Expression pattern of CYP24 in liver during ageing in long-term diabetes

Laminin α4 overexpression in the anterior lens capsule may contribute to the senescence of human lens epithelial cells in age-related cataract

Senescence is a leading cause of age-related cataract (ARC). The current study indicated that the senescence-associated protein, p53, total laminin (LM), LMα4, and transforming growth factor-beta1 (TGF-β1) in the cataractous anterior lens capsules (ALCs) increase with the grades of ARC. In cataractous ALCs, patient age, total LM, LMα4, TGF-β1, were all positively correlated with p53. In lens epithelial cell (HLE B-3) senescence models, matrix metalloproteinase-9 (MMP-9) alleviated senescence by decreasing the expression of total LM and LMα4; TGF-β1 induced senescence by increasing the expression of total LM and LMα4. Furthermore, MMP-9 silencing increased p-p38 and LMα4 expression; anti-LMα4 globular domain antibody alleviated senescence by decreasing the expression of p-p38 and LMα4; pharmacological inhibition of p38 MAPK signaling alleviated senescence by decreasing the expression of LMα4. Finally, in cataractous ALCs, positive correlations were found between LMα4 and total LM, as well as between LMα4 and TGF-β1. Taken together, our results implied that the elevated LMα4, which was possibly caused by the decreased MMP-9, increased TGF-β1 and activated p38 MAPK signaling during senescence, leading to the development of ARC. LMα4 and its regulatory factors show potential as targets for drug development for prevention and treatment of ARC.

Association of increased renal Cyp24a1 gene expression with low plasma 1,25-dihydroxyvitamin D levels in rats with streptozotocin-induced diabetes

Decreases in plasma vitamin D concentrations have been reported in diabetes, although the mechanism involved in this decrease is unclear. Here, we investigated the association between Cyp24a1, a vitamin D catabolic enzyme, and abnormalities in vitamin D metabolism in streptozotocin-induced diabetes rats, an animal model of type 1 diabetes. Plasma 1,25-dihydroxyvitamin D [1,25(OH)₂D] levels were significantly lower in streptozotocin-induced diabetes rats and renal Cyp24a1 mRNA expression levels were increased. Western blotting analysis of streptozotocin-induced diabetes rats kidney tissues with anti-CYP24A1 antibody showed a strong signal around 40 kDa, which differs from the predicted 50–55 kDa molecular weight for full-length Cyp24a1 and could represent the Cyp24a1-splicing variant that lacks exons 1 and 2. We observed high levels of renal Cyp24a1-splicing variant mRNA expression in streptozotocin-induced diabetes rats. We also confirmed transcriptional up-regulation of endogenous Cyp24a1 mRNA expression through glucocorticoid receptors by glucocorticoid in opossum kidney proximal cells. Taken together, our results indicated that high Cyp24a1 expression levels may play a role in the decrease of plasma 1,25(OH)₂D levels in streptozotocin-induced diabetes rats. High plasma corticosterone levels in diabetes may affect transcriptional regulation to promote increases in Cyp24a1 expression.

Ultrastructural characterization of vitamin D receptors and metabolizing enzymes in the lipid droplets of the fatty liver in rat

Vitamin D is a steroid hormone with numerous actions in the organism. There are strong evidences that relate vitamin D deficiency with liver lipid metabolism disturbances, but the mechanism of this action is still unknown. In our previous work we postulated the localization and accumulation of vitamin D receptor (VDR) in membrane of the lipid droplets (LDs) in hepatocytes. In this study, we applied the transmission electron microscopy (TEM) to confirm this hypothesis by using a long-term (6 months) high sucrose intake rat model that was previously found to be appropriate for research of the hepatic lipid accumulation. In addition to the VDR, we also found key vitamin D metabolizing enzymes, 1α-hydroxylase and CYP 24 associated with the membrane of the LDs. A light-microscopy data revealed significant increase in expression of VDR and CYP 24 in liver of high-sucrose treated rats, in comparison to controlones. According to the best of our knowledge, this is a first study confirming the presence of the VDR in the membrane of the LDs in general and also in particular in LDs of the hepatocytes that were accumulated as a consequence of the prolonged high sucrose intake. Moreover, we found association of main vitamin D metabolizing enzymes with LD membrane. These results provide a new insight in the possible relation of vitamin D signalling system with LD morphology and function and with the lipid metabolism in general.

Combined Treatment with Omega-3 Fatty Acid and Cholecalciferol Increases 1,25-Dihydroxyvitamin D Levels by Modulating Dysregulation of Vitamin D Metabolism in 5/6 Nephrectomy Rats

The protein 1α-hydroxylase (CYP27B1) was expressed in liver and omega-3 fatty acid (FA) elevated 1,25-dihydroxyvitamin D [1,25(OH)₂D] levels in dialysis patients. The aim of this study was to determine whether omega-3 FA and cholecalciferol have effects on vitamin D metabolism related to CYP27B1 and 24-hydroxylase (CYP24) activities in the kidney and liver of 5/6 nephrectomy (Nx) rats. Male Sprague–Dawley rats were divided into the following groups: sham control, 5/6 Nx, 5/6 Nx treated with cholecalciferol, 5/6 Nx treated with omega-3 FA, and 5/6 Nx treated with cholecalciferol/omega-3 FA. CYP27B1 and CYP24 expression were measured in the liver and kidney. Further, 1,25(OH)₂D and 25-hydroxyvitamin D [25(OH)D] levels were measured in serum. Among Nx groups, 1,25(OH)₂D and 25(OH)D levels were lowest in the 5/6 Nx group. CYP24 expression was increased in the kidney of the 5/6 Nx rat model, which was found to be reversed by omega-3 FA or cholecalciferol/omega-3 FA supplementation. Decreased CYP27B1 expression was observed in the liver of the 5/6 Nx rats and its expression was recovered by supplementation with cholecalciferol/omega-3 FA. In conclusion, omega-3 FA and cholecalciferol may synergistically increase 1,25(OH)₂D levels by inhibiting CYP24 expression in the kidney and liver and activating CYP27B1 expression in the liver of 5/6 Nx rats.

TGF-β1 Impairs Vitamin D-Induced and Constitutive Airway Epithelial Host Defense Mechanisms

Airway epithelium is an important site for local vitamin D (VD) metabolism; this can be negatively affected by inflammatory mediators. VD is an important regulator of respiratory host defense, for example, by increasing the expression of hCAP18/LL-37. TGF-β1 is increased in chronic obstructive pulmonary disease (COPD), and known to decrease the expression of constitutive host defense mediators such as secretory leukocyte protease inhibitor (SLPI) and polymeric immunoglobulin receptor (pIgR). VD has been shown to affect TGF-β1-signaling by inhibiting TGF-β1-induced epithelial-to-mesenchymal transition. However, interactions between VD and TGF-β1, relevant for the understanding host defense in COPD, are incompletely understood. Therefore, the aim of the present study was to investigate the combined effects of VD and TGF-β1 on airway epithelial cell host defense mechanisms. Exposure to TGF-β1 reduced both baseline and VD-induced expression of hCAP18/LL-37, partly by increasing the expression of the VD-degrading enzyme CYP24A1. TGF-β1 alone decreased the number of secretory club and goblet cells and reduced the expression of constitutive host defense mediators SLPI, s/lPLUNC and pIgR, effects that were not modulated by VD. These results suggest that TGF-β1 may decrease the respiratory host defense both directly by reducing the expression of host defense mediators, and indirectly by affecting VD-mediated effects such as expression of hCAP18/LL-37.