Prenatal diagnosis of vitamin D-dependent rickets, type II: response to 1,25-dihydroxyvitamin D in amniotic fluid cells and fetal tissues

The plasticity of DNA replication forks in response to clinically relevant genotoxic stress

Complete and accurate DNA replication requires the progression of replication forks through DNA damage, actively transcribed regions, structured DNA and compact chromatin. Recent studies have revealed a remarkable plasticity of the replication process in dealing with these obstacles, which includes modulation of replication origin firing, of the architecture of replication forks, and of the functional organization of the replication machinery in response to replication stress. However, these specialized mechanisms also expose cells to potentially dangerous transactions while replicating DNA. In this Review, we discuss how replication forks are actively stalled, remodelled, processed, protected and restarted in response to specific types of stress. We also discuss adaptations of the replication machinery and the role of chromatin modifications during these transactions. Finally, we discuss interesting recent data on the relevance of replication fork plasticity to human health, covering its role in tumorigenesis, its crosstalk with innate immunity responses and its potential as an effective cancer therapy target.

The role of vitamin D receptor in innate and adaptive immunity: a study in hereditary vitamin D-resistant rickets patients

CONTEXT

Vitamin D has regulatory effects on innate and adaptive immunity. Curiously, hereditary vitamin D-resistant rickets (HVDRR) patients show no increased incidence of infectious or autoimmune diseases.

OBJECTIVES

The aim of the study was to investigate the role of vitamin D and the vitamin D receptor (VDR) in innate and adaptive immune responses in monocytes and lymphocytes from HVDRR patients.

DESIGN AND METHODS

Fifteen HVDRR patients and 17 controls participated in the investigation. Activated monocytes (lipopolysaccharides) and lymphocytes (anti-CD3, CD28, and α-GalCer) were incubated with and without 25(OH)D3 (100 nM). The mRNA expressions of CYP27B1 and VDR; vitamin D response (TLR2); vitamin D response elements binding protein (hnRNP); antimicrobial peptides cathelicidin and β-defensin; the transcription factor enhancer binding proteins C/EBPα, C/EBPβ, and C/EBPε and enzymes involved in NO generation, Nos2, and Arginase1 were analyzed by RT-PCR. TNF-α, interferon-γ, IL-4, IL-10, and IL-17 concentrations in lymphocyte cultures media were measured by ELISA.

RESULTS

Cathelicidin expression was lower in HVDRR monocytes than in control monocytes. 25(OH)D3 increased significantly the expression of cathelicidin in control monocytes (2.3-fold) but only slightly in HVDRR monocytes. 25(OH)D3 increased the expression of VDR (2-fold), C/EBPε (2-fold), C/EBPβ (1.7-fold), and hnRNP and suppressed TLR2 only in control monocytes. Unexpectedly, 25(OH)D3 increased the expression of CYP27b1, C/EBPα, Nos2, and Arginase1 in HVDRR monocytes. TNFα and IL-17 concentrations were significantly higher in HVDRR lymphocyte cultures than in controls. 25(OH)D3 suppressed IL-17 only in control lymphocyte. 25(OH)D3 increased IL-4, IL-10, and interferon-γ concentrations in control lymphocyte media but not in HVDRR.

CONCLUSIONS

Our results demonstrate impairments in various components of innate immunity in HVDTRR patients' monocytes and a proinflammatory cytokine profile in their lymphocytes. The underlying VDR-independent compensatory mechanisms that protect HVDRR patients from infections and autoimmune diseases remain undetermined.

Calcitriol-resistant rickets due to vitamin D receptor defects

Calcitriol-resistant rickets (CRR) is an autosomal recessive disease due to a defect in the vitamin D receptor (VDR) or a site distal to it. The main characteristics are extreme rickets, with growth attenuation, osteomalacia, secondary hyperparathyroidism, severe dental caries, and alopecia. Serum studies reveal hypocalcemia, hypophosphatemia, very high calcitriol, and increased alkaline phosphatase levels. The clinical and chemical abnormalities do not respond to therapy with high-dose vitamin D, indicating target organ unresponsiveness. Eleven different mutations in the gene-encoding VDR have thus far been reported. They affect either the C-terminal ligand-binding region or the N-terminal DNA binding zinc-fingers sequences, with mutation hot spots identified at conserved sequences among the steroid-thyroid receptors superfamily. These result in impaired calcitriol binding to target organs, signified in vitro as failure of fibroblasts to bind [(3)H]calcitriol or to respond to calcitriol by 24-hydroxylase activity enhancement. Receptor studies and mutational analyses are used for prenatal diagnosis of CRR. Therapy with high-dose calcium overcomes the VDR defect, normalizes serum calcium, and maintains bone remodeling and mineral apposition. These responses to therapy have interesting implications upon our understanding of the potential role of calcium alone and that of vitamin D in bone physiology. Like other hormone-resistant diseases, CRR, with its various mutations, provides the opportunity for investigating the nature of vitamin D and of VDR physiology, which has been only partially explored to date.