APC mutations are associated with increased bone mineral density in patients with familial adenomatous polyposis

LRP5, Bone Mass Polymorphisms and Skeletal Disorders

The formation and maintenance of the gross structure and microarchitecture of the human skeleton require the concerted functioning of a plethora of morphogenic signaling processes. Through recent discoveries in the field of genetics, numerous genotypic variants have been implicated in pathologic skeletal phenotypes and disorders arising from the disturbance of one or more of these processes. For example, total loss-of-function variants of LRP5 were found to be the cause of osteoporosis-pseudoglioma syndrome (OPPG). LRP5 encodes for the low-density lipoprotein receptor-related protein 5, a co-receptor in the canonical WNT-β-catenin signaling pathway and a crucial protein involved in the formation and maintenance of homeostasis of the human skeleton. Beyond OPPG, other partial loss-of-function variants of LRP5 have been found to be associated with other low bone mass phenotypes and disorders, while LRP5 gain-of-function variants have been implicated in high bone mass phenotypes. This review introduces the roles that LRP5 plays in skeletal morphogenesis and discusses some of the structural consequences that result from abnormalities in LRP5. A greater understanding of how the LRP5 receptor functions in bone and other body tissues could provide insights into a variety of pathologies and their potential treatments, from osteoporosis and a variety of skeletal abnormalities to congenital disorders that can lead to lifelong disabilities.

A comparison of panoramic radiographic findings in patients with familial adenomatous polyposis and the general population: a multicenter study

OBJECTIVES

Familial adenomatous polyposis (FAP) is a hereditable disorder characterized by early and unremitting development of intestinal polyps and extraintestinal manifestations requiring multidisciplinary surveillance. Herein we describe a multicenter cross-sectional analysis of the dento-osseous radiographic findings of patients with FAP from North and South America.

STUDY DESIGN

Groups I and II included individuals with FAP diagnosed by standard clinical criteria. Patients were paired with age- and sex-matched participants without FAP. Panoramic radiograph of both cohorts, including children and adults, were analyzed.

RESULTS

Of 114 panoramic radiographs, 38 were from patients with FAP, composed of group I (n = 22) and group II (n = 16), and 76 were from matched control participants. Evaluators had excellent agreement on key findings (intraclass correlation coefficient = 0.89). The prevalence of osseous anomalies was higher in adults (75%) than in children (65.4%). Dental anomalies were also higher in children with FAP with a prevalence of 15.4%.

CONCLUSIONS

We describe important and significant differences in the prevalence of dento-osseous anomalies in children compared with adult patients with FAP. These findings warrant careful consideration and may influence multidisciplinary management of the condition. Conversely, the presence of these abnormalities in pediatric dental patients even if not diagnosed with FAP should be borne in mind as possibly indicating de novo or unrecognized disease.

Genetic Determinants of Inherited Endocrine Tumors: Do They Have a Direct Role in Bone Metabolism Regulation and Osteoporosis?

Endocrine tumors are neoplasms originating from specialized hormone-secreting cells. They can develop as sporadic tumors, caused by somatic mutations, or in the context of familial Mendelian inherited diseases. Congenital forms, manifesting as syndromic or non-syndromic diseases, are caused by germinal heterozygote autosomal dominant mutations in oncogenes or tumor suppressor genes. The genetic defect leads to a loss of cell growth control in target endocrine tissues and to tumor development. In addition to the classical cancer manifestations, some affected patients can manifest alterations of bone and mineral metabolism, presenting both as pathognomonic and/or non-specific skeletal clinical features, which can be either secondary complications of endocrine functioning primary tumors and/or a direct consequence of the gene mutation. Here, we specifically review the current knowledge on possible direct roles of the genes that cause inherited endocrine tumors in the regulation of bone modeling and remodeling by exploring functional in vitro and in vivo studies highlighting how some of these genes participate in the regulation of molecular pathways involved in bone and mineral metabolism homeostasis, and by describing the potential direct effects of gene mutations on the development of skeletal and mineral metabolism clinical features in patients.

Trabecular and cortical mandibular bone investigation in familial adenomatous polyposis patients

Mandibular cortical and trabecular bone abnormalities in patients with familial adenomatous polyposis (FAP) were evaluated using dental panoramic radiographs (DPR) radiomorphometric indices and fractal dimension (FD). Sixty DPRs from 15 FAP patients and 45 healthy controls were evaluated. FAP group was composed of 33.3% females and 66.6% males, age_mean = 37.2 years (SD 15.79). The non-FAP group was paired by gender and sex. The parameters analyzed were: FD of the trabecular bone in four regions of interest (ROI), mandibular cortical index (MCI) and width (MCW). FD values were lower for the FAP group. Statistically significance differences were shown by ROI 2 and 3 anteriorly to the mental foramen bilaterally, p = 0.001, and p = 0.006. The ROI 1 and 4, at the mandibular angle trabeculae, indicated statistical significances on the right side (p = 0.036) and no differences on the left side (p = 0.091). There was no significant difference in MCI and MCW when the groups were compared, MCW (L) p = 0.247, and MCW (R) p = 0.070. Fractal values of FAP patients' mandibular trabecular bone were lower than healthy controls. The radiomorphometric indices MCI and MCW were not useful for analyzing the cortical bone pattern. Therefore, FD is a promising tool for detection of abnormal bone structure in DPRs and for supporting the appropriate referral of FAP patients.

Cenani-Lenz syndrome and other related syndactyly disorders due to variants in LRP4, GREM1/FMN1, and APC: Insight into the pathogenesis and the relationship to polyposis through the WNT and BMP antagonistic pathways

Cenani-Lenz (C-L) syndrome is characterized by oligosyndactyly, metacarpal synostosis, phalangeal disorganization, and other variable facial and systemic features. Most cases are caused by homozygous and compound heterozygous missense and splice mutations of the LRP4 gene. Currently, the syndrome carries one OMIM number (212780). However, C-L syndrome-like phenotypes as well as other syndactyly disorders with or without metacarpal synostosis/phalangeal disorganization are also known to be associated with specific LRP4 mutations, adenomatous polyposis coli (APC) truncating mutations, genomic rearrangements of the GREM1-FMN1 locus, as well as FMN1 mutations. Surprisingly, patients with C-L syndrome-like phenotype caused by APC truncating mutations have no polyposis despite the increased levels of β catenin. The LRP4 and APC proteins act on the WNT (wingless-type integration site family) canonical pathway, whereas the GREM-1 and FMN1 proteins act on the bone morphogenetic protein (BMP) pathway. In this review, we discuss the different mutations associated with C-L syndrome, classify its clinical features, review familial adenomatous polyposis caused by truncating APC mutations and compare these mutations to the splicing APC mutation associated with syndactyly, and finally, explore the pathophysiology through a review of the cross talks between the WNT canonical and the BMP antagonistic pathways.

Intestinal Inflammation and Tumor Burden as Determinants for Bone Fragility in APC-Driven Tumorigenesis

BACKGROUND

Colorectal cancer (CRC) is a major cause of cancer-related deaths, and tumor-related comorbidities additionally lower life quality and survival. Mutations in the tumor suppressor adenomatous polyposis coli (APC) are associated with sporadic CRC and familial adenomatous polyposis (FAP), which results in the growth of multiple intestinal cancer lesions. In some cases, inflammatory bowel diseases (IBDs) are additionally observed in CRC patients. Although APC mutations have been shown to increase bone mineral density (BMD), inflammation is associated with reduced BMD and an elevated fracture risk in IBD patients.

METHODS

To determine the consequences of APC-driven intestinal tumorigenesis and additional inflammation on bone parameters, we utilized an APC1638N/+ mouse model. We treated 1 cohort of APC wild-type and mutant animals with dextran sodium sulfate (DSS) to induce colorectal inflammation. All mice were killed at the same age and stratified according to their tumor burden.

RESULTS

As expected, a heterozygous APC mutation increased intestinal tumor numbers and the cortical BMD. This effect on bone was abrogated in mice with high intestinal tumor numbers. Moreover, we found that high tumor burden elevated bone fragility in APC-mutated mice. After DSS treatment, there were no significant changes in bone parameters of control mice. In contrast, in combination with inflammation, bone biomechanical properties severely deteriorated at high tumor burdens in APC1638N/+ animals.

CONCLUSIONS

Together, not only were bone parameters affected by APC status and inflammation, but also high intestinal tumor numbers, especially when combined with inflammation, were associated with an osteoporotic phenotype.

Differential Bone Loss in Mouse Models of Colon Cancer Cachexia

Cachexia is a distinctive feature of colorectal cancer associated with body weight loss and progressive muscle wasting. Several mechanisms responsible for muscle and fat wasting have been identified, however it is not known whether the physiologic and molecular crosstalk between muscle and bone tissue may also contribute to the cachectic phenotype in cancer patients. The purpose of this study was to clarify whether tumor growth associates with bone loss using several experimental models of colorectal cancer cachexia, namely C26, HT-29, and Apc^Min/+. The effects of cachexia on bone structure and strength were evaluated with dual energy X-ray absorptiometry (DXA), micro computed tomography (μCT), and three-point bending test. We found that all models showed tumor growth consistent with severe cachexia. While muscle wasting in C26 hosts was accompanied by moderate bone depletion, no loss of bone strength was observed. However, HT-29 tumor bearing mice showed bone abnormalities including significant reductions in whole-body bone mineral density (BMD), bone mineral content (BMC), femoral trabecular bone volume fraction (BV/TV), trabecular number (Tb.N), and trabecular thickness (Tb.Th), but no declines in strength. Similarly, cachexia in the Apc^Min/+ mice was associated with significant decreases in BMD, BMC, BV/TV, Tb.N, and Tb.Th as well as decreased strength. Our data suggest that colorectal cancer is associated with muscle wasting and may be accompanied by bone loss dependent upon tumor type, burden, stage and duration of the disease. It is clear that preserving muscle mass promotes survival in cancer cachexia. Future studies will determine whether strategies aimed at preventing bone loss can also improve outcomes and survival in colorectal cancer cachexia.

Risk-reduction surgery in pediatric surgical oncology: A perspective

OBJECTIVE

A small percentage of pediatric solid cancers arise as a result of clearly identified inherited predisposition syndromes and nongenetic lesions. Evidence supports preemptive surgery for children with genetic [multiple endocrine neoplasia type 2 (MEN2), familial adenomatous polyposis syndrome (FAP), hereditary nonpolyposis colorectal cancer (HNPCC), and hereditary diffuse gastric cancer (HDGC) and nongenetic [thyroglossal duct cysts (TGDC), congenital pulmonary airway malformations (CPAM), alimentary tract duplication cysts (ATDC), and congenital choledochal cysts (CCC)] developmental anomalies. Our aim was to explore the utility of risk reduction surgery to treat and prevent cancer in children.

METHODS

A systematic review of the available peer-reviewed literature on PubMed was performed using a PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) search strategy, where possible. Search items included "risk reduction surgery", "hereditary cancer predisposition syndrome", "multiple endocrine neoplasia type 2", "familial adenomatous polyposis", "hereditary nonpolyposis colorectal cancer", "hereditary diffuse gastric cancer", "thyroglossal duct cysts", congenital pulmonary airway malformations", "alimentary tract duplication cysts", "malignant transformation", and "guidelines".

RESULTS

We identified 67 articles that met the inclusion criteria describing the indications for prophylactic surgery in surgical oncology. For the genetic predisposition syndromes, 7 studies were related to professional endorsed guidelines, 7 were related to surgery for MEN2, 11 were related to colectomy for FAP, 6 were related to colectomy for HNPCC, and 12 related to gastrectomy for HDGC. Articles for the nongenetic lesions included 5 for techniques related to TGDC resection, 9 for surgery for CPAMs, and 10 for resection of ATDCs. Guidelines and strategies varied significantly especially related to the extent and timing of surgical intervention; the exception was for the timing of thyroidectomy in children with MEN2.

CONCLUSION

Current evidence supporting prophylactic surgery in the management of pediatric cancer predisposition syndromes and nongenetic lesions is best delineated for thyroidectomy to prevent medullary thyroid cancer in children with MEN2 (Strength of Recommendation Grade B/C). Despite the lack of pediatric specific evidence-based recommendations regarding the appropriate extent and timing for risk-reduction surgery for FAP, HNPCC, HDGC and nongenetic anomalies, our review represents an opportunity towards understanding the postgenomic development of these lesions and provides current indications and techniques for preemptive cancer prevention surgery in children.

Oral manifestations in patients with familial adenomatous polyposis: A systematic review and meta-analysis

BACKGROUND AND AIM

The oral manifestations of familial adenomatous polyposis (FAP) have been reported in the recent literature. Therefore, there has been growing interest in the characterization of the dento-osseous anomalies because they may precede colorectal cancer and may be used as a diagnostic marker. This systematic review and meta-analysis was performed to evaluate the published evidence for what are the oral manifestations of FAP and their frequency in affected individuals.

METHODS

The search was performed at Cochrane Library, EMBASE, LILACS, PubMed, Scopus, and Web of Science for articles published up to March 2015. A grey literature search was conducted through Google Scholar. Reference lists of the included articles and additional studies identified by expert were screened for potential relevant studies. The methodology of selected studies was evaluated using the risk of bias checklist of the Agency for Healthcare Research and Quality.

RESULTS

Twenty observational studies totalizing 1635 individuals affected by FAP met the inclusion criteria. Osseous, dental, and oral mucosa alterations were observed in FAP patients. The meta-analysis showed the frequency of osseous jaw lesions, and the dental anomalies were 65.35% and 30.48%, respectively, and two studies suggested that oral mucosa vascular density is a phenotypic manifestation in patients with FAP. Most of the studies were evaluated as moderate risk of bias.

CONCLUSION

The most frequent oral manifestation on FAP patients is osseous jaw alterations. In the future, well-designed studies are necessary to classify osseous and dental anomalies in order to demonstrate the true prevalence of each alteration separately.

Osteoporosis: A Silent Disease with Complex Genetic Contribution

Osteoporosis is the most common multifactorial metabolic bone disorder worldwide with a strong genetic component. In this review, the evidence for a genetic contribution to osteoporosis and related phenotypes is summarized alongside with methods used to identify osteoporosis susceptibility genes. The key biological pathways involved in the skeleton and bone development are discussed with a particular focus on master genes clustered in these pathways and their mode of action. Furthermore, the most studied single nucleotide polymorphisms (SNPs) analyzed for their importance as genetic markers of the disease are presented. New data generated by next-generation sequencing in conjunction with extensive meta-analyses should contribute to a better understanding of the genetic basis of osteoporosis and related phenotype variability. These data could be ultimately used for identifying at-risk patients for disease prevention by both controlling environmental factors and providing possible therapeutic targets.

A Comprehensive Overview of Skeletal Phenotypes Associated with Alterations in Wnt/β-catenin Signaling in Humans and Mice

The Wnt signaling pathway plays key roles in differentiation and development and alterations in this signaling pathway are causally associated with numerous human diseases. While several laboratories were examining roles for Wnt signaling in skeletal development during the 1990s, interest in the pathway rose exponentially when three key papers were published in 2001-2002. One report found that loss of the Wnt co-receptor, Low-density lipoprotein related protein-5 (LRP5), was the underlying genetic cause of the syndrome Osteoporosis pseudoglioma (OPPG). OPPG is characterized by early-onset osteoporosis causing increased susceptibility to debilitating fractures. Shortly thereafter, two groups reported that individuals carrying a specific point mutation in LRP5 (G171V) develop high-bone mass. Subsequent to this, the causative mechanisms for these observations heightened the need to understand the mechanisms by which Wnt signaling controlled bone development and homeostasis and encouraged significant investment from biotechnology and pharmaceutical companies to develop methods to activate Wnt signaling to increase bone mass to treat osteoporosis and other bone disease. In this review, we will briefly summarize the cellular mechanisms underlying Wnt signaling and discuss the observations related to OPPG and the high-bone mass disorders that heightened the appreciation of the role of Wnt signaling in normal bone development and homeostasis. We will then present a comprehensive overview of the core components of the pathway with an emphasis on the phenotypes associated with mice carrying genetically engineered mutations in these genes and clinical observations that further link alterations in the pathway to changes in human bone.

Copy number variation of the APC gene is associated with regulation of bone mineral density

INTRODUCTION

Genetic studies of osteoporosis have commonly examined SNPs in candidate genes or whole genome analyses, but insertions and deletions of DNA, collectively called copy number variations (CNVs), also comprise a large amount of the genetic variability between individuals. Previously, SNPs in the APC gene have been strongly associated with femoral neck and lumbar spine volumetric bone mineral density in older men. In addition, familial adenomatous polyposis patients carrying heterozygous mutations in the APC gene have been shown to have significantly higher mean bone mineral density than age- and sex-matched controls suggesting the importance of this gene in regulating bone mineral density. We examined CNV within the APC gene region to test for association with bone mineral density.

METHODS

DNA was extracted from venous blood, genotyped using the Human Hap610 arrays and CNV determined from the fluorescence intensity data in 2070 Caucasian men and women aged 47.0 ± 13.0 (mean ± SD) years, to assess the effects of the CNV on bone mineral density at the forearm, spine and total hip sites.

RESULTS

Data for covariate adjusted bone mineral density from subjects grouped by APC CNV genotype showed significant difference (P=0.02-0.002). Subjects with a single copy loss of APC had a 7.95%, 13.10% and 13.36% increase in bone mineral density at the forearm, spine and total hip sites respectively, compared to subjects with two copies of the APC gene.

CONCLUSIONS

These data support previous findings of APC regulating bone mineral density and demonstrate that a novel CNV of the APC gene is significantly associated with bone mineral density in Caucasian men and women.

Osteoporosis self-assessment tool for Asians as a simple risk index of identifying a poor prognosis in women surgically treated for colorectal cancer

BACKGROUND

Osteoporosis and colorectal cancer (CRC) in older women are considered enormous public health burdens. The effects of osteoporosis on the oncologic outcome of CRC surgery are poorly understood. We evaluated the use of the Osteoporosis Self-assessment Tool for Asians (OSTA) for predicting postoperative outcome in older women after receiving surgical treatment of CRC.

MATERIALS AND METHODS

The present single-institution retrospective study analyzed patients who had undergone surgery for CRC in 2002-2008. To characterize the major population of women with osteoporosis, which consists of postmenopausal women, only patients aged 50 years and older were analyzed. Their OSTA scores were evaluated for correlations with cancer-specific survival after surgery for CRC by performing univariate, multivariate, and survival analyses.

RESULTS

During a 7-year period, 440 women were studied. The cancer-specific mortality and overall mortality rate was 28.4% and 33.4%, respectively. The univariate analyses revealed that significant predictors of cancer-specific mortality after CRC surgery were the International Union Against Cancer (UICC) stage, OSTA category, histologic grading, lymph node metastases, and tumor invasion depth. After risk adjustment, the UICC stage and OSTA risk index were independent predictors of mortality. A comparison of OSTA risk index among patients with different UICC stages showed that the accuracy of the index in predicting cancer-specific survival after CRC surgery was greatest for patients with stage II and III disease.

CONCLUSIONS

The UICC stage and OSTA risk status showed independent positive associations with postoperative mortality in aged female patients with CRC. Moreover, the OSTA index had a particularly strong association with cancer-specific mortality in patients with UICC stage II and III.

Update on Wnt signaling in bone cell biology and bone disease

For more than a decade, Wnt signaling pathways have been the focus of intense research activity in bone biology laboratories because of their importance in skeletal development, bone mass maintenance, and therapeutic potential for regenerative medicine. It is evident that even subtle alterations in the intensity, amplitude, location, and duration of Wnt signaling pathways affects skeletal development, as well as bone remodeling, regeneration, and repair during a lifespan. Here we review recent advances and discrepancies in how Wnt/Lrp5 signaling regulates osteoblasts and osteocytes, introduce new players in Wnt signaling pathways that have important roles in bone development, discuss emerging areas such as the role of Wnt signaling in osteoclastogenesis, and summarize progress made in translating basic studies to clinical therapeutics and diagnostics centered around inhibiting Wnt pathway antagonists, such as sclerostin, Dkk1 and Sfrp1. Emphasis is placed on the plethora of genetic studies in mouse models and genome wide association studies that reveal the requirement for and crucial roles of Wnt pathway components during skeletal development and disease.

Apc bridges Wnt/β-catenin and BMP signaling during osteoblast differentiation of KS483 cells

The canonical Wnt signaling pathway influences the differentiation of mesenchymal cell lineages in a quantitative and qualitative fashion depending on the dose of β-catenin signaling. Adenomatous polyposis coli (Apc) is the critical intracellular regulator of β-catenin turnover. To better understand the molecular mechanisms underlying the role of Apc in regulating the differentiation capacity of skeletal progenitor cells, we have knocked down Apc in the murine mesenchymal stem cell-like KS483 cells by stable expression of Apc-specific small interfering RNA. In routine culture, KSFrt-Apc(si) cells displayed a mesenchymal-like spindle shape morphology, exhibited markedly decreased proliferation and increased apoptosis. Apc knockdown resulted in upregulation of the Wnt/β-catenin and the BMP/Smad signaling pathways, but osteogenic differentiation was completely inhibited. This effect could be rescued by adding high concentrations of BMP-7 to the differentiation medium. Furthermore, KSFrt-Apc(si) cells showed no potential to differentiate into chondrocytes or adipocytes. These results demonstrate that Apc is essential for the proliferation, survival and differentiation of KS483 cells. Apc knockdown blocks the osteogenic differentiation of skeletal progenitor cells, a process that can be overruled by high BMP signaling.