The Asn19Lys substitution in the osteoclast inhibitory lectin (OCIL) gene is associated with a reduction of bone mineral density in postmenopausal women

The diverse roles of C-type lectin-like receptors in immunity

Our understanding of the C-type lectin-like receptors (CTLRs) and their functions in immunity have continued to expand from their initial roles in pathogen recognition. There are now clear examples of CTLRs acting as scavenger receptors, sensors of cell death and cell transformation, and regulators of immune responses and homeostasis. This range of function reflects an extensive diversity in the expression and signaling activity between individual CTLR members of otherwise highly conserved families. Adding to this diversity is the constant discovery of new receptor binding capabilities and receptor-ligand interactions, distinct cellular expression profiles, and receptor structures and signaling mechanisms which have expanded the defining roles of CTLRs in immunity. The natural killer cell receptors exemplify this functional diversity with growing evidence of their activity in other immune populations and tissues. Here, we broadly review select families of CTLRs encoded in the natural killer cell gene complex (NKC) highlighting key receptors that demonstrate the complex multifunctional capabilities of these proteins. We focus on recent evidence from research on the NKRP1 family of CTLRs and their interaction with the related C-type lectin (CLEC) ligands which together exhibit essential immune functions beyond their defined activity in natural killer (NK) cells. The ever-expanding evidence for the requirement of CTLR in numerous biological processes emphasizes the need to better understand the functional potential of these receptor families in immune defense and pathological conditions.

Heamatococcus pluvialis ameliorates bone loss in experimentally-induced osteoporosis in rats via the regulation of OPG/RANKL pathway

BACKGROUNDS

Osteoporosis prevailing in elderly involves a marked increase in bone resorption showing an initial fall in bone mineral density leading to a significant reduction in bone formation.

AIM

The present study aimed to investigate the effect of Heamatococcus pluvialis microalgae on osteoporosis in D-galactose-treated rats. The underlying mechanism was tracked targeting the osteoprotegerin (OPG)/ nuclear factor-κβ ligand (RANKL) pathway using micro-computed tomography scanning.

METHODS

Osteoporosis was induced in rats by intraperitoneal injection of D-galactose (200 mg/kg/day) for eight consecutive weeks. Osteoporotic rats were orally treated with H. pluvialis biomass (BHP; 450 mg/kg), its polar (PHP; 30 mg/kg) and carotenoid (CHP; 30 mg/kg) fractions for the last 2 weeks of D-Gal injection. Twenty four hours after the last dose of the treatments, tibia bones of the rats were scanned using micro-computed tomography scanning for bone mineral density (BMD), bone volume fraction (BV/TV), trabecular thickness/separation/number (Tb.Th, Tb.Sp, Tb.N) evaluation, blood samples were withdrawn and sera were used for biochemical assessment. Moreover, femur bones were examined histopathologically using several stains.

RESULTS

Induction of osteoporosis was associated with a marked reduction in BMD, BV/TV, Tb.Th, Tb.Sp, Tb.N and in serum levels of phosphorus and catalase. On the other hand, a significant elevation in serum levels of calcium, bone alkaline phosphatase (BALP) and interleukin-6 was observed. Moreover, up-regulation of OPG was detected in osteoporotic rats. Oral treatment with BHP, and PHP incremented tibia BMD and serum phosphorus level along with the decrease in serum levels of calcium, BALP, interleukin-6, OPG and RANKL. However, treatment with CHP almost restored all the fore mentioned parameters to normal values. Furthermore, the histopathological evaluation emphasized the biochemical outcomes.

CONCLUSION

H. pluvialis fractions rich in astaxanthin ameliorated bone loss in experimentally-induced osteoporosis in rats probably through the down-regulation of serum OPG in concurrence with up-regulation of serum RANKL.

Genome-wide association study for bone strength in laying hens

Bone fracture in egg laying hens is a growing welfare and economic concern in the industry. Although environmental conditions and management (especially nutrition) can exacerbate it, the primary cause of bone weakness and the resulting fractures is believed to have a genetic basis. To test this hypothesis, we performed a genome-wide association study to identify the loci associated with bone strength in laying hens. Genotype and phenotype data were obtained from 752 laying hens belonging to the same pure line population. These hens were genotyped for 580,961 SNPs, with 232,021 SNPs remaining after quality control. Each of the SNPs were tested for association with tibial breaking strength using the family-based score test for association. A total of 52 SNPs across chromosomes 1, 3, 8, and 16 were significantly associated with tibial breaking strength with the genome-wide significance threshold set as a corrected P value of 10e-5. Based on the local linkage disequilibrium around the significant SNPs, 5 distinct and novel QTLs were identified on chromosomes 1 (2 QTLs), 3 (1 QTL), 8 (1 QTL) and 16 (1 QTL). The strongest association was detected within the QTL region on chromosome 8, with the most significant SNP having a corrected P value of 4e-7. A number of candidate genes were identified within the QTL regions, including the BRD2 gene that is required for normal bone physiology. Bone-related pathways involving some of the genes were also identified including chloride channel activity, which regulates bone reabsorption, and intermediate filament organization, which plays a role in the regulation of bone mass. Our result supports previous studies that suggest that bone strength is highly regulated by genetics. It is therefore possible to reduce bone fractures in laying hens through genetic selection and ultimately improve hen welfare.

Sweet complementarity: the functional pairing of glycans with lectins

Carbohydrates establish the third alphabet of life. As part of cellular glycoconjugates, the glycans generate a multitude of signals in a minimum of space. The presence of distinct glycotopes and the glycome diversity are mapped by sugar receptors (antibodies and lectins). Endogenous (tissue) lectins can read the sugar-encoded information and translate it into functional aspects of cell sociology. Illustrated by instructive examples, each glycan has its own ligand properties. Lectins with different folds can converge to target the same epitope, while intrafamily diversification enables functional cooperation and antagonism. The emerging evidence for the concept of a network calls for a detailed fingerprinting. Due to the high degree of plasticity and dynamics of the display of genes for lectins the validity of extrapolations between different organisms of the phylogenetic tree yet is inevitably limited.

Association of the I264T variant in the sulfide quinone reductase-like (SQRDL) gene with osteoporosis in Korean postmenopausal women

To identify novel susceptibility variants for osteoporosis in Korean postmenopausal women, we performed a genome-wide association analysis of 1180 nonsynonymous single nucleotide polymorphisms (nsSNPs) in 405 individuals with osteoporosis and 722 normal controls of the Korean Association Resource cohort. A logistic regression analysis revealed 72 nsSNPs that showed a significant association with osteoporosis (p<0.05). The top 10 nsSNPs showing the lowest p-values (p = 5.2×10-4-8.5×10-3) were further studied to investigate their effects at the protein level. Based on the results of an in silico prediction of the protein's functional effect based on amino acid alterations and a sequence conservation evaluation of the amino acid residues at the positions of the nsSNPs among orthologues, we selected one nsSNP in the SQRDL gene (rs1044032, SQRDL I264T) as a meaningful genetic variant associated with postmenopausal osteoporosis. To assess whether the SQRDL I264T variant played a functional role in the pathogenesis of osteoporosis, we examined the in vitro effect of the nsSNP on bone remodeling. Overexpression of the SQRDL I264T variant in the preosteoblast MC3T3-E1 cells significantly increased alkaline phosphatase activity, mineralization, and the mRNA expression of osteoblastogenesis markers, Runx2, Sp7, and Bglap genes, whereas the SQRDL wild type had no effect or a negative effect on osteoblast differentiation. Overexpression of the SQRDL I264T variant did not affect osteoclast differentiation of the primary-cultured monocytes. The known effects of hydrogen sulfide (H2S) on bone remodeling may explain the findings of the current study, which demonstrated the functional role of the H2S-catalyzing enzyme SQRDL I264T variant in osteoblast differentiation. In conclusion, the results of the statistical and experimental analyses indicate that the SQRDL I264T nsSNP may be a significant susceptibility variant for osteoporosis in Korean postmenopausal women that is involved in osteoblast differentiation.

Complexity and Diversity of the NKR-P1:Clr (Klrb1:Clec2) Recognition Systems

The NKR-P1 receptors were identified as prototypical natural killer (NK) cell surface antigens and later shown to be conserved from rodents to humans on NK cells and subsets of T cells. C-type lectin-like in nature, they were originally shown to be capable of activating NK cell function and to recognize ligands on tumor cells. However, certain family members have subsequently been shown to be capable of inhibiting NK cell activity, and to recognize proteins encoded by a family of genetically linked C-type lectin-related ligands. Some of these ligands are expressed by normal, healthy cells, and modulated during transformation, infection, and cellular stress, while other ligands are upregulated during the immune response and during pathological circumstances. Here, we discuss historical and recent developments in NKR-P1 biology that demonstrate this NK receptor–ligand system to be far more complex and diverse than originally anticipated.

Single nucleotide polymorphisms in C-type lectin genes, clustered in the IBD2 and IBD6 susceptibility loci, may play a role in the pathogenesis of inflammatory bowel diseases

BACKGROUND AND AIM

The balance between microbes and host defence mechanisms at the mucosal frontier plays an important, yet unclarified role in the pathogenesis of inflammatory bowel disease (IBD). The importance of microorganisms in IBD is supported by the association of IBD with mutations in pattern recognition receptors (PRRs) such as NOD2 and TLR4. We aimed to examine whether polymorphisms in another type of PRRs, the so-called C-type lectin receptors (CLRs), are associated with IBD. Growing insights into the pathogenetic role of NOD2 mutations in Crohn's disease (CD) and the fact that the majority of CLR-encoding genes are located in IBD susceptibility loci provide strong arguments for further exploration of the role of CLRs in IBD.

METHODS

In this study, we selected four single nucleotide polymorphisms (SNPs) in different CLRs to determine whether there could be a role for these CLRs in IBD. Functional SNPs in the genes coding for the candidate CLRs DC-SIGN, LLT1, DCIR and MGL were examined. Genotyping of all SNPs was performed at the Academic Medical Center. In this study, around 1572 samples were included from a maximum of 621 CD patients, 457 ulcerative colitis (UC) patients and 586 healthy controls (HCs).

RESULTS AND CONCLUSION

No association was found between our IBD cohort and the candidate SNPs for DC-SIGN (CD/HC: P=0.25 and UC/HC: P=0.36), DCIR (CD/HC: P=0.22 and UC/HC: P=0.41) and MGL (CD/HC: P=0.37 and UC/HC: P=0.25). However, one polymorphism in LLT1 was found to be associated with our CD population (P<0.034). Our UC cohort was not associated with the variation in LLT1 (P=0.33). LLT1 is a ligand for the recently discovered CD161. CD161 is a new surface marker for human interleukin (IL)-17-producing Th17 cells. The Th17 phenotype has been linked to CD by the fact that IL-22, IL-17 and IL-23 receptor levels are increased in CD. The signal transduction pathways involving LLT1 and CD161 are not completely clarified and are currently under investigation in our laboratory.

Gene-gene interaction between CD40 and CD40L reduces bone mineral density and increases osteoporosis risk in women

SUMMARY

We have analysed the association of single-nucleotide polymorphisms (SNPs) in CD40 and CD40L genes with bone mineral density (BMD) in our women. Results showed that women with TT genotype for rs1883832 (CD40) and for rs1126535 (CD40L) SNPs displayed reduced BMD and increased risk for osteopenia/osteoporosis. Our data notwithstanding, the results need to be replicated.

INTRODUCTION

Recent data have revealed that the CD40/CD40L system can be implicated in bone metabolism regulation. Moreover, we previously demonstrated that rs1883832 in the CD40 gene was significantly associated with BMD and osteoporosis risk. The objective of the present work was to determine whether polymorphisms in CD40 and CD40L genes are associated with BMD and osteoporosis risk.

METHODS

We conducted an association study of BMD values with SNPs in CD40 and CD40L genes in a population of 811 women of which 693 and 711 had femoral neck (FN) and lumbar spine (LS) densitometric studies, respectively.

RESULTS

Women with the TT genotype for rs1883832 (CD40) showed a reduction in FN-BMD (P = 0.005) and LS-BMD (P = 0.020) when compared with women with the CC/CT genotype. Moreover, we found that rs1126535 (CD40L) was significantly associated with LS-BMD so that women with the TT genotype displayed lower BMD (P = 0.014) than did women with the CC/CT genotype. Interestingly, we have found a strong interaction between polymorphisms in these genes. Thus, women with the TT genotype for both rs1883832 and rs1126535 SNPs (TT + TT women) showed a lower age-adjusted BMD (Z-score) for FN (P = 0.0007) and LS (0.007) after adjusting by years since menopause, body mass index, smoking and menopausal status, densitometer type, hormone replacement therapy (HRT) use and HRT duration and after making the Bonferroni adjustment for multiple comparisons than did the remaining women. Logistic regression analysis adjusted by these covariates showed that TT + TT women had increased risk for FN (odds ratio (OR) = 2.76; P = 0.006) and LS (OR = 2.39; P = 0.020) osteopenia or osteoporosis than did the other women.

CONCLUSIONS

Our results suggest that interaction between genetic variants in the CD40 and CD40L genes exerts a role on BMD regulation. Further studies, which we welcome, are needed to replicate these data in other populations.

Common polymorphisms rather than rare genetic variants of the Runx2 gene are associated with femoral neck BMD in Spanish women

RUNX2 is a transcription factor essential for osteoblast differentiation and skeletal morphogenesis. Its mutation creates cleidocranial dysplasia (CCD), a disorder characterized by skeletal abnormalities and bone mineral density (BMD) alterations. The purpose of the present study has been to clarify whether polymorphisms affecting this gene could be associated with changes in BMD in women. To that end, we performed an association study of BMD values from 776 women with two single nucleotide polymorphisms (SNPs) located at P2 promoter (-1025 T>C) and at exon 2 (+198 G>A), and with a deletion polymorphism (17Ala>11Ala), also located at exon 2. We found an association of -1025 T>C SNP with femoral neck BMD (FN-BMD), being the women of TC/CC genotype who have higher BMD than women of TT genotype (P = 0.006). This association was independent of age, weight, menopausal status, or hormone replacement therapy (HRT) use as shown by regression analysis. When women of highest versus lowest quartile of BMD were compared, this association became more evident (P = 0.002), extending also to +198 G>A SNP (GA/AA women with higher FN-BMD; P < 0.05). In addition, we describe herein three novel rare variants in the polyglutamine domain of RUNX2 protein: an in-frame insertion and two deletions in exon 2, resulting in the insertions of 7 and deletions of 7 and 5 glutamines, respectively. These variants do not produce CCD, increased frequency of bone fracture, or BMD alterations. In conclusion, common polymorphisms in Runx2 are associated with FN-BMD. Nevertheless, rare variants that modify the polyglutamine domain of RUNX2 neither have any effect on BMD nor produce the CCD phenotype. These results underscore the significance of polymorphisms in the 5'-region of Runx2 in the determination of FN-BMD.

Inhibitory C-type lectin receptors in myeloid cells

C-type lectin receptors encoded by the natural killer gene complex play critical roles in enabling NK cell discrimination between self and non-self. In recent years, additional genes at this locus have been identified with patterns of expression that extend to cells of the myeloid lineage where many of the encoded inhibitory receptors have equally important functions as regulators of immune homeostasis. In the present review we highlight the roles of some of these receptors including recent insights gained with regard to the identification of exogenous and endogenous ligands, mechanisms of cellular inhibition and activation, regulated expression within different cellular and immune contexts, as well as functions that include the regulation of bone homeostasis and involvement in autoimmunity.

Molecular genetic studies of gene identification for osteoporosis: the 2009 update

Osteoporosis is a complex human disease that results in increased susceptibility to fragility fractures. It can be phenotypically characterized using several traits, including bone mineral density, bone size, bone strength, and bone turnover markers. The identification of gene variants that contribute to osteoporosis phenotypes, or responses to therapy, can eventually help individualize the prognosis, treatment, and prevention of fractures and their adverse outcomes. Our previously published reviews have comprehensively summarized the progress of molecular genetic studies of gene identification for osteoporosis and have covered the data available to the end of September 2007. This review represents our continuing efforts to summarize the important and representative findings published between October 2007 and November 2009. The topics covered include genetic association and linkage studies in humans, transgenic and knockout mouse models, as well as gene-expression microarray and proteomics studies. Major results are tabulated for comparison and ease of reference. Comments are made on the notable findings and representative studies for their potential influence and implications on our present understanding of the genetics of osteoporosis.

Osteoclast inhibitory lectin, an immune cell product that is required for normal bone physiology in vivo

Osteoclast inhibitory lectin (OCIL or clrb) is a member of the natural killer cell C-type lectins that have a described role mostly in autoimmune cell function. OCIL was originally identified as an osteoblast-derived inhibitor of osteoclast formation in vitro. To determine the physiological function(s) of OCIL, we generated ocil(-/-) mice. These mice appeared healthy and were fertile, with no apparent immune function defect, and phenotypic abnormalities were limited to bone. Histomorphometric analysis revealed a significantly lower tibial trabecular bone volume and trabecular number in the 10- and 16-week-old male ocil(-/-) mice compared with wild type mice. Furthermore, ocil(-/-) mice showed reduced bone formation rate in the 10-week-old females and 16-week-old males while Static markers of bone formation showed no significant changes in male or female ocil(-/-) mice. Examination of bone resorption markers in the long bones of ocil(-/-) mice indicated a transient increase in osteoclast number per unit bone perimeter. Enhanced osteoclast formation was also observed when either bone marrow or splenic cultures were generated in vitro from ocil(-/-) mice relative to wild type control cultures. Loss of ocil therefore resulted in osteopenia in adult mice primarily as a result of increased osteoclast formation and/or decreased bone formation. The enhanced osteoclastic activity led to elevated serum calcium levels, which resulted in the suppression of circulating parathyroid hormone in 10-week-old ocil(-/-) mice compared with wild type control mice. Collectively, our data suggest that OCIL is a physiological negative regulator of bone.