Zinc deficiency decreases the activity of calmodulin regulated cyclic nucleotide phosphodiesterases in vivo in selected rat tissues

Golgi Metal Ion Homeostasis in Human Health and Diseases

The Golgi apparatus is a membrane organelle located in the center of the protein processing and trafficking pathway. It consists of sub-compartments with distinct biochemical compositions and functions. Main functions of the Golgi, including membrane trafficking, protein glycosylation, and sorting, require a well-maintained stable microenvironment in the sub-compartments of the Golgi, along with metal ion homeostasis. Metal ions, such as Ca²⁺, Mn²⁺, Zn²⁺, and Cu²⁺, are important cofactors of many Golgi resident glycosylation enzymes. The homeostasis of metal ions in the secretory pathway, which is required for proper function and stress response of the Golgi, is tightly regulated and maintained by transporters. Mutations in the transporters cause human diseases. Here we provide a review specifically focusing on the transporters that maintain Golgi metal ion homeostasis under physiological conditions and their alterations in diseases.

Zinc inhibits osteoclast differentiation by suppression of Ca2+-Calcineurin-NFATc1 signaling pathway

BACKGROUND

Zinc, an essential trace element, inhibits osteoclast differentiation in vitro and in vivo. The molecular mechanism for the inhibitory effect of zinc, however, is poorly understood. The purpose of this study was to investigate the effect of zinc and determine its molecular mechanism on receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis in mouse bone marrow-derived monocyte cells (BMMs) and RAW264.7 cells.

RESULTS

In BMMs, zinc treatment during osteoclast differentiation decreased RANKL-induced osteoclast formation in a dose-dependent manner. We show that zinc suppressed the mRNA levels of nuclear factor of activated T-cells, cytoplasmic 1 (Nfatc1). Zinc also accumulated phospho-Nfatc1 (p-Nfatc1) in the cytosol in a dose-dependent manner and inhibited the translocation of Nfatc1 to the nucleus in RAW264.7 cells. Zinc suppressed the activities of Nfatc1 in the nucleus without changing the activities of NF-κB in RAW264.7 cells. In contrast, calcineurin activity decreased in response to zinc but its protein level was unchanged. RANKL-induced Ca2+ oscillations were inhibited by zinc treatment, but phospho-phospholipase Cγ1 (p-PLCγ1), the upstream signaling molecule of Ca2+ oscillations, was unaffected. Moreover, a constitutively active form of Nfatc1 obviously rescued suppression of osteoclastogenesis by zinc.

CONCLUSIONS

Taken together, these results demonstrate for the first time that the inhibitory effect of zinc during osteoclastogesis is caused by suppressing the Ca2+-Calcineurin-NFATc1 signaling pathway. Thus, zinc may be a useful therapeutic candidate for the prevention of bone loss caused by NFATc1 activation in osteoclasts.

Etiological relationships of parotid saliva cyclic nucleotides in patients with taste and smell dysfunction

OBJECTIVE

We previously demonstrated that parotid saliva cAMP and cGMP were lower in patients with taste and smell dysfunction than in normal subjects. We subsequently demonstrated parotid saliva cAMP and cGMP were inversely correlated with smell loss degree such that as smell loss severity increased parotid saliva cAMP and cGMP decreased proportionately. To learn more about these relationships we studied parotid saliva cAMP and cGMP with respect to aetiology of sensory loss in these patients.

DESIGN

Parotid saliva cAMP and cGMP in patients with smell loss (hyposmia) who participated in an open label fixed design controlled clinical trial with treatment with oral theophylline were evaluated with respect to their initial etiological diagnosis. Levels of cyclic nucleotides in each etiological category were compared to each other, to the entire patient group and to normal subjects.

RESULTS

Mean cAMP and cGMP in all patients combined were below those in normals, as previously described. However, categorized by aetiology, there was a stratification of levels of both cyclic nucleotides; some levels were below the normal mean and some were at or above the normal mean.

CONCLUSIONS

Parotid saliva cyclic nucleotides characterised in hyposmic patients by aetiology indicate (1) there are differential alterations in these nucleotides related to aetiology of sensory dysfunction and (2) these moieties measured prior to treatment indicate which patient groups may benefit from treatment with phosphodiesterase (PDE) inhibitors which increase levels of these moieties and thereby correct their sensory dysfunction.

Zinc depletion causes multiple defects in ovarian function during the periovulatory period in mice

Shortly before ovulation, the oocyte acquires developmental competence and granulosa cells undergo tremendous changes including cumulus expansion and luteinization. Zinc is emerging as a key regulator of meiosis in vitro, but a complete understanding of zinc-mediated effects during the periovulatory period is lacking. The present study uncovers the previously unknown role of zinc in maintaining meiotic arrest before ovulation. A zinc chelator [N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN)] caused premature germinal vesicle breakdown and associated spindle defects in denuded oocytes even in the presence of a phosphodiesterase 3A inhibitor (milrinone). TPEN also potently blocked cumulus expansion by blocking induction of expansion-related transcripts Has2, Ptx3, Ptgs2, and Tnfaip6 mRNA. Both meiotic arrest and cumulus expansion were rescued by exogenous zinc. Lack of cumulus expansion is due to an almost complete suppression of phospho-Sma- and Mad-related protein 2/3 signaling. Consistent with a decrease in phospho-Sma- and Mad-related protein 2/3 signaling, TPEN also decreased cumulus transcripts (Ar and Slc38a3) and caused a surprising increase in mural transcripts (Lhcgr and Cyp11a1) in cumulus cells. In vivo, feeding a zinc-deficient diet for 10 d completely blocked ovulation and compromised cumulus expansion. However, 42.5% of oocytes had prematurely resumed meiosis before human chorionic gonadotropin injection, underscoring the importance of zinc before ovulation. A more acute 3-d treatment with a zinc-deficient diet did not block ovulation but did increase the number of oocytes trapped in luteinizing follicles. Moreover, 23% of ovulated oocytes did not reach metaphase II due to severe spindle defects. Thus, acute zinc deficiency causes profound defects during the periovulatory period with consequences for oocyte maturation, cumulus expansion, and ovulation.

Influence of alimentary zinc deficiency on the concentration of the second messengers D-myo-inositol-1,4,5-trisphosphate (IP3) and s,n-1,2-diacylglycerol (DAG) in testes and brain of force-fed rats

The phosphatidylinositol-specific phospholipase C, presumably a Zn-metalloenzyme, catalyzes the hydrolysis of phosphatidylinositol-4,5-bisphosphate to inositol-1,4,5-trisphosphate (IP3) and s,n-1,2-diacylglycerol (DAG). The activity of phosphatidylinositol-specific phospholipase C was measured indirectly by determination of the metabolites IP3 and DAG in Zn deficiency. For this purpose 24 male Sprague-Dawley rats with an average live mass of 117 g were divided into 2 groups of 12 animals each. The Zn-deficient and the control group received a semisynthetic casein diet with a Zn content of 1.6 ppm and 115 ppm, respectively. In order to prevent the reduced feed intake that occurs in Zn deficiency and the associated energy and protein depletion from interfering with the experimental parameters, all animals were fed four times daily by gastric tube. This made it possible to supply all animals with adequate nutrients and to synchronize the feed intake exactly. After 12 d, the depleted rats were in a severe state of Zn deficiency, as demonstrated by the reduction of Zn in the serum and the femur by 74% and 43%, respectively, and the 28% lower serum activity of alkaline phosphatase. The radioimmunologically determined concentrations of IP3 were reduced by a significant 53% in the testes of the Zn-deficient rats (0.24 nmol IP3/g wet wt) compared to the control animals (0.51 nmol IP3/g wet wt), while the IP3 concentration in the brain was not affected by the alimentary Zn supply (1.7 and 1.6 nmol IP3/g wet wt, respectively). The DAG concentrations in the testes (474 vs 471 nmol DAG/g wet wt) and the brain (594 vs 640 nmol DAG/g wet wt), which were determined by radioenzymatic methods, showed no significant differences in relation to the alimentary Zn supply. The fact that the Zn concentration in the Zn-deficient rats was reduced only in the testes and not in the brain and that high concentrations of DAG may also result from other metabolic processes suggests that the phosphatidylinositol-specific phospholipase C in the mammalian organism is a Zn-metalloenzyme whose activity is reduced in alimentary Zn deficiency in tissues suffering Zn loss.

The effect of dietary zinc depletion and repletion on rats: Zn concentration in various tissues and activity of pancreatic gamma-glutamyl hydrolase (EC 3.4.22.12) as indices of Zn status

Unlike severe zinc deficiency, marginal Zn deficiency is difficult to identify in rats because no reliable indicator of suboptimal Zn status is currently available. We have previously observed reduced pancreatic gamma-glutamyl hydrolase (EC 3.4.22.12) activity and impaired pteroylpolyglutamate absorption in Zn-deficient rats. In the present study the effect of Zn depletion and repletion on the Zn concentration of various tissues and on the activity of this enzyme was investigated. The objective was to determine the sensitivity of these variables to Zn depletion and to evaluate their usefulness as indices of Zn status. Male Wistar rats (about 180 g), maintained from weanling on a purified Zn-adequate diet, were randomly allocated into twelve groups. A pretreatment control group was killed immediately. The remaining eleven groups were fed on a Zn-deficient diet and a group killed daily for 7 d (Zn-depleted groups). The remaining four groups were re-fed the Zn-adequate diet and a group killed daily (Zn-repleted groups). On analysis, pancreas and spleen Zn levels responded most rapidly to reduced Zn intake, followed by tibia, liver, kidney and plasma. Zn concentration was maintained in testes. Reduced plasma folate levels were also observed. A significant reduction in pancreatic gamma-glutamyl hydrolase activity before the depletion of many tissue Zn stores confirms the Zn sensitivity of the enzyme. It was concluded that future investigation into the inter-relationship between Zn and folate metabolism may be useful in identifying a sensitive, biochemical index of Zn status.