Parathyroid hormone induces adipocyte lipolysis via PKA-mediated phosphorylation of hormone-sensitive lipase

Non-adrenergic control of lipolysis and thermogenesis in adipose tissues

The enormous plasticity of adipose tissues, to rapidly adapt to altered physiological states of energy demand, is under neuronal and endocrine control. In energy balance, lipolysis of triacylglycerols and re-esterification of free fatty acids are opposing processes operating in parallel at identical rates, thus allowing a more dynamic transition from anabolism to catabolism, and vice versa. In response to alterations in the state of energy balance, one of the two processes predominates, enabling the efficient mobilization or storage of energy in a negative or positive energy balance, respectively. The release of noradrenaline from the sympathetic nervous system activates lipolysis in a depot-specific manner by initiating the canonical adrenergic receptor-G_s-protein-adenylyl cyclase-cyclic adenosine monophosphate-protein kinase A pathway, targeting proteins of the lipolytic machinery associated with the interface of the lipid droplets. In brown and brite adipocytes, lipolysis stimulated by this signaling pathway is a prerequisite for the activation of non-shivering thermogenesis. Free fatty acids released by lipolysis are direct activators of uncoupling protein 1-mediated leak respiration. Thus, pro- and anti-lipolytic mediators are bona fide modulators of thermogenesis in brown and brite adipocytes. In this Review, we discuss adrenergic and non-adrenergic mechanisms controlling lipolysis and thermogenesis and provide a comprehensive overview of pro- and anti-lipolytic mediators.

The combined effect of vitamin D and parathyroid hormone concentrations on glucose homeostasis in older patients with prediabetes: A cross-sectional study

BACKGROUND

The combined effect of vitamin D and parathyroid hormone on glucose homeostasis has not been adequately investigated. The aim of this study was to examine the role of parathyroid hormone/vitamin D axis on glucose homeostasis in elderly persons with prediabetes.

METHODS

Patients with prediabetes ( n = 144) and healthy age-matched controls ( n = 81) were included in this cross-sectional study. Study parameters included anthropometric characteristics, morning fasting glucose (fasting plasma glucose), insulin (fasting plasma insulin), parathyroid hormone, 25-hydroxyvitamin D, homeostasis model assessment of insulin resistance and homeostasis model assessment of β-cell function. Both groups were stratified into subgroups according to vitamin D status and tertiles of parathyroid hormone.

RESULTS

Both groups were comparable in terms of body mass index, 25-hydroxyvitamin D and parathyroid hormone status. In the prediabetes group, fasting plasma glucose differed significantly across parathyroid hormone tertiles, increasing from the first to the third tertile ( p = 0.011). There were higher fasting plasma glucose values in participants with vitamin D deficiency/parathyroid hormone third tertile compared to all other groups ( p = 0.031, 0.027 and 0.039, respectively).

CONCLUSION

Parathyroid hormone status is associated with impaired glucose homeostasis; hypovitaminosis D combined with high parathyroid hormone concentrations are associated with glycaemic dysregulation in elderly patients with prediabetes.

Gender specific association of parathyroid hormone and vitamin D with metabolic syndrome in population with preserved renal function

The association of parathyroid hormone (PTH) and vitamin D with Metabolic syndrome (MetS) was evaluated using representative data from the Korean population. Data from 7004 subjects aged 50 or older with preserved renal function (excluding chronic kidney disease stage 3b to 5) who were included in the Korean National Health and Nutrition Examination Survey between 2008 and 2010 were analysed. Higher PTH levels (pg/ml) were observed in subjects with MetS than in those without MetS among both genders (60.1 (58.6–61.6) vs. 62.4 (60.7–64.2) in males p = 0.018, 60.7 (59.4–62.1) vs. 63.9 (62.4–65.6) in females, p < 0.001). For females, PTH levels were significantly higher in subjects with MetS than in those without MetS after adjustment for possible covariates. Lower 25(OH)D levels were significantly associated with MetS only in male subjects (p = 0.004). As the number of MetS components increased, a significant rise in PTH levels (p for trend 0.005 in males and 0.024 in females) and a decrease in 25(OH)D levels (p for trend < 0.001 in males and 0.053 in females) were observed. In conclusion, among subjects with preserved renal function, PTH levels were possibly associated with MetS in females, whereas vitamin D levels exhibited a possible link to MetS in males.

Predictors of multiglandular disease in primary hyperparathyroidism

Background

Primary hyperparathyroidism (pHPT) is caused by single- or multiglandular disease (MGD). Patients with MGD have an increased risk of complications at surgery and for persistence and recurrence after surgery. The study evaluated whether preoperative clinical and biochemical characteristics could predict MGD in patients with pHPT.

Methods

We retrospectively evaluated patients operated 1989–2013 for first-time, non-hereditary pHPT. MGD was defined in patients with more than one pathological gland excised at surgery or with persistent hypercalcemia after the excision of a single pathological parathyroid gland, confirmed by histopathology. Clinical and biochemical variables were compared in patients with single- and multiglandular disease. Logistic regression was used to identify variables predicting MGD, yielding odds ratios (OR) with 95% confidence intervals (CI).

Results

There were 707 patients, of which 79 (11%) had MGD. Patients with MGD were more likely to have negative sestamibi scintigraphy than patients with single-gland disease, 15 of 49 (31%) vs. 70 of 402 (17%; p = 0.03), to suffer from diabetes (12 of 74, 16%) vs. 45 out of 626 patients (7.2%; p < 0.01) and had lower preoperative levels of urinary calcium (3.80 vs. 4.44 mmol/L; p = 0.04). Multivariable analysis identified negative scintigraphy (OR 2.42; 95% CI 1.18 to 4.79), diabetes (OR 2.75; 95% CI 1.31 to 4.97) and elevated levels of osteocalcin (OR 3.79, 95% CI: 1.75 to 8.21) as predictors of MGD.

Conclusion

Negative sestamibi scintigraphy, diabetes and elevated osteocalcin levels were predictors of MGD.

Endoplasmic reticulum (ER) stress and cAMP/PKA pathway mediated Zn-induced hepatic lipolysis

The present study was performed to determine the effect of Zn exposure influencing endoplasmic reticulum (ER) stress, explore the underlying molecular mechanism of Zn-induced hepatic lipolysis in a fish species of significance for aquaculture, yellow catfish Pelteobagrus fulvidraco. We found that waterborne Zn exposure evoked ER stress and unfolded protein response (UPR), and activated cAMP/PKA pathway, and up-regulated hepatic lipolysis. The increase in ER stress and lipolysis were associated with activation of cAMP/PKA signaling pathway. Zn also induced an increase in intracellular Ca²⁺ level, which could be partially prevented by dantrolene (RyR receptor inhibitor) and 2-APB (IP3 receptor inhibitor), demonstrating that the disturbed Ca²⁺ homeostasis in ER contributed to ER stress and dysregulation of lipolysis. Inhibition of ER stress by PBA attenuated UPR, inhibited the activation of cAMP/PKA pathway and resulted in down-regulation of lipolysis. Inhibition of protein kinase RNA-activated-like ER kinase (PERK) by GSK2656157 and inositol-requiring enzyme (IRE) by STF-083010 differentially influenced Zn-induced changes of lipid metabolism, indicating that PERK and IRE pathways played different regulatory roles in Zn-induced lipolysis. Inhibition of PKA by H89 blocked the Zn-induced activation of cAMP/PKA pathway with a concomitant inhibition of ER stress-mediated lipolysis. Taken together, our findings highlight the importance of the ER stress-cAMP/PKA axis in Zn-induced lipolysis, which provides new insights into Zn toxicology in fish and probably in other vertebrates.

Energy Metabolism of the Osteoblast: Implications for Osteoporosis

Osteoblasts, the bone-forming cells of the remodeling unit, are essential for growth and maintenance of the skeleton. Clinical disorders of substrate availability (e.g., diabetes mellitus, anorexia nervosa, and aging) cause osteoblast dysfunction, ultimately leading to skeletal fragility and osteoporotic fractures. Conversely, anabolic treatments for osteoporosis enhance the work of the osteoblast by altering osteoblast metabolism. Emerging evidence supports glycolysis as the major metabolic pathway to meet ATP demand during osteoblast differentiation. Glut1 and Glut3 are the principal transporters of glucose in osteoblasts, although Glut4 has also been implicated. Wnt signaling induces osteoblast differentiation and activates glycolysis through mammalian target of rapamycin, whereas parathyroid hormone stimulates glycolysis through induction of insulin-like growth factor-I. Glutamine is an alternate fuel source for osteogenesis via the tricarboxylic acid cycle, and fatty acids can be metabolized to generate ATP via oxidative phosphorylation although temporal specificity has not been established. More studies with new model systems are needed to fully understand how the osteoblast utilizes fuel substrates in health and disease and how that impacts metabolic bone diseases.

Calcium reduces vitamin D and glucocorticoid receptors in the visceral fat of obese male rats

Rats overfed during lactation show higher visceral adipose tissue (VAT) mass and metabolic dysfunctions at adulthood. As both vitamin D and glucocorticoids change adipogenesis, parameters related to metabolism and action of these hormones in the adipocyte can be altered in rats raised in small litters (SL). We also studied the antiobesity effects of high calcium diet since it decreases visceral fat in obesity models. On postnatal day (PN) 3, litter size was adjusted to 3pups/dam (SL) to induce overfeeding. Control litters (NL) remained with 10pups/dam until weaning. From PN120 to PN180, half of the SL rats were fed standard chow (SL) and the other half was fed a calcium-supplemented chow (SL-Ca, 10g CaCO3/kg). Both SL groups were heavier and hyperphagic when compared with the NL group; however, SL-Ca rats ate less than SL. SL-Ca rats had decreased VAT mass and adipocyte size, associated with lower hypothalamic NPY content, VAT fat acid synthase content and leptinemia. At PN120, SL rats had increased plasma 25(OH)D3, Cyp27b1 mRNA and glucocorticoid receptor (GR-α) in the VAT, but lower vitamin D receptor (Vdr) mRNA. At PN180, Cyp27b1 and GR-α remained higher, while Vdr normalized in SL rats. SL-Ca rats had normal VAT Cyp27b1 and GR-α, but lower Vdr Thus, higher body mass and glucocorticoid receptors in the VAT of SL rats are normalized by calcium-enriched diet, and Vdr expression in this tissue is reduced, suggesting a possible role of glucocorticoids and vitamin D in calcium action in the adipocyte.