Ablation Of Vitamin Research Articles

Ablation of Vitamin D Signaling in Cardiomyocytes Leads to Functional Impairment and Stimulation of Pro-Inflammatory and Pro-Fibrotic Gene Regulatory Networks in a Left Ventricular Hypertrophy Model in Mice.

The association between vitamin D deficiency and cardiovascular disease remains a controversial issue. This study aimed to further elucidate the role of vitamin D signaling in the development of left ventricular (LV) hypertrophy and dysfunction. To ablate the vitamin D receptor (VDR) specifically in cardiomyocytes, VDRfl/fl mice were crossed with Mlcv2-Cre mice. To induce LV hypertrophy experimentally by increasing cardiac afterload, transverse aortic constriction (TAC) was employed. Sham or TAC surgery was performed in 4-month-old, male, wild-type, VDRfl/fl, Mlcv2-Cre, and cardiomyocyte-specific VDR knockout (VDRCM-KO) mice. As expected, TAC induced profound LV hypertrophy and dysfunction, evidenced by echocardiography, aortic and cardiac catheterization, cardiac histology, and LV expression profiling 4 weeks post-surgery. Sham-operated mice showed no differences between genotypes. However, TAC VDRCM-KO mice, while having comparable cardiomyocyte size and LV fibrosis to TAC VDRfl/fl controls, exhibited reduced fractional shortening and ejection fraction as measured by echocardiography. Spatial transcriptomics of heart cryosections revealed more pronounced pro-inflammatory and pro-fibrotic gene regulatory networks in the stressed cardiac tissue niches of TAC VDRCM-KO compared to VDRfl/fl mice. Hence, our study supports the notion that vitamin D signaling in cardiomyocytes plays a protective role in the stressed heart.

Vitamin D receptor absence does not enhance intestinal tumorigenesis in ApcPirc/+rats.

ABSTRACTEpidemiological observations have prompted some to posit that elevated circulating vitamin D is responsible for reduced colon cancer in individuals residing near the equator. We have previously demonstrated that vitamin D has no effect on colon cancer in two rodent models of intestinal tumorigenesis. We have now extended this line of inquiry to ask whether ablation of vitamin D receptor (VDR) affects tumorigenesis. A VDR null rat was developed using Cas9-CRISPR technology, which allowed us to investigate whether 1,25(OH)D3 signaling through its receptor plays a role in intestinal tumorigenesis. Loss of VDR expression alone did not induce tumorigenesis, even in animals exposed to the inflammatory agent dextran sodium sulfate. These VDR−/− rats were then crossed with ApcPirc/+ rats, which are predisposed to the development of intestinal neoplasms. In combination with the Pirc/+ mutation, VDR loss did not enhance tumor multiplicity, growth, or progression in the colon or small intestine. This study demonstrates that the vitamin D receptor does not impact tumor development, and strongly supports previous findings that vitamin D itself does not play a role in colon cancer development or progression. Alternative explanations are needed for the original latitude hypothesis, as well as observational data in humans.This article has an associated First Person interview with the first author of the paper.

Ablation of Vitamin D Signaling Compromises Cerebrovascular Adaptation to Carotid Artery Occlusion in Mice.

Vitamin D insufficiency has been associated with increased incidence and severity of cerebrovascular disorders. We analyzed the impact of impaired vitamin D signaling on the anatomical and functional aspects of cerebrovascular adaptation to unilateral carotid artery occlusion (CAO), a common consequence of atherosclerosis and cause of ischemic stroke. Cerebrocortical blood flow (CoBF) showed a significantly increased drop and delayed recovery after CAO in mice carrying a functionally inactive vitamin D receptor (VDR) with the most sustained perfusion deficit in the temporal cortex. To identify the cause(s) for this altered adaptation, the extent of compensatory blood flow increase in the contralateral carotid artery and the morphology of pial collaterals between the anterior and middle cerebral arteries were determined. Whereas VDR deficiency had no significant influence on the contralateral carotid arterial blood flow increase, it was associated with decreased number and increased tortuosity of pial anastomoses resulting in unfavorable changes of the intracranial collateral circulation. These results indicate that VDR deficiency compromises the cerebrovascular adaptation to CAO with the most sustained consequences in the temporal cortex. The dysregulation can be attributed to the altered development and function of pial collateral circulation whereas extracranial vessels may not be impaired.

Tumor Autonomous Effects of Vitamin D Deficiency Promote Breast Cancer Metastasis.

Patients with breast cancer (BCa) frequently have preexisting vitamin D deficiency (low serum 25-hydroxyvitamin D) when their cancer develops. A number of epidemiological studies show an inverse association between BCa risk and vitamin D status in humans, although some studies have failed to find an association. In addition, several studies have reported that BCa patients with vitamin D deficiency have a more aggressive molecular phenotype and worse prognostic indicators. However, it is unknown whether this association is mechanistically causative and, if so, whether it results from systemic or tumor autonomous effects of vitamin D signaling. We found that ablation of vitamin D receptor expression within BCa cells accelerates primary tumor growth and enables the development of metastases, demonstrating a tumor autonomous effect of vitamin D signaling to suppress BCa metastases. We show that vitamin D signaling inhibits the expression of the tumor progression gene Id1, and this pathway is abrogated in vitamin D deficiency in vivo in 2 murine models of BCa. These findings are relevant to humans, because we discovered that the mechanism of VDR regulation of Inhibitor of differentiation 1 (ID1) is conserved in human BCa cells, and there is a negative correlation between serum 25-hydroxyvitamin D levels and the level of ID1 in primary tumors from patients with BCa.

Klotho Lacks a Vitamin D Independent Physiological Role in Glucose Homeostasis, Bone Turnover, and Steady-State PTH Secretion In Vivo

Apart from its function as co-receptor for fibroblast growth factor-23 (FGF23), Klotho is thought to regulate insulin signaling, intracellular oxidative stress, and parathyroid hormone (PTH) secretion in an FGF23 independent fashion. Here, we crossed Klotho deficient (Kl−/−) mice with vitamin D receptor (VDR) mutant mice to examine further vitamin D independent functions of Klotho. All mice were fed a rescue diet enriched with calcium, phosphorus, and lactose to prevent hyperparathyroidism in VDR mutants, and were killed at 4 weeks of age after double fluorochrome labeling. Kl−/− mice displayed hypercalcemia, hyperphosphatemia, dwarfism, organ atrophy, azotemia, pulmonary emphysema, and osteomalacia. In addition, glucose and insulin tolerance tests revealed hypoglycemia and profoundly increased peripheral insulin sensitivity in Kl−/− mice. Compound mutants were normocalcemic and normophosphatemic, did not show premature aging or organ atrophy, and were phenocopies of VDR mutant mice in terms of body weight, bone mineral density, bone metabolism, serum calcium, serum phosphate, serum PTH, gene expression in parathyroid glands, as well as urinary calcium and phosphate excretion. Furthermore, ablation of vitamin D signaling in double mutants completely normalized glucose and insulin tolerance, indicating that Klotho has no vitamin D independent effects on insulin signaling. Histomorphometry of pancreas islets showed similar beta cell volume per body weight in all groups of animals. In conclusion, our findings cast doubt on a physiologically relevant vitamin D and Fgf23 independent function of Klotho in the regulation of glucose metabolism, bone turnover, and steady-state PTH secretion in vivo.

Genetic Ablation of Vitamin D Activation Pathway Reverses Biochemical and Skeletal Anomalies in Fgf-23-Null Animals

Fibroblast growth factor-23 (FGF-23) is one of the circulating phosphaturic factors associated with renal phosphate wasting. Fgf-23-/- animals show extremely high serum levels of phosphate and 1,25-dihydroxyvitamin D3, along with abnormal bone mineralization and soft tissue calcifications. To determine the role of vitamin D in mediating altered phosphate homeostasis and skeletogenesis in the Fgf-23-/- mice, we generated mice lacking both the Fgf-23 and 1alpha-hydroxylase genes (Fgf-23-/-/1alpha(OH)ase-/-). In the current study, we have identified the cellular source of Fgf-23 in adult mice. In addition, loss of vitamin D activities from Fgf-23-/- mice reverses the severe hyperphosphatemia to hypophosphatemia, attributable to increased urinary phosphate wasting in Fgf-23-/-/1alpha(OH)ase-/- mice, possibly as a consequence of decreased expression of NaPi2a. Ablation of vitamin D from Fgf-23-/- mice resulted in further reduction of total bone mineral content and bone mineral density and reversed ectopic calcification of skeleton and soft tissues, suggesting that abnormal mineral ion homeostasis and impaired skeletogenesis in Fgf-23-/- mice are mediated through enhanced vitamin D activities. In conclusion, using genetic manipulation studies, we have provided evidence for an in vivo inverse correlation between Fgf-23 and vitamin D activities and for the severe skeletal and soft tissue abnormalities of Fgf-23-/- mice being mediated through vitamin D.

Ablation of vitamin D signaling rescues bone, mineral, and glucose homeostasis in Fgf-23 deficient mice

To explore further the role of the vitamin D axis for fibroblast growth factor-23 (FGF23) signaling, we mated Fgf-23 deficient ( Fgf-23 −/− ) mice and vitamin D receptor (VDR) mutant mice with a non-functioning VDR. To prevent secondary hyperparathyroidism in VDR and compound mutant mice, all mice were kept on a rescue diet enriched with calcium, phosphorus, and lactose. Consistent with previous findings, Fgf-23 −/− animals showed hypercalcemia, hyperphosphatemia, growth retardation, ectopic calcifications, severe osteoidosis, skin atrophy, and renal dysfunction. In addition, here we describe that Fgf-23 −/− mice are hypoglycemic, and have profoundly increased peripheral insulin sensitivity and improved subcutaneous glucose tolerance, but normal renal expression of the aging suppressor gene Klotho. Although VDR and double mutants on the rescue diet still had moderately elevated parathyroid hormone serum levels and lower bone mineral density compared to wild-type mice, double mutant mice were normocalcemic and normophosphatemic, and had normal body weight, normal renal function, and no ectopic calcifications. Ablation of vitamin D signaling in compound mutants also normalized subcutaneous glucose tolerance tests and insulin secretory response. In conclusion, our results indicate that the alterations in mineral and carbohydrate metabolism present in Fgf-23 −/− mice require an intact vitamin D signaling pathway.

Premature aging‐like phenotype in fibroblast growth factor 23 null mice is a vitamin D‐mediated process

Fibroblast growth factor 23 null mice (Fgf-23-/-) have a short lifespan and show numerous biochemical and morphological features consistent with premature aging-like phenotypes, including kyphosis, severe muscle wasting, hypogonadism, osteopenia, emphysema, uncoordinated movement, T cell dysregulation, and atrophy of the intestinal villi, skin, thymus, and spleen. Furthermore, increased vitamin D activities in homozygous mutants are associated with severe atherosclerosis and widespread soft tissue calcifications; ablation of vitamin D activity from Fgf-23-/- mice, by genetically deleting the 1alpha(OH)ase gene, eliminates atherosclerosis and ectopic calcifications and significantly rescues premature aging-like features of Fgf-23-/- mice, resulting in prolonged survival of Fgf-23-/-/1alpha(OH)ase-/- double mutants. Our results indicate a novel role of Fgf-23 in developing premature aging-like features through regulating vitamin D homeostasis. Finally, our data support a new model of interactions among Fgf-23, vitamin D, and klotho, a gene described as being associated with premature aging process.

ABNORMAL BEHAVIORAL ORGANIZATION OF GROOMING IN MICE LACKING THE VITAMIN D RECEPTOR GENE

Vitamin D is a steroid hormone with several important functions in the nervous system. Numerous human and animal data link alterations in the vitamin D system to various behavioral disorders. Grooming is an important element of rodent behavior with a general pattern of cephalocaudal progression (paw licking – nose/face wash – body wash – tail/genitals wash). Here we studied whether genetic ablation of vitamin D nuclear receptors (VDR) in mice may be associated with altered behavioral sequencing of grooming. Overall, VDR null mutant mice showed abnormal grooming, including a higher percentage of “incorrect” transitions and longer duration of “incorrect” grooming (contrary to the cephalocaudal progression); a higher percentage of interrupted grooming bouts; and the atypical regional distribution of grooming (more leg grooming, less body and tail/genitals grooming), compared to their wild-type controls. Grooming of heterozygous mice was similar to the wild-type group, indicating that abnormal grooming patterning is inherited as a recessive. In contrast, behavioral sequencing of another complex behavior (mating with a female) was unaltered in all three genotypes, suggesting grooming-specific abnormal sequencing in these mutant mice. Our results suggest that a neurosteroid vitamin D and VDR may play an important role in controlling sequencing of grooming in mice, and further confirm the important role of the vitamin D system and VDR in the regulation of behavior.