Acid-induced off-response of PKD2L1 channel in Xenopus oocytes and its regulation by Ca(2.)

Culture of cerebrospinal fluid-contacting neurons from neonatal mouse spinal cord

Cerebrospinal fluid-contacting neurons (CSF-cNs) act crucial role in chemosensory and mechanosensory function in spinal cord. Recently, CSF-cNs were found to be an immature neuron and may be involved in spinal cord injury recovery. But how to culture it and explore its function in vitro are not reported in previous research. Here, we first reported culture and identification of CSF-cNs in vitro. We first established a protocol for in vitro culture of CSF-cNs from the cervical spinal cord of mice within 24 h after birth. Polycystic kidney disease 2-like 1 (PKD2L1)+ cells were isolated by fluorescence-activated cell sorting and expressed the neuron marker β-tubulin III and CSF-cNs marker GABA. Intriguingly, PKD2L1+ cells formed neurosphere and expressed neural stem cell markers Nestin, Sox2 and GFAP. Thus, our research provided culture and isolation of CSF-cNs and this facilitate the investigation the CSF-cNs function in vitro.

Inhibition of TRPP3 by calmodulin through Ca2+/calmodulin-dependent protein kinase II

Transient receptor potential (TRP) polycystin-3 (TRPP3) is a non-selective cation channel activated by Ca2+ and protons and is involved in regulating ciliary Ca2+ concentration, hedgehog signaling and sour tasting. The TRPP3 channel function and regulation are still not well understood. Here we investigated regulation of TRPP3 by calmodulin (CaM) by means of electrophysiology and Xenopus oocytes as an expression model. We found that TRPP3 channel function is enhanced by calmidazolium, a CaM antagonist, and inhibited by CaM through binding of the CaM N-lobe to a TRPP3 C-terminal domain not overlapped with the EF-hand. We further revealed that the TRPP3/CaM interaction promotes phosphorylation of TRPP3 at threonine 591 by Ca2+/CaM-dependent protein kinase II, which mediates the inhibition of TRPP3 by CaM.

Polycystin Channel Complexes

Polycystin subunits can form hetero- and homotetrameric ion channels in the membranes of various compartments of the cell. Homotetrameric polycystin channels are voltage- and calcium-modulated, whereas heterotetrameric versions are proposed to be ligand- or autoproteolytically regulated. Their importance is underscored by variants associated with autosomal dominant polycystic kidney disease and by vital roles in fertilization and embryonic development. The diversity in polycystin assembly and subcellular distribution allows for a multitude of sensory functions by this class of channels. In this review, we highlight their recent structural and functional characterization, which has provided a molecular blueprint to investigate the conformational changes required for channel opening in response to unique stimuli. We consider each polycystin channel type individually, discussing how they contribute to sensory cell biology, as well as their impact on the physiology of various tissues.

Enhanced β-adrenergic response in mice with dominant-negative expression of the PKD2L1 channel

Polycystic kidney disease (PKD) is the most common genetic cause of kidney failure in humans. Among the various PKD-related molecules, PKD2L1 forms cation channels, but its physiological importance is obscure. In the present study, we established a transgenic mouse line by overexpressing the dominant-negative form of the mouse PKD2L1 gene (i.e., lacking the pore-forming domain). The resulting PKD2L1del-Tg mice exhibited supraventricular premature contraction, as well as enhanced sensitivity to β-adrenergic stimulation and unstable R-R intervals in electrocardiography. During spontaneous atrial contraction, PKD2L1del-Tg atria showed enhanced sensitivity to isoproterenol, norepinephrine, and epinephrine. Action potential recording revealed a shortened action potential duration in PKD2L1del-Tg atria in response to isoproterenol. These findings indicated increased adrenergic sensitivity in PKD2L1del-Tg mice, suggesting that PKD2L1 is involved in sympathetic regulation.

Structural basis for Ca2+ activation of the heteromeric PKD1L3/PKD2L1 channel

The heteromeric complex between PKD1L3, a member of the polycystic kidney disease (PKD) protein family, and PKD2L1, also known as TRPP2 or TRPP3, has been a prototype for mechanistic characterization of heterotetrametric TRP-like channels. Here we show that a truncated PKD1L3/PKD2L1 complex with the C-terminal TRP-fold fragment of PKD1L3 retains both Ca²⁺ and acid-induced channel activities. Cryo-EM structures of this core heterocomplex with or without supplemented Ca²⁺ were determined at resolutions of 3.1 Å and 3.4 Å, respectively. The heterotetramer, with a pseudo-symmetric TRP architecture of 1:3 stoichiometry, has an asymmetric selectivity filter (SF) guarded by Lys2069 from PKD1L3 and Asp523 from the three PKD2L1 subunits. Ca²⁺-entrance to the SF vestibule is accompanied by a swing motion of Lys2069 on PKD1L3. The S6 of PKD1L3 is pushed inward by the S4-S5 linker of the nearby PKD2L1 (PKD2L1-III), resulting in an elongated intracellular gate which seals the pore domain. Comparison of the apo and Ca²⁺-loaded complexes unveils an unprecedented Ca²⁺ binding site in the extracellular cleft of the voltage-sensing domain (VSD) of PKD2L1-III, but not the other three VSDs. Structure-guided mutagenic studies support this unconventional site to be responsible for Ca²⁺-induced channel activation through an allosteric mechanism.

Hydrophobic pore gates regulate ion permeation in polycystic kidney disease 2 and 2L1 channels

PKD2 and PKD1 genes are mutated in human autosomal dominant polycystic kidney disease. PKD2 can form either a homomeric cation channel or a heteromeric complex with the PKD1 receptor, presumed to respond to ligand(s) and/or mechanical stimuli. Here, we identify a two-residue hydrophobic gate in PKD2L1, and a single-residue hydrophobic gate in PKD2. We find that a PKD2 gain-of-function gate mutant effectively rescues PKD2 knockdown-induced phenotypes in embryonic zebrafish. The structure of a PKD2 activating mutant F604P by cryo-electron microscopy reveals a π- to α-helix transition within the pore-lining helix S6 that leads to repositioning of the gate residue and channel activation. Overall the results identify hydrophobic gates and a gating mechanism of PKD2 and PKD2L1.

Mutations in the cation channel PKD2 cause human autosomal dominant polycystic kidney disease but its channel function and gating mechanism are poorly understood. Here authors study PKD2 using electrophysiology and cryo-EM, which identifies hydrophobic gates and proposes a gating mechanism for PKD2.

Translational profiling of dorsal root ganglia and spinal cord in a mouse model of neuropathic pain

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Translational landscape in DRG and spinal cord in SNI assay of neuropathic pain was established.

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ERK is a central hub of both transcriptionally and translationally controlled genes.

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Changes in translation efficiency and mRNA levels occur in the opposite direction for multiple mRNAs.

Acute pain serves as a protective mechanism, guiding the organism away from actual or potential tissue injury. In contrast, chronic pain is a debilitating condition without any obvious physiological function. The transition to, and the maintenance of chronic pain require new gene expression to support biochemical and structural changes within the pain pathway. The regulation of gene expression at the level of mRNA translation has emerged as an important step in the control of protein expression in the cell. Recent studies show that signaling pathways upstream of mRNA translation, such as mTORC1 and ERK, are upregulated in chronic pain conditions, and their inhibition effectively alleviates pain in several animal models. Despite this progress, mRNAs whose translation is altered in chronic pain conditions remain largely unknown. Here, we performed genome-wide translational profiling of dorsal root ganglion (DRG) and spinal cord dorsal horn tissues in a mouse model of neuropathic pain, spared nerve injury (SNI), using the ribosome profiling technique. We identified distinct subsets of mRNAs that are differentially translated in response to nerve injury in both tissues. We discovered key converging upstream regulators and pathways linked to mRNA translational control and neuropathic pain. Our data are crucial for the understanding of mechanisms by which mRNA translation promotes persistent hypersensitivity after nerve injury.

A biomimetic bioelectronic tongue: A switch for On- and Off- response of acid sensations

The perception of sour taste in mammals is important for its basic modality properties and avoiding toxic substances. We explore a biomimetic bioelectronic tongue, which integrate MEA (microelectrode array) and taste receptor cell for acid detection as a switch. However, the acid-sensing mechanism and coding of the taste receptor cells in the periphery is not well understood, with long-standing debate. Therefore, we firstly construct a Hodgkin-Huxley type mathematical model of whole-cell acid-sensing taste receptor cells based on the electrophysiologic patch clamp recordings with different acid sensitive receptor expressing and different acidic stimulations. ASICs and PKDL channels are two most promising candidates for acidic sensation. ASICs channels contribute to the On response, and PKDL channels coding the Offset stimulations respectively, which function as a pair for switch. Therefore, with the advantage of effective and noninvasive detection for MEA, a sour taste biosensor based on MEA and taste receptor cells was designed and established to detect sour response from the elementary acid sensitive taste receptor cells during and after stimulus. From simulation and extracelluar potential recordings, we found the biomimetic bioelectronic tongue was acid-sensitive, as acid stimulation pH decrease, the firing frequency significantly increase. Furthermore, this reliable and effective MEA based bioelectronic tongue functioned as a switch for stimulation On and Off. This study provided a powerful platform to recognize sour stimulation and help elucidate the sour taste sensation and coding mechanism.

Regulation of TRPP3 Channel Function by N-terminal Domain Palmitoylation and Phosphorylation

Transient receptor potential polycystin-3 (TRPP3) is a cation channel activated by calcium and proton and is involved in hedgehog signaling, intestinal development, and sour tasting. How TRPP3 channel function is regulated remains poorly understood. By N-terminal truncation mutations, electrophysiology, and Xenopus oocyte expression, we first identified fragment Asp-21-Ser-42 to be functionally important. We then found that deletion mutant Δ1-36 (TRPP3 missing fragment Met-1-Arg-36) has a similar function as wild-type TRPP3, whereas Δ1-38 is functionally dead, suggesting the importance of Val-37 or Cys-38. Further studies found that Cys-38, but not Val-37, is functionally critical. Cys-38 is a predicted site of palmitoylation, and indeed TRPP3 channel activity was inhibited by palmitoylation inhibitor 2-bromopalmitate and rescued by palmitoylation substrate palmitic acid. The TRPP3 N terminus (TRPP3NT, Met-1-Leu-95) localized along the plasma membrane of HEK293 cells but stayed in the cytoplasm with 2-bromopalmitate treatment or C38A mutation, indicating that TRPP3NT anchors to the surface membrane through palmitoylation at Cys-38. By acyl-biotin exchange assays, we showed that TRPP3, but not mutant C38A, is indeed palmitoylated. When putative phosphorylation sites near Cys-38 were mutated to Asp or Glu to mimic phosphorylation, only T39D and T39E reduced TRPP3 function. Furthermore, TRPP3NT displayed double bands in which the upper band was abolished by λ phosphatase treatment or T39A mutation. However, palmitoylation at Cys-38 and phosphorylation at Thr-39 independently regulated TRPP3 channel function, in contrast to previous reports about correlated palmitoylation with a proximate phosphorylation. Palmitoylation at Cys-38 represents a novel mechanism of functional regulation for TRPP3.