Kazuhiro Takekoshi

Elovl6 promotes nonalcoholic steatohepatitis.

Nonalcoholic steatohepatitis (NASH) is associated with obesity and type 2 diabetes, and an increased risk for liver cirrhosis and cancer. ELOVL family member 6, elongation of very long chain fatty acids (Elovl6), is a microsomal enzyme that regulates the elongation of C12‐16 saturated and monounsaturated fatty acids (FAs). We have shown previously that Elovl6 is a major target for sterol regulatory element binding proteins in the liver and that it plays a critical role in the development of obesity‐induced insulin resistance by modifying FA composition. To further investigate the role of Elovl6 in the development of NASH and its underlying mechanism, we used three independent mouse models with loss or gain of function of Elovl6, and human liver samples isolated from patients with NASH. Our results demonstrate that (1) Elovl6 is a critical modulator for atherogenic high‐fat diet–induced inflammation, oxidative stress, and fibrosis in the liver; (2) Elovl6 expression is positively correlated with severity of hepatosteatosis and liver injury in NASH patients; and (3) deletion of Elovl6 reduces palmitate‐induced activation of the NLR family pyrin domain‐containing 3 inflammasome; this could be at least one of the underlying mechanisms by which Elovl6 modulates the progress of NASH. Conclusion: Hepatic long‐chain fatty acid composition is a novel determinant in NASH development, and Elovl6 could be a potential therapeutic target for the prevention and treatment of NASH. (HEPATOLOGY 2012;56:2199–2208)

Effects of orexin on cultured porcine adrenal medullary and cortex cells

New orexigenic peptides called orexins have recently been described in the neurons of the lateral hypothalamus and perifornical area. No orexins have been found in the adipose tissues or visceral organs, including the adrenal gland. However, expression of the orexin receptor (OXR) in the rat adrenal gland has been reported. With regard to the effects of orexins on peripheral organs, we previously reported that orexins suppress catecholamine synthesis and secretion in the rat pheochromocytoma cell line PC12. To further clarify the pharmacological effects of orexins on peripheral organs, we examined the effects of orexin-A on catecholamine, cortisol, and aldosterone secretion, using cultured porcine adrenal glands. We initially confirmed the expression of the orexin receptor (OXR-1) in cultured porcine adrenal medulla and cortex. Orexin-A (1000 nM) significantly increased the release of both epinephrine (E) and norepinephrine (NE) from porcine adrenal medullary cells. Similarly, orexin-A (> or = 100 nM) significantly increased the release of both cortisol and aldosterone from porcine adrenal cortex cells. Orexin-A (100 nM) significantly inhibited basal and the PACAP-induced increase in cAMP levels in adrenal medullary cells. Conversely, orexin-A (>o = 100 nM) significantly increased the cAMP level in adrenal cortex cells. These results indicate that orexin-A induces the release of catecholamine from porcine adrenal medullary cells, and aldosterone and cortisol from the cortex cells and has opposite effects on cAMP levels in adrenal medulla and cortex.

Clinicopathological study of SDHB mutation-related pheochromocytoma and sympathetic paraganglioma

Pheochromocytoma (PCC) and paraganglioma (PGL) are genetically and phenotypically heterogeneous catecholamine-producing neoplasms. They can occur sporadically or as a part of hereditary disease. Approximately 30% of PCC/PGL are believed to be caused by germline mutations (Welander et al. 2011). Of these, succinate dehydrogenase subunit B (SDHB) gene mutation is considered a high-risk factor for malignancy. Loss of heterozygosity at the SDHB locus (1p36)wasobserved inall tumorswithSDHBmutation, and Gimenez-Roqueplo et al. (2003) strongly suggested that SDHB is a tumor suppressorgene. Subsequently, loss of SDHB protein immunoreactivity in SDHB-mutated PCC/PGL (SDHB–PCC/PGL) was reported with 100% sensitivity and 84% specificity (van Nederveen et al. 2009). Thus, SDHB immunohistochemistry can be used to screen SDHB– PCC/PGL using paraffin-embedded pathological materials. SDHB mutation is the only established factor that indicates future metastasis. Therefore, it is important to analyze the histological characteristics of SDHB–PCC/PGL. It is generally accepted that it is difficult to distinguish histological differences between benign and malignant PCC/PGL. The current consensus is that a long-term follow-up is required after the surgery to screen for recurrence or metastasis in all PCC/PGL patients, regardless whether hereditary or sporadic in origin. Kimura et al. (2014) proposed a histological grading system called the Grading of Adrenal PCC and PGL (GAPP) classification for predicting metastasis. GAPP is composed of six factors: histological pattern, cellularity, presence or absence of comedo-type necrosis, vascular or capsular invasion, Ki67labeling index (%), and elevated catecholamine type. Each factor was assigned a point and the number of points was summated. Tumor scores of 0–2, 3–6, and 7–10 were classified into well differentiated (WD), moderately

Sterol regulatory element-binding protein-1 determines plasma remnant lipoproteins and accelerates atherosclerosis in low-density lipoprotein receptor-deficient mice.

Objective—Sterol regulatory element–binding protein-1 (SREBP-1) is nutritionally regulated and is known to be a key transcription factor regulating lipogenic enzymes. The goal of this study was to evaluate the roles of SREBP-1 in dyslipidemia and atherosclerosis. Methods and Results—Transgenic mice that overexpress SREBP-1c in the liver and SREBP-1-deficient mice were crossed with low-density lipoprotein receptor (LDLR)–deficient mice, and the plasma lipids and atherosclerosis were analyzed. Hepatic SREBP-1c overexpression in LDLR-deficient mice caused postprandial hypertriglyceridemia, increased very-low-density lipoprotein (VLDL) cholesterol, and decreased high-density lipoprotein cholesterol in plasma, which resulted in accelerated aortic atheroma formation. Conversely, absence of SREBP-1 suppressed Western diet–induced hyperlipidemia in LDLR-deficient mice and ameliorated atherosclerosis. In contrast, bone marrow-specific SREBP-1 deficiency did not alter the development of atherosclerosis. The size of nascent VLDL particles secreted from the liver was increased in SREBP-1c transgenic mice and reduced in SREBP-1-deficient mice, accompanied by upregulation and downregulation of phospholipid transfer protein expression, respectively. Conclusion—Hepatic SREBP-1c determines plasma triglycerides and remnant cholesterol and contributes to atherosclerosis in hyperlipidemic states. Hepatic SREBP-1c also regulates the size of nascent VLDL particles.

Expression of mRNA for PACAP and its receptors in intra- and extra-adrenal human pheochromocytomas and their relationship to catecholamine synthesis.

PURPOSE Pituitary adenylate cyclase-activating polypeptide (PACAP), a member of the secretin/glucagons/vasoactive intestinal peptide family, induces the expression of catecholamine-synthesizing enzymes in adrenal medullary cells. In addition, PACAP and its receptor have been detected in human pheochromocytoma tissues, though it is not yet known whether PACAP enhances the expression of genes encoding catecholamine-synthesizing enzymes. To address this question, we analyzed PACAP, PACAP receptor, and tyrosine hydroxylase (TH) and phenylethanolamine-N-methyltransferase (PNMT) mRNAs in pheochromocytomas. METHODS The levels of the mRNA for PACAP and vasoactive intestinal peptide (VIP), and their receptors, and for TH and PNMT were measured by RT-PCR or real-time PCR analysis, and the concentrations of catecholamines were measured by HPLC in 24 intra-adrenal and six extra-adrenal pheochromocytomas. RESULTS mRNA expression of PACAP and its receptor VPAC1R were detected in many pheochromocytomas (24/30 and 29/30, respectively), but mRNA expression of the PAC1R and VPAC2R receptor subtypes were detected in only one of six extra-adrenal pheochromocytomas. PACAP mRNA expression correlated with TH (p=0.0018) and PNMT (p=0.05) mRNA expression, as well as epinephrine (p=0.0342) levels in 16 intra-adrenal pheochromocytomas. CONCLUSION Our findings support a possible role for PACAP in the regulation of expression of genes encoding catecholamine-synthesizing enzymes in intra-adrenal pheochromocytomas.

Angiotensin subtype-2 receptor (AT2 ) negatively regulates subtype-1 receptor (AT1 ) in signal transduction pathways in cultured porcine adrenal medullary chromaffin cells.

Background Two distinct types of angiotensin II (AngII) receptors, AT1 and AT2, have been cloned. We have shown previously that stimulation of AT2 reduces intracellular cyclic guanosine monophosphate (cGMP) levels in cultured porcine chromaffin cells in which AT2 is the predominantly expressed receptor. However, it has not been determined whether AT1 or AT2 affects signal transduction pathways involving mitogen-activated protein kinases (MAPKs) and signal transducers and activators of transcription (STATs) in chromaffin cells. Also, it is unclear whether cGMP/protein kinase G (PKG) is involved in the regulation of MAPKs and STATs in these cells. Design Chromaffin cells were derived from porcine adrenal medulla. The effects of AngII alone (representing physiological conditions), AngII plus CV-11974 (an AT1 antagonist, which simulates specific AT2 stimulation), AngII plus PD 123319 (an AT2 antagonist, which simulates specific AT1 stimulation), and 8-Br-cGMP (a membrane-permeable cGMP analogue) alone on MAPKs (ERKs, JNK, p-38 MAPK) and STATs (STATs 1, 3 and 5) activity were measured. Methods Phosphorylated MAPKs (extracellular signal-related kinases (ERKs), c-jun N-terminal kinase (JNK) and p38 MAPK) and STATs (STATs 1, 3 and 5) were measured by immunoprecipitation–Western blot analysis (IP–Western blot). Results AT1 stimulation markedly increased expression of ERKs, JNK, p38 MAPK via Ca2+-dependent protein kinase C (PKC) isoforms (cPKC), as well as STATs 1, 3 and 5 in cultured porcine chromaffin cells. In contrast, AT2 stimulation markedly decreased the expression of these signaling molecules. Also, 8-Br-cGMP alone induced increases in ERKs, JNK, p38 MAPK, and STATs 1, 3 and 5. Because AT2 inhibits cGMP production, we speculate that AT2 may act to suppress cGMP production, which in turn reduces the activity of both MAPKs and STATs in chromaffin cells. Conclusion AT2 negatively regulates AT1 in signal transduction pathways in chromaffin cells.

Effects of natriuretic peptides (ANP, BNP, CNP) on catecholamine synthesis and TH mRNA levels in PC12 cells.

Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) are present in adrenal chromaffin cells, and are co-secreted with catecholamines suggesting that these natriuretic peptides (NPs) may modulate functions of chromaffin cells in an autocrine and/or paracrine manner. Therefore, we investigated the effects of NPs on tyrosine hydroxylase (TH: a rate-limiting enzyme in biosynthesis of catecholamine) mRNA in rat pheochromocytoma PC12 cells. It was also determined whether the cyclic GMP/cGMP-dependent protein kinase (cGMP/PKG) pathway was involved in theses effects. Finally, we examined the effects of NPs on intracellular catecholamine content to confirm increase of catecholamine synthesis following TH mRNA induction. NPs (0.1 microM) induced significant increases of the TH mRNA (ANP= BNP> CNP). Also, the effects of NPs on TH mRNA were mimicked by 8-bromo cyclic GMP (1mM), and were blocked by KT5823 (1 microM) (inhibitor PKG) or LY83583 (1 microM) (guanylate cyclase inhibitor). Moreover, NPs were shown to induce significant increases of intracellular catecholamine contents (ANP= BNP> CNP). These findings suggest that NPs induced increases of TH mRNA through cGMP/PKG dependent mechanisms, which, in turn, resulted in stimulation of catecholamine synthesis in PC12 cells.

ENHANCED EXPRESSION OF mRNA CODING FOR THE ADRENALINE- SYNTHESIZING ENZYME PHENYLETHANOLAMINE-N-METHYL TRANSFERASE IN ADRENALINE-SECRETING PHEOCHROMOCYTOMAS

PURPOSE In some pheochromocytomas, the tumors contain and secrete greater amounts of adrenaline than do normal adrenal medullas. It is not yet known how adrenaline synthesis is enhanced in the adrenaline-secreting pheochromocytomas. MATERIALS AND METHODS As a first step toward understanding the molecular mechanisms by which adrenaline synthesis is controlled in these tumors, we measured the level of mRNA coding for the adrenaline-synthesizing enzyme phenylethanolamine N-methyl transferase (PNMT) and the content of adrenaline in the pheochromocytomas (n = 9), including 3 cases of the adrenaline-secreting type (one of the patients had bilateral pheochromocytomas), and in normal adrenal medullas (n = 7). We then measured the concentration of cortisol, which is thought to regulate the PNMT activity. Finally, we examined the expression of the mRNA for Egr-1, which was recently reported to be a transcriptional factor regulating PNMT gene expression. RESULTS In the 4 tissue specimens from 3 adrenaline-secreting pheochromocytomas, the contents of adrenaline and the PNMT mRNA expression were considerably greater than those of the normal adrenal medullas. PNMT immunoreactivity was only detected in the adrenaline-secreting tumors. Three of the 4 specimens showed high concentrations of cortisol. To show the capacity for cortisol production locally in the pheochromocytoma tissues, we showed the expression of a glucocorticoid biosynthetic enzyme, 17alpha-hydroxylase, in the tumors by Western blotting. PNMT expression was found to be associated with 17alpha-hydroxylase expression in the tumors. The glucocorticoid receptor expression was also correlated with PNMT expression in the tumors and the expression of Egr-1 was also high in 3 of the 4 specimens. CONCLUSIONS These findings indicate that adrenaline production in adrenaline-secreting pheochromocytomas is primarily controlled by the level of PNMT gene expression, and that the gene expression may be enhanced by both cortisol and Egr-1.

Inhibition of Ubiquitin Ligase F-box and WD Repeat Domain-containing 7α (Fbw7α) Causes Hepatosteatosis through Krüppel-like Factor 5 (KLF5)/Peroxisome Proliferator-activated Receptor γ2 (PPARγ2) Pathway but Not SREBP-1c Protein in Mice

F-box and WD repeat domain-containing 7α (Fbw7α) is the substrate recognition component of a ubiquitin ligase that controls the degradation of factors involved in cellular growth, including c-Myc, cyclin E, and c-Jun. In addition, Fbw7α degrades the nuclear form of sterol regulatory element-binding protein (SREBP)-1a, a global regulator of lipid synthesis, particularly during mitosis in cultured cells. This study investigated the in vivo role of Fbw7α in hepatic lipid metabolism. siRNA knockdown of Fbw7α in mice caused marked hepatosteatosis with the accumulation of triglycerides. However, inhibition of Fbw7α did not change the level of nuclear SREBP-1 protein or the expression of genes involved in fatty acid synthesis and oxidation. In vivo experiments on the gain and loss of Fbw7α function indicated that Fbw7α regulated the expression of peroxisome proliferator-activated receptor (PPAR) γ2 and its target genes involved in fatty acid uptake and triglyceride synthesis. These genes included fatty acid transporter Cd36, diacylglycerol acyltransferase 1 (Dgat1), and fat-specific protein 27 (Cidec). The regulation of PPARγ2 by Fbw7α was mediated, at least in part, by the direct degradation of the Krüppel-like factor 5 (KLF5) protein, upstream of PPARγ2 expression. Hepatic Fbw7α contributes to normal fatty acid and triglyceride metabolism, functions that represent novel aspects of this cell growth regulator.

Novel Germline Mutations in the SDHB and SDHD Genes in Japanese Pheochromocytomas

The SDHA, SDHB, SDHC, and SDHD genes code for subunits of succinate dehydrogenase (SDH), which forms part of the mitochondrial respiratory chain. Germline mutations in the genes encoding SDHB and SDHD have been reported in familial paragangliomas/pheochromocytomas and in apparently sporadic pheochromocytomas. SDHB and SDHD mutations are widely distributed along the genes with no apparent hot spots. SDHB mutations are often detected in malignant and extra-adrenal pheochromocytomas. SDHD mutations are also detected frequently in head and neck paragangliomas. We sequenced the entire coding regions of the SDHB and SDHD genes in 17 pheochromocytomas. Weidentified novel heterozygous G to A point mutations at the first base of intron 3 of the SDHB gene in a malignant extra-adrenal abdominal pheochromocytoma patient, and at the first base of codon 111 of the SDHD gene in an adrenal pheochromocytoma patient. Further, we confirmed the SDHD mutation by DHPLC. The prevalence of SDHB and SDHD mutations in pheochromocytomas we examined was 12% (2/17). Thus, we identified two novel SDH mutations in Japanese pheochromocytomas. Further studies will investigate the oncogenic potential of these mutations.