Checkpoint kinase Chk2 controls renal Cyp27b1 expression, calcitriol formation, and calcium-phosphate metabolism. Pflugers Arch. 2014;Epub ahead of print. [PMID: 25319519 DOI: 10.1007/s00424-014-1625-9]

Inhibition of Estrogen Sulfotransferase (SULT1E1/EST) Ameliorates Ischemic Acute Kidney Injury in Mice

BACKGROUND

Studies have suggested that estrogens may protect mice from AKI. Estrogen sulfotransferase (SULT1E1, or EST) plays an important role in estrogen homeostasis by sulfonating and deactivating estrogens, but studies on the role of SULT1E1 in AKI are lacking.

METHODS

We used the renal ischemia-reperfusion model to investigate the role of SULT1E1 in AKI. We subjected wild-type mice, Sult1e1 knockout mice, and Sult1e1 knockout mice with liver-specific reconstitution of SULT1E1 expression to bilateral renal ischemia-reperfusion or sham surgery, either in the absence or presence of gonadectomy. We assessed relevant biochemical, histologic, and gene expression markers of kidney injury. We also used wild-type mice treated with the SULT1E1 inhibitor triclosan to determine the effect of pharmacologic inhibition of SULT1E1 on AKI.

RESULTS

AKI induced the expression of Sult1e1 in a tissue-specific and sex-specific manner. It induced expression of Sult1e1 in the liver in both male and female mice, but Sult1e1 induction in the kidney occurred only in male mice. Genetic knockout or pharmacologic inhibition of Sult1e1 protected mice of both sexes from AKI, independent of the presence of sex hormones. Instead, a gene profiling analysis indicated that the renoprotective effect was associated with increased vitamin D receptor signaling. Liver-specific transgenic reconstitution of SULT1E1 in Sult1e1 knockout mice abolished the protection in male mice but not in female mice, indicating that Sult1e1's effect on AKI was also tissue-specific and sex-specific.

CONCLUSIONS

SULT1E1 appears to have a novel function in the pathogenesis of AKI. Our findings suggest that inhibitors of SULT1E1 might have therapeutic utility in the clinical management of AKI.

Intestinal Ca2+ absorption revisited: A molecular and clinical approach

Ca2+ has an important role in the maintenance of the skeleton and is involved in the main physiological processes. Its homeostasis is controlled by the intestine, kidney, bone and parathyroid glands. The intestinal Ca2+ absorption occurs mainly via the paracellular and the transcellular pathways. The proteins involved in both ways are regulated by calcitriol and other hormones as well as dietary factors. Fibroblast growth factor 23 (FGF-23) is a strong antagonist of vitamin D action. Part of the intestinal Ca2+ movement seems to be vitamin D independent. Intestinal Ca2+ absorption changes according to different physiological conditions. It is promoted under high Ca2+ demands such as growth, pregnancy, lactation, dietary Ca2+ deficiency and high physical activity. In contrast, the intestinal Ca2+ transport decreases with aging. Oxidative stress inhibits the intestinal Ca2+ absorption whereas the antioxidants counteract the effects of prooxidants leading to the normalization of this physiological process. Several pathologies such as celiac disease, inflammatory bowel diseases, Turner syndrome and others occur with inhibition of intestinal Ca2+ absorption, some hypercalciurias show Ca2+ hyperabsorption, most of these alterations are related to the vitamin D endocrine system. Further research work should be accomplished in order not only to know more molecular details but also to detect possible therapeutic targets to ameliorate or avoid the consequences of altered intestinal Ca2+ absorption.

Quantitative Trait Locus and Integrative Genomics Revealed Candidate Modifier Genes for Ectopic Mineralization in Mouse Models of Pseudoxanthoma Elasticum

Pseudoxanthoma elasticum, a prototype of heritable multisystem ectopic mineralization disorders, is caused by mutations in the ABCC6 gene encoding a putative efflux transporter, ABCC6. The phenotypic spectrum of pseudoxanthoma elasticum varies, and the correlation between genotype and phenotype has not been established. To identify genetic modifiers, we performed quantitative trait locus analysis in inbred mouse strains that carry the same hypomorphic allele in Abcc6 yet with highly variable ectopic mineralization phenotypes of pseudoxanthoma elasticum. Abcc6 was confirmed as a major determinant for ectopic mineralization in multiple tissues. Integrative analysis using functional genomics tools that included GeneWeaver, String, and Mouse Genome Informatics identified a total of nine additional candidate modifier genes that could influence the organ-specific ectopic mineralization phenotypes. Integration of the candidate genes into the existing ectopic mineralization gene network expands the current knowledge on the complexity of the network that, as a whole, governs ectopic mineralization in soft connective tissues.

In Vivo Detection and Measurement of Aortic Aneurysm and Dissection in Mouse Models Using Microcomputed Tomography with Contrast Agent

Objectives

The aim of this study was to evaluate the potential of microcomputed tomography (micro-CT) using the intravascular contrast agent ExiTron nano 12000 for aorta imaging and monitoring the dynamic changing process of the aorta in mouse models with aortic aneurysm and dissection.

Materials and Methods

Experiments were performed on healthy mice and mice with aortic dissection. Mice that were developing aortic dissection and healthy mice underwent micro-CT imaging after injection of ExiTron nano 12000. Time-dependent signal enhancement (at 1, 2, 3, 6, and 12 hours after intravenous injection of the contrast agent, respectively) in the aorta of healthy mice was measured to confirm the optimal imaging time of aorta. Various contrast agent doses (70, 100, and 150 μl per 25 g mouse, respectively) were investigated to determine the optimal required dose for imaging of the aorta. The mice were scanned with micro-CT at 1, 14, and 28 days after onset of aneurysm and dissection to monitor the dynamic changing process of the aorta. Mouse aortas were stained with hematoxylin and eosin staining, and the diameter of the aorta was measured and compared with those obtained by micro-CT.

Results

Time-dependent signal enhancement in the aorta shows that the contrast agent has a long blood half-life of 6 hours, with a peak enhancement at 2 hours after injection. Injection of 100 μl ExiTron nano 12000 per 25 g mouse allows for effective visualization of the aorta. Micro-CT combined with contrast agent can monitor the changing process of the aorta in the mouse model of aortic aneurysm and dissection dynamically. The values of the diameter of the aortas obtained from the in vivo micro-CT imaging were compared with those obtained from histology and showed a significant correlation (R² = 0.96).

Conclusions

These data demonstrate that in vivo micro-CT is an accurate and feasible technique to detect aortic aneurysm or dissection in a mouse model, and the micro-CT technique using the innovative contrast agent ExiTron nano 12000 allows for monitoring various processes dynamically such as aortic remodeling in longitudinal studies.

A preclinical micro-computed tomography database including 3D whole body organ segmentations

The gold-standard of preclinical micro-computed tomography (μCT) data processing is still manual delineation of complete organs or regions by specialists. However, this method is time-consuming, error-prone, has limited reproducibility, and therefore is not suitable for large-scale data analysis. Unfortunately, robust and accurate automated whole body segmentation algorithms are still missing. In this publication, we introduce a database containing 225 murine 3D whole body μCT scans along with manual organ segmentation of most important organs including heart, liver, lung, trachea, spleen, kidneys, stomach, intestine, bladder, thigh muscle, bone, as well as subcutaneous tumors. The database includes native and contrast-enhanced, regarding spleen and liver, μCT data. All scans along with organ segmentation are freely accessible at the online repository Figshare. We encourage researchers to reuse the provided data to evaluate and improve methods and algorithms for accurate automated organ segmentation which may reduce manual segmentation effort, increase reproducibility, and even reduce the number of required laboratory animals by reducing a source of variability and having access to a reliable reference group.

Comparison of small animal CT contrast agents

Non-invasive in vivo small animal computed tomography (CT) imaging provides high resolution bone scans but cannot differentiate between soft tissues. For most applications injections of contrast agents (CAs) are necessary. Aim of this study was to uncover the advantages and disadvantages of commercially available CT CAs (ExiTron nano 12 000 and 6000, eXIA 160 and 160XL, Fenestra VC and LC) regarding their pharmacokinetics, toxicological side-effects and the influence of anesthesia on the biodistribution, based on an injection volume of 100 μL/25 g body weight. The pharmacokinetics of the CAs were determined for up to five days. The CA-induced toxicological/physiological side-effects were evaluated by determining blood counts, liver enzymes, thyroxine and total protein values, pro-inflammatory mediators (messenger ribonucleic acid (mRNA)), histology and immunohistochemistry. ExiTron nano 12 000 and 6000 yielded a long-term contrast enhancement (CE) in the liver and spleen for up to five days. Some of the evaluated CAs did not show any CE at all. Anesthesia did not impair the CAs' biodistribution. The CAs differentially affected the body weight, blood counts, liver enzymes, thyroxine and total protein values. ExiTron nano 12 000 and 6000 induced histiocytes in the liver and spleen. Moreover, ExiTron nano 12 000 and eXIA 160 enhanced tumor necrosis factor (TNF) mRNA expression levels in the kidneys. Thus, we recommend ExiTron nano 12 000 and 6000 when multiple injections should be avoided. We recommend careful selection of the employed CA in order to achieve an acceptable CE in the organs of interest and to avoid influences on the animal physiology. Copyright © 2016 John Wiley & Sons, Ltd.

Molecular aspects of intestinal calcium absorption

Intestinal Ca²⁺ absorption is a crucial physiological process for maintaining bone mineralization and Ca²⁺ homeostasis. It occurs through the transcellular and paracellular pathways. The first route comprises 3 steps: the entrance of Ca²⁺ across the brush border membranes (BBM) of enterocytes through epithelial Ca²⁺ channels TRPV6, TRPV5, and Ca_v1.3; Ca²⁺ movement from the BBM to the basolateral membranes by binding proteins with high Ca²⁺ affinity (such as CB_9k); and Ca²⁺ extrusion into the blood. Plasma membrane Ca²⁺ ATPase (PMCA1b) and sodium calcium exchanger (NCX1) are mainly involved in the exit of Ca²⁺ from enterocytes. A novel molecule, the 4.1R protein, seems to be a partner of PMCA1b, since both molecules co-localize and interact. The paracellular pathway consists of Ca²⁺ transport through transmembrane proteins of tight junction structures, such as claudins 2, 12, and 15. There is evidence of crosstalk between the transcellular and paracellular pathways in intestinal Ca²⁺ transport. When intestinal oxidative stress is triggered, there is a decrease in the expression of several molecules of both pathways that inhibit intestinal Ca²⁺ absorption. Normalization of redox status in the intestine with drugs such as quercetin, ursodeoxycholic acid, or melatonin return intestinal Ca²⁺ transport to control values. Calcitriol [1,25(OH)₂D₃] is the major controlling hormone of intestinal Ca²⁺ transport. It increases the gene and protein expression of most of the molecules involved in both pathways. PTH, thyroid hormones, estrogens, prolactin, growth hormone, and glucocorticoids apparently also regulate Ca²⁺ transport by direct action, indirect mechanism mediated by the increase of renal 1,25(OH)₂D₃ production, or both. Different physiological conditions, such as growth, pregnancy, lactation, and aging, adjust intestinal Ca²⁺ absorption according to Ca²⁺ demands. Better knowledge of the molecular details of intestinal Ca²⁺ absorption could lead to the development of nutritional and medical strategies for optimizing the efficiency of intestinal Ca²⁺ absorption and preventing osteoporosis and other pathologies related to Ca²⁺ metabolism.