Takuhiro Sonoyama

Natriuretic Peptides/cGMP/cGMP-dependent Protein Kinase Cascades Promote Muscle Mitochondrial Biogenesis and Prevent Obesity.

OBJECTIVE Natriuretic peptides (NPs) have been characterized as vascular hormones that regulate vascular tone via guanylyl cyclase (GC), cyclic GMP (cGMP), and cGMP-dependent protein kinase (cGK). Recent clinical studies have shown that plasma NP levels were lower in subjects with the metabolic syndrome. The present study was conducted to elucidate the roles for NP/cGK cascades in energy metabolism. RESEARCH DESIGN AND METHODS We used three types of genetically engineered mice: brain NP (BNP) transgenic (BNP-Tg), cGK-Tg, and guanylyl cyclase-A (GCA) heterozygous knockout (GCA+/−) mice and analyzed the metabolic consequences of chronic activation of NP/cGK cascades in vivo. We also examined the effect of NPs in cultured myocytes. RESULTS BNP-Tg mice fed on high-fat diet were protected against diet-induced obesity and insulin resistance, and cGK-Tg mice had reduced body weight even on standard diet; surprisingly, giant mitochondria were densely packed in the skeletal muscle. Both mice showed an increase in muscle mitochondrial content and fat oxidation through upregulation of peroxisome proliferator–activated receptor (PPAR)-γ coactivator (PGC)-1α and PPARδ. The functional NP receptors, GCA and guanylyl cyclase-B, were downregulated by feeding a high-fat diet, while GCA+/− mice showed increases in body weight and glucose intolerance when fed a high-fat diet. NPs directly increased the expression of PGC-1α and PPARδ and mitochondrial content in cultured myocytes. CONCLUSIONS The findings together suggest that NP/cGK cascades can promote muscle mitochondrial biogenesis and fat oxidation, as to prevent obesity and glucose intolerance. The vascular hormone, NP, would contribute to coordinated regulation of oxygen supply and consumption.

Adipogenic differentiation of human induced pluripotent stem cells: Comparison with that of human embryonic stem cells

Induced pluripotent stem (iPS) cells were recently established from human fibroblasts. In the present study we investigated the adipogenic differentiation properties of four human iPS cell lines and compared them with those of two human embryonic stem (ES) cell lines. After 12 days of embryoid body formation and an additional 10 days of differentiation on Poly‐l‐ornithine and fibronectin‐ coated dishes with adipogenic differentiation medium, human iPS cells exhibited lipid accumulation and transcription of adipogenesis‐related molecules such as C/EBPα, PPARγ2, leptin and aP2. These results demonstrate that human iPS cells have an adipogenic potential comparable to human ES cells.

Transplantation of vascular cells derived from human embryonic stem cells contributes to vascular regeneration after stroke in mice.

BackgroundWe previously demonstrated that vascular endothelial growth factor receptor type 2 (VEGF-R2)-positive cells induced from mouse embryonic stem (ES) cells can differentiate into both endothelial cells (ECs) and mural cells (MCs) and these vascular cells construct blood vessel structures in vitro. Recently, we have also established a method for the large-scale expansion of ECs and MCs derived from human ES cells. We examined the potential of vascular cells derived from human ES cells to contribute to vascular regeneration and to provide therapeutic benefit for the ischemic brain.MethodsPhosphate buffered saline, human peripheral blood mononuclear cells (hMNCs), ECs-, MCs-, or the mixture of ECs and MCs derived from human ES cells were intra-arterially transplanted into mice after transient middle cerebral artery occlusion (MCAo).ResultsTransplanted ECs were successfully incorporated into host capillaries and MCs were distributed in the areas surrounding endothelial tubes. The cerebral blood flow and the vascular density in the ischemic striatum on day 28 after MCAo had significantly improved in ECs-, MCs- and ECs+MCs-transplanted mice compared to that of mice injected with saline or transplanted with hMNCs. Moreover, compared to saline-injected or hMNC-transplanted mice, significant reduction of the infarct volume and of apoptosis as well as acceleration of neurological recovery were observed on day 28 after MCAo in the cell mixture-transplanted mice.ConclusionTransplantation of ECs and MCs derived from undifferentiated human ES cells have a potential to contribute to therapeutic vascular regeneration and consequently reduction of infarct area after stroke.

The role of mineralocorticoid receptor expression in brain remodeling after cerebral ischemia.

Mineralocorticoid receptors (MRs) are classically known to be expressed in the distal collecting duct of the kidney. Recently it was reported that MR is identified in the heart and vasculature. Although MR expression is also found in the brain, it is restricted to the hippocampus and cerebral cortex under normal condition, and the role played by MRs in brain remodeling after cerebral ischemia remains unclear. In the present study, we used the mouse 20-min middle cerebral artery occlusion model to examine the time course of MR expression and activity in the ischemic brain. We found that MR-positive cells remarkably increased in the ischemic striatum, in which MR expression is not observed under normal conditions, during the acute and, especially, subacute phases after stroke and that the majority of MR-expressing cells were astrocytes that migrated to the ischemic core. Treatment with the MR antagonist spironolactone markedly suppressed superoxide production within the infarct area during this period. Quantitative real-time RT-PCR revealed that spironolactone stimulated the expression of neuroprotective or angiogenic factors, such as basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF), whereas immunohistochemical analysis showed astrocytes to be cells expressing bFGF and VEGF. Thereby the incidence of apoptosis was reduced. The up-regulated bFGF and VEGF expression also appeared to promote endogenous angiogenesis and blood flow within the infarct area and to increase the number of neuroblasts migrating toward the ischemic striatum. By these beneficial effects, the infarct volume was significantly reduced in spironolactone-treated mice. Spironolactone may thus provide therapeutic neuroprotective effects in the ischemic brain after stroke.

C-Type Natriuretic Peptide as a New Regulator of Food Intake and Energy Expenditure

The physiological implication of C-type natriuretic peptide (CNP) including energy metabolism has not been elucidated, because of markedly short stature in CNP-null mice. In the present study we analyzed food intake and energy expenditure of CNP-null mice with chondrocyte-targeted CNP expression (CNP-Tg/Nppc(-/-) mice), in which marked skeletal dysplasia was rescued, to investigate the significance of CNP under minimal influences of skeletal phenotypes. In CNP-Tg/Nppc(-/-) mice, body weight and body fat ratio were reduced by 24% and 32%, respectively, at 20 wk of age, and decreases of blood glucose levels during insulin tolerance tests were 2-fold exaggerated at 17 wk of age, as compared with CNP-Tg/Nppc(+/+) mice. Urinary noradrenalin excretion of CNP-Tg/Nppc(-/-) mice was greater than that of CNP-Tg/Nppc(+/+) mice by 28%. In CNP-Tg/Nppc(-/-) mice, rectal temperature at 1600 h was higher by 1.1 C, and uncoupling protein-1 mRNA expression in the brown adipose tissue was 2-fold increased, which was canceled by propranolol administration, as compared with CNP-Tg/Nppc(+/+) mice. Oxygen consumption was significantly increased in CNP-Tg/Nppc(-/-) mice compared with that in CNP-Tg/Nppc(+/+) mice. Food intake of CNP-Tg/Nppc(-/-) mice upon ad libitum feeding and refeeding after 48 h starvation were reduced by 21% and 61%, respectively, as compared with CNP-Tg/Nppc(+/+) mice. This study unveiled a new aspect of CNP as a molecule regulating food intake and energy expenditure. Further analyses on precise mechanisms of CNP actions would lead to the better understanding of the significance of the CNP/guanylyl cyclase-B system in food intake and energy expenditure.

Inhibition of hepatic damage and liver fibrosis by brain natriuretic peptide

Anti‐fibrotic and organ protective effects of brain natriuretic peptide (BNP) have been reported. In this study, effects of BNP on liver fibrosis were examined in the carbon tetrachloride (CCl4)‐induced liver fibrosis model using BNP‐transgenic (Tg) and wild‐type (WT) mice. Twice‐a‐week intraperitoneal injections of CCl4 for 8 weeks resulted in massive liver fibrosis, augmented transforming growth factor (TGF)‐β1 and type I procollagen α1 chain (Col1a1) mRNA expression, and the hepatic stellate cell (HSC) activation in WT mice, all of which were significantly suppressed in Tg mice. These observations indicate that BNP inhibits liver fibrosis by attenuating the activation of HSCs.

Adrenal reserve function after unilateral adrenalectomy in patients with primary aldosteronism.

Objective: After unilateral adrenalectomy (uADX) in patients with a unilateral aldosterone-producing adenoma (APA), the remaining contralateral adrenal gland is generally considered sufficient to support life. However, few studies have compared adrenal reserve function before and after uADX. Therefore, we closely evaluated adrenal cortisol secretory function before and after uADX in patients with unilateral APA. Methods: Patients who were diagnosed with APA and underwent uADX for unilateral APA were initially included in this study. Patients with subclinical Cushings syndrome (SCS) or Cushings syndrome were excluded on suspicion of autonomous cortisol secretion. Fourteen patients were finally evaluated. Morning basal serum cortisol and plasma adrenocorticotropin hormone (ACTH) levels were measured, and ACTH stimulation tests under 1-mg dexamethasone suppression (dex-ACTH test) were performed before and after uADX. Results: No patient developed clinical adrenal insufficiency. Basal cortisol levels were not significantly different before and after uADX. However, basal ACTH levels were significantly elevated after uADX. In addition, peak cortisol levels on the dex-ACTH test decreased in all patients after uADX. The peak cortisol level after uADX was 86.6 (81.4–92.4)% of the level before uADX. Conclusion: The adrenal cortisol secretory response to ACTH stimulation is mildly reduced after uADX in patients with unilateral APA without SCS or Cushings syndrome, although their basal cortisol level is sustained by elevated ACTH. These data will be important as a point of discussion when patients with unilateral APA consider either uADX or specific pharmacotherapy as treatment options.

Significance of dopamine D 1 receptor signalling for steroidogenic differentiation of human induced pluripotent stem cells

Human induced pluripotent stem cells (hiPSCs) are expected to be both a revolutionary cell source for regenerative medicine and a powerful tool to investigate the molecular mechanisms underlying human cell development in vitro. In the present study, we tried to elucidate the steroidogenic differentiation processes using hiPSC-derived intermediate mesoderm (IM) that is known to be the origin of the human adrenal cortex and gonads. We first performed chemical screening to identify small molecules that induce steroidogenic differentiation of IM cells expressing Odd-skipped related 1 (OSR1), an early IM marker. We identified cabergoline as an inducer of 3β-hydroxysteroid dehydrogenase, an essential enzyme for adrenogonadal steroidogenesis. Although cabergoline is a potent dopamine D2 receptor agonist, additional experiments showed that cabergoline exerted effects as a low-affinity agonist of D1 receptors by increasing intracellular cyclic AMP. Further analysis of OSR1+ cells transfected with steroidogenic factor-1/adrenal 4 binding protein revealed that D1 receptor agonist upregulated expression of various steroidogenic enzymes and increased secretion of steroid hormones synergistically with adrenocorticotropic hormone. These results suggest the importance of dopamine D1 receptor signalling in steroidogenic differentiation, which contributes to effective induction of steroidogenic cells from hiPSCs.

PS 14-79 ROLE OF ENDOGENOUS ADRENOCORTICOTROPIC HORMONE ON CIRCADIAN ALDOSTERONE RHYTHM IN PATIENTS WITH PRIMARY ALDOSTERONISM

Objective: We recently reported that stimulation with high-dose adrenocorticotropin (ACTH) caused different responses in terms of aldosterone secretion in aldosterone-producing adenomas (APAs) and idiopathic hyperaldosteronism (IHA) in patients with primary aldosteronism (PA). However, the role of endogenous ACTH in aldosterone secretion in PA has not been systematically evaluated. In this study, we examined diurnal changes in plasma aldosterone concentration (PAC), and changes in PAC after dexamethasone administration in patients with suspected PA, in order to evaluate the effect of endogenous ACTH on aldosterone secretion. Design and Method: Seventy-three patients admitted to Kyoto University Hospital with suspected PA were included. Patients were classified into non-PA, IHA, and APA groups according to the results of captopril challenge test and adrenal venous sampling. PAC at 09.00 (PAC0900), 23.00 (PAC2300), and after 1 mg dexamethasone suppression (PACdex) were measured and compared among the three groups. The PAC2300/PAC0900, and PACdex/PAC0900 ratios were also analyzed. Results: PAC2300 and PACdex were lower than PAC0900 in all three groups. There were no significant differences in PAC2300/PAC0900 among the three groups. However, PACdex/PAC0900 was significantly lower in the APA group compared with the non-PA and IHA groups. Conclusions: The results of this study indicate that aldosterone secretion in APA patients is more strongly dependent on endogenous ACTH than in IHA and non-PA patients. The results also suggest that factors other than ACTH, such as clock genes, may cause diurnal changes in aldosterone secretion in IHA and non-PA patients.