opportunities for identifying specific modulators targeting ion channels for new therapy.

Voltage-dependent dynamics of the BK channel cytosolic gating ring are coupled to the membrane-embedded voltage sensor

In humans, large conductance voltage- and calcium-dependent potassium (BK) channels are regulated allosterically by transmembrane voltage and intracellular Ca²⁺. Divalent cation binding sites reside within the gating ring formed by two Regulator of Conductance of Potassium (RCK) domains per subunit. Using patch-clamp fluorometry, we show that Ca²⁺ binding to the RCK1 domain triggers gating ring rearrangements that depend on transmembrane voltage. Because the gating ring is outside the electric field, this voltage sensitivity must originate from coupling to the voltage-dependent channel opening, the voltage sensor or both. Here we demonstrate that alterations of the voltage sensor, either by mutagenesis or regulation by auxiliary subunits, are paralleled by changes in the voltage dependence of the gating ring movements, whereas modifications of the relative open probability are not. These results strongly suggest that conformational changes of RCK1 domains are specifically coupled to the voltage sensor function during allosteric modulation of BK channels.

Infectious Entry and Neutralization of Pathogenic JC Polyomaviruses

Progressive multifocal leukoencephalopathy (PML) is a lethal brain disease caused by uncontrolled replication of JC polyomavirus (JCV). JCV strains recovered from the brains of PML patients carry mutations that prevent the engagement of sialylated glycans, which are thought to serve as receptors for the infectious entry of wild-type JCV. In this report, we show that non-sialylated glycosaminoglycans (GAGs) can serve as alternative attachment receptors for the infectious entry of both wild-type and PML mutant JCV strains. After GAG-mediated attachment, PML mutant strains engage non-sialylated non-GAG co-receptor glycans, such as asialo-GM1. JCV-neutralizing monoclonal antibodies isolated from patients who recovered from PML appear to block infection by preventing the docking of post-attachment co-receptor glycans in an apical pocket of the JCV major capsid protein. Identification of the GAG-dependent/sialylated glycan-independent alternative entry pathway should facilitate the development of infection inhibitors, including recombinant neutralizing antibodies.

Renal and colonic potassium transporters in the pregnant rat

Gestational potassium retention, most of which occurs during late pregnancy, is essential for fetal development. The purpose of this study was to examine mechanisms underlying changes in potassium handling by the kidney and colon in pregnancy. We found that potassium intake and renal excretion increased in late pregnancy while fecal potassium excretion remained unchanged and that pregnant rats exhibited net potassium retention. By quantitative PCR we found markedly increased H+-K+-ATPase type 2 (HKA2) mRNA expression in the cortex and outer medullary of late pregnant vs. virgin. Renal outer medullary potassium channel (ROMK) mRNA was unchanged in the cortex, but apical ROMK abundance (by immunofluorescence) was decreased in pregnant vs. virgin in the distal convoluted tubule (DCT) and connecting tubule (CNT). Big potassium-α (BKα) channel-α protein abundance in intercalated cells in the cortex and outer medullary collecting ducts (by immunohistochemistry) fell in late pregnancy. In the distal colon we found increased HKA2 mRNA and protein abundance (Western blot) and decreased BKα protein with no observed changes in mRNA. Therefore, the potassium retention of pregnancy is likely to be due to increased collecting duct potassium reabsorption (via increased HKA2), decreased potassium secretion (via decreased ROMK and BK), as well as increased colonic reabsorption via HKA2.

Activation of voltage-dependent K+ channels strongly limits hypoxia-induced elevation of [Ca2+ ]i in rat carotid body glomus cells

KEY POINTS

We studied the role of the large-conductance Ca²⁺ -activated K⁺ channel (BK) and voltage-dependent K⁺ channels (Kv) on [Ca²⁺ ]_i responses to a wide range of hypoxia at different resting cell membrane potential (E_m ). BK/Kv were mostly closed at rest in normoxia. BK/Kv became basally active when cells were depolarized by elevated [KCl]_o (>12 mm). Regardless of whether BK/Kv were closed or basally open, hypoxia-induced elevation of [Ca²⁺ ]_i was enhanced 2- to 3-fold by inhibitors of BK/Kv. Hypoxia-induced elevation of [Ca²⁺ ]_i was enhanced ∼2-fold by an inhibitor of Kv2, a major Kv in rat glomus cells. Hypoxia did not inhibit BK in inside-out patches. Our study supports a scheme in which activation of BK/Kv strongly limits the magnitude of hypoxia-induced [Ca²⁺ ]_i rise, with Kv having a much greater effect than BK.

ABSTRACT

Large-conductance K_Ca (BK) and other voltage-dependent K⁺ channels (Kv) are highly expressed in carotid body (CB) glomus cells, but their role in hypoxia-induced excitation is still not well defined and remains controversial. We addressed this issue by studying the effects of inhibitors of BK (IBTX) and BK/Kv (TEA/4-AP) on [Ca²⁺ ]_i responses to a wide range of hypoxia at different levels of resting cell membrane potential (E_m ). IBTX and TEA/4-AP did not affect the basal [Ca²⁺ ]_i in isolated glomus cells bathed in 5 mm KCl_o , but elicited transient increases in [Ca²⁺ ]_i in cells that were moderately depolarized (11-20 mV) by elevation of [KCl]_o (12-20 mm). Thus, BK and Kv were mostly closed at rest and activated by depolarization. Four different levels of hypoxia (mild, moderate, severe, anoxia) were used to produce a wide range of [Ca²⁺ ]_i elevation (0-700 nm). IBTX did not affect the rise in [Ca²⁺ ]_i , but TEA/4-AP strongly (∼3-fold) enhanced [Ca²⁺ ]_i rise by moderate and severe levels of hypoxia. Guangxitoxin, a Kv2 blocker, inhibited the whole-cell current by ∼50%, and enhanced 2-fold the [Ca²⁺ ]_i rise elicited by moderate and severe levels of hypoxia. Anoxia did not directly affect BK, but activated BK via depolarization. Our findings do not support the view that hypoxia inhibits BK/Kv to initiate or maintain the hypoxic response. Rather, our results show that BK/Kv are activated as glomus cells depolarize in response to hypoxia, which then limits the rise in [Ca²⁺ ]_i . Inhibition of Kv may provide a mechanism to enhance the chemosensory activity of the CB and ventilation.

Alcohol Regulates BK Surface Expression via Wnt/β-Catenin Signaling

It has been suggested that drug tolerance represents a form of learning and memory, but this has not been experimentally established at the molecular level. We show that a component of alcohol molecular tolerance (channel internalization) from rat hippocampal neurons requires protein synthesis, in common with other forms of learning and memory. We identify β-catenin as a primary necessary protein. Alcohol increases β-catenin, and blocking accumulation of β-catenin blocks alcohol-induced internalization in these neurons. In transfected HEK293 cells, suppression of Wnt/β-catenin signaling blocks ethanol-induced internalization. Conversely, activation of Wnt/β-catenin reduces BK current density. A point mutation in a putative glycogen synthase kinase phosophorylation site within the S10 region of BK blocks internalization, suggesting that Wnt/β-catenin directly regulates alcohol-induced BK internalization via glycogen synthase kinase phosphorylation. These findings establish de novo protein synthesis and Wnt/β-catenin signaling as critical in mediating a persistent form of BK molecular alcohol tolerance establishing a commonality with other forms of long-term plasticity.

SIGNIFICANCE STATEMENT

Alcohol tolerance is a key step toward escalating alcohol consumption and subsequent dependence. Our research aims to make significant contributions toward novel, therapeutic approaches to prevent and treat alcohol misuse by understanding the molecular mechanisms of alcohol tolerance. In our current study, we identify the role of a key regulatory pathway in alcohol-induced persistent molecular changes within the hippocampus. The canonical Wnt/β-catenin pathway regulates BK channel surface expression in a protein synthesis-dependent manner reminiscent of other forms of long-term hippocampal neuronal adaptations. This unique insight opens the possibility of using clinically tested drugs, targeting the Wnt/β-catenin pathway, for the novel use of preventing and treating alcohol dependency.

Onset and progression of de novo donor-specific anti-human leukocyte antigen antibodies after BK polyomavirus and preemptive immunosuppression reduction

BACKGROUND

BK polyomavirus (BKPyV) viremia/nephropathy and reduction in immunosuppression following viremia may increase the risk of alloimmune activation and allograft rejection. This study investigates the impact of BKPyV viremia on de novo donor anti-human leukocyte antigen (HLA)-specific antibodies (dnDSA).

PATIENTS AND METHODS

All primary renal transplants at East Carolina University from March 1999 to December 2010, with at least 1 post-transplant BKPyV viral load testing, were analyzed. Patients were negative for anti-HLA antibodies to donor antigens (tested via single antigen beads) at transplantation and at first BKPyV testing.

RESULTS

Nineteen of 174 patients (11%) tested positive for BKPyV viremia. Within 24 months of BKPyV viremia detection, 79% of BKPyV-viremic patients developed dnDSA. Only 20% of BKPyV viremia-persistent cases, compared to 86% of BKPyV viremia-resolved cases, developed dnDSA (P = 0.03). Poor allograft survival was evident in BKPyV viremia-persistent patients (60% failure by 2 years post BKPyV diagnosis) and in BKPyV viremia-resolved patients with dnDSA (5-year post BKPyV diagnosis allograft survival of 48%).

CONCLUSIONS

Post-transplant BKPyV viremia and preemptive immunosuppression reduction is associated with high rates of dnDSA. When preemptively treating BKPyV viremia, dnDSA should be monitored to prevent allograft consequences.

Down-regulation of the large conductance Ca(2+)-activated K(+) channel expression in C57BL/6J cochlea

CONCLUSION

The large conductance Ca(2+)-activated K(+ )channels (BK) expression is decreased in the cochleae of age-related hearing loss (AHL) mice. BK channel may be associated with AHL.

OBJECTIVE

AHL is the most common among elderly persons. BK channels act as sensors for membrane voltage and intracellular Ca(2+ )and are essential for hearing. To investigate the distribution of BK channel in the cochleae of C57BL/6J mice, and the relationship between the expression of BK channel and the etiology of AHL.

METHODS

BK expression was studied in the cochleae of C57BL/6J mice at various ages (4, 12, 26, 52 weeks). The expressions of BK at the protein and mRNA levels were detected by immunofluorescence technique, western blot and quantitative real time PCR.

RESULTS

In comparison with 4-week-old mice, BK expressions in the cochleae at 12, 26 and 52 weeks of age were significantly and gradually decreased at both the protein and the mRNA levels. The immunofluorescence technique showed the BK channel was located in the hair cells and cells of the spiral ganglion, spiral ligament and stria vascularis and its expression also decreased with aging.

Rapid estrogen actions on ion channels: A survey in search for mechanisms

A survey of nearly two hundred reports shows that rapid estrogenic actions can be detected across a range of kinds of estrogens, a range of doses, on a wide range of tissue, cell and ion channel types. Striking is the fact that preparations of estrogenic agents that do not permeate the cell membrane almost always mimic the actions of the estrogenic agents that do permeate the membrane. All kinds of estrogens, ranging from natural ones, through receptor modulators, endocrine disruptors, phytoestrogens, agonists, and antagonists to novel G-1 and STX, have been reported to be effective. For actions on specific types of ion channels, the possibility of opposing actions, in different cases, is the rule, not the exception. With this variety there is no single, specific action mechanism for estrogens per se, although in some cases estrogens can act directly or via some signaling pathways to affect ion channels. We infer that estrogens can bind a large number of substrates/receptors at the membrane surface. As against the variety of subsequent routes of action, this initial step of the estrogen's binding action is the key.

BK Channels in the Vertebrate Inner Ear

The perception of complex acoustic stimuli begins with the deconstruction of sound into its frequency components. This spectral processing occurs first and foremost in the inner ear. In vertebrates, two very different strategies of frequency analysis have evolved. In nonmammalian vertebrates, the sensory hair cells of the inner ear are intrinsically electrically tuned to a narrow band of acoustic frequencies. This electrical tuning relies on the interplay between BK channels and voltage-gated calcium channels. Systematic variations in BK channel density and kinetics establish a gradient in electrical resonance that enables the coding of a broad range of acoustic frequencies. In contrast, mammalian hair cells are extrinsically tuned by mechanical properties of the cochlear duct. Even so, mammalian hair cells also express BK channels. These BK channels play critical roles in various aspects of mammalian auditory signaling, from developmental maturation to protection against acoustic trauma. This review summarizes the anatomical localization, biophysical properties, and functional contributions of BK channels in vertebrate inner ears. Areas of future research, based on an updated understanding of the biology of both BK channels and the inner ear, are also highlighted. Investigation of BK channels in the inner ear continues to provide fertile research grounds for examining both BK channel biophysics and the molecular mechanisms underlying signal processing in the auditory periphery.

Roles and Regulation of Renal K Channels

More than two dozen types of potassium channels, with different biophysical and regulatory properties, are expressed in the kidney, influencing renal function in many important ways. Recently, a confluence of discoveries in areas from human genetics to physiology, cell biology, and biophysics has cast light on the special function of five different potassium channels in the distal nephron, encoded by the genes KCNJ1, KCNJ10, KCNJ16, KCNMA1, and KCNN3. Research aimed at understanding how these channels work in health and go awry in disease has transformed our understanding of potassium balance and provided new insights into mechanisms of renal sodium handling and the maintenance of blood pressure. This review focuses on recent advances in this rapidly evolving field.

Airway Surface Dehydration by Transforming Growth Factor β (TGF-β) in Cystic Fibrosis Is Due to Decreased Function of a Voltage-dependent Potassium Channel and Can Be Rescued by the Drug Pirfenidone

Transforming growth factor β1 (TGF-β1) is not only elevated in airways of cystic fibrosis (CF) patients, whose airways are characterized by abnormal ion transport and mucociliary clearance, but TGF-β1 is also associated with worse clinical outcomes. Effective mucociliary clearance depends on adequate airway hydration, governed by ion transport. Apically expressed, large-conductance, Ca(2+)- and voltage-dependent K(+) (BK) channels play an important role in this process. In this study, TGF-β1 decreased airway surface liquid volume, ciliary beat frequency, and BK activity in fully differentiated CF bronchial epithelial cells by reducing mRNA expression of the BK γ subunit leucine-rich repeat-containing protein 26 (LRRC26) and its function. Although LRRC26 knockdown itself reduced BK activity, LRRC26 overexpression partially reversed TGF-β1-induced BK dysfunction. TGF-β1-induced airway surface liquid volume hyper-absorption was reversed by the BK opener mallotoxin and the clinically useful TGF-β signaling inhibitor pirfenidone. The latter increased BK activity via rescue of LRRC26. Therefore, we propose that TGF-β1-induced mucociliary dysfunction in CF airways is associated with BK inactivation related to a LRRC26 decrease and is amenable to treatment with clinically useful TGF-β1 inhibitors.

Functional coupling of TRPV4, IK, and SK channels contributes to Ca(2+)-dependent endothelial injury in rodent lung

Our previous work has shown that the increased lung endothelial permeability response to 14,15-epoxyeicosatrienoic acid (14,15-EET) in rat lung requires Ca(2+) entry via vanilloid type-4 transient receptor potential (TRPV4) channels. Recent studies suggest that activation of TRPV4 channels in systemic vascular endothelium prolongs agonist-induced hyperpolarization and amplifies Ca(2+) entry by activating Ca(2+)-activated K(+) (KCa) channels, resulting in vessel relaxation. Activation of endothelial KCa channels thus has potential to increase the electrochemical driving force for Ca(2+) influx via TRPV4 channels and to amplify permeability responses to TRPV4 activation in lung. To examine this hypothesis, we used Western blot analysis, electrophysiological recordings, and isolated-lung permeability measurements to document expression of TRPV4 and KCa channels and the potential for functional coupling. The results show that rat pulmonary microvascular endothelial cells express TRPV4 and 3 KCa channels of different conductances: large (BK), intermediate (IK), and small (SK3). However, TRPV4 channel activity modulates the IK and SK3, but not the BK, channel current density. Furthermore, the TRPV4-mediated permeability response to 14,15-EET in mouse lung is significantly attenuated by pharmacologic blockade of IK and SK3, but not BK, channels. Collectively, this functional coupling suggests that endothelial TRPV4 channels in rodent lung likely form signaling microdomains with IK and SK3 channels and that the integrated response dictates the extent of lung endothelial injury caused by 14,15-EET.

Viral-induced CD28 loss evokes costimulation independent alloimmunity

BACKGROUND

Belatacept, a B7-specific fusion protein, blocks CD28-B7 costimulation and prevents kidney allograft rejection. However, it is ineffective in a sizable minority of patients. Although T-cell receptor and CD28 engagement are known to initiate T-cell activation, many human antigen-experienced T-cells lose CD28, and can be activated independent of CD28 signals. We posit that these cells are central drivers of costimulation blockade resistant rejection (CoBRR) and propose that CoBRR might relate to an accumulation of CD28(-) T-cells resulting from viral antigen exposure.

MATERIALS AND METHODS

We infected C57BL/6 mice with polyomavirus (a BK virus analog), murine cytomegalovirus (a human cytomegalovirus analog), and gammaherpesvirus (HV68; an Epstein-Barr virus analog) and assessed for CD28 expression relative to mock infection controls. We then used mixed lymphocyte reaction (MLR) assays to assess the alloreactive response of these mice against major histocompatibility complex-mismatched cells.

RESULTS

We demonstrated that infection with polyomavirus, murine CMV, and HV68 can induce CD28 downregulation in mice. We showed that these analogs of clinically relevant human viruses enable lymphocytes from infected mice to launch an anamnestic, costimulation blockade resistant, alloreactive response against major histocompatibility complex-mismatched cells without prior alloantigen exposure. Further analysis revealed that gammherpesvirus-induced oligoclonal T-cell expansion is required for the increased alloreactivity.

CONCLUSIONS

Virus exposure results in reduced T-cell expression of CD28, the target of costimulation blockade therapy. These viruses also contribute to increased alloreactivity. Thus, CD28 downregulation after viral infection may play a seminal role in driving CoBRR.

BK channel activators and their therapeutic perspectives

The large conductance calcium- and voltage-activated K⁺ channel (KCa1.1, BK, MaxiK) is ubiquitously expressed in the body, and holds the ability to integrate changes in intracellular calcium and membrane potential. This makes the BK channel an important negative feedback system linking increases in intracellular calcium to outward hyperpolarizing potassium currents. Consequently, the channel has many important physiological roles including regulation of smooth muscle tone, neurotransmitter release and neuronal excitability. Additionally, cardioprotective roles have been revealed in recent years. After a short introduction to the structure, function and regulation of BK channels, we review the small organic molecules activating BK channels and how these tool compounds have helped delineate the roles of BK channels in health and disease.

The role of the BK channel in ethanol response behaviors: evidence from model organism and human studies

Alcohol abuse is a significant public health problem. Understanding the molecular effects of ethanol is important for the identification of at risk individuals, as well as the development of novel pharmacotherapies. The large conductance calcium sensitive potassium (BK) channel has emerged as an important player in the behavioral response to ethanol in genetic studies in several model organisms and in humans. The BK channel, slo-1, was identified in a forward genetics screen as a major ethanol target in C. elegans for the effects of ethanol on locomotion and egg-laying behaviors. Regulation of the expression of the BK channel, slo, in Drosophila underlies the development of rapid tolerance to ethanol and benzyl alcohol sedation. Rodent expression studies of the BK-encoding KCNMA1 gene have identified regulation of mRNA levels in response to ethanol exposure, and knock out studies in mice have demonstrated that the β subunits of the BK channel, β1 and β4, can modulate ethanol sensitivity of the channel in electrophysiological preparations, and can influence drinking behavior. In human genetics studies, both KCNMA1 and the genes encoding β subunits of the BK channel have been associated with alcohol dependence. This review describes the genetic data for a role for BK channels in mediating behavioral responses to ethanol across these species.

Host cell autophagy promotes BK virus infection

Autophagy is important for a variety for virus life cycles. We sought to determine the role of autophagy in human BK polyomavirus (BKPyV) infection. The addition excess amino acids during viral infection reduced BKPyV infection. Perturbing autophagy levels using inhibitors, 3-MA, bafilomycin A1, and spautin-1, also reduced infection, while rapamycin treatment of host cells increased infection. siRNA knockdown of autophagy genes, ATG7 and Beclin-1, corresponded to a decrease in BKPyV infection. BKPyV infection not only correlated with autophagosome formation, but also virus particles localized to autophagy-specific compartments early in infection. These data support a novel role for autophagy in the promotion of BKPyV infection.

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Amino acid supplementation decreases BKPyV infection.

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Autophagy inhibitors, 3-MA, bafilomycin A, and spautin-1, decrease BKPyV infection, while rapamycin increases infection.

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Inhibitors are most effective when added early in viral life cycle.

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Knockdown of autophagy genes, Beclin-1 and ATG7, in host cells decreases BKPyV infection levels.

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BKPyV localizes to LC3+ autophagosome 3 h post infection.

Regulation of renal potassium secretion: molecular mechanisms

A new understanding of renal potassium balance has emerged as the molecular underpinnings of potassium secretion have become illuminated, highlighting the key roles of apical potassium channels, renal outer medullary potassium channel (ROMK) and Big Potassium (BK), in the aldosterone-sensitive distal nephron and collecting duct. These channels act as the final-regulated components of the renal potassium secretory machinery. Their activity, number, and driving forces are precisely modulated to ensure potassium excretion matches dietary potassium intake. Recent identification of the underlying regulatory mechanisms at the molecular level provides a new appreciation of the physiology and reveals a molecular insight to explain the paradoxic actions of aldosterone on potassium secretion. Here, we review the current state of knowledge in the field.

Tissue kallikrein mediates neurite outgrowth through epidermal growth factor receptor and flotillin-2 pathway in vitro

Tissue kallikrein (TK) was previously shown to take most of its biological effects through bradykinin receptors. In this study, we assumed that TK mediated neurite outgrowth was independent of bradykinin receptors. To test the hypothesis, we investigated TK-induced neurite outgrowth and its signaling mechanisms in cultured primary neurons and human SH-SY5Y cells. We found that TK stimulation could increase the number of processes and mean process length of primary neurons, which were blocked by epidermal growth factor receptor (EGFR) inhibitor or down-regulation, small interfering RNA for flotillin-2 and extracellular signal-regulated kinase (ERK) 1/2 inhibitor. Moreover, TK-induced neurite outgrowth was associated with EGFR and ERK1/2 activation, which were inhibited by EGFR antagonist or RNA interference and flotillin-2 knockdown. Interestingly, inhibition of bradykinin receptors had no significant effects on EGFR and ERK1/2 phosphorylation. In the present research, our data also suggested that EGFR and flotillin-2 formed constitutive complex that translocated to around the nuclei in the TK stimulation. In sum, our findings provided evidence that TK could promote neurite outgrowth via EGFR, flotillin-2 and ERK1/2 signaling pathway in vitro.

Role of integrated cancer nanomedicine in overcoming drug resistance

Cancer remains a major killer of mankind. Failure of conventional chemotherapy has resulted in recurrence and development of virulent multi drug resistant (MDR) phenotypes adding to the complexity and diversity of this deadly disease. Apart from displaying classical physiological abnormalities and aberrant blood flow behavior, MDR cancers exhibit several distinctive features such as higher apoptotic threshold, aerobic glycolysis, regions of hypoxia, and elevated activity of drug-efflux transporters. MDR transporters play a pivotal role in protecting the cancer stem cells (CSCs) from chemotherapy. It is speculated that CSCs are instrumental in reviving tumors after the chemo and radiotherapy. In this regard, multifunctional nanoparticles that can integrate various key components such as drugs, genes, imaging agents and targeting ligands using unique delivery platforms would be more efficient in treating MDR cancers. This review presents some of the important principles involved in development of MDR and novel methods of treating cancers using multifunctional-targeted nanoparticles. Illustrative examples of nanoparticles engineered for drug/gene combination delivery and stimuli responsive nanoparticle systems for cancer therapy are also discussed.

Nongenomic bronchodilating action elicited by dehydroepiandrosterone (DHEA) in a guinea pig asthma model

Primates secrete large amounts of the precursor steroid dehydroepiandrosterone (DHEA); in humans, its levels are low during childhood and start declining after the fourth decade. It has been postulated that the progressive decline in DHEA levels may be related with the severity of asthma associated with age. To determine whether DHEA may regulate the airway smooth muscle (ASM) activity, isolated tracheal rings with and without epithelium from male guinea pigs were isometrically recorded to characterize the response of ASM to DHEA at different concentrations on KCl- and carbachol (CCh)-induced contraction as well as on ovalbumin (OVA)-induced contraction in sensitized guinea pigs. Additionally, we used barometric plethysmography in sensitized guinea pigs in order to compare changes of the lung resistance increased by the antigen challenge to OVA in the absence and presence of different doses of DHEA. DHEA concentration-dependently abolished the contraction to KCl, CCh and OVA, and no differences were found in preparations with and without epithelium. DHEA-induced relaxation was not modified by the suppression of protein synthesis or transcription, pharmacological inhibition of nitric oxide (NO) synthase, nor by antagonist of β2-adrenergic receptors or an inhibitor of the 3β-HSD enzyme. Likewise, Ca(2+)-induced contraction in Ca(2+)-free depolarized tissues was antagonized by DHEA, and the contraction to the L-type voltage-dependent calcium channel activator (Bay K 8644) was inhibited by DHEA. Furthermore, DHEA prevented OVA-induced increases in lung resistance. These results indicate that DHEA-induced relaxation in ASM is a nongenomic (membrane) action and is not produced after its bioconversion. The data suggest that DHEA-induced relaxation is an epithelium- and NO-independent mechanism that involves a blockade of voltage-dependent calcium channels and possible non-selective cation channels.

TRPM7 triggers Ca2+ sparks and invadosome formation in neuroblastoma cells

Cell migration depends on the dynamic formation and turnover of cell adhesions and is tightly controlled by actomyosin contractility and local Ca2+ signals. The divalent cation channel TRPM7 (Transient Receptor Potential cation channel, subfamily Melastatin, member 7) has recently received much attention as a regulator of cell adhesion, migration and (localized) Ca2+ signaling. Overexpression and knockdown of TRPM7 affects actomyosin contractility and the formation of cell adhesions such as invadosomes and focal adhesions, but the role of TRPM7-mediated Ca2+ signals herein is currently not understood. Using Total Internal Reflection Fluorescence (TIRF) Ca2+ fluorometry and a novel automated analysis routine we have addressed the role of Ca2+ in the control of invadosome dynamics in N1E-115 mouse neuroblastoma cells. We find that TRPM7 promotes the formation of highly repetitive and localized Ca2+ microdomains or "Ca2+ sparking hotspots" at the ventral plasma membrane. Ca2+ sparking appears strictly dependent on extracellular Ca2+ and is abolished by TRPM7 channel inhibitors such as waixenicin-A. TRPM7 inhibition also induces invadosome dissolution. However, invadosome formation is (functionally and spatially) dissociated from TRPM7-mediated Ca2+ sparks. Rather, our data indicate that TRPM7 affects actomyosin contractility and invadosome formation independent of Ca2+ influx.

Release of biologically active kinin peptides, Met-Lys-bradykinin and Leu-Met-Lys-bradykinin from human kininogens by two major secreted aspartic proteases of Candida parapsilosis

In terms of infection incidence, the yeast Candida parapsilosis is the second after Candida albicans as causative agent of candidiases in humans. The major virulence factors of C. parapsilosis are secreted aspartic proteases (SAPPs) which help the pathogen to disseminate, acquire nutrients and dysregulate the mechanisms of innate immunity of the host. In the current work we characterized the action of two major extracellular proteases of C. parapsilosis, SAPP1 and SAPP2, on human kininogens, proteinaceous precursors of vasoactive and proinflammatory bradykinin-related peptides, collectively called the kinins. The kininogens, preferably the form with lower molecular mass, were effectively cleaved by SAPPs, with the release of two uncommon kinins, Met-Lys-bradykinin and Leu-Met-Lys-bradykinin. While optimal at acidic pH (4-5), the kinin release yield was only 2-3-fold lower at neutral pH. These peptides were able to interact with cellular kinin receptors of B2 subtype and to stimulate the human endothelial cells HMEC-1 to increased secretion of proinflammatory interleukins (ILs), IL-1β and IL-6. The analysis of the stability of SAPP-generated kinins in plasma suggested that they are biologically equivalent to bradykinin, the best agonist of B2 receptor subtype and can be quickly converted to des-Arg(9)-bradykinin, the agonist of inflammation-inducible B1 receptors.

Proline rich-oligopeptides: diverse mechanisms for antihypertensive action

Bradykinin-potentiating peptides from Bothrops jararaca (Bj) discovered in the early 1960s, were the first natural inhibitors of the angiotensin-converting enzyme (ACE). These peptides belong to a large family of snake venom proline-rich oligopeptides (PROs). One of these peptides, Bj-PRO-9a, was essential for defining ACE as effective drug target and development of captopril, an active site-directed inhibitor of ACE used worldwide for the treatment of human arterial hypertension. Recent experimental evidences demonstrated that cardiovascular effects exerted by different Bj-PROs are due to distinct mechanisms besides of ACE inhibition. In the present work, we have investigated the cardiovascular actions of four Bj-PROs, namely Bj-PRO-9a, -11e, -12b and -13a. Bj-PRO-9a acts upon ACE and BK activities to promote blood pressure reduction. Although the others Bj-PROs are also able to inhibit the ACE activity and to potentiate the BK effects, our results indicate that antihypertensive effect evoked by them involve new mechanisms. Bj-PRO-11e and Bj-PRO-12b involves induction of [Ca(2+)]i transients by so far unknown receptor proteins. Moreover, we have suggested argininosuccinate synthetase and M3 muscarinic receptor as targets for cardiovascular effects elicited by Bj-PRO-13a. In summary, the herein reported results provide evidence that Bj-PRO-mediated effects are not restricted to ACE inhibition or potentiation of BK-induced effects and suggest different actions for each peptide for promoting arterial pressure reduction. The present study reveals the complexity of the effects exerted by Bj-PROs for cardiovascular control, opening avenues for the better understanding of blood pressure regulation and for the development of novel therapeutic approaches.

Membrane microdomain determines the specificity of receptor-mediated modulation of Kv7/M potassium currents

The Kv7/M current is one of the major mechanisms controlling neuronal excitability, which can be modulated by activation of the G protein-coupled receptor (GPCR) via distinct signaling pathways. Membrane microdomains known as lipid rafts have been implicated in the specificity of various cell signaling pathways. The aim of this study was to understand the role of lipid rafts in the specificity of Kv7/M current modulation by activation of GPCR. Methyl-β-cyclodextrin (MβCD), often used to disrupt the integrity of lipid rafts, significantly reduced the bradykinin receptor (B2R)-induced but not muscarinic receptor (M1R)-induced inhibition of the Kv7/M current. B2R and related signaling molecules but not M1R were found in caveolin-containing raft fractions of the rat superior cervical ganglia. Furthermore, activation of B2R resulted in translocation of additional B2R into the lipid rafts, which was not observed for the activation of M1R. The increase of B2R-induced intracellular Ca(2+) was also greatly reduced after MβCD treatment. Finally, B2R but not M1R was found to interact with the IP3 receptor. In conclusion, the present study implicates an important role for lipid rafts in mediating specificity for GPCR-mediated inhibition of the Kv7/M current.

Modeling interactions between voltage-gated Ca (2+) channels and KCa1.1 channels

High voltage-activated (HVA) Cav channels form complexes with KCa1.1 channels, allowing reliable activation of KCa1.1 current through a nanodomain interaction. We recently found that low voltage-activated Cav3 calcium channels also create KCa1.1-Cav3 complexes. While coimmunoprecipitation studies again supported a nanodomain interaction, the sensitivity to calcium chelating agents was instead consistent with a microdomain interaction. A computational model of the KCa1.1-Cav3 complex suggested that multiple Cav3 channels were necessary to activate KCa1.1 channels, potentially causing the KCa1.1-Cav3 complex to be more susceptible to calcium chelators. Here, we expanded the model and compared it to a KCa1.1-Cav2.2 model to examine the role of Cav channel conductance and kinetics on KCa1.1 activation. As found for direct recordings, the voltage-dependent and kinetic properties of Cav3 channels were reflected in the activation of KCa1.1 current, including transient activation from lower voltages than other KCa1.1-Cav complexes. Substantial activation of KCa1.1 channels required the concerted activity of several Cav3.2 channels. Combined with the effect of EGTA, these results suggest that the Ca²⁺ domains of several KCa1.1-Cav3 complexes need to cooperate to generate sufficient [Ca²⁺]_i, despite the physical association between KCa1.1 and Cav3 channels. By comparison, Cav2.2 channels were twice as effective at activating KCa1.1 channels and a single KCa1.1-Cav2.2 complex would be self-sufficient. However, even though Cav3 channels generate small, transient currents, the regulation of KCa1.1 activity by Cav3 channels is possible if multiple complexes cooperate through microdomain interactions.

Endothelial calcium dynamics, connexin channels and blood-brain barrier function

Situated between the circulation and the brain, the blood-brain barrier (BBB) protects the brain from circulating toxins while securing a specialized environment for neuro-glial signaling. BBB capillary endothelial cells exhibit low transcytotic activity and a tight, junctional network that, aided by the cytoskeleton, restricts paracellular permeability. The latter is subject of extensive research as it relates to neuropathology, edema and inflammation. A key determinant in regulating paracellular permeability is the endothelial cytoplasmic Ca(2+) concentration ([Ca(2+)]i) that affects junctional and cytoskeletal proteins. Ca(2+) signals are not one-time events restricted to a single cell but often appear as oscillatory [Ca(2+)]i changes that may propagate between cells as intercellular Ca(2+) waves. The effect of Ca(2+) oscillations/waves on BBB function is largely unknown and we here review current evidence on how [Ca(2+)]i dynamics influence BBB permeability.

Chronic cough and pain: Janus faces in sensory neurobiology?

Both chronic cough and chronic pain are critical clinical issues in which a large number of patients remain unsatisfied with available treatments. These conditions have considerable effects on sufferers' quality of life, who often show co-morbidities such as anxiety and depression. There is therefore a pressing need to find new effective therapies. The basic neurobiological mechanisms and pathologies of these two conditions show substantial homologies. However, whilst chronic pain has received a great deal of attention over the last few decades, the same cannot be said for the neurological underpinnings of chronic cough. There is a substantial literature around mechanisms of chronic pain which is likely to be useful in advancing knowledge about the pathologies of chronic cough. Here we compare the basic pain and cough pathways, in addition to the clinical features and possible pathophysiologies of each; including mechanisms of peripheral and central sensitisation which may underlie symptoms such as hyperalgesia and allodynia, and hypertussitvity and allotussivity. Due to the substantial overlap that emerges, it is likely that therapies may be effective over both areas.

Kinin-B2 receptor exerted neuroprotection after diisopropylfluorophosphate-induced neuronal damage

The kinin-B2 receptor (B2BKR) activated by its endogenous ligand bradykinin participates in various metabolic processes including the control of arterial pressure and inflammation. Recently, functions for this receptor in brain development and protection against glutamate-provoked excitotoxicity have been proposed. Here, we report neuroprotective properties for bradykinin against organophosphate poisoning using acute hippocampal slices as an in vitro model. Following slice perfusion for 10min with diisopropylfluorophosphate (DFP) to initiate the noxious stimulus, responses of pyramidal neurons upon an electric impulse were reduced to less than 30% of control amplitudes. Effects on synaptic-elicited population spikes were reverted when preparations had been exposed to bradykinin 30min after challenging with DFP. Accordingly, bradykinin-induced population spike recovery was abolished by HOE-140, a B2BKR antagonist. However, the kinin-B1 receptor (B1BKR) agonist Lys-des-Arg(9)-bradykinin, inducing the phosphorylation of mitogen-activated protein kinase (MEK/MAPK) and cell death, abolished bradykinin-mediated neuroprotection, an effect, which was reverted by the ERK inhibitor PD98059. In agreement with pivotal B1BKR functions in this process, antagonism of endogenous B1BKR activity alone was enough for restoring population spike activity. On the other hand pralidoxime, an oxime, reactivating acetylcholinesterase (AChE) after organophosphate poisoning, induced population spike recovery after DFP exposure in the presence of bradykinin and Lys-des-Arg(9)-bradykinin. Lys-des-Arg(9)-bradykinin did not revert protection exerted by pralidoxime, however when instead bradykinin and Ly-des-Arg(9)-bradykinin were superfused together, recovery of population spikes diminished. These findings again confirm the neuroprotective feature of bradykinin, which is, diminished by its endogenous metabolites, stimulating the B1BKR, providing a novel understanding of the physiological roles of these receptors.