Cav3.2 deletion attenuates nonalcoholic fatty liver disease in mice

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease and represents the main cause of liver cirrhosis and hepatocellular carcinoma. Cav3.2 is a T-type calcium channel that is widely present in tissues throughout the body and plays a vital role in energy and metabolic balance. However, the effects of Cav3.2 on the NFALD remain unclear. Here, we investigated the role of Cav3.2 channel in the development and progression of NAFLD. After 16 weeks on a high-fat diets (HFD), Cav3.2 knockout (Cav3.2 KO) improved hepatic steatosis, liver injury and metabolic syndrome in an NAFLD mouse model. We provided evidence that Cav3.2 KO inhibited HFD-induced hepatic oxidative stress, inflammation and hepatocyte apoptosis. In addition, Cav3.2 KO also attenuated hepatic lipid accumulation, oxidative stress, inflammation and hepatocyte apoptosis in palmitic acid/oleic acid (PAOA)-treated primary hepatocytes. These results suggest that therapeutic approaches targeting Cav3.2 provide effective approaches for treating NAFLD.

Targeting intrinsically disordered regions facilitates discovery of calcium channels 3.2 inhibitory peptides for adeno-associated virus-mediated peripheral analgesia

ABSTRACT

Ample data support a prominent role of peripheral T-type calcium channels 3.2 (Ca V 3.2) in generating pain states. Development of primary sensory neuron-specific inhibitors of Ca V 3.2 channels is an opportunity for achieving effective analgesic therapeutics, but success has been elusive. Small peptides, especially those derived from natural proteins as inhibitory peptide aptamers (iPAs), can produce highly effective and selective blockade of specific nociceptive molecular pathways to reduce pain with minimal off-target effects. In this study, we report the engineering of the potent and selective iPAs of Ca V 3.2 from the intrinsically disordered regions (IDRs) of Ca V 3.2 intracellular segments. Using established prediction algorithms, we localized the IDRs in Ca V 3.2 protein and identified several Ca V 3.2iPA candidates that significantly reduced Ca V 3.2 current in HEK293 cells stably expressing human wide-type Ca V 3.2. Two prototype Ca V 3.2iPAs (iPA1 and iPA2) derived from the IDRs of Ca V 3.2 intracellular loops 2 and 3, respectively, were expressed selectively in the primary sensory neurons of dorsal root ganglia in vivo using recombinant adeno-associated virus (AAV), which produced sustained inhibition of calcium current conducted by Ca V 3.2/T-type channels and significantly attenuated both evoked and spontaneous pain behavior in rats with neuropathic pain after tibial nerve injury. Recordings from dissociated sensory neurons showed that AAV-mediated Ca V 3.2iPA expression suppressed neuronal excitability, suggesting that Ca V 3.2iPA treatment attenuated pain by reversal of injury-induced neuronal hypersensitivity. Collectively, our results indicate that Ca V 3.2iPAs are promising analgesic leads that, combined with AAV-mediated delivery in anatomically targeted sensory ganglia, have the potential to be a selective peripheral Ca V 3.2-targeting strategy for clinical treatment of pain.

Evolutionary insights into T-type Ca2+ channel structure, function, and ion selectivity from the Trichoplax adhaerens homologue

The role of T-type calcium channels in animals without nervous systems is unknown. Smith et al. characterize TCa_v3 from Trichoplax adhaerens, finding expression in neurosecretory-like cells and preference for Ca²⁺ over Na⁺ via strong extracellular Ca²⁺ block, despite low selectivity for Ca²⁺ in the pore.

Four-domain voltage-gated Ca²⁺ (Ca_v) channels play fundamental roles in the nervous system, but little is known about when or how their unique properties and cellular roles evolved. Of the three types of metazoan Ca_v channels, Ca_v1 (L-type), Ca_v2 (P/Q-, N- and R-type) and Ca_v3 (T-type), Ca_v3 channels are optimized for regulating cellular excitability because of their fast kinetics and low activation voltages. These same properties permit Ca_v3 channels to drive low-threshold exocytosis in select neurons and neurosecretory cells. Here, we characterize the single T-type calcium channel from Trichoplax adhaerens (TCa_v3), an early diverging animal that lacks muscle, neurons, and synapses. Co-immunolocalization using antibodies against TCa_v3 and neurosecretory cell marker complexin labeled gland cells, which are hypothesized to play roles in paracrine signaling. Cloning and in vitro expression of TCa_v3 reveals that, despite roughly 600 million years of divergence from other T-type channels, it bears the defining structural and biophysical features of the Ca_v3 family. We also characterize the channel’s cation permeation properties and find that its pore is less selective for Ca²⁺ over Na⁺ compared with the human homologue Ca_v3.1, yet it exhibits a similar potent block of inward Na⁺ current by low external Ca²⁺ concentrations (i.e., the Ca²⁺ block effect). A comparison of the permeability features of TCa_v3 with other cloned channels suggests that Ca²⁺ block is a locus of evolutionary change in T-type channel cation permeation properties and that mammalian channels distinguish themselves from invertebrate ones by bearing both stronger Ca²⁺ block and higher Ca²⁺ selectivity. TCa_v3 is the most divergent metazoan T-type calcium channel and thus provides an evolutionary perspective on Ca_v3 channel structure–function properties, ion selectivity, and cellular physiology.

Inhibitory peptidergic modulation of C. elegans serotonin neurons is gated by T-type calcium channels

Serotonin is an evolutionarily ancient molecule that functions in generating and modulating many behavioral states. Although much is known about how serotonin acts on its cellular targets, how serotonin release is regulated in vivo remains poorly understood. In the nematode C. elegans, serotonin neurons that drive female reproductive behavior are directly modulated by inhibitory neuropeptides. Here, we report the isolation of mutants in which inhibitory neuropeptides fail to properly modulate serotonin neurons and the behavior they mediate. The corresponding mutations affect the T-type calcium channel CCA-1 and symmetrically re-tune its voltage-dependencies of activation and inactivation towards more hyperpolarized potentials. This shift in voltage dependency strongly and specifically bypasses the behavioral and cell physiological effects of peptidergic inhibition on serotonin neurons. Our results indicate that T-type calcium channels are critical regulators of a C. elegans serotonergic circuit and demonstrate a mechanism in which T-type channels functionally gate inhibitory modulation in vivo.

Role of T-type channels in vasomotor function: team player or chameleon?

Low-voltage-activated T-type calcium channels play an important role in regulating cellular excitability and are implicated in conditions, such as epilepsy and neuropathic pain. T-type channels, especially Cav3.1 and Cav3.2, are also expressed in the vasculature, although patch clamp studies of isolated vascular smooth muscle cells have in general failed to demonstrate these low-voltage-activated calcium currents. By contrast, the channels which are blocked by T-type channel antagonists are high-voltage activated but distinguishable from their L-type counterparts by their T-type biophysical properties and small negative shifts in activation and inactivation voltages. These changes in T-channel properties may result from vascular-specific expression of splice variants of Cav3 genes, particularly in exon 25/26 of the III-IV linker region. Recent physiological studies suggest that T-type channels make a small contribution to vascular tone at low intraluminal pressures, although the relevance of this contribution is unclear. By contrast, these channels play a larger role in vascular tone of small arterioles, which would be expected to function at lower intra-vascular pressures. Upregulation of T-type channel function following decrease in nitric oxide bioavailability and increase in oxidative stress, which occurs during cardiovascular disease, suggests that a more important role could be played by these channels in pathophysiological situations. The ability of T-type channels to be rapidly recruited to the plasma membrane, coupled with their subtype-specific localisation in signalling microdomains where they could modulate the function of calcium-dependent ion channels and pathways, provides a mechanism for rapid up- and downregulation of vasoconstriction. Future investigation into the molecules which govern these changes may illuminate novel targets for the treatment of conditions such as therapy-resistant hypertension and vasospasm.

T-type Ca2+ channels in normal and abnormal brain functions

Low-voltage-activated T-type Ca(2+) channels are widely expressed in various types of neurons. Once deinactivated by hyperpolarization, T-type channels are ready to be activated by a small depolarization near the resting membrane potential and, therefore, are optimal for regulating the excitability and electroresponsiveness of neurons under physiological conditions near resting states. Ca(2+) influx through T-type channels engenders low-threshold Ca(2+) spikes, which in turn trigger a burst of action potentials. Low-threshold burst firing has been implicated in the synchronization of the thalamocortical circuit during sleep and in absence seizures. It also has been suggested that T-type channels play an important role in pain signal transmission, based on their abundant expression in pain-processing pathways in peripheral and central neurons. In this review, we will describe studies on the role of T-type Ca(2+) channels in the physiological as well as pathological generation of brain rhythms in sleep, absence epilepsy, and pain signal transmission. Recent advances in studies of T-type channels in the control of cognition will also be briefly discussed.

The many faces of T-type calcium channels

Since the discovery of low-voltage-activated T-type calcium channels in sensory neurons and the initial characterization of their physiological function mainly in inferior olive and thalamic neurons, studies on neuronal T-type currents have predominantly focused on the generation of low-threshold spike (and associated action potential burst firing) which is strictly conditioned by a preceding hyperpolarization. This T-type current mediated activity has become an archetype of the function of these channels, constraining our view of the potential physiological and pathological roles that they may play in controlling the excitability of single cells and neural networks. However, greatly helped by the recent availability of the first potent and selective antagonists for this class of calcium channels, novel T-type current functions are rapidly being uncovered, including their surprising involvement in neuronal excitability at depolarized membrane potentials and their complex control of dendritic integration and neurotransmitter release. These and other data summarized in this short review clearly indicate a much wider physiological involvement of T-type channels in neuronal activity than previously expected.

T-type Ca²⁺ channels in absence epilepsy

Low-voltage-activated T-type Ca²⁺ channels are highly expressed in the thalamocortical circuit, suggesting that they play a role in this brain circuit. Indeed, low-threshold burst firing mediated by T-type Ca²⁺ channels has long been implicated in the synchronization of the thalamocortical circuit. Over the past few decades, the conventional view has been that rhythmic burst firing mediated by T-type channels in both thalamic reticular nuclie (TRN) and thalamocortical (TC) neurons are equally critical in the generation of thalamocortical oscillations during sleep rhythms and spike-wave-discharges (SWDs). This review broadly investigates recent studies indicating that even though both TRN and TC nuclei are required for thalamocortical oscillations, the contributions of T-type channels to TRN and TC neurons are not equal in the genesis of sleep spindles and SWDs. T-type channels in TC neurons are an essential component of SWD generation, whereas the requirement for TRN T-type channels in SWD generation remains controversial at least in the GBL model of absence seizures. Therefore, a deeper understanding of the functional consequences of modulating each T-type channel subtype could guide the development of therapeutic tools for absence seizures while minimizing side effects on physiological thalamocortical oscillations. This article is part of a Special Issue entitled: Calcium channels.

Expression of CaV3.2 T-type Ca²⁺ channels in a subpopulation of retinal type-3 cone bipolar cells

Retinal bipolar cells and ganglion cells are known to possess voltage-gated T-type Ca(2+) channels. Previous electrophysiological recording studies suggested that there is differential expression of different T-type Ca(2+) channel α1 subunits among bipolar cells. The detailed expression patterns of the individual T-type Ca(2+) channel subunits in the retina, however, remain unknown. In this study, we examined the expression of the Ca(V)3.2 Ca(2+) channel α1 subunit in the mouse retina using immunohistochemical analysis and patch-clamp recordings together with a Ca(V)3.2 knock out (KO) mouse line. The specificity of a Ca(V)3.2 Ca(2+) channel antibody was first confirmed in recombinant T-type Ca(2+) channels expressed in human embryonic kidney (HEK) cells and in Ca(V)3.2 KO mice. Our immunohistochemical analysis indicates that the Ca(V)3.2 antibody labels a subgroup of type-3 cone bipolar cells (CBCs), the PKAβII-immunopositive type-3 CBCs. The labeling was observed throughout the cell including dendrites and axon terminals. Our patch-clamp recording results further demonstrate that Ca(V)3.2 Ca(2+) channels contribute to the T-type Ca(2+) current in a subpopulation of type-3 CBCs. The findings of this study provide new insights into understanding the functional roles of T-type Ca(2+) channels in retinal processing.

Role of pertussis toxin-sensitive G-protein, K+ channels, and voltage-gated Ca2+ channels in the antinociceptive effect of inosine

Inosine is the first metabolite of adenosine. It exerts an antinociceptive effect by activating the adenosine A(1) and A(2A) receptors. We have previously demonstrated that inosine exhibits antinociceptive properties in acute and chronic mice models of nociception. The aim of this study was to investigate the involvement of pertussis toxin-sensitive G-protein-coupled receptors, as well as K(+) and Ca(2+) channels, in the antinociception promoted by inosine in the formalin test. Mice were pretreated with pertussis toxin (2.5 μg/site, i.t., an inactivator of G(i/0) protein); after 7 days, they received inosine (10 mg/kg, i.p.) or morphine (2.5 mg/kg, s.c., used as positive control) immediately before the formalin test. Another group of animals received tetraethylammonium (TEA) or 4-aminopyridine (4-AP) (1 μg/site, i.t., a non-specific voltage-gated K(+) channel blockers), apamin (50 ng/site, i.t., a small conductance Ca(2+)-activated K(+) channel blocker), charybdotoxin (250 pg/site, i.t., a large-conductance Ca(2+)-activated K(+) channel blocker), glibenclamide (100 μg/site, i.t., an ATP-sensitive K(+) channel blocker) or CaCl(2) (200 nmol/site, i.t.). Afterwards, the mice received inosine (10 mg/kg, i.p.), diclofenac (10 mg/kg, i.p., a positive control), or morphine (2.5 mg/kg, s.c., a positive control) immediately before the formalin test. The antinociceptive effect of inosine was reversed by the pre-administration of pertussis toxin (2.5 μg/site, i.t.), TEA, 4-aminopyridine, charybdotoxin, glibenclamide, and CaCl(2), but not apamin. Further, all K(+) channel blockers and CaCl(2) reversed the antinociception induced by diclofenac and morphine, respectively. Taken together, these data suggest that the antinociceptive effect of inosine is mediated, in part, by pertussis toxin-sensitive G-protein coupled receptors and the subsequent activation of voltage gated K(+) channel, large conductance Ca(2+)-activated and ATP-sensitive K(+) channels or inactivation of voltage-gated Ca(2+) channels. Finally, small conductance Ca(2+)-activated K(+) channels are not involved in the antinociceptive effect of inosine.

ZnT-1 enhances the activity and surface expression of T-type calcium channels through activation of Ras-ERK signaling

Zinc transporter-1 (ZnT-1) is a putative zinc transporter that confers cellular resistance from zinc toxicity. In addition, ZnT-1 has important regulatory functions, including inhibition of L-type calcium channels and activation of Raf-1 kinase. Here we studied the effects of ZnT-1 on the expression and function of T-type calcium channels. In Xenopus oocytes expressing voltage-gated calcium channel (CaV) 3.1 or CaV3.2, ZnT-1 enhanced the low-threshold calcium currents ( IcaT) to 182 ± 15 and 167.95 ± 9.27% of control, respectively ( P < 0.005 for both channels). As expected, ZnT-1 also enhanced ERK phosphorylation. Coexpression of ZnT-1 and nonactive Raf-1 blocked the ZnT-1-mediated ERK phosphorylation and abolished the ZnT-1-induced augmentation of IcaT. In mammalian cells (Chinese hamster ovary), coexpression of CaV3.1 and ZnT-1 increased the IcaT to 166.37 ± 6.37% compared with cells expressing CaV3.1 alone ( P < 0.01). Interestingly, surface expression measurements using biotinylation or total internal reflection fluorescence microscopy indicated marked ZnT-1-induced enhancement of CaV3.1 surface expression. The MEK inhibitor PD-98059 abolished the ZnT-1-induced augmentation of surface expression of CaV3.1. In cultured murine cardiomyocytes (HL-1 cells), transient exposure to zinc, leading to enhanced ZnT-1 expression, also enhanced the surface expression of endogenous CaV3.1 channels. Consistently, in these cells, endothelin-1, a potent activator of Ras-ERK signaling, enhanced the surface expression of CaV3.1 channels in a PD-98059-sensitive manner. Our findings indicate that ZnT-1 enhances the activity of CaV3.1 and CaV3.2 through activation of Ras-ERK signaling. The augmentation of CaV3.1 currents by Ras-ERK activation is associated with enhanced trafficking of the channel to the plasma membrane.

Gene transcription and splicing of T-type channels are evolutionarily-conserved strategies for regulating channel expression and gating

T-type calcium channels operate within tightly regulated biophysical constraints for supporting rhythmic firing in the brain, heart and secretory organs of invertebrates and vertebrates. The snail T-type gene, LCa(v)3 from Lymnaea stagnalis, possesses alternative, tandem donor splice sites enabling a choice of a large exon 8b (201 aa) or a short exon 25c (9 aa) in cytoplasmic linkers, similar to mammalian homologs. Inclusion of optional 25c exons in the III-IV linker of T-type channels speeds up kinetics and causes hyperpolarizing shifts in both activation and steady-state inactivation of macroscopic currents. The abundant variant lacking exon 25c is the workhorse of embryonic Ca(v)3 channels, whose high density and right-shifted activation and availability curves are expected to increase pace-making and allow the channels to contribute more significantly to cellular excitation in prenatal tissue. Presence of brain-enriched, optional exon 8b conserved with mammalian Ca(v)3.1 and encompassing the proximal half of the I-II linker, imparts a ~50% reduction in total and surface-expressed LCa(v)3 channel protein, which accounts for reduced whole-cell calcium currents of +8b variants in HEK cells. Evolutionarily conserved optional exons in cytoplasmic linkers of Ca(v)3 channels regulate expression (exon 8b) and a battery of biophysical properties (exon 25c) for tuning specialized firing patterns in different tissues and throughout development.

Calcium Channels in the Development, Maturation, and Function of Spermatozoa

A proper dialogue between spermatozoa and the egg is essential for conception of a new individual in sexually reproducing animals. Ca2+ is crucial in orchestrating this unique event leading to a new life. No wonder that nature has devised different Ca2+-permeable channels and located them at distinct sites in spermatozoa so that they can help fertilize the egg. New tools to study sperm ionic currents, and image intracellular Ca2+ with better spatial and temporal resolution even in swimming spermatozoa, are revealing how sperm ion channels participate in fertilization. This review critically examines the involvement of Ca2+ channels in multiple signaling processes needed for spermatozoa to mature, travel towards the egg, and fertilize it. Remarkably, these tiny specialized cells can express exclusive channels like CatSper for Ca2+ and SLO3 for K+, which are attractive targets for contraception and for the discovery of novel signaling complexes. Learning more about fertilization is a matter of capital importance; societies face growing pressure to counteract rising male infertility rates, provide safe male gamete-based contraceptives, and preserve biodiversity through improved captive breeding and assisted conception initiatives.

Regulation and function of Cav3.1 T-type calcium channels in IGF-I-stimulated pulmonary artery smooth muscle cells

Arterial smooth muscle cells enter the cell cycle and proliferate in conditions of disease and injury, leading to adverse vessel remodeling. In the pulmonary vasculature, diverse stimuli cause proliferation of pulmonary artery smooth muscle cells (PASMCs), pulmonary artery remodeling, and the clinical condition of pulmonary hypertension associated with significant health consequences. PASMC proliferation requires extracellular Ca(2+) influx that is intimately linked with intracellular Ca(2+) homeostasis. Among the primary sources of Ca(2+) influx in PASMCs is the low-voltage-activated family of T-type Ca(2+) channels; however, up to now, mechanisms for the action of T-type channels in vascular smooth muscle cell proliferation have not been addressed. The Ca(v)3.1 T-type Ca(2+) channel mRNA is upregulated in cultured PASMCs stimulated to proliferate with insulin-like growth factor-I (IGF-I), and this upregulation depends on phosphatidylinositol 3-kinase/Akt signaling. Multiple stimuli that trigger an acute rise in intracellular Ca(2+) in PASMCs, including IGF-I, also require the expression of Ca(v)3.1 Ca(2+) channels for their action. IGF-I also led to cell cycle initiation and proliferation of PASMCs, and, when expression of the Ca(v)3.1 Ca(2+) channel was knocked down by RNA interference, so were the expression and activation of cyclin D, which are necessary steps for cell cycle progression. These results confirm the importance of T-type Ca(2+) channels in proper progression of the cell cycle in PASMCs stimulated to proliferate by IGF-I and suggest that Ca(2+) entry through Ca(v)3.1 T-type channels in particular interacts with Ca(2+)-dependent steps of the mitogenic signaling cascade as a central component of vascular remodeling in disease.

Calcium channel functions in pain processing

Voltage-gated calcium channels (VGCC) play obligatory physiological roles, including modulation of neuronal: functions, synaptic plasticity, neurotransmitter release and gene transcription. Dysregulation and maladaptive changes in VGCC expression and activities may occur in the sensory pathway under various pathological conditions that could contribute to the development of pain. In this review, we summarized the most recent findings on the regulation of VGCC expression and physiological functions in the sensory pathway, and in dysregulation and maladaptive changes of VGCC under pain-inducing conditions. The implications of: these changes in understanding the mechanisms of pain transduction and in new drug design are also discussed.