I-Shing Yu

Impaired Phosphorylation of Na(+)-K(+)-2cl(-) Cotransporter by Oxidative Stress-Responsive Kinase-1 Deficiency Manifests Hypotension and Bartter- Like Syndrome

Na+-K+-2Cl− cotransporters (NKCCs), including NKCC1 and renal-specific NKCC2, and the Na+-Cl− cotransporter (NCC) play pivotal roles in the regulation of blood pressure (BP) and renal NaCl reabsorption. Oxidative stress-responsive kinase-1 (OSR1) is a known upstream regulator of N(K)CCs. We generated and analyzed global and kidney tubule-specific (KSP) OSR1 KO mice to elucidate the physiological role of OSR1 in vivo, particularly on BP and kidney function. Although global OSR1−/− mice were embryonically lethal, OSR1+/− mice had low BP associated with reduced phosphorylated (p) STE20 (sterile 20)/SPS1-related proline/alanine-rich kinase (SPAK) and p-NKCC1 abundance in aortic tissue and attenuated p-NKCC2 abundance with increased total and p-NCC expression in the kidney. KSP-OSR1−/− mice had normal BP and hypercalciuria and maintained significant hypokalemia on a low-K+ diet. KSP-OSR1−/− mice exhibited impaired Na+ reabsorption in the thick ascending loop on a low-Na+ diet accompanied by remarkably decreased expression of p-NKCC2 and a blunted response to furosemide, an NKCC2 inhibitor. The expression of total SPAK and p-SPAK was significantly increased in parallel to that of total NCC and p-NCC despite unchanged total NKCC2 expression. These results suggest that, globally, OSR1 is involved in the regulation of BP and renal tubular Na+ reabsorption mainly via the activation of NKCC1 and NKCC2. In the kidneys, NKCC2 but not NCC is the main target of OSR1 and the reduced p-NKCC2 in KSP-OSR1−/− mice may lead to a Bartter-like syndrome.

Mice Deficient in Collapsin Response Mediator Protein-1 Exhibit Impaired Long-Term Potentiation and Impaired Spatial Learning and Memory

Collapsing response mediator protein-1 (CRMP-1) was initially identified in brain and has been implicated in plexin-dependent neuronal function. The high amino acid sequence identity among the five CRMPs has hindered determination of the functions of each individual CRMP. We generated viable and fertile CRMP-1 knock-out (CRMP-1−/−) mice with no evidence of gross abnormality in the major organs. CRMP-1−/− mice exhibited intense microtubule-associated protein 2 (MAP2) staining in the proximal portion of the dendrites, but reduced and disorganized MAP2 staining in the distal dendrites of hippocampal CA1 pyramidal cells. Immunoreactivity to GAP-43 (growth-associated protein-43) and PSD95 (postsynaptic density-95) (a postsynaptic membrane adherent cytoskeletal protein) was also decreased in the CA1 region of the knock-out mice. These changes were consistent with the mutant mice showing a reduction in long-term potentiation (LTP) in the CA1 region and impaired performance in hippocampal-dependent spatial learning and memory tests. CRMP-1−/− mice showed a normal synapsin I labeling pattern in CA1 and normal paired-pulse facilitation. These findings provide the first evidence suggesting that CRMP-1 may be involved in proper neurite outgrowth in the adult hippocampus and that loss of CRMP-1 may affect LTP maintenance and spatial learning and memory.

Inhibition of miR-146a prevents enterovirus-induced death by restoring the production of type I interferon

There are no antivirals or vaccines available to treat Enterovirus 71 (EV71) infections. Although the type I interferon response, elicited upon virus infection, is critical to establishing host antiviral innate immunity, EV71 fails to induce this response efficiently. Here we provide new insights into potential anti-EV71 therapy by showing that neutralization of EV71-induced miR-146a prevents death in mice by restarting the production of type I interferon. EV71 infection upregulates miR-146a, which targets IRAK1 and TRAF6 involved in TLR signalling and type I interferon production. We further identify AP1 as being responsible for the EV71-induced expression of miR-146a. Surprisingly, knocking out miR-146a or neutralizing virus-induced miR-146a by specific antagomiR restores expressions of IRAK1 and TRAF6, augments IFNβ production, inhibits viral propagation and improves survival in the mouse model. Our results suggest that enterovirus-induced miR-146a facilitates viral pathogenesis by suppressing IFN production and provide a clue to developing preventive and therapeutic strategies for enterovirus infections.

The Expression Level of Septin12 Is Critical for Spermiogenesis

Septins belong to a family of polymerizing GTP-binding proteins that are required for many cellular functions, such as membrane compartmentalization, vesicular trafficking, mitosis, and cytoskeletal remodeling. One family member, septin12, is expressed specifically in the testis. In this study, we found septin12 expressed in multiple subcellular compartments during terminal differentiation of mouse germ cells. In humans, the testicular tissues of men with either hypospermatogenesis or maturation arrest had lower levels of SEPTIN12 transcripts than normal men. In addition, increased numbers of spermatozoa with abnormal head, neck, and tail morphologies lacked SEPT12 immunostaining signals, as compared with normal spermatozoa. To elucidate the role of septin12, we generated 129 embryonic stem cells containing a septin12 mutant allele with a deletion in the exons that encode the N-terminal GTP-binding domain. Most chimeras derived from the targeted embryonic stem cells were infertile, and the few fertile chimeras only produced offspring with a C57BL/6 background. Semen analysis of the infertile chimeras showed a decreased sperm count, decreased sperm motility, and spermatozoa with defects involving all subcellular compartments. The testicular phenotypes included maturation arrest of germ cells at the spermatid stage, sloughing of round spermatids, and increased apoptosis of germ cells. Electron microscopic examination of spermatozoa showed misshapen nuclei, disorganized mitochondria, and broken acrosomes. Our data indicate that Septin12 expression levels are critical for mammalian spermiogenesis.

Severe metabolic acidosis causes early lethality in NBC1 W516X knock-in mice as a model of human isolated proximal renal tubular acidosis

We have identified a novel homozygous nonsense mutation (W516X) in the kidney-type electrogenic sodium bicarbonate cotransporter 1 (NBC1) in a patient with isolated proximal renal tubular acidosis (pRTA). To specifically address the pathogenesis of this mutation, we created NBC1 W516X knock-in mice to match the patients abnormalities. The expression of NBC1 mRNA and protein in the kidneys of NBC1(W516X/W516X) mice were virtually absent, indicating that nonsense-mediated mRNA decay (NMD) is involved in the defective transcription and translation of this mutation. These mice not only recapitulated the phenotypes of this patient with growth retardation, pRTA, and ocular abnormalities, but also showed anemia, volume depletion, prerenal azotemia, and several organ abnormalities, culminating in dehydration and renal failure with early lethality before weaning. In isolated renal proximal tubules, both NBC1 activity and the rate of bicarbonate absorption were markedly reduced. Unexpectedly, there was no compensatory increase in mRNA of distal acid/base transporters. Sodium bicarbonate but not saline administration to these mutant mice markedly prolonged their survival, decreased their protein catabolism and attenuated organ abnormalities. The prolonged survival time uncovered the development of corneal opacities due to corneal edema. Thus, NBC1(W516X/W516X) mice with pRTA represent an animal model for metabolic acidosis and may be useful for testing therapeutic inhibition of NMD in vivo.

Generation and analysis of the thiazide-sensitive Na+ -Cl- cotransporter (Ncc/Slc12a3) Ser707X knockin mouse as a model of Gitelman syndrome.

Gitelman syndrome (GS) is characterized by salt‐losing hypotension, hypomagnesemia, hypokalemic metabolic alkalosis, and hypocalciuria. To better model human GS caused by a specific mutation in the thiazide‐sensitive Na+‐Cl− cotransporter (NCC) gene SLC12A3, we generated a nonsense Ncc Ser707X knockin mouse corresponding to human p.Ser710X (c.2135C>A), a recurrent mutation with severe phenotypes in Chinese GS patients. Compared with wild‐type or heterozygous littermates, homozygous (Hom) knockin mice fully recapitulated the phenotype of human GS. The markedly reduced Ncc mRNA and virtually absent Ncc protein expression in kidneys of Hom mice was primarily due to nonsense‐mediated mRNA decay (NMD) surveillance mechanisms. Expression of epithelial Na+ channel (Enac), Ca2+ channels (Trpv5 and Trpv6), and K+ channels (Romk1 and maxi‐K) were significantly increased. Late distal convoluted tubules (DCT) volume was increased and DCT cell ultrastructure appeared intact. High K+ intake could not correct hypokalemia but caused a further increase in maxi‐K but not Romk1 expression. Renal tissue from a patient with GS also showed the enhanced TRPV5 and ROMK1 expression in distal tubules. We suggest that the upregulation of TRPV5/6 and of ROMK1 and Maxi‐K may contribute to hypocalciuria and hypokalemia in Ncc Ser707X knockin mice and human GS, respectively. Hum Mutat 31:1–13, 2010.

Rescue of the genetically engineered Cul4b mutant mouse as a potential model for human X-linked mental retardation

Mutation in CUL4B, which encodes a scaffold protein of the E3 ubiquitin ligase complex, has been found in patients with X-linked mental retardation (XLMR). However, early deletion of Cul4b in mice causes prenatal lethality, which has frustrated attempts to characterize the phenotypes in vivo. In this report, we successfully rescued Cul4b mutant mice by crossing female mice in which exons 4-5 of Cul4b were flanked by loxP sequences with Sox2-Cre male mice. In Cul4b-deficient (Cul4b(Δ)/Y) mice, no CUL4B protein was detected in any of the major organs, including the brain. In the hippocampus, the levels of CUL4A, CUL4B substrates (TOP1, β-catenin, cyclin E and WDR5) and neuronal markers (MAP2, tau-1, GAP-43, PSD95 and syn-1) were not sensitive to Cul4b deletion, whereas the number of parvalbumin (PV)-positive GABAergic interneurons was decreased in Cul4b(Δ)/Y mice, especially in the dentate gyrus (DG). Some dendritic features, including the complexity, diameter and spine density in the CA1 and DG hippocampal neurons, were also affected by Cul4b deletion. Together, the decrease in the number of PV-positive neurons and altered dendritic properties in Cul4b(Δ)/Y mice imply a reduction in inhibitory regulation and dendritic integration in the hippocampal neural circuit, which lead to increased epileptic susceptibility and spatial learning deficits. Our results identify Cul4b(Δ)/Y mice as a potential model for the non-syndromic model of XLMR that replicates the CUL4B-associated MR and is valuable for the development of a therapeutic strategy for treating MR.

Incorporation of the factor IX Padua mutation into FIX-Triple improves clotting activity in vitro and in vivo.

Using gain-of-function factor IX (FIX) for replacement therapy for haemophilia B (HB) is an attractive strategy. We previously reported a high-activity FIX, FIX-Triple (FIX-V86A/E277A/R338A) as a good substitute for FIX-WT (wild-type) in protein replacement therapy, gene therapy, and cell therapy. Here we generated a new recombinant FIX-TripleL (FIX-V86A/E277A/R338L) by replacing the alanine at residue 338 of FIX-Triple with leucine as in FIX-Padua (FIX-R338L). Purified FIX-TripleL exhibited 22-fold higher specific clotting activity and 15-fold increased binding affinity to activated FVIII compared to FIX-WT. FIX-TripleL increased the therapeutic potential of FIX-Triple by nearly 100% as demonstrated with calibrated automated thrombogram and thromboelastography. FIX-TripleL demonstrated a normal clearance rate in HB mice. The clotting activity of FIX-TripleL was consistently 2- to 3-fold higher in these mice than that of FIX-Triple or FIX-R338L. Gene delivery of adeno-associated virus (AAV) in HB mice showed that FIX-TripleL had 15-fold higher specific clotting activity than FIX-WT, and this activity was significantly better than FIX-Triple (10-fold) or FIX-R338L (6-fold). At a lower viral dose, FIX-TripleL improved FIX activity from sub-therapeutic to therapeutic levels. Under physiological conditions, no signs of adverse thrombotic events were observed in long-term AAV-FIX-treated C57Bl/6 mice. Hepatocellular adenomas were observed in the high- but not the medium- or the low-dose AAV-treated mice expressing FIX-WT or FIX-Triple, indicating the advantages of using hyperfunctional FIX variants to reduce viral doses while maintaining therapeutic clotting activity. Thus, incorporation of the FIX Padua mutation significantly improves the clotting function of FIX-Triple so as to optimise protein replacement therapy and gene therapy.

Phosphorylation Regulates NCC Stability and Transporter Activity In Vivo

A T60M mutation in the thiazide-sensitive sodium chloride cotransporter (NCC) is common in patients with Gitelmans syndrome (GS). This mutation prevents Ste20-related proline and alanine-rich kinase (SPAK)/oxidative stress responsive kinase-1 (OSR1)-mediated phosphorylation of NCC and alters NCC transporter activity in vitro. Here, we examined the physiologic effects of NCC phosphorylation in vivo using a novel Ncc T58M (human T60M) knock-in mouse model. Ncc(T58M/T58M) mice exhibited typical features of GS with a blunted response to thiazide diuretics. Despite expressing normal levels of Ncc mRNA, these mice had lower levels of total Ncc and p-Ncc protein that did not change with a low-salt diet that increased p-Spak. In contrast to wild-type Ncc, which localized to the apical membrane of distal convoluted tubule cells, T58M Ncc localized primarily to the cytosolic region and caused an increase in late distal convoluted tubule volume. In MDCK cells, exogenous expression of phosphorylation-defective NCC mutants reduced total protein expression levels and membrane stability. Furthermore, our analysis found diminished total urine NCC excretion in a cohort of GS patients with homozygous NCC T60M mutations. When Wnk4(D561A/+) mice, a model of pseudohypoaldosteronism type II expressing an activated Spak/Osr1-Ncc, were crossed with Ncc(T58M/T58M) mice, total Ncc and p-Ncc protein levels decreased and the GS phenotype persisted over the hypertensive phenotype. Overall, these data suggest that SPAK-mediated phosphorylation of NCC at T60 regulates NCC stability and function, and defective phosphorylation at this residue corrects the phenotype of pseudohypoaldosteronism type II.

Establishment of a Knock-In Mouse Model with the SLC26A4 c.919-2A>G Mutation and Characterization of Its Pathology

Recessive mutations in the SLC26A4 gene are a common cause of hereditary hearing impairment worldwide. Previous studies have demonstrated that different SLC26A4 mutations may have different pathogenetic mechanisms. In the present study, we established a knock-in mouse model (i.e., Slc26a4tm1Dontuh/tm1Dontuh mice) homozygous for the c.919-2A>G mutation, which is a common mutation in East Asians. Mice were then subjected to audiologic assessment, a battery of vestibular evaluations, and inner ear morphological studies. All Slc26a4tm1Dontuh/tm1Dontuh mice revealed profound hearing loss, whereas 46% mice demonstrated pronounced head tilting and circling behaviors. There was a significant difference in the vestibular performance between wild-type and Slc26a4tm1Dontuh/tm1Dontuh mice, especially those exhibiting circling behavior. Inner ear morphological examination of Slc26a4tm1Dontuh/tm1Dontuh mice revealed an enlarged endolymphatic duct, vestibular aqueduct and sac, atrophy of stria vascularis, deformity of otoconia in the vestibular organs, consistent degeneration of cochlear hair cells, and variable degeneration of vestibular hair cells. Audiologic and inner ear morphological features of Slc26a4tm1Dontuh/tm1Dontuh mice were reminiscent of those observed in humans. These features were also similar to those previously reported in both knock-out Slc26a4−/− mice and Slc26a4loop/loop mice with the Slc26a4 p.S408F mutation, albeit the severity of vestibular hair cell degeneration appeared different among the three mouse strains.