Millan S. Patel

Cbfa1-independent decrease in osteoblast proliferation, osteopenia, and persistent embryonic eye vascularization in mice deficient in Lrp5, a Wnt coreceptor

The low-density lipoprotein receptor–related protein (Lrp)-5 functions as a Wnt coreceptor. Here we show that mice with a targeted disruption of Lrp5 develop a low bone mass phenotype. In vivo and in vitro analyses indicate that this phenotype becomes evident postnatally, and demonstrate that it is secondary to decreased osteoblast proliferation and function in a Cbfa1-independent manner. Lrp5 is expressed in osteoblasts and is required for optimal Wnt signaling in osteoblasts. In addition, Lrp5-deficient mice display persistent embryonic eye vascularization due to a failure of macrophage-induced endothelial cell apoptosis. These results implicate Wnt proteins in the postnatal control of vascular regression and bone formation, two functions affected in many diseases. Moreover, these features recapitulate human osteoporosis-pseudoglioma syndrome, caused by LRP5 inactivation.

The Molecular Clock Mediates Leptin-Regulated Bone Formation

The hormone leptin is a regulator of bone remodeling, a homeostatic function maintaining bone mass constant. Mice lacking molecular-clock components (Per and Cry), or lacking Per genes in osteoblasts, display high bone mass, suggesting that bone remodeling may also be subject to circadian regulation. Moreover, Per-deficient mice experience a paradoxical increase in bone mass following leptin intracerebroventricular infusion. Thus, clock genes may mediate the leptin-dependent sympathetic regulation of bone formation. We show that expression of clock genes in osteoblasts is regulated by the sympathetic nervous system and leptin. Clock genes mediate the antiproliferative function of sympathetic signaling by inhibiting G1 cyclin expression. Partially antagonizing this inhibitory loop, leptin also upregulates AP-1 gene expression, which promotes cyclin D1 expression, osteoblast proliferation, and bone formation. Thus, leptin determines the extent of bone formation by modulating, via sympathetic signaling, osteoblast proliferation through two antagonistic pathways, one of which involves the molecular clock.

WNT7b mediates macrophage-induced programmed cell death in patterning of the vasculature

Macrophages have a critical role in inflammatory and immune responses through their ability to recognize and engulf apoptotic cells. Here we show that macrophages initiate a cell-death programme in target cells by activating the canonical WNT pathway. We show in mice that macrophage WNT7b is a short-range paracrine signal required for WNT-pathway responses and programmed cell death in the vascular endothelial cells of the temporary hyaloid vessels of the developing eye. These findings indicate that macrophages can use WNT ligands to influence cell-fate decisions—including cell death—in adjacent cells, and raise the possibility that they do so in many different cellular contexts.

22q11.2 Distal Deletion: A Recurrent Genomic Disorder Distinct from DiGeorge Syndrome and Velocardiofacial Syndrome

Microdeletions within chromosome 22q11.2 cause a variable phenotype, including DiGeorge syndrome (DGS) and velocardiofacial syndrome (VCFS). About 97% of patients with DGS/VCFS have either a common recurrent approximately 3 Mb deletion or a smaller, less common, approximately 1.5 Mb nested deletion. Both deletions apparently occur as a result of homologous recombination between nonallelic flanking low-copy repeat (LCR) sequences located in 22q11.2. Interestingly, although eight different LCRs are located in proximal 22q, only a few cases of atypical deletions utilizing alternative LCRs have been described. Using array-based comparative genomic hybridization (CGH) analysis, we have detected six unrelated cases of deletions that are within 22q11.2 and are located distal to the approximately 3 Mb common deletion region. Further analyses revealed that the rearrangements had clustered breakpoints and either a approximately 1.4 Mb or approximately 2.1 Mb recurrent deletion flanked proximally by LCR22-4 and distally by either LCR22-5 or LCR22-6, respectively. Parental fluorescence in situ hybridization (FISH) analyses revealed that none of the available parents (11 out of 12 were available) had the deletion, indicating de novo events. All patients presented with characteristic facial dysmorphic features. A history of prematurity, prenatal and postnatal growth delay, developmental delay, and mild skeletal abnormalities was prevalent among the patients. Two patients were found to have a cardiovascular malformation, one had truncus arteriosus, and another had a bicuspid aortic valve. A single patient had a cleft palate. We conclude that distal deletions of chromosome 22q11.2 between LCR22-4 and LCR22-6, although they share some characteristic features with DGS/VCFS, represent a novel genomic disorder distinct genomically and clinically from the well-known DGS/VCF deletion syndromes.

The New Field of Neuroskeletal Biology

The fields of neuroscience and bone biology have recently converged following the discovery that bone remodeling is directly regulated by the brain. This work has defined bone remodeling as one of the cardinal physiological functions of the body, subject to homeostatic regulation and integrated with the other major physiological functions by the hypothalamus. Central to this discovery was the definition of the adipocyte-derived hormone leptin as a regulator of both arms of bone remodeling, formation and resorption, through its action on the ventromedial hypothalamus and subsequently via the sympathetic nervous system to osteoblasts. The characterization of the sympathetic nervous system as a regulator of bone remodeling has led to several large clinical studies demonstrating a substantial protective effect of ß-blockers, particularly ß1-blockers, on fracture risk. Studies in model organisms have reinforced the role of the central nervous system in the regulation of bone remodeling in vivo by the identification of several additional genes, namely cocaine and amphetamine regulated transcript (Cart), melanocortin 4 receptor (Mc4R), neuropeptide Y (NPY), Y2 receptor, cannabinoid receptor CB1 (Cnbr1), and the genes of the circadian clock. These genes have several common features, including high levels of expression in the hypothalamus and the ability to regulate other major physiological functions in addition to bone remodeling including energy homeostasis, body weight, and reproduction. We review the major pathways that define the new field of neuroskeletal biology and identify further avenues of inquiry.

Abnormal pericyte recruitment as a cause for pulmonary hypertension in Adams-Oliver syndrome.

Adams–Oliver syndrome (AOS) consists of congenital scalp defects with variable limb defects of unknown pathogenesis. We report on two children with AOS plus additional features including intrauterine growth retardation (IUGR), cutis marmorata telangiectatica congenita (CMTC), pulmonary hypertension (PH), intracranial densities shown in one case to be sites of active bleeding and osteopenia. Autopsy in one case revealed defective vascular smooth muscle cell/pericyte coverage of the vasculature associated with two blood vessel abnormalities. Pericyte absence correlated with vessel dilatation while hyperproliferation of pericytes correlated with vessel stenosis. These findings suggest a unifying pathogenic mechanism for the abnormalities seen in AOS. These and previously reported cases establish that a subset of AOS patients is at high risk for PH.

Associations of the Collagen Type Iα1 Sp1 Polymorphism with Five-Year Rates of Bone Loss in Older Adults

Abstract. The collagen type Iα1 Sp1 (ColIA1) polymorphism has been associated with reduced bone mineral density (BMD) and increased prevalence of osteoporosis. This study examines associations of the ColIA1 genotype with BMD and 5-year rates of change in BMD in elderly men and women. The 243 subjects, aged 65 years and older, were participants in two consecutive studies lasting a total of 5-years. BMD of the total body, femoral neck, and lumbar spine were made by dual-energy X-ray absorptiometry (DXA). The distribution of the genotypes (155 in the SS genotype, 79 in Ss, and 9 in ss) was proportionately similar to those reported by others. Baseline BMD did not differ significantly at any skeletal site. Unadjusted 5-year percent changes in BMD differed significantly by genotype only at the total body (P= 0.009), where the change was −0.29 ± 0.21 (SEM) in the SS genotype, −0.60 ± 0.25 in the Ss genotype, and −3.01 ± 0.72 in the ss genotype. This 9.4% increase in bone loss of the ss genotype relative to the SS genotype was reduced to an 8.9% increase after adjustment for sex, age, weight, and supplementation group. Results at the femoral neck were directionally similar, but not statistically significant. No effect of genotype on change in spine BMD was observed. In conclusion, bone loss from the total body was significantly greater in elderly men and women who were homozygous for the s allele compared with heterozygotes and SS homozygotes. This finding suggests a possible explanation for the association of the ColIA1 polymorphism with increased rates of osteoporotic fracture, but should be interpreted with caution because of the small number of subjects in the unfavorable ss genotype.

Calcium and Vitamin D Intake and Mortality: Results from the Canadian Multicentre Osteoporosis Study (CaMos)

CONTEXT Calcium and vitamin D are recommended for bone health, but there are concerns about adverse risks. Some clinical studies suggest that calcium intake may be cardioprotective, whereas others report increased risk associated with calcium supplements. Both low and high serum levels of 25-hydroxyvitamin D have been associated with increased mortality. OBJECTIVE The purpose of this study was to determine the association between total calcium and vitamin D intake and mortality and heterogeneity by source of intake. DESIGN The Canadian Multicentre Osteoporosis Study cohort is a population-based longitudinal cohort with a 10-year follow-up (1995-2007). SETTING This study included randomly selected community-dwelling men and women. PARTICIPANTS A total of 9033 participants with nonmissing calcium and vitamin D intake data and follow-up were studied. EXPOSURE Total calcium intake (dairy, nondairy food, and supplements) and total vitamin D intake (milk, yogurt, and supplements) were recorded. OUTCOME The outcome variable was all-cause mortality. RESULTS There were 1160 deaths during the 10-year period. For women only, we found a possible benefit of higher total calcium intake, with a hazard ratio of 0.95 (95% confidence interval, 0.89-1.01) per 500-mg increase in daily calcium intake and no evidence of heterogeneity by source; use of calcium supplements was also associated with reduced mortality, with hazard ratio of 0.78 (95% confidence interval, 0.66-0.92) for users vs nonusers with statistically significant reductions remaining among those with doses up to 1000 mg/d. These associations were not modified by levels of concurrent vitamin D intake. No definitive associations were found among men. CONCLUSIONS Calcium supplements, up to 1000 mg/d, and increased dietary intake of calcium may be associated with reduced risk of mortality in women. We found no evidence of mortality benefit or harm associated with vitamin D intake.

Severe, fetal-onset form of olivopontocerebellar hypoplasia in three sibs: PCH type 5?

We present three siblings with a precise onset of fetal seizure‐like activity who had severe olivopontocerebellar hypoplasia (OPCH) and degeneration. Autopsies at 20, 27, and 37 weeks gestation showed diffuse central nervous system volume loss that was most marked for the cerebellum and brain stem structures. Neuropathological abnormalities included dysplastic, C‐shaped inferior olivary nuclei, absent or immature dentate nuclei, and cell paucity more marked for the cerebellar vermis than the hemispheres. Delayed development was seen in layer 2 of the cerebral cortex and in Purkinje cells of the cerebellum. Prenatal monitoring defined a developmental window of 16–18 weeks gestation when ultrasonic assessment of cerebellar width was used for prenatal diagnosis. We discuss our findings in the context of the differential diagnosis for infantile (O)PCH and propose a classification scheme for the pontocerebellar hypoplasias. These patients represent the earliest reported with OPCH and provide unique information regarding the developmental neuropathology of this condition.

Alleles of the Estrogen Receptor α‐Gene and an Estrogen Receptor Cotranscriptional Activator Gene, Amplified in Breast Cancer‐1 (AIB1), Are Associated with Quantitative Calcaneal Ultrasound

Quantitative bone ultrasound (QUS) has a significant heritable component. Because estrogen is required for attainment of peak bone mass, we studied alleles of two genes, estrogen receptor α (ER1) and amplified in breast cancer‐1 (AIB1), for their association with QUS. In a volunteer sample of 663 white women aged 18–35 years, bone ultrasound attenuation (BUA), speed of sound (SOS), and heel stiffness index (SI), the latter consisting of the component measures of BUA and SOS, were measured at the right calcaneus by QUS. Subjects were genotyped for the ER1 polymorphisms Xba I and Pvu II and for the AIB1 polyglutamine tract polymorphism. In a multiple regression analysis, ER1 genotype was an independent predictor of QUS‐SI (p = 0.03). Because AIB1 and ER1 enhance gene expression in a coordinate manner, we also searched for interactions. A gene‐by‐gene interaction effect was seen for QUS‐SI (p = 0.009), QUS‐BUA (p = 0.03), and QUS‐SOS (p = 0.004). These remained significant after the inclusion of clinically relevant variables into the final regression model. Overall, these clinical and genetic factors accounted for up to 16% of the variance in peak QUS; the genetic markers alone accounted for 4–7%. This is the first demonstration of specific genetic effects on calcaneal QUS encoded by alleles of genes directly involved in mediating estrogen effects on bone.