Yoshinori Hiraoka

Nardilysin Enhances Ectodomain Shedding of Heparin-binding Epidermal Growth Factor-like Growth Factor through Activation of Tumor Necrosis Factor-α-converting Enzyme

Like other members of the epidermal growth factor family, heparin-binding epidermal growth factor-like growth factor (HB-EGF) is synthesized as a transmembrane protein that can be shed enzymatically to release a soluble growth factor. Ectodomain shedding is essential to the biological functions of HB-EGF and is strictly regulated. However, the mechanism that induces the shedding remains unclear. We have recently identified nardilysin (N-arginine dibasic convertase (NRDc)), a metalloendopeptidase of the M16 family, as a protein that specifically binds HB-EGF (Nishi, E., Prat, A., Hospital, V., Elenius, K., and Klagsbrun, M. (2001) EMBO J. 20, 3342-3350). Here, we show that NRDc enhances ectodomain shedding of HB-EGF. When expressed in cells, NRDc enhanced the shedding in cooperation with tumor necrosis factor-α-converting enzyme (TACE; ADAM17). NRDc formed a complex with TACE, a process promoted by phorbol esters, general activators of ectodomain shedding. NRDc enhanced TACE-induced HB-EGF cleavage in a peptide cleavage assay, indicating that the interaction with NRDc potentiates the catalytic activity of TACE. The metalloendopeptidase activity of NRDc was not required for the enhancement of HB-EGF shedding. Notably, a reduction in the expression of NRDc caused by RNA interference was accompanied by a decrease in ectodomain shedding of HB-EGF. These results indicate the essential role of NRDc in HB-EGF ectodomain shedding and reveal how the shedding is regulated by the modulation of sheddase activity.

Nardilysin regulates axonal maturation and myelination in the central and peripheral nervous system

Axonal maturation and myelination are essential processes for establishing an efficient neuronal signaling network. We found that nardilysin (N-arginine dibasic convertase, also known as Nrd1 and NRDc), a metalloendopeptidase enhancer of protein ectodomain shedding, is a critical regulator of these processes. Nrd1−/− mice had smaller brains and a thin cerebral cortex, in which there were less myelinated fibers with thinner myelin sheaths and smaller axon diameters. We also found hypomyelination in the peripheral nervous system (PNS) of Nrd1−/− mice. Neuron-specific overexpression of NRDc induced hypermyelination, indicating that the level of neuronal NRDc regulates myelin thickness. Consistent with these findings, Nrd1−/− mice had impaired motor activities and cognitive deficits. Furthermore, NRDc enhanced ectodomain shedding of neuregulin1 (NRG1), which is a master regulator of myelination in the PNS. On the basis of these data, we propose that NRDc regulates axonal maturation and myelination in the CNS and PNS, in part, through the modulation of NRG1 shedding.

Enhancement of α‐secretase cleavage of amyloid precursor protein by a metalloendopeptidase nardilysin

Amyloid‐β (Aβ) peptide, the principal component of senile plaques in the brains of patients with Alzheimer’s disease, is derived from proteolytic cleavage of amyloid precursor protein (APP) by β‐ and γ‐secretases. Alternative cleavage of APP by α‐secretase occurs within the Aβ domain and precludes generation of Aβ peptide. Three members of the ADAM (a disintegrin and metalloprotease) family of proteases, ADAM9, 10 and 17, are the main candidates for α‐secretases. However, the mechanism that regulates α‐secretase activity remains unclear. We have recently demonstrated that nardilysin (EC 3.4.24.61, N‐arginine dibasic convertase; NRDc) enhances ectodomain shedding of heparin‐binding epidermal growth factor‐like growth factor through activation of ADAM17. In this study, we show that NRDc enhances the α‐secretase activity of ADAMs, which results in a decrease in the amount of Aβ generated. When expressed with ADAMs in cells, NRDc dramatically increased the secretion of α‐secretase‐cleaved soluble APP and reduced the amount of Aβ peptide generated. A peptide cleavage assay in vitro also showed that recombinant NRDc enhances ADAM17‐induced cleavage of the peptide substrate corresponding to the α‐secretase cleavage site of APP. A reduction of endogenous NRDc by RNA interference was accompanied by a decrease in the cleavage by α‐secretase of APP and increase in the amount of Aβ generated. Notably, NRDc is clearly expressed in cortical neurons in human brain. Our results indicate that NRDc is involved in the metabolism of APP through regulation of the α‐secretase activity of ADAMs, which may be a novel target for the treatment of Alzheimer’s disease.

Ectodomain shedding of TNF-α is enhanced by nardilysin via activation of ADAM proteases

Tumor necrosis factor-alpha (TNF-alpha) is released from cells by proteolytic cleavage of a membrane-anchored precursor. The TNF-alpha-converting enzyme (TACE/ADAM17) is the major sheddase for ectodomain shedding of TNF-alpha. At present, however, it is poorly understood how its catalytic activity is regulated. Here, we show that nardilysin (N-arginine dibasic convertase; NRDc) enhanced TNF-alpha shedding. In a cell-based shedding assay, expression of NRDc synergistically enhanced TACE-induced TNF-alpha shedding. A peptide cleavage assay in vitro showed that recombinant NRDc enhances the cleavage of TNF-alpha induced by TACE. Notably, co-incubation of NRDc completely reversed the inhibitory effect of a physiological concentration of salt on TACEs activity in vitro. Overexpression of NRDc in TACE-deficient fibroblasts resulted in an increase in the amount of TNF-alpha released. Co-expression of NRDc with ADAM10 promoted the release compared with the sole expression of ADAM10. These results suggested that NRDc enhances TNF-alpha shedding through activation of not only TACE but ADAM10. Our results indicate the involvement of NRDc in ectodomain shedding of TNF-alpha, which may be a novel target for anti-inflammatory therapies.

Nardilysin and ADAM proteases promote gastric cancer cell growth by activating intrinsic cytokine signalling via enhanced ectodomain shedding of TNF‐α

Nardilysin (NRDc), a metalloendopeptidase of the M16 family, promotes ectodomain shedding of the precursor forms of various growth factors and cytokines by enhancing the protease activities of ADAM proteins. Here, we show the growth‐promoting role of NRDc in gastric cancer cells. Analyses of clinical samples demonstrated that NRDc protein expression was frequently elevated both in the serum and cancer epithelium of gastric cancer patients. After NRDc knockdown, tumour cell growth was suppressed both in vitro and in xenograft experiments. In gastric cancer cells, NRDc promotes shedding of pro‐tumour necrosis factor‐alpha (pro‐TNF‐α), which stimulates expression of NF‐κB‐regulated multiple cytokines such as interleukin (IL)‐6. In turn, IL‐6 activates STAT3, leading to transcriptional upregulation of downstream growth‐related genes. Gene silencing of ADAM17 or ADAM10, representative ADAM proteases, phenocopied the changes in cytokine expression and cell growth induced by NRDc knockdown. Our results demonstrate that gastric cancer cell growth is maintained by autonomous TNF‐α–NF‐κB and IL‐6–STAT3 signalling, and that NRDc and ADAM proteases turn on these signalling cascades by stimulating ectodomain shedding of TNF‐α.

Critical roles of nardilysin in the maintenance of body temperature homoeostasis

Body temperature homoeostasis in mammals is governed centrally through the regulation of shivering and non-shivering thermogenesis and cutaneous vasomotion. Non-shivering thermogenesis in brown adipose tissue (BAT) is mediated by sympathetic activation, followed by PGC-1α induction, which drives UCP1. Here we identify nardilysin (Nrd1 and NRDc) as a critical regulator of body temperature homoeostasis. Nrd1−/− mice show increased energy expenditure owing to enhanced BAT thermogenesis and hyperactivity. Despite these findings, Nrd1−/− mice show hypothermia and cold intolerance that are attributed to the lowered set point of body temperature, poor insulation and impaired cold-induced thermogenesis. Induction of β3-adrenergic receptor, PGC-1α and UCP1 in response to cold is severely impaired in the absence of NRDc. At the molecular level, NRDc and PGC-1α interact and co-localize at the UCP1 enhancer, where NRDc represses PGC-1α activity. These findings reveal a novel nuclear function of NRDc and provide important insights into the mechanism of thermoregulation.

Nardilysin prevents amyloid plaque formation by enhancing α-secretase activity in an Alzheimer's disease mouse model

Amyloid beta (Aβ) peptide, the main component of senile plaques in patients with Alzheimers disease (AD), is derived from proteolytic cleavage of amyloid precursor protein (APP) by β- and γ-secretases. Alpha-cleavage of APP by α-secretase has a potential to preclude the generation of Aβ because it occurs within the Aβ domain. We previously reported that a metalloendopeptidase, nardilysin (N-arginine dibasic convertase; NRDc) enhances α-cleavage of APP, which results in the decreased generation of Aβ in vitro. To clarify the in vivo role of NRDc in AD, we intercrossed transgenic mice expressing NRDc in the forebrain with an AD mouse model. Here we demonstrate that the neuron-specific overexpression of NRDc prevents Aβ deposition in the AD mouse model. The activity of α-secretase in the mouse brain was enhanced by the overexpression of NRDc, and was reduced by the deletion of NRDc. However, reactive gliosis adjacent to the Aβ plaques, one of the pathological features of AD, was not affected by the overexpression of NRDc. Taken together, our results indicate that NRDc controls Aβ formation through the regulation of α-secretase.

Nardilysin Is Required for Maintaining Pancreatic β-Cell Function.

Type 2 diabetes (T2D) is associated with pancreatic β-cell dysfunction, manifested by reduced glucose-stimulated insulin secretion (GSIS). Several transcription factors enriched in β-cells, such as MafA, control β-cell function by organizing genes involved in GSIS. Here we demonstrate that nardilysin (N-arginine dibasic convertase; Nrd1 and NRDc) critically regulates β-cell function through MafA. Nrd1−/− mice showed glucose intolerance and severely decreased GSIS. Islets isolated from Nrd1−/− mice exhibited reduced insulin content and impaired GSIS in vitro. Moreover, β-cell-specific NRDc-deficient (Nrd1delβ) mice showed a diabetic phenotype with markedly reduced GSIS. MafA was specifically downregulated in islets from Nrd1delβ mice, whereas overexpression of NRDc upregulated MafA and insulin expression in INS832/13 cells. Chromatin immunoprecipitation assay revealed that NRDc is associated with Islet-1 in the enhancer region of MafA, where NRDc controls the recruitment of Islet-1 and MafA transcription. Our findings demonstrate that NRDc controls β-cell function via regulation of the Islet-1–MafA pathway.

Comparison of serum lipid management between elderly and non-elderly patients with and without coronary heart disease (CHD).

Serum lipid management in patients aged ≥ 75 has not been precisely explored. We, therefore, compared the serum lipid management between the two age groups with and without coronary heart disease (CHD). We, therefore, retrospectively reviewed medical charts of patients who were hospitalized in the departments of internal medicine during a period of 14 months. Serum lipid goal attainment was explored by applying the lipid goals for patients aged < 75 to those aged ≥ 75. In 1988 enrolled patients, 717 subjects (36.1%) were aged ≥ 75. Among them, 41.3% and 32.4% of the patients had CHD, 44.2% and 41.0% were primary prevention at high-risk, and 14.5% and 14.6% were primary prevention at moderate-risk in patients aged ≥ 75 and aged < 75, respectively. Serum LDL-C goal achievement rates in CHD were 66.9% and 65.0% in patients aged ≥ 75 and < 75, respectively (p = 0.334). In the primary prevention at high-risk, these rates were 73.5% and 63.3%, in patients aged ≥ 75 and < 75, respectively (p = 0.001). They were 77.9% and 58.1% in primary prevention at moderate-risk aged ≥ 75 and < 75, respectively (p < 0.001). In CHD, lipid-lowering medication subscription rates were significantly lower in patients aged ≥ 75 (60.1%) than those aged < 75 (73.8%, p < 0.001). In conclusion, in CHD, serum lipid goal attainment was comparable between the two age groups although the lipid-lowering drugs were less frequently prescribed in patients aged ≥ 75. Without CHD, it was significantly better in patients aged ≥ 75 than those aged < 75 although the lipid-lowering drug subscription rates were comparable between the two age groups.

Serum Lipid Goal Attainment in Chronic Kidney Disease (CKD) Patients under the Japan Atherosclerosis Society (JAS) 2012 Guidelines

AIM According to the Japan Atherosclerosis Society 2012 guidelines (JAS2012-GL), chronic kidney disease (CKD) has newly been added to the high-risk group in terms of atherosclerotic cardiovascular diseases. We therefore explored the lipid target level achievement rates under the JAS2012-GL in real-world clinical practice. METHODS We retrospectively reviewed the medical charts of patients who were hospitalized at the Nephrology Department at Kobe City Medical Center General Hospital in the period from April 1, 2012 to May 31, 2013 and explored the serum lipid target level achievement rates. Patients without lipid data or those undergoing regular dialysis because of chronic renal failure were excluded. In this study, the CKD group (CKD-G) did not include CKD patients under secondary prevention for coronary heart disease (CHD) or diabetes mellitus (DM). RESULTS The CKD-G included 146 (81.1%) of the 180 enrolled patients. According to the JAS2012-GL, 100% of the CKD-G patients were categorized into the high-risk group, although only 12.1% of the CKD-G subjects were at high risk according to the JAS2007-GL. Under the JAS2012-GL, the LDL cholesterol (LDL-C) and non-HDL cholesterol (non-HDL-C) target level achievement rates for CKD-G were 71.4% and 68.1%, respectively. According to the JAS2007-GL, these rates were 81.3% and 79.1%, respectively, and, under both guidelines, these rates were 71.7% and 72.1% for primary prevention DM and 66.7% and 66.7% for CHD, respectively. CONCLUSIONS After the revision of the JAS-GL in 2012, the LDL-C and non-HDL-C target level achievement rates for CKD-G were reduced by approximately 10%; however, they remained similar to those for DM and higher than those for CHD.