It has been thought that adipocytes lack proliferative ability and do not revert to precursor cells. However, numerous findings that challenge this notion have also been reported. The idea that adipocytes dedifferentiate to fibroblast-like cells with increasing cell number was reported in 1975. This possibility has been ignored despite knowledge gained in the 1990s regarding adipocyte differentiation. Several studies on proliferation and dedifferentiation of adipocytes have been published, most of which were conducted from the perspective of regenerative medicine. However, the concept of proliferation of adipocytes remains unclear. In this study, we postulate a new population of adipocytes, which consist of small sized cells (less than 20 μm in diameter) expressing adipocyte markers, such as adiponectin and peroxisome proliferator-activated receptor γ (PPARγ), but not possessing large lipid droplets. These cells show marked ability to incorporate 5-bromo-2′-deoxyuridine (BrdU), for which reason we termed them “small proliferative adipocytes (SPA)”. In addition, SPA are observed in the stromal vascular fraction. Since SPA are morphologically different from mature adipocytes, we regarded them as committed progenitor cells. When proliferation of adipocytes in vivo is assessed by measuring BrdU incorporation and expression levels of proliferating cell nuclear antigen (PCNA) in isolated fractions of adipocytes from adipose tissues, subcutaneous SPA proliferate less actively than visceral SPA. Treatment with pioglitazone increases the number of proliferating SPA in subcutaneous, but not visceral, fat, suggesting that SPA may be important in regulating systemic insulin sensitivity and glucose metabolism.
Our previous study reported that thyroid-stimulating hormone (TSH) promotes cholesterol synthesis via the cyclic adenosine monophosphate/protein kinase A/cAMP regulatory element-binding protein (cAMP/PKA/CREB) pathway after binding to TSH receptors (TSHR) in the liver. The hepatic cAMP/PKA/CREB pathway also plays an important role in maintaining fasting glucose homeostasis. These findings implied a possible role for TSH in hepatic glucose metabolism. In this study, we used TSH receptor knockout mice (Tshr-ko mice) to clarify the effect of Tshr deletion on hepatic glucose metabolism, and investigated whether the effects of TSH directly regulate hepatic gluconeogenesis in HepG2 cells. Tshr-ko mice exhibited decreased fasting blood glucose levels, increased insulin sensitivity but normal level of fasting plasma insulin. Tshr deletion impaired hepatic glucose production by down-regulating the expression of glucose-6-phosphatase (G6P) and phosphoenolpyruvate pyruvate carboxylase (PEPCK) mRNA, two rate-limiting enzymes in hepatic gluconeogenesis, and enhancing the abundance of hepatic glucokinase (GK), the first enzyme regulating glycogen synthesis. Moreover, Tshr deletion inhibited the protein expression of hepatic phospho-CREB and increased the protein expression of hepatic phospho-AMP-activated protein kinase (p-AMPK), two up-stream regulators of PEPCK and G6P mRNA. In HepG2 cells, TSH increased the expression of G6P and PEPCK at mRNA level. These results indicated the simulative effects of TSH on hepatic glucose production in vivo and in vitro, suggesting a novel role for TSH in hepatic glucose metabolism.
A 73-year-old woman with malignant insulinoma was treated with 100 μg/day octreotide for unresected insulinoma and liver metastases. The daily administration of the drug induced hyperglycemia after dinner in addition to existing fasting hypoglycemia possibly because this drug suppressed both insulin and glucagon secretion and its blood concentration was unstable. After replacing a daily injection of octreotide with a monthly injection of octreotide long-acting repeatable (LAR), blood glucose levels stabilized within the normal range. The findings of the present study showed that octreotide LAR could be useful for the long-term treatment of unresectable insulinomas.
The screening of dysglycemia in the non-fasting state is a challenging issue in healthcare practice. We investigated whether the additional measurement of circulating adiponectin levels could improve screening performance. We used a database of 1190 Japanese employees with metabolic risk factors, who underwent a 75-g oral glucose tolerance test (OGTT), following non-fasting health check-ups. Dysglycemia was defined as fasting glucose levels ≥6.1 mmol/L or 2-hr glucose levels ≥7.8 mmol/L during the OGTT. Logistic regression analysis revealed that decreased adiponectin levels were associated with dysglycemia, independently of postprandial glucose (PG) and hemoglobin A1c (HbA1c) levels, as well as other health check-up data (p<0.01). The trivariate model with PG, HbA1c, and adiponectin levels (PG+A1c+ADN model) had a larger area under the receiver operating characteristic curves (AUC) than the bivariate model with only PG and HbA1c levels (0.746 vs. 0.729; p=0.01). However, the AUC of the multivariate model with PG, HbA1c, and other health check-up data, but not adiponectin levels (PG+A1c+Other model) was 0.815, much larger than that of the PG+A1c+ADN model (p<0.01). The addition of adiponectin levels to the PG+A1c+Other model had a significantly larger AUC than the A1c+PG+Other model only in the subgroup without abdominal obesity (p=0.01), but not in the overall population (p=0.06) or in the subgroup with abdominal obesity (p=0.62). In conclusion, circulating adiponectin levels were independently associated with dysglycemia in non-fasting Japanese employees with metabolic risk factors, but they improved the screening capacity only in those without abdominal obesity.
The prevalence of primary aldosteronism (PA) is around 3-15% in patients with hypertension. Hypertension is a frequent complication of type 2 diabetes mellitus (DM) because of the close etiological relationship between these two diseases. However, the possibility of PA in patients with DM and hypertension is often overlooked and the prevalence of PA in patients with DM and hypertension in Japan is unknown. We enrolled 124 hospitalized patients with both DM and hypertension. PA was diagnosed according to the modified criteria for Japanese patients. We examined the prevalence of PA and compared clinical characteristics between patients with and without PA. In another analysis of 43 patients with a confirmed diagnosis of PA, we compared the characteristics of patients with and without DM. Overall, 14/124 patients with DM and hypertension (11.3%) were diagnosed with PA. Multivariate logistic regression showed that the duration of DM was significantly shorter in the PA group. Fisher’s direct probability test revealed that history of hypertension before the diagnosis of DM was a significant factor in patients with PA. Treatment with an angiotensin II receptor blocker (ARB) did not affect the diagnosis of PA in these patients. Among 43 patients with PA, those with DM were significantly older and the delay to the diagnosis of PA was significantly longer compared with patients without DM. In conclusion, almost 10% of patients with DM and hypertension actually have PA. More extensive screening for PA is recommended in patients with DM and hypertension, regardless of the use of ARBs.
Thyroid hormone is a potent regulator of metabolic and energy homeostasis implicated in various metabolic diseases. Fibroblast growth factor 21(FGF21) is a systemic metabolic regulator known to modulate various biological functions similar to the actions of thyroid hormone. We investigated the differences in plasma FGF21 concentrations in patients with varying thyroid function. Ninety drug-naïve subjects who underwent thyroid evaluation at Seoul National University Bundang Hospital were enrolled and classified into euthyroid, subclinical hypothyroid, and overtly hypothyroid groups. Biochemical markers and plasma FGF21 levels were measured and analyzed. The mean age of the subjects was 42.6 ± 9.1 years. The mean body mass index (BMI), waist circumference, and fasting glucose concentrations were similar between groups. Overtly hypothyroid subjects exhibited significantly higher concentrations of total cholesterol, triglyceride, and LDL-cholesterol than the other groups (p<0.01). Mean plasma FGF21 concentrations in euthyroid, subclinical hypothyroid and overtly hypothyroid groups were 43.2 ± 39.2 pg/mL, 63.6 ± 73.6 pg/mL, and 101.5 ± 74.9 pg/mL, respectively (p<0.01 between groups). Plasma FGF21 concentrations remained significantly higher in overtly hypothyroid subjects after adjusting for serum triglyceride concentrations (p<0.005). Multivariate analysis revealed a significant positive linear relationship between serum TSH concentrations and plasma FGF21 concentrations (β = 0.192, p = 0.002) and a significant negative linear relationship between free T4 and plasma FGF21 concentrations (β = −0.382, p = 0.037) after adjusting for gender, BMI and serum concentrations of triglycerides and glucose. Plasma FGF21 levels were significantly increased in patients with hypothyroidism independently of BMI, or lipid or glucose metabolism.
Thyroid nodules that exhibit focal uptake of fluorine-18 (18F)-fluorodeoxyglucose (FDG) are relatively frequent. Although the clinical features and associated mechanisms of FDG-avid lesions in both thyroid cancer and cytologically indeterminate nodules have been extensively studied, not much information is available on benign nodules. Therefore, in this retrospective study, the clinical, serological, and sonographic features of 15 benign FDG-avid nodules were compared with those of 17 non-avid lesions. Univariate analysis indicated that the FDG-positive and -negative nodules were similar with regard to age, gender, thyroid stimulating hormone (TSH), anti-thyroglobulin antibodies, tumor size, 4 B-mode sonographic findings (i.e., shape, margin, texture, and echo level), and/or elasticity. The presence of intranodular blood flow and the absence of a cystic component were associated with a greater possibility of positive FDG uptake. Multivariate analysis showed that vascularity was the only independent factor predicting FDG uptake. Across a wide range of tumor types, the extent of FDG uptake is positively correlated with tumor perfusion; this observation is consistent with the results of this study, which shows that FDG uptake in benign thyroid nodules is associated with increased vascularity.
The predominant risk factor of metabolic syndrome is intra-abdominal fat accumulation, which is determined by waist circumference, waist-hip ratio measurements and visceral fat area (VFA); the latter can be accurately measured by performing computed tomography (CT). In addition to environmental factors, genetic factors play an important role in obesity and fat distribution. New genetic loci associated with body mass index (BMI) and adiposity have been identified by genome-wide association studies (GWASs). This study utilized CT to investigate whether single nucleotide polymorphisms (SNPs) that confer susceptibility to higher BMI are associated with VFA, subcutaneous fat area (SFA), and the ratio of VFA to SFA (V/S ratio). We measured the VFA and SFA of 1424 obese Japanese subjects (BMI ≥ 25 kg/m2, 635 men and 789 women) who were genotyped for 13 single nucleotide polymorphisms (SNPs) reported by recent GWASs, namely, TNNI3K rs1514175, PTBP2 rs1555543, ADCY3 rs713586, IRS1 rs2943650, POC5 rs2112347, NUDT3 rs206936, LINGO2 rs10968576, STK33 rs4929949, MTIF3 rs4771122, SPRY2 rs534870, MAP2K5 rs2241423, QPCTL rs2287019, and ZC3H4 rs3810291. The G-allele of NUDT3 rs206936 was significantly associated with increased BMI (P = 5.3 × 10-5) and SFA (P = 0.00039) in the obese Japanese women. After adjustment with BMI, the association between rs206936 and SFA was not observed. This significant association was not observed in the men. The other SNPs analyzed were not significantly associated with BMI, VFA, SFA, or V/S ratio. Our results suggest that NUDT3 rs206936 is associated with BMI in Japanese women.
Obesity consists of hypertrophy and hyperplasia of adipocytes. Although the number of adipocytes is influenced by anatomical location, nutritional environment, hormone and genetic variation, it has been thought to be determined by the proliferation of precursor cells and subsequent differentiation. However, our recent research has identified the population of small adipocytes less than 20 μm in diameter, exhibiting tiny or no lipid droplets and expressing adipocyte marker proteins (small proliferative adipocytes: SPA) in isolated adipocytes. Notably, 5-bromo-2′-deoxyuridine (BrdU) incorporation and proliferating cell nuclear antigen (PCNA) expression were detected in these cells. In this study, we investigated the role of SPA in development of adipose tissue using genetically obese diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats and their non-obese and non-diabetic littermates, Long-Evans Tokushima Otsuka (LETO) rats. Proliferation of SPA was determined by measurement of PCNA at the protein level in isolated fractions of adipocytes with collagenase digestion. In general, expression levels of PCNA rose, reached a maximum, and declined in adipose tissues during aging. The expression levels of PCNA were maximum in epididymal fat at 32 w and 12 w of age in LETO and OLETF, respectively. They reached the maximum at 20 w of age both in LETO and OLETF in mesenteric fat. Although the PCNA expression level was higher in OLETF in the early period, it reversed later. Enlargement of adipocytes developed during aging, which was enhanced when the expression levels of PCNA declined. These results suggest that proliferation of SPA may prevent adipocyte hypertrophy and the resultant development of metabolic disorders.
Combined pituitary hormone deficiency (CPHD), isolated hypogonadotropic hypogonadism (IHH), Kallmann syndrome (KS), and septo-optic dysplasia (SOD) are genetically related conditions caused by abnormal development of the anterior midline in the forebrain. Although mutations in the fibroblast growth factor receptor 1 (FGFR1) gene have been implicated in the development of IHH, KS, and SOD, the relevance of FGFR1 abnormalities to CPHD remains to be elucidated. Here, we report a Japanese female patient with CPHD and FGFR1 haploinsufficiency. The patient was identified through copy-number analyses and direct sequencing of FGFR1 performed for 69 patients with CPHD. The patient presented with a combined deficiency of GH, LH and FSH, and multiple neurological abnormalities. In addition, normal TSH values along with a low free T4 level indicated the presence of central hypothyroidism. Molecular analyses identified a heterozygous ~ 8.5 Mb deletion involving 56 genes and pseudogenes. None of these genes except FGFR1 have been associated with brain development. No FGFR1 abnormalities were identified in the remaining 68 patients, although two patients carried nucleotide substitutions (p.V102I and p.S107L) that were assessed as benign polymorphism by in vitro functional assays. These results indicate a possible role of FGFR1 in anterior pituitary function and the rarity of FGFR1 abnormalities in patients with CPHD.