Compartment-specific regulation of NaV1.7 in sensory neurons after acute exposure to TNF-α.

Tumor necrosis factor α (TNF-α) is a major pro-inflammatory cytokine, important in many diseases, that sensitizes nociceptors through its action on a variety of ion channels, including voltage-gated sodium (NaV) channels. We show here that TNF-α acutely upregulates sensory neuron excitability and current density of threshold channel NaV1.7. Using electrophysiological recordings and live imaging, we demonstrate that this effect on NaV1.7 is mediated by p38 MAPK and identify serine 110 in the channel's N terminus as the phospho-acceptor site, which triggers NaV1.7 channel insertion into the somatic membrane. We also show that the N terminus of NaV1.7 is sufficient to mediate this effect. Although acute TNF-α treatment increases NaV1.7-carrying vesicle accumulation at axonal endings, we did not observe increased channel insertion into the axonal membrane. These results identify molecular determinants of TNF-α-mediated regulation of NaV1.7 in sensory neurons and demonstrate compartment-specific effects of TNF-α on channel insertion in the neuronal plasma membrane.

One-STAGE Tip Method for TMT-Based Proteomic Analysis of a Minimal Amount of Cells.

Liquid chromatography-tandem mass spectrometry (LC-MS)-based profiling of proteomes with isobaric tag labeling from low-quantity biological and clinical samples, including needle-core biopsies and laser capture microdissection, has been challenging due to the limited amount and sample loss during preparation. To address this problem, we developed OnM (On-Column from Myers et al. and mPOP)-modified on-column method combining freeze-thaw lysis of mPOP with isobaric tag labeling of On-Column method to minimize sample loss. OnM is a method that processes the sample in one-STAGE tip from cell lysis to tandem mass tag (TMT) labeling without any transfer of the sample. In terms of protein coverage, cellular components, and TMT labeling efficiency, the modified On-Column (or OnM) displayed similar performance to the results from Myers et al. To evaluate the lower-limit processing capability of OnM, we utilized OnM for multiplexing and were able to quantify 301 proteins in a TMT 9-plex with 50 cells per channel. We optimized the method as low as 5 cells per channel in which we identified 51 quantifiable proteins. OnM method is a low-input proteomics method widely applicable and capable of identifying and quantifying proteomes from limited samples, with tools that are readily available in a majority of proteomic laboratories.

Phosphorylation states greatly regulate the activity and gating properties of Cav 3.1 T-type Ca2+ channels.

Cav 3.1 T-type Ca2+ channels play pivotal roles in neuronal low-threshold spikes, visceral pain, and pacemaker activity. Phosphorylation has been reported to potently regulate the activity and gating properties of Cav 3.1 channels. However, systematic identification of phosphorylation sites (phosphosites) in Cav 3.1 channel has been poorly investigated. In this work, we analyzed rat Cav 3.1 protein expressed in HEK-293 cells by mass spectrometry, identified 30 phosphosites located at the cytoplasmic regions, and illustrated them as a Cav 3.1 phosphorylation map which includes the reported mouse Cav 3.1 phosphosites. Site-directed mutagenesis of the phosphosites to Ala residues and functional analysis of the phospho-silent Cav 3.1 mutants expressed in Xenopus oocytes showed that the phospho-silent mutation of the N-terminal Ser18 reduced its current amplitude with accelerated current kinetics and negatively shifted channel availability. Remarkably, the phospho-silent mutations of the C-terminal Ser residues (Ser1924, Ser2001, Ser2163, Ser2166, or Ser2189) greatly reduced their current amplitude without altering the voltage-dependent gating properties. In contrast, the phosphomimetic Asp mutations of Cav 3.1 on the N- and C-terminal Ser residues reversed the effects of the phospho-silent mutations. Collectively, these findings demonstrate that the multiple phosphosites of Cav 3.1 at the N- and C-terminal regions play crucial roles in the regulation of the channel activity and voltage-dependent gating properties.

Sites and Regulation of L-Type Ca2+ Channel Cav1.2 Phosphorylation in Brain.

Cav1.2 channel phosphorylation plays an important role in regulating neuronal plasticity by action potential-dependent Ca2+ entry. Most studies of Cav1.2 regulation by phosphorylation have been reported in heart and muscles. Here, we identified phosphorylation sites of neuronal Cav1.2 channel protein purified from rat brain using mass spectrometry. The functional characterization of these phosphorylation sites showed altered voltage-dependent biophysical properties of the channel, without affecting current density. These results show that neuronal Cav1.2 channel is regulated by phosphorylation in a complex mechanism involving multiple phosphorylation sites.

Constitutive Phosphorylation as a Key Regulator of TRPM8 Channel Function.

In mammals, environmental cold sensing conducted by peripheral cold thermoreceptor neurons mostly depends on TRPM8, an ion channel that has evolved to become the main molecular cold transducer. This TRP channel is activated by cold, cooling compounds, such as menthol, voltage, and rises in osmolality. TRPM8 function is regulated by kinase activity that phosphorylates the channel under resting conditions. However, which specific residues, how this post-translational modification modulates TRPM8 activity, and its influence on cold sensing are still poorly understood. By mass spectrometry, we identified four serine residues within the N-terminus (S26, S29, S541, and S542) constitutively phosphorylated in the mouse ortholog. TRPM8 function was examined by Ca2+ imaging and patch-clamp recordings, revealing that treatment with staurosporine, a kinase inhibitor, augmented its cold- and menthol-evoked responses. S29A mutation is sufficient to increase TRPM8 activity, suggesting that phosphorylation of this residue is a central molecular determinant of this negative regulation. Biophysical and total internal reflection fluorescence-based analysis revealed a dual mechanism in the potentiated responses of unphosphorylated TRPM8: a shift in the voltage activation curve toward more negative potentials and an increase in the number of active channels at the plasma membrane. Importantly, basal kinase activity negatively modulates TRPM8 function at cold thermoreceptors from male and female mice, an observation accounted for by mathematical modeling. Overall, our findings suggest that cold temperature detection could be rapidly and reversibly fine-tuned by controlling the TRPM8 basal phosphorylation state, a mechanism that acts as a dynamic molecular brake of this thermo-TRP channel function in primary sensory neurons.SIGNIFICANCE STATEMENT Post-translational modifications are one of the main molecular mechanisms involved in adjusting the sensitivity of sensory ion channels to changing environmental conditions. Here we show, for the first time, that constitutive phosphorylation of the well-conserved serine 29 within the N-terminal domain negatively modulates TRPM8 channel activity, reducing its activation by agonists and decreasing the number of active channels at the plasma membrane. Basal phosphorylation of TRPM8 acts as a key regulator of its function as the main cold-transduction channel, significantly contributing to the net response of primary sensory neurons to temperature reductions. This reversible and dynamic modulatory mechanism opens new opportunities to regulate TRPM8 function in pathologic conditions where this thermo-TRP channel plays a critical role.

TMPRSS11a is a novel age-altered, tissue specific regulator of migration and wound healing.

Aging is a gradual biological process characterized by a decrease in cellular and organism functions. Aging-related processes involve changes in the expression and activity of several proteins. Here, we identified the transmembrane protease serine 11a (TMPRSS11a) as a new age-specific protein that plays an important role in skin wound healing. TMPRSS11a levels increased with age in rodent and human skin and gingival samples. Strikingly, overexpression of TMPRSS11a decreased cell migration and spreading, and inducing cellular senescence. Mass spectrometry, bioinformatics, and functional analyses revealed that TMPRSS11a interacts with integrin ß1 through an RGD sequence contained within the C-terminal domain and that this motif was relevant for cell migration. Moreover, TMPRSS11a was associated with cellular senescence, as shown by overexpression and downregulation experiments. In agreement with tissue-specific expression of TMPRSS11a, shRNA-mediated downregulation of this protein improved wound healing in the skin, but not in the skeletal muscle of old mice, where TMPRSS11a is undetectable. Collectively, these findings indicate that TMPRSS11a is a tissue-specific factor relevant for wound healing, which becomes elevated with aging, promoting cellular senescence and inhibiting cell migration and skin repair.

Comparative Proteomic Analysis of the Mesenchymal Stem Cells Secretome from Adipose, Bone Marrow, Placenta and Wharton's Jelly.

Mesenchymal stem cells (MSCs) have the potential to be a viable therapy against various diseases due to their paracrine effects, such as secretion of immunomodulatory, trophic and protective factors. These cells are known to be distributed within various organs and tissues. Although they possess the same characteristics, MSCs from different sources are believed to have different secretion potentials and patterns, which may influence their therapeutic effects in disease environments. We characterized the protein secretome of adipose (AD), bone marrow (BM), placenta (PL), and Wharton's jelly (WJ)-derived human MSCs by using conditioned media and analyzing the secretome by mass spectrometry and follow-up bioinformatics. Each MSC secretome profile had distinct characteristics depending on the source. However, the functional analyses of the secretome from different sources showed that they share similar characteristics, such as cell migration and negative regulation of programmed cell death, even though differences in the composition of the secretome exist. This study shows that the secretome of fetal-derived MSCs, such as PL and WJ, had a more diverse composition than that of AD and BM-derived MSCs, and it was assumed that their therapeutic potential was greater because of these properties.

Tyrosine Phosphorylation of the Kv2.1 Channel Contributes to Injury in Brain Ischemia.

In brain ischemia, oxidative stress induces neuronal apoptosis, which is mediated by increased activity of the voltage-gated K+ channel Kv2.1 and results in an efflux of intracellular K+. The molecular mechanisms underlying the regulation of Kv2.1 and its activity during brain ischemia are not yet fully understood. Here this study provides evidence that oxidant-induced apoptosis resulting from brain ischemia promotes rapid tyrosine phosphorylation of Kv2.1. When the tyrosine phosphorylation sites Y124, Y686, and Y810 on the Kv2.1 channel are mutated to non-phosphorylatable residues, PARP-1 cleavage levels decrease, indicating suppression of neuronal cell death. The tyrosine residue Y810 on Kv2.1 was a major phosphorylation site. In fact, cells mutated Y810 were more viable in our study than were wild-type cells, suggesting an important role for this site during ischemic neuronal injury. In an animal model, tyrosine phosphorylation of Kv2.1 increased after ischemic brain injury, with an observable sustained increase for at least 2 h after reperfusion. These results demonstrate that tyrosine phosphorylation of the Kv2.1 channel in the brain may play a critical role in regulating neuronal ischemia and is therefore a potential therapeutic target in patients with brain ischemia.

Norquetiapine blocks the human cardiac sodium channel Nav1.5 in a state-dependent manner.

Quetiapine, an atypical antipsychotic drug, is used for the treatment of schizophrenia and acute mania. Although a previous report showed that quetiapine blocked hERG potassium current, quetiapine has been considered relatively safe in terms of cardiovascular side effects. In the present study, we used the whole-cell patch-clamp technique to investigate the effect that quetiapine and its major metabolite norquetiapine can exert on human cardiac sodium channels (hNav1.5). The half-maximal inhibitory concentrations of quetiapine and norquetiapine at a holding potential of -90 mV near the resting potential of cardiomyocytes were 30 and 6 µM, respectively. Norquetiapine as well as quetiapine was preferentially bound in the inactivated state of the hNav1.5 channel. Norquetiapine slowed the recovery from inactivation of hNav1.5 and consequently induced strong use-dependent inhibition. Our results indicate that norquetiapine blocks hNav1.5 current in concentration-, state- and use-dependent manners, suggesting that the blockade of hNav1.5 current by norquetiapine may shorten the cardiac action potential duration and reduce the risk of QT interval prolongation induced by the inhibition of hERG potassium currents.

Common Repository of FBS Proteins (cRFP) To Be Added to a Search Database for Mass Spectrometric Analysis of Cell Secretome.

We propose to use cRFP (common Repository of FBS Proteins) in the MS (mass spectrometry) raw data search of cell secretomes. cRFP is a small supplementary sequence list of highly abundant fetal bovine serum proteins added to the reference database in use. The aim behind using cRFP is to prevent the contaminant FBS proteins from being misidentified as other proteins in the reference database, just as we would use cRAP (common Repository of Adventitious Proteins) to prevent contaminant proteins present either by accident or through unavoidable contacts from being misidentified as other proteins. We expect it to be widely used in experiments where the proteins are obtained from serum-free media after thorough washing of the cells, or from a complex media such as SILAC, or from extracellular vesicles directly.

Protein kinase A-induced phosphorylation at the Thr154 affects stability of DJ-1.

INTRODUCTION: Most cases of Parkinson's disease (PD) are sporadic, but genetic variations have been discovered in PD patients. PARK7/DJ-1 is a known cause of early-onset autosomal-recessive PD and is implicated in neuroprotection against oxidative stress. Although several post-translational modifications of DJ-1 have been proposed, phospho-modification of DJ-1 and its functional consequences have been less studied. METHODS: Putative phosphorylation sites of DJ-1 were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS analysis). Subsequently, phosphorylation site of DJ-1 was confirmed by in vitro kinase assay and cell-based pull-down assay. Impaired dimer formation of phospho-null mutant was measured using DSS crosslinking assay and immunoprecipitation assay. To evaluate physiological consequences of this event, protein stability of DJ-1 WT and DJ-1 phospho-null mutant were compared using cycloheximide chase assay and ubiquitination assay. RESULTS: Here, we showed that DJ-1 directly bound to the catalytic subunit of protein kinase A (PKAcα). We found that PKAcα is responsible for phosphorylation of DJ-1 at the T154 residue. Interestingly, dimerization of DJ-1 was not detected in a DJ-1 T154A mutant. Furthermore, stability of the DJ-1 T154A mutant was dramatically reduced compared with that of wild-type DJ-1. We found that DJ-1 T154A was prone to degradation by the ubiquitin proteasome system (UPS). CONCLUSION: We identified a novel phosphorylation site of DJ-1. Furthermore, we determined protein kinase A that is responsible for this posttranslational modification. Finally, we demonstrated physiological consequences of this event focusing on dimerization and protein stability of DJ-1.

Cell-penetrating artificial mitochondria-targeting peptide-conjugated metallothionein 1A alleviates mitochondrial damage in Parkinson's disease models.

An excess of reactive oxygen species (ROS) relative to the antioxidant capacity causes oxidative stress, which plays a role in the development of Parkinson's disease (PD). Because mitochondria are both sites of ROS generation and targets of ROS damage, the delivery of antioxidants to mitochondria might prevent or alleviate PD. To transduce the antioxidant protein human metallothionein 1A (hMT1A) into mitochondria, we computationally designed a cell-penetrating artificial mitochondria-targeting peptide (CAMP). The recombinant CAMP-conjugated hMT1A fusion protein (CAMP-hMT1A) successfully localized to the mitochondria. Treating a cell culture model of PD with CAMP-hMT1A restored tyrosine hydroxylase expression and mitochondrial activity and reduced ROS production. Furthermore, injection of CAMP-hMT1A into the brain of a mouse model of PD rescued movement impairment and dopaminergic neuronal degeneration. CAMP-hMT1A delivery into mitochondria might be therapeutic against PD by alleviating mitochondrial damage, and we predict that CAMP could be used to deliver other cargo proteins to the mitochondria.

Identification and characterization of site-specific N-glycosylation in the potassium channel Kv3.1b.

The potassium ion channel Kv3.1b is a member of a family of voltage-gated ion channels that are glycosylated in their mature form. In the present study, we demonstrate the impact of N-glycosylation at specific asparagine residues on the trafficking of the Kv3.1b protein. Large quantities of asparagine 229 (N229)-glycosylated Kv3.1b reached the plasma membrane, whereas N220-glycosylated and unglycosylated Kv3.1b were mainly retained in the endoplasmic reticulum (ER). These ER-retained Kv3.1b proteins were susceptible to degradation, when co-expressed with calnexin, whereas Kv3.1b pools located at the plasma membrane were resistant. Mass spectrometry analysis revealed a complex type Hex3 HexNAc4 Fuc1 glycan as the major glycan component of the N229-glycosylated Kv3.1b protein, as opposed to a high-mannose type Man8 GlcNAc2 glycan for N220-glycosylated Kv3.1b. Taken together, these results suggest that trafficking-dependent roles of the Kv3.1b potassium channel are dependent on N229 site-specific glycosylation and N-glycan structure, and operate through a mechanism whereby specific N-glycan structures regulate cell surface expression.

Global analysis of ginsenoside Rg1 protective effects in ß-amyloid-treated neuronal cells.

BACKGROUND: A number of reports have described the protective effects of ginsenoside Rg1 (Rg1) in Alzheimer's disease (AD). However, the protective mechanisms of Rg1 in AD remain elusive. METHODS: To investigate the potential mechanisms of Rg1 in ß-amyloid peptide-treated SH-SY5Y cells, a comparative proteomic analysis was performed using stable isotope labeling with amino acids in cell culture combined with nano-LC-MS/MS. RESULTS: We identified a total of 1,149 proteins in three independent experiments. Forty-nine proteins were significantly altered by Rg1 after exposure of the cells to ß-amyloid peptides. The protein interaction network analysis showed that these altered proteins were clustered in ribosomal proteins, mitochondria, the actin cytoskeleton, and splicing proteins. Among these proteins, mitochondrial proteins containing HSD17B10, AARS2, TOMM40, VDAC1, COX5A, and NDUFA4 were associated with mitochondrial dysfunction in the pathogenesis of AD. CONCLUSION: Our results suggest that mitochondrial proteins may be related to the protective mechanisms of Rg1 in AD.

Potential urine proteomics biomarkers for primary nephrotic syndrome.

BACKGROUND: Nephrotic syndrome (NS) is a nonspecific kidney disorder, commonly caused by minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), and membranous nephropathy (MN). Here we analyzed urinary protein profiles, aiming to discover disease-specific biomarkers of these three common diseases in NS. METHODS: Sixteen urine samples were collected from patients with biopsy-proven NS and healthy controls. After removal of high-abundance proteins, the urinary protein profile was analyzed by LC-MS/MS to generate a discovery set. For validation, ELISA was used to analyze the selected proteins in 61 urine samples. RESULTS: The discovery set included 228 urine proteins, of which 22 proteins were differently expressed in MCD, MN, and FSGS. Among these, C9, CD14, and SERPINA1 were validated by ELISA. All three proteins were elevated in MCD, MN, and FSGS groups compared with in IgA nephropathy and healthy controls. When a regression model was applied, receiver operating characteristic analysis clearly discriminated MCD from the other causative diseases in NS. CONCLUSIONS: We developed a disease-specific protein panel that discriminated between three main causes of NS. Through this pilot study, we suggest that urine proteomics could be a non-invasive and clinically available tool to discriminate MCD from MN and FSGS.

Proteomic analysis reveals that the protective effects of ginsenoside Rb1 are associated with the actin cytoskeleton in ß-amyloid-treated neuronal cells.

BACKGROUND: The ginsenoside Rb1 (Rb1) is the most abundant compound in the root of Panax ginseng. Recent studies have shown that Rb1 has a neuroprotective effect. However, the mechanisms underlying this effect are still unknown. METHODS: We used stable isotope labeling with amino acids in cell culture, combined with quantitative mass spectrometry, to explore a potential protective mechanism of Rb1 in ß-amyloid-treated neuronal cells. RESULTS: A total of 1,231 proteins were commonly identified from three replicate experiments. Among these, 40 proteins were significantly changed in response to Rb1 pretreatment in ß-amyloid-treated neuronal cells. Analysis of the functional enrichments and protein interactions of altered proteins revealed that actin cytoskeleton proteins might be linked to the regulatory mechanisms of Rb1. The CAP1, CAPZB, TOMM40, and DSTN proteins showed potential as molecular target proteins for the functional contribution of Rb1 in Alzheimer's disease (AD). CONCLUSION: Our proteomic data may provide new insights into the protective mechanisms of Rb1 in AD.

TRPM4 Is a Novel Component of the Adhesome Required for Focal Adhesion Disassembly, Migration and Contractility.

Cellular migration and contractility are fundamental processes that are regulated by a variety of concerted mechanisms such as cytoskeleton rearrangements, focal adhesion turnover, and Ca2+ oscillations. TRPM4 is a Ca2+-activated non-selective cationic channel (Ca2+-NSCC) that conducts monovalent but not divalent cations. Here, we used a mass spectrometry-based proteomics approach to identify putative TRPM4-associated proteins. Interestingly, the largest group of these proteins has actin cytoskeleton-related functions, and among these nine are specifically annotated as focal adhesion-related proteins. Consistent with these results, we found that TRPM4 localizes to focal adhesions in cells from different cellular lineages. We show that suppression of TRPM4 in MEFs impacts turnover of focal adhesions, serum-induced Ca2+ influx, focal adhesion kinase (FAK) and Rac activities, and results in reduced cellular spreading, migration and contractile behavior. Finally, we demonstrate that the inhibition of TRPM4 activity alters cellular contractility in vivo, affecting cutaneous wound healing. Together, these findings provide the first evidence, to our knowledge, for a TRP channel specifically localized to focal adhesions, where it performs a central role in modulating cellular migration and contractility.

PTPσ functions as a presynaptic receptor for the glypican-4/LRRTM4 complex and is essential for excitatory synaptic transmission.

Leukocyte common antigen-related receptor protein tyrosine phosphatases--comprising LAR, PTPδ, and PTPσ--are synaptic adhesion molecules that organize synapse development. Here, we identify glypican 4 (GPC-4) as a ligand for PTPσ. GPC-4 showed strong (nanomolar) affinity and heparan sulfate (HS)-dependent interaction with the Ig domains of PTPσ. PTPσ bound only to proteolytically cleaved GPC-4 and formed additional complex with leucine-rich repeat transmembrane protein 4 (LRRTM4) in rat brains. Moreover, single knockdown (KD) of PTPσ, but not LAR, in cultured neurons significantly reduced the synaptogenic activity of LRRTM4, a postsynaptic ligand of GPC-4, in heterologous synapse-formation assays. Finally, PTPσ KD dramatically decreased both the frequency and amplitude of excitatory synaptic transmission. This effect was reversed by wild-type PTPσ, but not by a HS-binding-defective PTPσ mutant. Our results collectively suggest that presynaptic PTPσ, together with GPC-4, acts in a HS-dependent manner to maintain excitatory synapse development and function.

Casein kinase-mediated phosphorylation of serine 839 is necessary for basolateral localization of the Ca²âº-activated non-selective cation channel TRPM4.

Transient receptor potential melastatin-like 4 (TRPM4) is a Ca(2+)-activated non-selective cation channel expressed in a wide range of human tissues. TRPM4 participates in a variety of physiological processes such as T cell activation, myogenic vasoconstriction, and allergic reactions. TRPM4 Ca(2+) sensitivity is enhanced by calmodulin (CaM) and phosphathydilinositol 4, 5-bisphosphate (PI(4,5)P2) binding, as well as, under certain conditions, PKC activation. However, information as to the mechanisms of modulation of this channel remains unknown, including direct identification of phosphorylation sites on TRPM4 and their role in channel features. Here, we use mass-spectrometric-based proteomic approaches (immunoprecipitation and tandem mass spectrometry) to unambiguously identify S839 as a phosphorylation site present on human TRPM4 expressed in a human cell line. Site-directed mutagenesis employing a serine to alanine mutation to eliminate phosphorylation, and a phospho-mimetic aspartate mutation, as well as biochemical and immunocytochemical experiments, revealed a role for S839 phosphorylation in the basolateral expression of TRPM4 channels in epithelial cells. Moreover, we demonstrated that casein kinase 1 (CK1) phosphorylates S839 and is responsible for the basolateral localization of TRPM4.

Quantitative proteomic analysis reveals mitochondrial protein changes in MPP(+)-induced neuronal cells.

Parkinson's disease (PD) is a common neurodegenerative disorder pathologically characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. To further explore potential functional mechanisms of PD, we performed a comparative proteomic analysis using stable isotope labeling with amino acids in cell culture (SILAC) combined with nano-LC tandem mass spectrometry (nano-LC MS). In total, 1740 proteins were identified in MPP(+)-treated SH-SY5Y cells. Our comparative proteomic analysis indicated that a total of 39 proteins were differentially expressed in SH-SY5Y cells responding to MPP(+) treatment. Of these, 14 altered proteins were clustered in the mitochondria, 5 proteins were already reported as related to PD, and the remaining proteins were newly identified in this study. Together, our data further define that the mitochondria play an important role in regulating PD through multiple and complex mechanisms and provide new insights into the functional contribution of mitochondrial proteins in PD.