In adrenal fasciculata cells stimulated by ACTH, Ca²⁺ and cAMP play indispensable roles as second messengers in cortisol production. However, whether their second messengers cooperatively or independently participate in steroid production remains unclear. We focused on the roles of Ca²⁺ and cAMP in cortisol production in bovine adrenal fasciculata cells stimulated by ACTH for a relatively short period (1 h). Incubation of the cells with 100 pM ACTH in Ca²⁺-containing (normal) medium for 1 h increased cortisol production without affecting cAMP content. In contrast, treatment of the cells with the peptide at a higher concentration (1 nM) significantly augmented both cortisol production and cAMP content. However, ACTH did not increase either of them in the Ca²⁺-free medium. ACTH rapidly increased the intracellular free Ca²⁺ concentration ([Ca²⁺]_i) in the normal medium, but did not influence [Ca²⁺]_i in the Ca²⁺-free medium, indicating that ACTH caused Ca²⁺ influx into the cells. ACTH-induced Ca²⁺ influx and cortisol production were suppressed by a voltage-sensitive L-type Ca²⁺ channel blocker but not by a T-type, N-type, or P-type Ca²⁺ channel blocker. In contrast, dibutyryl cAMP, a cell-permeable cAMP analog, greatly enhanced cortisol production in the normal or Ca²⁺-free medium and slowly caused Ca²⁺ influx into the cells. These results strongly suggest that Ca²⁺, as a second messenger, is more critical than cAMP for cortisol production. However, both second messengers jointly participate in the production in adrenal fasciculata cells stimulated by ACTH.

Immune checkpoint inhibitors (ICIs) are used for various malignancies, although they frequently cause immune-related adverse events involving the thyroid gland (thyroid irAEs). We conducted a retrospective cohort study to elucidate thyroid function outcomes. Fifty of 639 patients who received PD-1 blockade therapy met criteria and were divided into the following groups: thyrotoxicosis with subsequent hypothyroidism (Toxic-Hypo, n = 21); thyrotoxicosis without subsequent hypothyroidism (Toxic, n = 9); and hypothyroidism without prior thyrotoxicosis (Hypo, n = 20). The Toxic-Hypo group developed thyroid irAEs earlier than the Toxic group (26 vs. 91 days; p < 0.001), and had higher serum free T4 levels (3.210 vs. 1.880 ng/dL; p = 0.011). In addition, positive anti-thyroglobulin antibodies (TgAbs) at thyroid irAE onset were more common in the Toxic-Hypo group (93.3%) than in the Toxic group (0.0%; p = 0.005) and Hypo group (44.4%; p = 0.007). The Toxic-Hypo group developed severe hypothyroidism and required larger levothyroxine (LT4) doses than the Hypo group (75 vs. 25 μg/day; p = 0.007). We predicted that patients with positive TgAbs who developed severe thyrotoxicosis within 4 weeks after the first ICI administration would develop subsequent hypothyroidism. We treated 4 such patients with prompt LT4 replacement, characterized by LT4 initiation after thyrotoxicosis improvement and quick dose titration. Their euthyroid state was successfully maintained, in contrast with patients receiving conventional replacement. In conclusion, rapid-onset severe thyrotoxicosis in patients with TgAbs correlated with a high likelihood of subsequent hypothyroidism. Accordingly, prompt LT4 replacement is suggested to prevent a severely hypothyroid state.

Over 100 years have passed since insulin was first administered to a diabetic patient. Since then great strides have been made in diabetes research. It has determined where insulin is secreted from, which organs it acts on, how it is transferred into the cell and is delivered to the nucleus, how it orchestrates the expression pattern of the genes, and how it works with each organ to maintain systemic metabolism. Any breakdown in this system leads to diabetes. Thanks to the numerous researchers who have dedicated their lives to cure diabetes, we now know that there are three major organs where insulin acts to maintain glucose/lipid metabolism: the liver, muscles, and fat. The failure of insulin action on these organs, such as insulin resistance, result in hyperglycemia and/or dyslipidemia. The primary trigger of this condition and its association among these tissues still remain to be uncovered. Among the major organs, the liver finely tunes the glucose/lipid metabolism to maintain metabolic flexibility, and plays a crucial role in glucose/lipid abnormality due to insulin resistance. Insulin resistance disrupts this tuning, and selective insulin resistance arises. The glucose metabolism loses its sensitivity to insulin, while the lipid metabolism maintains it. The clarification of its mechanism is warranted to reverse the metabolic abnormalities due to insulin resistance. This review will provide a brief historical review for the progress of the pathophysiology of diabetes since the discovery of insulin, followed by a review of the current research clarifying our understanding of selective insulin resistance.

Diabetic nephropathy is a public health problem worldwide. Our understanding of the molecular machinery, as well as the clinical therapies for diabetic nephropathy, has evolved dramatically in recent years. However, even with this progress, there are residual risks of kidney failure and cardiovascular events in patients with diabetes. Rho-associated, coiled-coil-containing protein kinase (ROCK) is activated in response to various pathologic stimuli in the context of diabetes. The contribution of ROCK has been investigated in vivo using gene deletion rodent models and specific inhibitors, which are providing key insights into the pathologic function of ROCK in diabetic nephropathy. ROCK has two isoforms, ROCK1 and ROCK2. Both isoforms are expressed in the kidney, including mesangial cells, podocytes, and endothelial cells. ROCK1 blunts AMP-activated protein kinase (AMPK), while ROCK2 negatively regulates peroxisome proliferator-activated receptor α (PPARα) to inhibit fatty acid oxidation, both of which lead to structural and functional impairment of glomeruli in diabetes. Of note, ROCK signaling is activated in the kidney of animal models and patients with diabetes. In addition, an observational study has shown that fasudil hydrochloride, an ATP-competitive selective ROCK inhibitor, significantly attenuated proteinuria among patients with diabetes. These findings highlight the promising prospects for the development of a ROCK-centered approach against the progression of diabetic nephropathy.

Testosterone plays a key role in the maintenance of physical and mental functions in men. Age-related testosterone decline is closely associated with sarcopenia and muscle deterioration, while testosterone decline is linked with the etiology and prevention of diseases such as angina pectoris, arteriosclerosis, obesity, metabolic syndrome, and dementia. Late-onset hypogonadism (LOH) is defined as a disease characterized by age-related testosterone decline and associated clinical symptoms. Testosterone replacement therapy improves health-related QOL in patients with LOH.

Paraneoplastic syndromes are defined by symptoms or signs resulting from damage to organs or tissues that are remote from the site of malignant neoplasms or its metastasis. They are due to tumor secretion of functional hormones or peptides or are related to immune cross-reactivity with the host tissue. In particular, paraneoplastic endocrine syndromes are mainly caused by ectopic hormone production by the tumor such as PTHrP in humoral hypercalcemia in malignancy and ACTH in ectopic ACTH syndrome. Recently, it has been reported that a specific form of hypophysitis is caused as an immune-mediated paraneoplastic syndrome; paraneoplastic autoimmune hypophysitis, in which an ectopic pituitary antigen expression in the tumor evoked autoimmunity against pituitary-specific antigens, resulting in hypophysitis and exhibiting the injury of specific anterior pituitary cells by cytotoxic T cells. This novel clinical entity, paraneoplastic autoimmune hypophysitis consists of several conditions such as anti-PIT-1 hypophysitis and a part of isolated ACTH deficiency and immune checkpoint inhibitor-related hypophysitis with common mechanisms. These conditions can explain at least in part, the underlying mechanisms of acquired specific pituitary hormone deficiencies. In addition, it is important to apply a comprehensive discipline of onco-immuno-endocrinology to understand the pathophysiology and this approach; the expansion and application of immune-mediated paraneoplastic syndrome to endocrine diseases may give a new clue to understand pathophysiology of the autoimmunity against endocrine organs.

Decidualization is a process of differentiation of human endometrial stromal cells (hESCs) accompanied by dramatic changes in cellular functions. This process is critical for embryo implantation and the establishment of pregnancy. Impairment of decidualization of hESCs leads to implantation failure, miscarriage, and unexplained infertility. The present review focuses on the metabolic changes in hESCs during decidualization. One of the changes taking place is in the glucose metabolism. Glucose uptake increases during decidualization because glucose is essential for the decidualization of hESCs. In hESCs, GLUT1 is highly expressed and involved in the increase of glucose uptake during decidualization. The up-regulation of GLUT1 is mediated by an epigenetic mechanism, which is regulated by CCAAT enhancer-binding protein β (C/EBPβ) and Wilms tumor 1 (WT1). Another metabolic change is in the lipid metabolism. Lipid accumulation in hESCs increases during decidualization. This increase is mediated by very low-density lipoprotein receptor (VLDLR). The up-regulation of VLDLR is regulated by WT1. In contrast to glucose, lipid is not essential for decidualization of hESCs. Endometrial cells have been implicated as important sources of nutrition for the embryo. hESCs may increase glucose and lipid storage so that they can supply them to the embryo during the implantation process. Taken together, decidualization is the process accompanied by metabolic changes, which may be associated with successful implantation.

After the discovery of GnRH, GnRH neurons have been considered to represent the final common pathway for the neural control of reproduction. There is now compelling data in mammals that two populations of kisspeptin neurons constitute two different systems to control the episodic and surge release of GnRH/LH for the control of different aspects of reproduction, follicular development and ovulation. However, accumulating evidence indicates that kisspeptin neurons in non-mammalian species do not serve as a regulator of reproduction, and the non-mammalian species are believed to show only surge release of GnRH to trigger ovulation. Therefore, the GnRH neurons in non-mammalian species may offer simpler models for the study of their functions in neuroendocrine regulation of reproduction, especially ovulation. Our research group has taken advantage of many unique technical advantages of small fish brain for the study of anatomy and physiology of GnRH neurons, which underlie regular ovulatory cycles during the breeding season. Here, recent advances in multidisciplinary study of GnRH neurons are reviewed, with a focus on studies using small teleost fish models.

The symptoms of diabetes insipidus may be masked by the concurrence of adrenal insufficiency and emerge after the administration of hydrocortisone, occasionally at high doses. To elucidate the mechanism underlying polyuria induced by the administration of high-dose corticosteroids in the deficiency of arginine vasopressin (AVP), we first examined the secretion of AVP in three patients in whom polyuria was observed only after the administration of high-dose corticosteroids. Next, we examined the effects of dexamethasone or aldosterone on water balance in wild-type and familial neurohypophyseal diabetes insipidus (FNDI) model mice. A hypertonic saline test showed that AVP secretion was partially impaired in all patients. In one patient, there were no apparent changes in AVP secretion before and after the administration of high-dose corticosteroids. In FNDI mice, unlike dexamethasone, the administration of aldosterone increased urine volumes and decreased urine osmolality. Immunohistochemical analyses showed that, after the administration of aldosterone in FNDI mice, aquaporin-2 expression was decreased in the apical membrane and increased in the basolateral membrane in the collecting duct. These changes were not observed in wild-type mice. The present data suggest that treatment with mineralocorticoids induces polyuria by reducing aquaporin-2 expression in the apical membrane of the kidney in partial AVP deficiency.

Familial partial lipodystrophy (FPLD) 3 is a rare genetic disorder caused by peroxisome proliferator-activated receptor γ gene (PPARG) mutations. Most cases have been reported in Western patients. Here, we describe a first pedigree of FPLD 3 in Japanese. The proband was a 51-year-old woman. She was diagnosed with fatty liver at age 32 years, dyslipidemia at age 37 years, and diabetes mellitus at age 41 years. Her body mass index was 18.5 kg/m², and body fat percentage was 19.2%. On physical examination, she had less subcutaneous fat in the upper limbs than in other sites. On magnetic resonance imaging, atrophy of subcutaneous adipose tissue was seen in the upper limbs and lower legs. Fasting serum C-peptide immunoreactivity was high (3.4 ng/mL), and the plasma glucose disappearance rate was low (2.07%/min) on an insulin tolerance test, both suggesting apparent insulin resistance. The serum total adiponectin level was low (2.3 μg/mL). Mild fatty liver was seen on abdominal computed tomography. On genetic analysis, a P495L mutation in PPARG was identified. The same mutation was also seen in her father, who had non-obese diabetes mellitus, and FPLD 3 was diagnosed. Modest increases in body fat and serum total adiponectin were seen with pioglitazone treatment. Attention should be paid to avoid overlooking lipodystrophy syndromes even in non-obese diabetic patients if they show features of insulin resistance.

The thyrotropin receptor (TSHR) plays critical roles in thyroid growth and function and in the pathogenesis of several thyroid diseases including Graves’ hyperthyroidism and ophthalmopathy, non-autoimmune hyperthyroidism and thyroid cancer. Several low-molecular weight compounds (LMWCs) and anti-TSHR monoclonal antibodies (mAbs) with receptor antagonistic and inverse agonistic activities have been reported. The former binds to the pocket formed by the receptor transmembrane bundle, and the latter to the extracellular TSH binding site. Both are effective inhibitors of TSH/thyroid stimulating antibody-stimulated cAMP and/or hyaluronic acid production in TSHR-expressing cells. Anti-insulin-like growth factor 1 inhibitors are also found to inhibit TSHR signaling. Each agent has advantages and disadvantages; for example, mAbs have a higher affinity and longer half-life but are more costly than LMWCs. At present, mAbs appear most promising, yet the development of more efficacious LMWCs is desirable. These agents are anticipated to be efficacious not only for the above-mentioned diseases but also for resistance to thyroid hormone and have utility for thyroid cancer radionuclide scintigraphy/therapy as a new theranostic.

Findings of preclinical studies and recent phase I/II clinical trials have shown that mesenchymal stem cells (MSCs) play a significant role in the development of diabetic kidney disease (DKD). Thus, MSCs have attracted increasing attention as a novel regenerative therapy for kidney diseases. This review summarizes recent literature on the roles and potential mechanisms, including hyperglycemia regulation, anti-inflammation, anti-fibrosis, pro-angiogenesis, and renal function protection, of MSC-based treatment methods for DKD. This review provides novel insights into understanding the pathogenesis of DKD and guiding the development of biological therapies.

Cushing’s disease is an endocrine disorder characterized by hypercortisolism, mainly caused by autonomous production of ACTH from pituitary adenomas. Autonomous ACTH secretion results in excess cortisol production from the adrenal glands, and corticotroph adenoma cells disrupt the normal cortisol feedback mechanism. Pan-histone deacetylase (HDAC) inhibitors inhibit cell proliferation and ACTH production in AtT-20 corticotroph tumor cells. A selective HDAC6 inhibitor has been known to exert antitumor effects and reduce adverse effects related to the inhibition of other HDACs. The current study demonstrated that the potent and selective HDAC6 inhibitor tubastatin A has inhibitory effects on proopiomelanocortin (Pomc) and pituitary tumor-transforming gene 1 (Pttg1) mRNA expression, involved in cell proliferation. The phosphorylated Akt/Akt protein levels were increased after treatment with tubastatin A. Therefore, the proliferation of corticotroph cells may be regulated through the Akt-Pttg1 pathway. Dexamethasone treatment also decreased the Pomc mRNA level. Combined tubastatin A and dexamethasone treatment showed additive effects on the Pomc mRNA level. Thus, tubastatin A may have applications in the treatment of Cushing’s disease.

Inorganic phosphate (Pi) in the mammalian body is balanced by its influx and efflux through the intestines, kidneys, bones, and soft tissues, at which several sodium/Pi co-transporters mediate its active transport. Pi homeostasis is achieved through the complex counter-regulatory feedback balance between fibroblast growth factor 23 (FGF23), 1,25-dihydroxyvitamin D (1,25(OH)₂D), and parathyroid hormone. FGF23, which is mainly produced by osteocytes in bone, plays a central role in Pi homeostasis and exerts its effects by binding to the FGF receptor (FGFR) and αKlotho in distant target organs. In the kidneys, the main target, FGF23 promotes the excretion of Pi and suppresses the production of 1,25(OH)₂D. Deficient and excess FGF23 result in hyperphosphatemia and hypophosphatemia, respectively. FGF23-related hypophosphatemic rickets/osteomalacia include tumor-induced osteomalacia and various genetic diseases, such as X-linked hypophosphatemic rickets. Coverage by the national health insurance system in Japan for the measurement of FGF23 and the approval of burosumab, an FGF23-neutralizing antibody, have had a significant impact on the diagnosis and treatment of FGF23-related hypophosphatemic rickets/osteomalacia. Some of the molecules responsible for genetic hypophosphatemic rickets/osteomalacia are highly expressed in osteocytes and function as local regulators of FGF23 production. A number of systemic factors also regulate FGF23 levels. Although the mechanisms responsible for Pi sensing in mammals have not yet been elucidated in detail, recent studies have suggested the involvement of FGFR1. The further clarification of the mechanisms by which osteocytes detect Pi levels and regulate FGF23 production will lead to the development of better strategies to treat hyperphosphatemic and hypophosphatemic conditions.

Adipose tissue is a complex heterogeneous tissue composed of adipocytes along with several non-adipocyte populations, including blood, stromal, endothelial, and progenitor cells, as well as extracellular matrix (ECM) components. As obesity progresses, the adipose tissue expands dynamically through adipocyte hypertrophy and/or hyperplasia. This expansion requires continuous ECM remodeling to properly accommodate the size increase as well as functional changes. Upon reaching a hypertrophic threshold beyond the adipocyte buffering capacity, excess ECM components are deposited, causing fibrosis and ultimately resulting in unhealthy metabolic maladaptation. These complex ECM remodeling processes in adipose tissues are regulated by the local environment, several key mediators, and genetic factors that are closely linked to insulin sensitivity. It is crucial to understand how adipocytes interact with nonadipocyte populations and various mediators (i.e., immune cells, ECM components, and adipokines) during these processes. This mini-review provides an overview of the latest research into the biology of obesity-induced adipose tissue fibrosis and its related clinical manifestations, providing insight for further studies aimed at controlling metabolic syndrome and its comorbidities.

A new meal tolerance test (MTT) using a 75 g glucose- and high fat-containing meal was applied to classify glucose intolerance in morbidly obese patients. According to the MTT data, the concordance rate of diagnosis was 82.5% compared to the 75 g oral glucose tolerance test (OGTT) in patients with normal glucose tolerance (NGT, n = 40). In the NGT patients, the insulinogenic index (r = 0.833), Matsuda index (r = 0.752), and disposition index (r = 0.845) calculated from the MTT data were each significantly (p < 0.001) correlated with those derived from the OGTT data. However, in patients with impaired glucose tolerance (IGT, n = 23) or diabetes mellitus (DM, n = 17), the postprandial glucose levels post-MTT were significantly lower than those post-OGTT, without increases in the postprandial insulin levels post-MTT. Thus, the severity of glucose intolerance measured by the MTT was milder than that indicated by the OGTT. Plasma levels of both glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) were increased at the postprandial state, but only the GIP levels post-MTT were significantly higher than those post-OGTT. The enhancement of glucose disposal rates in patients with NGT or IGT after the MTT was associated with increased GIP levels. The postprandial hypertriglyceridemia induced by the MTT was associated with insulin resistance, but it was not associated with the impaired insulinogenic index or the disposition index. These results indicate that the new MTT is clinically useful to evaluate both abnormal glucose and triglyceride excursions caused by abnormal insulin sensitivity and secretions of insulin and gut hormones in morbidly obese patients.

Plasma renin activity (PRA) is lower in patients with diabetic nephropathy (DN) than in healthy individuals. However, the association, if any, between PRA and renal outcomes in patients with DN remains uncertain. In a 2-year prospective observational study, we aimed to investigate the association of PRA with the decline in kidney function in patients with DN. We studied 97 patients with DN who were categorized according to tertile (T1–T3) of PRA. The annual changes in estimated glomerular filtration rate (eGFR) (mL/min/1.73 m²/year) were determined from the slope of the linear regression curve for eGFR. The secondary endpoint was defined as a composite of the doubling of serum creatinine or end-stage renal disease. Results showed that kidney function rapidly declined with lower tertiles of PRA (median value [interquartile range] of the annual eGFR changes: –8.8 [–18.5 to –4.2] for T1, –8.0 [–14.3 to –3.2] for T2, and –3.1 [–6.3 to –2.0] for T3; p for trend <0.01). Multivariable linear regression analyses showed that, compared with T3, T1 was associated with a larger annual change in eGFR (coefficient, –4.410; 95% confidence interval [CI], –7.910 to –0.909 for T1). Composite renal events occurred in 46 participants. In multivariable Cox analysis, the lower tertiles of PRA (T1 and T2) were associated with higher incidences of the composite renal outcome (T2: hazard ratio [HR], 4.78; 95% CI, 1.64–13.89; T1: HR, 4.85; 95% CI 1.61–14.65) than T3. In conclusion, low PRA is independently associated with poor renal outcomes in patients with DN.

The burden of disease of X-linked hypophosphatemia (XLH) in East Asia is poorly understood. This was a cross-sectional study using an online questionnaire to evaluate health-related quality of life (HRQOL) and disease complications in Japanese and Korean patients with XLH. Adults with XLH and the caregivers of children <18 years of age with XLH in Japan and Korea were surveyed. Respondents disclosed demographic data, family history, diagnostic history, medical history, surgical history, disease-specific clinical symptoms, treatment, medications, and use of ancillary equipment. Patient-reported outcomes (PROs; the Western Ontario and McMaster Universities Osteoarthritis Index, the brief pain inventory, and the 36-item short form health survey version 2) were used to assess pain, disability, and HRQOL in adults. Of those surveyed, all 14 children (100%) and 30/32 adults (93.8%) were receiving treatment for XLH. However, despite oral phosphate and active vitamin D use, short stature, gait abnormalities, dental conditions, and decreased physical function were reported. Stapling of the growth plates was reported in 14.3% of children but no adults. Adult patients reported high rates of bone pain (59.4%) and joint pain (65.6%). Caregivers of children with XLH also reported the occurrence of bone pain (35.7%) and joint pain (35.7%). Many adult patients had a history of impaired renal function (9.5%), nephrocalcinosis (15.6%), hyperparathyroidism (15.6%), and parathyroidectomy (6.3%), all of which are associated with conventional XLH treatments. These data show that patients (both pediatric and adult) continue to have symptoms such as pain, disability, and various complications despite receiving conventional therapies.

Metabolic syndrome (MetS) is cluster of metabolic diseases, including abdominal obesity, hyperglycemia, high blood pressure, and dyslipidemia, that directly escalate the risk of type 2 diabetes, heart disease, and stroke. Thioredoxin-interacting protein (TXNIP) is a binding protein for thioredoxin, a molecule that is a key inhibitor of cellular oxidation, and thus regulates the cellular redox state. Epigenetic alteration of the TXNIP-encoding locus has been associated with components of MetS. In the present study, we sought to determine whether the level of TXNIP methylation in blood is associated with MetS in the general Japanese population. DNA was extracted from the peripheral blood cells of 37 subjects with and 392 subjects without MetS. The level of TXNIP methylation at cg19693031 was assessed by the bisulfite-pyrosequencing method. We observed that TXNIP methylation levels were lower in MetS subjects (median 74.9%, range 71.7–78.4%) than in non-MetS subjects (median 77.7%, range 74.4–80.5%; p = 0.0024). Calculation of the confounding factor-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for hypomethylation revealed that subjects with MetS exhibited significantly higher ORs for hypomethylation than did those without MetS (OR, 2.92; 95% CI, 1.33–6.62; p = 0.009). Our findings indicated that lower levels of TXNIP methylation are associated with MetS in the general Japanese population. Altered levels of DNA methylation in TXNIP at cg19693031 might play an important role in the pathogenesis of MetS.

The Japanese Society of Thyroid Pathology and the Japan Association of Endocrine Surgeons developed the eighth edition of the General Rules for the Description of Thyroid Cancer (GRDTC) in December 2019. This article describes the pathological diagnosis of the GRDTC, which has been improved through repeated revisions based on the experience of Japanese pathologists and translated into English to introduce the Japanese diagnostic standard to foreign countries. In this edition of the GRDTC, the histopathological classification and descriptions differ in some respects from those of the fourth edition of the World Health Organization (WHO) classification as revised in 2017. For example, the GRDTC does not adopt the concept of borderline lesions (FT-UMP, WDT-UMP, and NIFTP) of the WHO, taking into consideration the popular histological criteria accepted by Japanese pathologists. The cytological reporting system of the GRDTC was partly modified from the Bethesda system in 2015. It has an additional cyst fluid category separated from the unsatisfactory category that has been demonstrated to be useful in Japan. This translated edition makes it easy to submit Japanese clinicopathological studies of thyroid tumors in an international journal. We also wish to contribute to the improvement, standardization, and globalization of the pathological diagnosis of thyroid tumors.