Novel Vitamin D Receptor Mutations in Hereditary Vitamin D Resistant Rickets in Chinese

Impact of Vitamin D Receptor Genotypes on Taiwan Hallux Valgus

BACKGROUND/AIM

Hallux valgus (HV) is the most prevalent deformity affecting the forefoot; however, its genetic etiology remains unclear. In the literature, vitamin D receptor (VDR) genotypes have been reported to be associated with the risk of skeletal malformations accompanied by inflammation. This study aimed to examine the hypothesis that VDR genotypes are associated with the risk of HV.

MATERIALS AND METHODS

The VDR rs731236, rs1544410, rs2228570 and rs7975232 genotypes of 150 HV patients and 600 non-HV subjects were determined using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) methodology and examined regarding their associations with HV risk.

RESULTS

The results showed that none of the genetic frequency distributions of VDR rs731236, rs1544410, rs2228570, or rs7975232 were significant between the HV cases and non-HV controls (p for trend=0.4055, 0.2170, 0.7220, 0.5509, respectively). Additionally, allelic frequency analysis showed that none of the allelic frequencies of VDR rs731236, rs1544410, rs2228570, or rs7975232 were significantly distributed (p=0.2285, 0.1572, 0.9278, and 0.5547, respectively). Furthermore, stratified analysis showed that no correlation was observed between VDR rs731236 and different age groups (either younger or older than 51) or sex (p=0.3953 and p=0.9576). Moreover, no correlation was found between VDR rs731236 genotype and the risk of HV in individuals within subgroups of height, weight, or body mass index (BMI) (p=0.8317, 0.5346, and p=0.8783, respectively).

CONCLUSION

VDR rs731236, rs1544410, rs2228570, and rs7975232 may not serve as indicators for a higher risk of HV.

Vitamin D Status and Immune Response in Hospitalized Patients with Moderate and Severe COVID-19

A low 25-hydroxyvitamin D (25(OH)D) level is considered as an independent risk factor for COVID-19 severity. However, the association between vitamin D status and outcomes in COVID-19 is controversial. In the present study we investigate the association between the serum 25(OH)D level, immune response, and clinical disease course in patients with COVID-19. A total of 311 patients hospitalized with COVID-19 were enrolled. For patients with a vitamin D deficiency/insufficiency, the prevalence of severe COVID-19 was higher than in those with a normal 25(OH)D level (p < 0.001). The threshold of 25(OH)D level associated with mortality was 11.4 ng/mL (p = 0.003, ROC analysis). The frequency of CD3+CD4+ T helper (Th) cells was decreased in patients with 25(OH)D level ≤ 11.4 ng/mL, compared to healthy controls (HCs). There were no differences in the frequency of naive, central memory (CM), effector memory (EM), and terminally differentiated effector memory Th cells in patients with COVID-19 compared to HCs. The frequency of T-follicular helpers was decreased both in patients with 25(OH)D level > 11.4 ng/mL (p < 0.001) and 25(OH)D level ≤ 11.4 ng/mL (p = 0.003) compared to HCs. Patients with 25(OH)D level > 11.4 ng/mL had an increased frequency of Th2 CM (p = 0.010) and decreased Th17 CM (p < 0.001). While the frequency of Th2 EM was significantly increased, the frequency of Th17 EM was significantly decreased in both groups compared to HCs. Thus, 25(OH)D level is an independent risk factor for the disease severity and mortality in patients with COVID-19. We demonstrate that the serum 25(OH)D level ≤ 11.4 ng/mL is associated with the stimulation of Th2 and the downregulation of Th17 cell polarization of the adaptive immunity in patients with COVID-19.

Hereditary 1,25-dihydroxyvitamin D-resistant rickets (HVDRR): clinical heterogeneity and long-term efficacious management of eight patients from four unrelated Arab families with a loss of function VDR mutation

BACKGROUND

Vitamin D regulates the concentrations of calcium and phosphate in blood and promotes the growth and remodeling of bones. The circulating active form of vitamin D, 1,25-dihydroxyvitamin D, binds to the vitamin D receptor (VDR), which heterodimerizes with the retinoid X receptor to regulate the expression of target genes. Inactivating mutations in the VDR gene cause hereditary vitamin D-resistant rickets (HVDRR), a rare disorder characterized by an early onset of rickets, growth retardation, skeletal deformities, hypocalcemia, hypophosphatemia and secondary hyperparathyroidism, and in some cases alopecia.

METHODS

We describe eight new HVDRR patients from four unrelated consanguineous families. The VDR gene was sequenced to identify mutations. The management of patients over a period of up to 11 years following the initial diagnosis is assessed.

RESULTS

Although all patients exhibit main features of HVDRR and carry the same c.885C>A (p.Y295*) loss of function mutation in the VDR gene, there was heterogeneity of the manifestations of HVDRR-associated phenotypes and developmental milestones. These eight patients were successfully treated over a period of 11 years. All clinical symptoms were improved except alopecia.

CONCLUSIONS

The study concludes that VDR sequencing and laboratory tests are essential to confirm HVDRR and to assess the effectiveness of the treatment.

Inhibition of Stat3 signaling ameliorates atrophy of the soleus muscles in mice lacking the vitamin D receptor

Background

Although skeletal muscle wasting has long been observed as a clinical outcome of impaired vitamin D signaling, precise molecular mechanisms that mediate the loss of muscle mass in the absence of vitamin D signaling are less clear. To determine the molecular consequences of vitamin D signaling, we analyzed the role of signal transducer and activator of transcription 3 (Stat3) signaling, a known contributor to various muscle wasting pathologies, in skeletal muscles.

Methods

We isolated soleus (slow) and tibialis anterior (fast) muscles from mice lacking the vitamin D receptor (VDR^−/−) and used western blot analysis, quantitative RTPCR, and pharmacological intervention to analyze muscle atrophy in VDR^−/− mice.

Results

We found that slow and fast subsets of muscles of the VDR^−/− mice displayed elevated levels of phosphorylated Stat3 accompanied by an increase in Myostatin expression and signaling. Consequently, we observed reduced activity of mammalian target of rapamycin (mTOR) signaling components, ribosomal S6 kinase (p70S6K) and ribosomal S6 protein (rpS6), that regulate protein synthesis and cell size, respectively. Concomitantly, we observed an increase in atrophy regulators and a block in autophagic gene expression. An examination of the upstream regulation of Stat3 levels in VDR^−/− muscles revealed an increase in IL-6 protein expression in the soleus, but not in the tibialis anterior muscles. To investigate the involvement of satellite cells (SCs) in atrophy in VDR^−/− mice, we found that there was no significant deficit in SC numbers in VDR^−/− muscles compared to the wild type. Unlike its expression within VDR^−/− fibers, Myostatin levels in VDR^−/− SCs from bulk muscles were similar to those of wild type. However, VDR^−/− SCs induced to differentiate in culture displayed increased p-Stat3 signaling and Myostatin expression. Finally, VDR^−/− mice injected with a Stat3 inhibitor displayed reduced Myostatin expression and function and restored active p70S6K and rpS6 levels, resulting in an amelioration of loss of muscle mass in the soleus muscles.

Conclusions

The loss of muscle mass in slow muscles in the absence of vitamin D signaling is due to elevated levels of phosphorylated Stat3 that leads to an increase in Myostatin signaling, which in turn decreases protein synthesis and fiber size through the phosphorylation of p70S6K and rpS6, respectively.

Electronic supplementary material

The online version of this article (doi:10.1186/s13395-017-0121-2) contains supplementary material, which is available to authorized users.