Role of the vitamin D3 pathway in healthy and diseased skin – facts, contradictions and hypotheses

Abstract: Irradiation of human keratinocytes with UVB (280–320 nm) in vitro and in vivo activates the metabolism of 7‐dehydrocholesterol to hormonally active calcitriol. The production of calcitriol in the skin strongly depends on the photosynthesis of vitamin D₃ which is biologically inactive in the first instance. Vitamin D₃ serves as the starting substrate for two subsequent enzymatic hydroxylation steps in epidermal keratinocytes. Both the amount of vitamin D₃ and the activity of anabolic and catabolic vitamin D hydroxylases determine the cutaneous level of calcitriol. The hormonally active metabolite of vitamin D₃ regulates a huge number of genes in keratinocytes, and thus acts in an autocrine and/or paracrine manner. This local pathway of vitamin D₃ is unique, but its relevance for healthy and diseased skin is widely unknown, yet. Experimental findings implicate several questions: ( 1 ) Is UVB‐induced formation of calcitriol involved in regulation of growth and differentaition of epidermal cells as well as immunological and skin protective processes? ( 2 ) What endogenous and exogenous factors including drugs affect the cutaneous vitamin D₃ pathway? From a therapeutical point of view, it has been known for a long time that topical application of calcitriol and its analogs can improve hyperproliferative skin diseases like psoriasis. In spite of many encouraging studies in recent years, the fields of the routinely therapeutical application of calcitriol or vitamin D analogs in dermatology (e.g. treatment of immunological, inflammatory, malignancies and infectious skin diseases) have not been intensified. Why is that?     

Monitoring left ventricular dilation in mice with PET.

Molecular imaging by small-animal PET is an important noninvasive means to phenotype transgenic mouse models in vivo. When investigating pathologies of the left ventricular (LV) myocardium, the serial assessment of LV volumes is important. By this, the presence of LV dilation as a sign of developing heart failure can be detected. Whereas PET is usually used to derive biochemical and molecular information, functional parameters such as ventricular volumes are generally measured using echocardiography or MRI. In this study, a novel method to monitor LV dilation in mice with PET is presented and evaluated using cardiac MRI. METHODS: A semiautomatic 3-dimensional algorithm was used to delineate the LV myocardial wall on static PET images depicting myocardial glucose metabolism ((18)F-FDG PET) for 20 mice: 10 wild-type and 10 genetically modified littermates designed to develop a dilative cardiomyopathy phenotype (cardiomyocyte-specific knockout of survivin). The volume enclosed by the 3-dimensional midmyocardial contour was calculated as a measure for LV volume for each mouse. Data were compared with ventricular volumes measured by MRI in the same animals. RESULTS: LV volumes obtained by PET and MRI correlated well (R = 0.89) for hearts with small and large left ventricles. In accordance with the hypothesis, the LV volumes were increased significantly for transgenic mice examined at an older age compared with those examined at a younger age (MRI: 160.5 +/- 25.7 microL vs. 114.7 +/- 15.2 microL [P = 0.012]; PET: 129.3 +/- 15.3 microL vs. 73.8 +/- 15.0 microL [P < 0.001], all values shown as mean +/- SD; for MRI, mean of end-diastolic and end-systolic volumes are given), whereas they did not for their wild-type littermates (MRI: 106.2 +/- 12.3 microL vs. 94.7 +/- 14.6 microL [P = 0.214]; PET: 82.6 +/- 20.9 microL vs. 65.0 +/- 16.9 microL [P = 0.185]). CONCLUSION: Evaluation and quantitation of LV dilation in both control and cardiomyopathic mice can be reliably and serially performed using small-animal PET and (18)F-FDG, yielding useful functional information in addition to metabolic data.     

Assessment of the reliability and validity of panoramic imaging for assessment of mandibular condyle morphology using both MRI and clinical examination as the gold standard.

OBJECTIVES: The purpose of this study was to evaluate both reliability and validity of the assessment of the shape of the mandibular condyle in panoramic images of the TMJ. STUDY DESIGN: Forty subjects were included and were examined according to the Research Diagnostic Criteria for Temporomandibular Disorders. Panoramic radiographs (PRs) and magnetic resonance images (MRIs) were completed for all subjects. Both MRIs and PRs were rated by raters blinded to the clinical diagnosis. Kappa statistics were used to compare the results of the raters of the PRs. Additionally, the specificity and the sensitivity of the PRs were calculated for 2 scenarios: one with MRI and the other with clinical findings as the gold standard. RESULTS: The sensitivity was 0.94 (specificity = 0.45) for the assumption that MRI is the gold standard and 0.86 (specificity = 0.49) for the assumption that the clinical examination is the gold standard. For reliability, the results for kappa ranged from 0.06 to 0.327. CONCLUSION: It can be concluded that PRs are not a reliable method of accurately judging the shape of the mandibular condyle.     

The effect of estrogens and dietary calcium deficiency on the extracellular matrix of articular cartilage in G?ttingen miniature pigs.

Clinical observations have suggested that estrogens are involved in the pathogenesis of postmenopausal osteoarthritis (OA). However, positive and negative associations between the incidence of OA and serum estrogen concentrations have been reported. In contrast to this, osteoporosis is regarded as a disease with a strong estrogen-dependent component. Moreover, there is an interaction between estrogen and calcium deficiency: calcium supplementation potentiates the effect of estrogen therapy. The present study was designed to investigate how estrogen deficiency affects the articular cartilage depending on calcium supply. The distribution of different types of glycosaminoglycans and collagens can be used as an indicator for extracellular matrix changes induced by estrogen deficiency. Different levels of dietary calcium were therefore fed to intact and ovariectomized G?ttingen miniature pigs for one year before articular cartilage was harvested. The histochemical staining for heavy sulfated glycosaminoglycans in the extracellular matrix of ovariectomized miniature pigs, especially of those fed with a low calcium diet, was stronger in comparison to intact animals. In intact animals type II-collagen was immunodetected in all zones of unmineralized and mineralized articular cartilage, while immunostaining for this protein was negative to weak in the deep radiated fiber zone of ovariectomized minipigs. These results suggest that the synthesis of heavy sulfated glycosaminoglycans and immunohistochemically detectable type II-collagen is possibly influenced by estrogen deficiency. In conclusion, under estrogen deficiency, the extracellular matrix of articular cartilage underwent similar changes to those observed in physiologically aging cartilage where keratan sulfate is increased as a heavy sulfated glycosaminoglycan.     

Sclerotomal origin of smooth muscle cells in the wall of the avian dorsal aorta.

The dorsal aorta is the earliest formed intraembryonic blood vessel. It is composed of an inner lining consisting of endothelial cells and an outer wall consisting of smooth muscle cells (SMCs) and fibrocytes. Aortic SMCs have been suggested to arise from several developmental lineages. Cephalic neural crest provides SMCs of the proximal part of the aorta, and SMCs of the distal part are derived from the paraxial mesoderm. Here, we show by using quail-chick chimerization that in the avian embryo, SMCs in the wall of the dorsal aorta at trunk level arise from the sclerotome. Our findings indicate a two-step process of aortic wall formation. First, non-paraxial mesoderm-derived mural cells accumulate at the floor of the aorta. We refer to these cells as primary SMCs. Second, SMCs from the sclerotome are recruited to the roof and sides of the aorta, eventually replacing the primary SMCs in the aortic floor.