Search for Periodic Time Variations of the Solar

We report a search for time variations of the solar ^{8}B neutrino flux using 5804 live days of Super-Kamiokande data collected between May 31, 1996, and May 30, 2018. Super-Kamiokande measured the precise time of each solar neutrino interaction over 22 calendar years to search for solar neutrino flux modulations with unprecedented precision. Periodic modulations are searched for in a dataset comprising five-day interval solar neutrino flux measurements with a maximum likelihood method. We also applied the Lomb-Scargle method to this dataset to compare it with previous reports. The only significant modulation found is due to the elliptic orbit of the Earth around the Sun. The observed modulation is consistent with astronomical data: we measured an eccentricity of (1.53±0.35)%, and a perihelion shift of (-1.5±13.5) days.

Erratum: Search for Cosmic-Ray Boosted Sub-GeV Dark Matter Using Recoil Protons at Super-Kamiokande [Phys. Rev. Lett. 130, 031802 (2023)].

This corrects the article DOI: 10.1103/PhysRevLett.130.031802.

Search for Cosmic-Ray Boosted Sub-GeV Dark Matter Using Recoil Protons at Super-Kamiokande.

We report a search for cosmic-ray boosted dark matter with protons using the 0.37 megaton×years data collected at Super-Kamiokande experiment during the 1996-2018 period (SKI-IV phase). We searched for an excess of proton recoils above the atmospheric neutrino background from the vicinity of the Galactic Center. No such excess is observed, and limits are calculated for two reference models of dark matter with either a constant interaction cross section or through a scalar mediator. This is the first experimental search for boosted dark matter with hadrons using directional information. The results present the most stringent limits on cosmic-ray boosted dark matter and exclude the dark matter-nucleon elastic scattering cross section between 10^{-33}cm^{2} and 10^{-27}cm^{2} for dark matter mass from 1 MeV/c^{2} to 300 MeV/c^{2}.

Loss of IκBζ Drives Dentin Formation via Altered H3K4me3 Status.

Enforced enrichment of the active promoter marks trimethylation of histone H3 lysine 4 (H3K4me3) and acetylation of histone H3 lysine 27 (H3K27ac) by inhibiting histone demethylases and deacetylases is positively associated with hard tissue formation through the induction of osteo/odontogenic differentiation. However, the key endogenous epigenetic modulator of odontoblasts to regulate the expression of genes coding dentin extracellular matrix (ECM) proteins has not been identified. We focused on nuclear factor (NF)-κB inhibitor ζ (IκBζ), which was originally identified as the transcriptional regulator of NF-κB and recently regarded as the NF-κB-independent epigenetic modulator, and found that IκBζ null mice exhibit a thicker dentin width and narrower pulp chamber, with aged mice having more marked phenotypes. At 6 mo of age, dentin fluorescent labeling revealed significantly accelerated dentin synthesis in the incisors of IκBζ null mice. In the molars of IκBζ null mice, marked tertiary dentin formation adjacent to the pulp horn was observed. Mechanistically, the expression of COL1A2 and COL1A1 collagen genes increased more in the odontoblast-rich fraction of IκBζ null mice than in wild type in vivo, similar to human odontoblast-like cells transfected with small interfering RNA for IκBζ compared with cells transfected with control siRNA in vitro. Furthermore, the direct binding of IκBζ to the COL1A2 promoter suppressed COL1A2 expression and the local active chromatin status marked by H3K4me3. Based on whole-genome identification of H3K4me3 enrichment, ECM and ECM organization-related gene loci were selectively activated by the knockdown of IκBζ, which consistently resulted in the upregulation of these genes. Collectively, this study suggested that IκBζ is the key negative regulator of dentin formation in odontoblasts by inhibiting dentin ECM- and ECM organization-related gene expression through an altered local chromatin status marked by H3K4me3. Therefore, IκBζ is a potential target for epigenetically improving the clinical outcomes of dentin regeneration therapies such as pulp capping.

The use of SPECT/CT to assess resorptive activity in mandibular condyles.

The aim of this study was to clarify the clinical significance of bone metabolism in the mandibular condyles in determining condylar resorptive changes. Twelve condyles of patients with idiopathic condylar resorption and degenerative joint disease were analysed using 99mTc HMDP SPECT/CT at baseline and subsequent computed tomography during the follow-up period. Twenty-two healthy condyles were enrolled as controls. After generating three-dimensional SPECT/CT images, two independent observers scored the degree of condylar uptake and measured the morphological changes in the condylar height and condylar volume. In the group with positive condylar uptake, the follow-up computed tomography showed significant decreases in condylar height (-1.69 ± 0.93 mm) and condylar volume (-12.51 ± 10.30%) when compared to healthy controls (condylar height, 0.09 ± 0.54 mm; condylar volume, -0.29 ± 4.22%) (P < 0.001). Moreover, the degree of uptake correlated with the changes in condylar height (observer 1, P = 0.012; observer 2, P = 0.039) and condylar volume (observer 1, P = 0.005; observer 2, P = 0.037). These results suggest that condylar bone metabolism is closely related to the resorptive activity. Thus, SPECT/CT would be useful in the prognostic evaluation or determination of treatment strategies for idiopathic condylar resorption and degenerative joint disease.

Clinical Outcomes of Post-exposure Prophylaxis following Occupational Exposure to Human Immunodeficiency Virus at Dental Departments of Hiroshima University Hospital.

BACKGROUND: Dental professionals have so many opportunities to use injection needles and sharp instruments during dental treatment that they face an increased risk of needlestick injuries. This retrospective study reports the utilization and clinical outcomes of occupational post-exposure prophylaxis (PEP) with anti-retroviral agents after being potentially exposed to HIV at the dental departments of Hiroshima University Hospital. OBJECTIVE: This study reports the utilization and clinical outcomes of occupational post-exposure prophylaxis (PEP) with antiretroviral agents after being potentially exposed to HIV at dental departments of Hiroshima University Hospital. METHODS: Data on the clinical status of HIV-infected source patients and information on HIV-exposed dental professionals from 2007 to 2018 were collected. RESULTS: Five dentists with an average experience of 5.6 years (1-15 years) were exposed. The averaged CD4-positive cell number and HIV-RNA load were 1176 (768-1898) /µl and less than 20 copies/ml, respectively, in all the patients. Two of the five HIV exposed dentists received PEP. Three months after the exposures, all of their results were negative in HIV antibody/antigen tests. CONCLUSION: ; These data might support the concept of "undetectable equals untransmittable", although HIV exposure in this study was not through sexual transmission.

Oral environment and taste function of Japanese HIV-infected patients treated with antiretroviral therapy.

The aim of the study was to evaluate the oral environment and the taste function of Japanese HIV-infected patients treated with antiretroviral therapy. Their median age of 73 patients taking anti-HIV drugs was 46 years. The median period of taking anti-HIV drugs was 30 months. The oral condition was evaluated by measurement of oral moisture, amount of saliva secretion, the number of oral bacteria, presence of oral candida, a taste test, and the number of missing teeth. The levels of oral moisture and secreted saliva were significantly lower in the HIV-infected group than in the healthy volunteer (control) group. The HIV-infected group showed a more robust decrease in taste sensation than the control group. The number of missing teeth was significantly higher in the HIV-infected group than in the control group. Furthermore, all of the evaluated oral conditions were worse in the HIV-infected patients whose CD4+ T lymphocyte counts were less than 500/mm3 than in the control group. It became clear that the patients taking anti-HIV drugs, especially the CD4+ count < 500/mm3 group, had a deteriorated oral environment and dysgeusia, suggesting that the management of oral hygiene is necessary to maintain oral health, which leads to systemic health.

Heparin-LL37 complexes are less cytotoxic for human dental pulp cells and have undiminished antimicrobial and LPS-neutralizing abilities.

AIM: To investigate whether glycosaminoglycans (GAGs) binding to high-dose LL37 eliminates its cytotoxicity to dental pulp cells (hDPCs) whilst retaining undiminished antimicrobial and LPS-neutralizing abilities. METHODOLOGY: hDPCs were stimulated with varying concentrations of LL37, and their cell viability was analysed by MTT. Then, high-dose LL37 (10 µmol L-1 ) was bound to varying concentrations of three GAGs, heparin, chondroitin sulphate and hyaluronic acid, and their cytotoxic effects on hDPCs and antimicrobial effects were evaluated and compared. Furthermore, the LPS-neutralizing ability of heparin (5 µg mL-1 )-LL37 (10 µmol L-1 ) complexes, which were found to be less cytotoxic for hDPCs with undiminished antimicrobial ability, was investigated. Statistical analysis was performed using one-way analysis of variance (anova), followed by Dunnett's test. P values below 0.05 were considered significant. RESULTS: LL37 significantly reduced the cell viability of hDPCs in a dose-dependent manner (P < 0.01). LL37 (10 µmol L-1 ) binding to heparin within a limited concentration range (2~6 µg mL-1 ) eliminated the cytotoxicity for hDPCs (P < 0.01) whilst exerting potent antimicrobial effects against Streptococcus mutans, Streptococcus sobrinus, Streptococcus salivarius, Aggegatibacter actinomycetemcomitans and Escherichia coli. LL37 (10 µmol L-1 ) binding to chondroitin sulphate exhibited similar functions (P < 0.01); however, the effective chondroitin sulphate concentration was highly restricted (3 µg mL-1 ). LL37 (10 µmol L-1 ) binding to hyaluronic acid was unable to abrogate the cytotoxicity of LL37 even at higher concentrations (10 and 100 µg mL-1 ). Moreover, exogenous addition of LPS dose-dependently reduced the amount of LL37 precipitated with the heparin-LL37 agarose beads (P < 0.01), and the released LL37 simultaneously neutralized the pro-inflammatory ability of LPS in macrophages (P < 0.01). CONCLUSIONS: Heparin-LL37 complexes generated at suitable concentration ratios are easy to make, are less cytotoxic and are broad-range antimicrobial materials that can neutralize LPS by providing LL37 in accordance with the amount of free LPS. They may be a potential treatment to save dental pulp tissue from the acute inflammation exacerbated by invading bacteria and the LPS they release.

Eradication of Helicobacter pylori in a Living Donor Liver Transplant Recipient With Immunosuppressive Therapy of Cyclosporine A: A Case Report.

A 54-year-old woman underwent living donor liver transplantation (LDLT) for primary biliary cholangitis (PBC) three years earlier. She took cyclosporine A (CyA) 150 mg/day as immunosuppression for prevention of rejection and PBC recurrence. Routine upper gastrointestinal endoscopy showed chronic atrophic gastritis and hyperplastic polyp, and rapid urease test was positive. Anti-Helicobacter pylori (H. pylori) serum IgG was elevated to 51 U/ml. We performed H. pylori eradication therapy with amoxicillin, clarithromycin and lansoprazole measuring the blood CyA concentration every day. Although the blood CyA concentration reached a peak (the concentration 2 hours after the administration: 818 ng/ml) on the second day, she did not develop renal dysfunction or other obvious adverse effects. Five weeks after the treatment, we confirmed eradication of H. pylori with the urea breath test. We herein reported a case of successful eradication of H. pylori in a LDLT recipient on immunosuppressive therapy with CyA without adverse effects.

Successful Treatment of Stricture of Duct-to-Duct Biliary Anastomosis After Living-Donor Liver Transplantation of the Left Lobe: A Case Report.

Biliary complications, such as stricture or obstruction, after living-donor liver transplantation (LDLT) remain major problems to be solved. Magnetic compression anastomosis (MCA) is a minimally invasive method of biliary anastomosis without surgery in patients with biliary stricture or obstruction. A 66-year-old woman had undergone LDLT for end-stage liver disease for primary biliary cholangitis 20 months previously at another hospital. Computerized tomography showed dilation of the intrahepatic bile duct (B2). Because B2 was invisible with the use of endoscopic retrograde cholangiopancreatography, percutaneous transhepatic biliary drainage (PTBD) was performed for treatment of cholangitis. The rendezvous technique failed because a guidewire could not pass through the biliary stricture. Therefore, we decided to perform MCA. A parent magnet was endoscopically placed distally in the common bile duct of the stricture, and a daughter magnet attached to a guidewire was inserted proximally through the fistula tract of the PTBD. Both magnets were positioned across the stricture, and the 2 magnets were pulled to each other by magnetic power, to sandwich the stricture. By 14 days after MCA, a fistula between B2 and the common bile duct was created. At 28 days after MCA, the magnets were removed distally and a 16-French tube was placed across the fistula. At 7 months after MCA, that tube was removed. In conclusion, when a conventional endoscopic or percutaneous approach including the rendezvous technique fails, MCA is a good technique for biliary stricture after LDLT.

Significance of Portal Venous Velocity in Short-term Graft Function in Living Donor Liver Transplantation.

BACKGROUND: Graft regeneration and functional recovery after reperfusion of transplanted graft are very important for successful living donor liver transplantation (LDLT). The aim of this study was to evaluate the significance of postoperative portal venous velocity (PVV) in short-term recovery of graft function in LDLT. PATIENTS AND METHODS: From February 2007 through December 2015, we performed 17 primary LDLTs, which were included in the present study. The patients ranged in age from 12 to 65 years (mean: 50 years), and 11 were female patients. Postoperatively, Doppler ultrasonography was performed daily to measure PVV (cm/s), and liver function parameters were measured daily. The change in PVV (ΔPVV) was defined as follows: ΔPVV = PVV on postoperative day (POD) 1 - PVV on POD 7. Maximal value of serum aspartate aminotransferase (ASTmax) and maximal value of serum alanine transaminase (ALTmax) at 24 hours after graft reperfusion were used as parameters of reperfusion injury. Correlation analyses were performed as follows: (1) correlation of ΔPVV and PVV on POD 1 (PVV-POD 1) with the values such as ASTmax, ALTmax, other liver function parameters on POD 7 and graft regeneration rate; (2) correlation of ASTmax and ALTmax with other liver function parameters on POD 7. RESULTS: ΔPVV significantly correlated with the values of serum total bilirubin (P < .01), prothrombin time (P < .01), and platelet count (P < .05), and PVV-POD 1 significantly correlated with the values of serum total bilirubin (P < .05) and prothrombin time (P < .05). CONCLUSION: ΔPVV and PVV-POD 1 may be useful parameters of short-term functional recovery of the transplant liver in LDLT.

Adenosine Increases Hepatic Artery Flow in Liver Transplant Recipients: A Pilot Study.

BACKGROUND: The aim of this study was to assess the effect of low-dose adenosine on hepatic artery flow (HAF) when administered intraoperatively by continuous infusion. MATERIALS AND METHODS: Between January 2009 and August 2009, 74 patients underwent orthotopic liver transplantation (OLT). Ten patients were enrolled for adenosine treatment, and 64 non-study patients served as controls. After arterial reperfusion, a 16-G central venous catheter was placed in the gastroduodenal artery, and adenosine was continuously infused at doses ranging from 0.7 to 2.8 µg/kg/min for 30 min. HAF and portal vein flow were measured using a transit time flow meter before adenosine infusion, during infusion, and 10 min after infusion. Liver function tests were monitored routinely, duplex ultrasonography was performed on postoperative day 1, and the hepatic artery resistive index measured. The patients were followed for 1 year. RESULTS: Adenosine significantly increased HAF at doses from 0.7 to 2.8 µg/kg/min. The smallest increase in HAF was 24% above the baseline; in 80% of patients, the increase in HAF was >50% of the baseline values. In 2 patients, HAF was increased by >300%. The dosing started at 0.7 µg/kg/min, and 6 of 10 patients responded. Three patients required an increase to 1.4 µg/kg/min. Doses >2.8 µg/kg/min did not further increase HAF. One patient showed a minimal response regardless of the dose. There were no differences between the adenosine group and control group with respect to liver function (aspartate aminotransferase, alanine aminotransferase, total bilirubin, and International Normalized Ratio), platelet count on POD2, hepatic artery resistive index, and post-transplant length of stay, intensive care days, or 1-year patient survival rates. CONCLUSIONS: This pilot study established that adenosine administered directly into the hepatic artery produces a similar effect on HAF in cadaveric liver transplant recipients to that found in the laboratory without producing systemic side effects.

Clinical utility of three-dimensional SPECT/CT imaging as a guide for the resection of medication-related osteonecrosis of the jaw.

In recent years, proactive surgical treatment has been reported to be effective for medication-related osteonecrosis of the jaw (MRONJ). However, an uncertain resection entails the risk of recurrence, whereas an extensive surgical procedure may lead to a marked reduction in quality of life as a result of reduced masticatory function and poor cosmesis. Therefore, radiological assessment can be helpful to accurately localize MRONJ before surgery. The integrated single-photon emission computed tomography and computed tomography system (SPECT/CT) allows oral and maxillofacial surgeons to identify an area of MRONJ, especially when three-dimensional (3D) SPECT and CT fusion images are offered. A patient for whom 3D SPECT and CT image fusion (as developed in the radiology department of the study institution) contributed to determining the extent of the lesion, thereby leading to a favourable patient prognosis, is reported herein. There was exact correlation between the histological and radiological results.

The differential expression of mgl mRNA by Porphyromonas gingivalis affects the production of methyl mercaptan.

OBJECTIVE: A large number of individuals have halitosis. The total amount of volatile sulfur compounds, which are the main cause of halitosis, has been correlated with periodontitis following bacterial infection. In this study, Porphyromonas gingivalis (Pg), a major periodontopathogenic bacterium, was isolated from patients with halitosis by the amplification of 16S rRNA, and the ability of isolated Pg to produce methyl mercaptan (CH3 SH) was determined to clarify the relationship between halitosis and Pg infection. MATERIALS AND METHODS: CH3 SH concentrations were measured in patients using Oral Chroma. The production of CH3 SH by Pg standard and clinical strains was also measured in vitro. Real-time PCR was performed to compare the expression of mgl mRNA (which encoded l-methionine-a-deamino-g-mercaptomethane-lyase) among the Pg strains. The production of CH3 SH and the expression of mgl mRNA were also determined to assess the effects of oriental medicine. RESULTS: The production of CH3 SH and the expression of mgl mRNA strongly correlated with each other in the presence of l-methionine. The expression of mgl mRNA by Pg W83 was strongly inhibited by magnoliaceae. CONCLUSION: The production of CH3 SH was correlated with the expression of mgl. Furthermore, the oriental medicine, magnoliaceae, may represent a potential treatment for halitosis.

LL37 induces VEGF expression in dental pulp cells through ERK signalling.

AIM: To examine the in vitro effects of LL37 on the expression of vascular endothelial growth factor (VEGF) in human pulp cells and to identify the intracellular signalling pathway involved. METHODOLOGY: Pulp cells at passage 6 were treated with 10 µg mL(-1) synthesized LL37, and an inhibition assay was performed with MAPK or NF-κB inhibitors to determine the possible signalling pathway. VEGF mRNA, VEGF protein and phosphorylated ERK1/2 levels were determined by real-time PCR, ELISA and Western blot, respectively. Data were analysed using t-tests. RESULTS: LL37 significantly increased both the mRNA and protein levels of VEGF in pulp cells (P < 0.01). However, pre-treatment with an ERK kinase inhibitor suppressed these increases. Furthermore, the inhibitor blocked LL37-induced ERK1/2 phosphorylation. CONCLUSIONS: LL37 activated the ERK pathway to boost VEGF secretion from human pulp cells. Because of this angiogenic effect and its reported induction of pulp cell migration and antimicrobial activity against cariogenic bacteria, LL37 may be applicable as a pulp capping material.

Interleukin-8 induces DNA synthesis, migration and down-regulation of cleaved caspase-3 in cultured human gingival epithelial cells.

BACKGROUND AND OBJECTIVE: Migration of the junctional epithelium occurs in association with the formation of a periodontal pocket. Although the migration of junctional epithelium is known to be related to the proliferation and migration of gingival junctional epithelial cells, the mechanism has not been clarified. In patients with periodontitis, the levels of interleukin-8 (IL-8) in both gingival tissue and gingival crevicular fluid are dramatically increased. IL-8 has broad bioactive functions. In this study, we examined the role of IL-8 in DNA synthesis, migration and protection against apoptosis in cultured human gingival epithelial cells (HGEC). MATERIAL AND METHODS: DNA synthesis was estimated by measuring the incorporation of bromodeoxyuridine. The migration of gingival epithelial cells was assessed in a wound-healing assay. The expression of integrin beta-1 was analyzed using immunofluorescence confocal microscopy and western blotting. Cleaved caspase-3 was detected using western blotting and a Caspase-Glo assay kit. RESULTS: IL-8 increased the synthesis of DNA in HGEC, and the maximal effect was seen at 25 or 50 ng/mL of IL-8. In addition, 50 ng/mL of IL-8 induced cell migration, and a neutralizing antibody of integrin beta-1 inhibited the migration. IL-8 also activated expression of integrin beta-1. Furthermore, IL-8 reduced the Aggregatibacter actinomycetemcomitans-induced increase in caspase-3 expression in HGEC. CONCLUSION: IL-8 may facilitate the migration of gingival junctional epithelium by enhancing DNA synthesis, migration and preventing apoptosis of gingival epithelial cells.

Irsogladine maleate inhibits Porphyromonas gingivalis-mediated expression of toll-like receptor 2 and interleukin-8 in human gingival epithelial cells.

BACKGROUND AND OBJECTIVE: Periodontitis is an infectious disease caused by an interaction between the host and periodontopathogenic bacteria. Regulating the immune response in human gingival epithelial cells (HGEC) may contribute to the prevention of periodontitis. Irsogladine maleate (IM) has previously been shown to regulate inflammation and the cell-cell junctional barrier in HGEC. In addition to these functions, control of bacterial recognition is important for preventing inflammation in periodontal tissue. Innate immunity in gingival epithelium is the first line of defense and plays a crucial role against bacterial challenge. Therefore, the effect of IM on regulating toll-like receptor 2 (TLR2), which is part of the innate immunity, was determined in this study. MATERIAL AND METHODS: OBA-9, an immortalized human gingival epithelial cell line, and primary cultured HGEC were used in this study. Real-time PCR and western blotting were performed in OBA-9 or HGEC stimulated with whole cells of Porphyromonas gingivalis or with lipopolysaccharide (LPS) derived from P. gingivalis (PgLPS) in the presence or absence of IM to determine expression of TLR2 mRNA and production of TLR2 protein. Small interfering RNA (siRNA) against TLR2 was transfected into OBA-9 to clarify the association between the induction of TLR2 and interleukin-8 (IL-8) production. RESULTS: The addition of IM into P. gingivalis or PgLPS-induced OBA-9 suppressed IL-8 production (p < 0.01). The addition of IM also abolished the induction of TLR2 by P. gingivalis or PgLPS in OBA-9 and primary cultured HGEC (p < 0.01). The suppressive effect of IM on the induction of TLR2 was also confirmed by immunohistostaining. Stimulation with peptidoglycan, a specific ligand for TLR2, suppressed the expression of toll-like receptor 4 (TLR4) mRNA in the presence of IM (p < 0.01). However, LPS derived from Escherichia coli, a ligand for TLR4, did not induce the expression of TLR2 mRNA. The PgLPS-induced expression of TLR4 mRNA was abolished by IM. Knockdown of TLR2 by siRNA transfection resulted in a weaker response of induction of IL8 mRNA in P. gingivalis or PgLPS-stimulated OBA-9. CONCLUSION: These results suggest that IM suppresses the induction of IL-8 production by regulating increased levels of TLR2.

Brain-derived neurotrophic factor prevents the endothelial barrier dysfunction induced by interleukin-1ß and tumor necrosis factor-α.

BACKGROUND AND OBJECTIVE: Brain-derived neurotrophic factor (BDNF) promotes the regeneration of periodontal tissue. Although a local inflammatory step is required to initiate the subsequent process of tissue regeneration, excessive inflammation may inhibit or delay tissue regeneration. Therefore, the regulation of inflammation is essential for periodontal tissue regeneration. In the present study, we examined the influence of BDNF on the human microvascular endothelial cell (HMVEC) barrier dysfunction induced by interleukin (IL)-1ß or tumor necrosis factor (TNF)-α to determine the effects of BDNF on the regulation of local inflammation in periodontal tissue regeneration. MATERIAL AND METHODS: Endothelial permeability was analyzed using a Dextran transport assay with transwell plates. The expression of vascular endothelial (VE)-cadherin was assessed by immunoblotting and immunofluorescence microscopy. RESULTS: BDNF (25 ng/mL) inhibited increase induced in endothelial permeability by IL-1ß and TNF-α. IL-1ß and TNF-α decreased VE-cadherin protein levels, while BDNF recovered the reduction in HMVECs. BDNF protected the increase induced in endothelial permeability by IL-1ß and TNF-α through TrkB. The single addition of BDNF into the culture increased the expression of VE-cadherin in HMVECs. CONCLUSION: BDNF played an important role in inhibiting endothelial barrier dysfunction, which suggests that it may assist in enhancing periodontal tissue regeneration.

Stress-induced ceramide generation and apoptosis via the phosphorylation and activation of nSMase1 by JNK signaling.

Neutral sphingomyelinase (nSMase) activation in response to environmental stress or inflammatory cytokine stimuli generates the second messenger ceramide, which mediates the stress-induced apoptosis. However, the signaling pathways and activation mechanism underlying this process have yet to be elucidated. Here we show that the phosphorylation of nSMase1 (sphingomyelin phosphodiesterase 2, SMPD2) by c-Jun N-terminal kinase (JNK) signaling stimulates ceramide generation and apoptosis and provide evidence for a signaling mechanism that integrates stress- and cytokine-activated apoptosis in vertebrate cells. An nSMase1 was identified as a JNK substrate, and the phosphorylation site responsible for its effects on stress and cytokine induction was Ser-270. In zebrafish cells, the substitution of Ser-270 for alanine blocked the phosphorylation and activation of nSMase1, whereas the substitution of Ser-270 for negatively charged glutamic acid mimicked the effect of phosphorylation. The JNK inhibitor SP600125 blocked the phosphorylation and activation of nSMase1, which in turn blocked ceramide signaling and apoptosis. A variety of stress conditions, including heat shock, UV exposure, hydrogen peroxide treatment, and anti-Fas antibody stimulation, led to the phosphorylation of nSMase1, activated nSMase1, and induced ceramide generation and apoptosis in zebrafish embryonic ZE and human Jurkat T cells. In addition, the depletion of MAPK8/9 or SMPD2 by RNAi knockdown decreased ceramide generation and stress- and cytokine-induced apoptosis in Jurkat cells. Therefore the phosphorylation of nSMase1 is a pivotal step in JNK signaling, which leads to ceramide generation and apoptosis under stress conditions and in response to cytokine stimulation. nSMase1 has a common central role in ceramide signaling during the stress and cytokine responses and apoptosis.