Biology subjects

Choi, C.

Publications and source records attributed to Choi, C..

26 records · Page 2Linked to original sources

bioRxiv2020

KCC2 is required for the survival of mature neurons but not for their development

The K+/Cl- co-transporter KCC2 (SLC12A5) allows mature neurons in the CNS to maintain low intracellular Cl- levels that are critical in mediating fast hyperpolarizing synaptic inhibition via type A {gamma}-aminobutyric acid receptors GABAARs. In accordance with this, compromised KCC2 activity results in seizures but whether such deficits directly contribute to the subsequent changes in neuronal viability that lead to epileptogenesis, remains to be assessed. Canonical hyperpolarizing GABAAR currents develop postnatally which reflect a progressive increase in KCC2 expression levels and activity. To investigate the role that KCC2 plays in regulating neuronal viability and architecture we have conditionally ablated KCC2 expression in developing and mature neurons. Decreasing KCC2 expression resulted in the rapid activation of the extrinsic apoptotic pathway, in mature hippocampal neurons. Intriguingly, direct pharmacological inhibition of KCC2 in mature neurons resulted in the rapid activation of the extrinsic apoptotic pathway. In contrast, ablating KCC2 expression in immature neurons had no discernable effects on their subsequent development, arborization or dendritic structure. However ablating KCC2 expression in immature neurons was sufficient to prevent the subsequent postnatal development of hyperpolarizing GABAAR currents. Collectively, our results demonstrate that KCC2 plays a critical role in neuronal survival by limiting apoptosis, and mature neurons are highly sensitive to loss of KCC2 function. In contrast KCC2 appears to play a minimal role in mediating neuronal development or architecture.

neuroscience↗

bioRxiv2020

Isolation and characterization of multi-protein complexes enriched in the K-Cl co-transporter 2 from brain plasma membranes

Kcc2 plays a critical role in determining the efficacy of synaptic inhibition, however, the cellular mechanism neurons use to regulate its membrane trafficking, stability and activity are ill-defined. To address these issues, we used affinity purification to isolate stable multi-protein complexes of Kcc2 from the plasma membrane of murine forebrain. We resolved these using Blue-native polyacrylamide gel electrophoresis (BN-PAGE) coupled to LC-MS/MS. Purified Kcc2 migrated as distinct molecular species of 300, 600 and 800 kDa following BN-PAGE. In excess of 90% coverage of the soluble N and C-termini of Kcc2 was obtained. The 300kDa species largely contained Kcc2, which is consistent with a dimeric quaternary structure for this transporter. Intriguingly, lower levels of Kcc1 were also found in this species suggesting the existence of "mixed" Kcc2/Kcc1 heterodimers. The 600 and 800 kDa species represented stable multi-protein complexes of Kcc2. We identified a set of novel structural, ion transporting and signaling protein interactors, that are present at both excitatory and inhibitory synapses, consistent with the proposed association of Kcc2. These included spectrins, ankyrins, and the IP3 receptor. We also identified interactors more directly associated with phosphorylation; Akap5 and Lmtk3. Finally, we used LC-MS/MS on highly purified endogenous plasma membrane Kcc2 to detect phosphorylation sites. We detected 11 sites with high confidence, including known and novel sites. Collectively our experiments demonstrate that Kcc2 is associated with components of the neuronal cytoskeleton and signaling molecules that may act to regulate transporter membrane trafficking, stability, and activity.

neuroscience↗

bioRxiv2020

Optoacoustic imaging of GLP-1 Receptor with a near-infrared exendin-4 analog

Limitations in current imaging tools have long challenged the imaging of small pancreatic islets in animal models. Here, we report the first development and in vivo validation testing of a broad spectrum and high absorbance near infrared optoacoustic contrast agent, E4x12-Cy7. Our near infrared tracer (E4x12-Cy7) is based on the amino acid sequence of exendin-4 and targets the glucagon-like peptide-1 receptor (GLP-1R). Cell assays confirmed that E4x12-Cy7 has a high binding affinity (IC50 = 4.6 {+/-} 0.8 nM). Using the multi-spectral optoacoustic tomography (MSOT), we imaged E4x12-Cy7 and optoacoustically visualized {beta}-cell insulinoma xenografts in vivo for the first time. In the future, similar optoacoustic tracers that are specific for {beta}-cells and combines optoacoustic and fluorescence imaging modalities could prove to be important tools for monitoring the pancreas for the progression of diabetes.

bioengineering↗

bioRxiv2020

The K-Cl co-transporter 2 is a point of convergence for multiple autism spectrum disorder and epilepsy risk gene products.

KCC2 plays a critical role in determining the efficacy of synaptic inhibition and deficits in its activity lead to epilepsy and neurodevelopmental delay. Here we use unbiased proteomic analyses to demonstrate that KCC2 forms stable protein complexes in the neuronal plasma membrane with 96 autism and/or epilepsy risk gene (ASD/Epi) products including ANKB, ANKG, CNTN1, ITPR1, NCKAP1, SCN2A, SHANK3, SPTAN1, and SPTBN1. Many of these proteins are also targets of Fragile-X mental retardation protein (FMRP), the inactivation of which is the leading monogenic cause of autism. Accordingly, the expression of a subset of these KCC2-binding partners was decreased in Fmr1 knockout mice. Fmr1 knockout compromised KCC2 phosphorylation, a key regulatory mechanism for transporter activity and the postnatal development of GABAergic inhibition. Thus, KCC2 is a point of convergence for multiple ASD/Epi risk genes and therapies targeting this transporter may have broad utility in alleviating these heterogeneous disorders and their associated epilepsies.

neuroscience↗

bioRxiv2019

High-phytate/low-calcium diet is a risk factor for crystal nephropathies, renal phosphate wasting, and bone loss

Phosphate overload contributes to mineral bone disorders associated with crystal nephropathies. Phytate, the major form of phosphorus in plant seeds, is known as an indigestible and negligible in humans. However, the mechanism and adverse effects of high-phytate intake on Ca2+ and phosphate absorption and homeostasis are unknown. Here we show that excessive intake of phytate with a low-Ca2+ diet fed to rats contributed to the development of crystal nephropathies, renal phosphate wasting, and bone loss through tubular dysfunction secondary to dysregulation of intestinal calcium and phosphate absorption. Moreover, Ca2+ supplementation alleviated the detrimental effects of excess dietary phytate on bone and kidney through excretion of undigested Ca2+-phytate, which prevented a vicious cycle of intestinal phosphate overload and renal phosphate wasting while improving intestinal Ca2+ bioavailability. Thus, we demonstrate that phytate is digestible without a high-Ca2+ diet and a risk factor for phosphate overloading and developing crystal nephropathies and bone disease.

physiology↗

bioRxiv2019

Species-specific InDel markers for authentication of the Korean herbs Zanthoxylum schinifolium and Zanthoxylum piperitum

ObjectiveZanthoxylum schinifolium and Zanthoxylum piperitum are the sources of the well-known traditional Korean herbal medicines \"sancho\" (prickly ash) and \"chopi\" (Korean pepper), respectively. Sancho and chopi are often indiscriminately mixed due to the similar appearance of the herbal materials when used as spices and herbal medicines. Moreover, commercial sancho and chopi products often contain adulterants, which could compromise drug efficacy and safety.\n\nMethodsIn this study, we developed hypervariable InDel markers to distinguish between sancho and chopi products by comparing the complete chloroplast genome sequences of four Zanthoxylum species deposited in NCBI GenBank.\n\nResultsComparative analyses of the nucleotide diversity (Pi) of these Zanthoxylum genomes revealed four hypervariable divergent sites (trnH-psbA, psbZ-trnG, trnfM-rps14, and trnF-ndhK) with Pi > 0.025 among 520 windows. Of these four regions, including two genic and two intergenic regions, only psbZ-trnG yielded accurate PCR amplification results between commercial sancho and chopi products from the Korean herbal medicine market. We therefore selected psbZ-trnG, an InDel-variable locus with high discriminatory powers, as a candidate DNA barcode locus.\n\nConclusionThis InDel marker could be used as a valuable, simple, and efficient tool for identifying these medicinal herbs, thereby increasing the safety of these spices and herbal materials in the commercial market.

bioinformatics↗

bioRxiv2018

DUSP28 is a novel biomarker responsible for aggravating malignancy via the autocrine signaling pathways in metastatic pancreatic cancer

Pancreatic cancer remains one of the most dangerous cancers with a grave prognosis. We previously reported that pancreatic cancer cells can secrete dual specificity phosphatise 28 (DUSP28) to the cultured medium. However, its biological function is poorly understood. Here, we have identified the function of DUSP28 in human metastatic pancreatic cancer. Treatment with recombinant DUSP28 (rDUSP28) significantly increased the migration, invasion, and viability of metastatic pancreatic cancer cells through the activation of CREB, AKT, and ERK1/2 signaling pathways. Furthermore, rDUSP28 acted as an oncogenic reagent through the interaction with integrin 1 in metastatic pancreatic cancer cells. In addition, rDUSP28 induced pro-angiogenic effects in human umbilical vein endothelial cells (HUVECs). Administration of rDUSP28 also produced tumor growth in vivo. Notably, sDUSP28 can easily be detected by immunoassay. The results establish the rationale for sDUSP28 as a promising therapeutic target and biomarker for metastatic pancreatic cancer patients.

cancer biology↗

bioRxiv2018

Analysis of the Resuscitation-Availability of Viable-But-Nonculturable Cells of Vibrio parahaemolyticus upon Exposure to the Refrigerator Temperature

Major pathogenic strains of Vibrio parahaemolyticus can enter into the viable-but-nonculturable (VBNC) state when subjected to environmental conditions commonly encountered during food processing. Especially, VBNC cells can be recovered to the culturable state reversibly by removing the causative stress, expressing higher levels of virulence factors. Therefore, the aim of this study was to determine if VBNC V. parahaemolyticus strains retain the resuscitation-availability upon eliminating the adverse condition, followed by the enrichment in developed resuscitation-facilitating buffers. Bacterial cells were shown to enter into the VBNC state in artificial sea water (ASW, pH 6) microcosms at 4{degrees}C within 70 days. VBNC cells were harvested, inoculated in formulated resuscitation-buffers, and then incubated at 25{degrees}C for several days. TSB (pH 8) supplemented with 3% NaCl (TSBA) exhibited the higher resuscitation-availability of VBNC cells. It was also shown that TSBA containing 10,000 U/mg/protein catalase, 2% sodium pyruvate, 20 mM MgSO4, 5 mM ethylenediaminetetraacetic acid (EDTA), and cell free supernatants extracted from the pure cultures of V. parahaemolyticus was more effective in resuscitating VBNC cells of V. parahaemolyticus, showing by 7.69-8.91 log10 CFU/ml.\n\nIMPORTANCEGenerally, higher concentrations ([≤]40%) of NaCl are used for preserving different sorts of food products from bacterial contaminations. However, it was shown from the present study that strains of V. parahaemolyticus were able to persist in maintaining the cellular viability, thereby entering into the VBNC state upon exposure to the refrigerator temperature for 80 days. Hence, the ability of VBNC V. parahaemolyticus to re-enter into the culturable state was examined, using various resuscitation buffers that were formulated in this study. VBNC cells re-gained the culturability successfully when transferred onto the resuscitation-buffer D, and then incubated at 25{degrees}C for several days. Resuscitation-facilitating agent D is consisting of antioxidizing agents, mineral, an emulsifier, and cell free supernatants from the actively growing cells of V. parahaemolyticus. It appeared that such a reversible conversion of VBNC cells to the culturable state would depend on multiple resuscitation-related channels.

microbiology↗