Regucalcin increases Ca2+-ATPase activity in the mitochondria of brain tissues of normal and transgenic rats

Regucalcin ameliorates Doxorubicin-induced cytotoxicity in Cos-7 kidney cells and translocates from the nucleus to the mitochondria

Doxorubicin (DOX) is a potent anti-cancer drug, which can have unwanted side-effects such as cardiac and kidney toxicity. A detailed investigation was undertaken of the acute cytotoxic mechanisms of DOX on kidney cells, using Cos-7 cells as kidney cell model. Cos-7 cells were exposed to DOX for a period of 24 hours over a range of concentrations and the LC50 was determined to be 7µM. Further investigations showed that cell death was mainly via apoptosis involving Ca2+ and caspase 9, in addition to autophagy. Regucalcin (RGN), a cytoprotective protein found mainly in liver and kidney tissues, was overexpressed in Cos-7 cells and shown to protect against DOX-induced cell death. Subcellular localization studies in Cos-7 cells showed RGN to be strongly correlated with the nucleus. However, upon treatment with DOX for 4 hours, which induced membrane blebbing in some cells, the localization appeared to be correlated more with the mitochondria in these cells. It is yet to be determined whether this translocation is part of the cytoprotective mechanism or a consequence of chemically-induced cell stress.

Regucalcin confers resistance to amyloid-β toxicity in neuronally differentiated PC12 cells

Amyloid‐β (Aβ), a primary component of amyloid plaques, has been widely associated with the pathogenesis of Alzheimer's disease. The Ca²⁺‐binding protein regucalcin (RGN) plays multiple roles in maintaining cell functions by regulating intracellular calcium homeostasis, various signaling pathways, and gene expression systems. Here, we investigated the functional role of RGN against Aβ‐induced cytotoxicity in neuronally differentiated PC12 cells. Overexpression of RGN reduced Aβ‐induced apoptosis by reducing mitochondrial dysfunction and caspase activation. It also attenuated Aβ‐induced reactive oxygen species production and oxidative damage and decreased Aβ‐induced nitric oxide (NO) overproduction, upregulation of inducible NO synthase by nuclear factor‐κB, and nitrosative damage. Interestingly, the genetic disruption of RGN increased the susceptibility of neuronally differentiated PC12 cells to Aβ toxicity. Thus, RGN possesses antioxidant activity against Aβ‐induced oxidative and nitrosative stress and may play protective roles against Aβ‐induced neurotoxicity in Alzheimer's disease.

Long-term culture with lipopolysaccharide induces dose-dependent cytostatic and cytotoxic effects in THP-1 monocytes

Monocytes act as a first line of defence against invading pathogens and their dysfunctions seem to be a key factor in many immune disorders. However, the data on mechanisms underlying these dysfunctions remain elusive. In this study, we evaluated the effects of long-term (168h) lipopolysaccharide exposure on monocytes at low density cultures (1×10⁵cells/ml). Treatment with low dose LPS (≤5μg/ml) resulted in oxidative stress induction followed by p21 pathway activation, permanent cell cycle arrest and SASP development. Furthermore, high dose LPS (≥10μg/ml) induced cell death involving mitochondrial pathways, death receptors as well as p21-dependent DNA damage response activation mediated by ROS generation and TNF-α release. Additionally, exposure to high dose of LPS resulted in THP-1 monocytes differentiation to macrophages. In conclusion, long-term culture with LPS exerts in low density monocytes cytostatic/cytotoxic effects in a dose-dependent manner by inducing senescence associated with chronic inflammation at low doses and initiation of cell death at higher doses. These findings shed new light on understanding of monocytes dysfunction, an issue relevant to chronic inflammation and many immune disorders.

Regucalcin expression in bovine tissues and its regulation by sex steroid hormones in accessory sex glands

Regucalcin (RGN) is a mammalian Ca2+-binding protein that plays an important role in intracellular Ca2+ homeostasis. Recently, RGN has been identified as a target gene for sex steroid hormones in the prostate glands and testis of rats and humans, but no studies have focused on RGN expression in bovine tissues. Thus, in the present study, we examined RGN mRNA and protein expression in the different tissues and organs of veal calves and beef cattle. Moreover, we investigated whether RGN expression is controlled through sex steroid hormones in bovine target tissues, namely the bulbo-urethral and prostate glands and the testis. Sex steroid hormones are still illegally used in bovine husbandry to increase muscle mass. The screening of the regulation and function of anabolic sex steroids via modified gene expression levels in various tissues represents a new approach for the detection of illicit drug treatments. Herein, we used quantitative PCR, western blot and immunohistochemistry analyses to demonstrate RGN mRNA and protein expression in bovine tissues. In addition, estrogen administration down-regulated RGN gene expression in the accessory sex glands of veal calves and beef cattle, while androgen treatment reduced RGN gene expression only in the testis. The confirmation of the regulation of RGN gene expression through sex steroid hormones might facilitate the potential detection of hormone abuse in bovine husbandry. Particularly, the specific response in the testis suggests that this tissue is ideal for the detection of illicit androgen administration in veal calves and beef cattle.

The diverse roles of calcium-binding protein regucalcin in cell biology: from tissue expression and signalling to disease

Regucalcin (RGN) is a calcium (Ca(2+))-binding protein widely expressed in vertebrate and invertebrate species, which is also known as senescence marker protein 30, due to its molecular weight (33 kDa) and a characteristically diminished expression with the aging process. RGN regulates intracellular Ca(2+) homeostasis and the activity of several proteins involved in intracellular signalling pathways, namely, kinases, phosphatases, phosphodiesterase, nitric oxide synthase and proteases, which highlights its importance in cell biology. In addition, RGN has cytoprotective effects reducing intracellular levels of oxidative stress, also playing a role in the control of cell survival and apoptosis. Multiple factors have been identified regulating the cell levels of RGN transcripts and protein, and an altered expression pattern of this interesting protein has been found in cases of reproductive disorders, neurodegenerative diseases and cancer. Moreover, RGN is a serum-secreted protein, and its levels have been correlated with the stage of disease, which strongly suggests the usefulness of this protein as a potential biomarker for monitoring disease onset and progression. The present review aims to discuss the available information concerning RGN expression and function in distinct cell types and tissues, integrating cellular and molecular mechanisms in the context of normal and pathological conditions. Insight into the cellular actions of RGN will be a key step towards deepening the knowledge of the biology of several human diseases.

Dioscin, a natural steroid saponin, shows remarkable protective effect against acetaminophen-induced liver damage in vitro and in vivo

The aim of the study was to investigate the protective effect of dioscin against APAP-induced hepatotoxicity. In the in vitro tests, HepG2 cells were given APAP pretreatment with or without dioscin. In the in vivo experiments, mice were orally administrated dioscin for five days and then given APAP. Some biochemical and morphology parameters were assayed and the possible mechanism was investigated. Dioscin improved AST release, mitochondrial dysfunction, apoptosis and necrosis of HepG2 cells induced by APAP. Following administration of dioscin, APAP-induced hepatotoxicity in mice was significantly attenuated. Furthermore, the liver cell apoptosis and necrosis, and hepatic mitochondrial edema were also prevented. Fifteen differentially expressed proteins were found by using proteomics, and six of them, Suox, Krt18, Rgn, Prdx1, MDH and PNP were validated. These proteins may be involved in the hepatoprotective effect of dioscin and might cooperate with the levels of Ca(2+) in mitochondria, decreased expression of ATP2A2, and decreased mitochondrial cardiolipin. In addition, dioscin inhibited APAP-induced activation and expression of CYP2E1, up-regulated the expression of Bcl-2 and Bid, and inhibited the expression of Bax, Bak and p53. Dioscin showed a remarkable protective effect against APAP-induced hepatotoxicity by adjusting mitochondrial function. These results indicated that dioscin has the capability on the treatment of liver injury.

Regucalcin (RGN/SMP30) alters agonist- and thapsigargin-induced cytosolic [Ca2+] transients in cells by increasing SERCA Ca(2+)ATPase levels

Regucalcin (RGN), also reported as senescence marker protein-30 (SMP30), plays a role in Ca(2+) homeostasis by modulating a number of Ca(2+)-dependent proteins. RGN also plays a cyto-protective role and its decrease is linked to age-related diseases and cell death. This study shows that RGN reduces agonist (histamine)-induced Ca(2+) transients in RGN(+) transfected COS-7 cells (RGN(+)) and also increases their Ca(2+) storage capacity. These observations are explained by RGN(+) cells having increased mRNA and protein expression levels of sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA). Therefore down-regulation of RGN expression may contribute to characteristics of age-dependent Ca(2+) homeostasis dis-regulation, by decreasing SERCA levels.