Amyloid beta peptide is elevated in osteoporotic bone tissues and enhances osteoclast function.
OBJECTIVE
Epidemiological studies show that patients with Alzheimer's disease (AD) have an increased risk of developing osteoporotic hip fracture. However, whether abnormal amyloid beta peptide (Aβ) deposition, one of the pathological hallmarks of AD, also occurs in osteoporosis and the relationship between Aβ and human osteoporosis remain unknown. This study addressed these issues.


METHODS
Forty-five female patients (osteoporosis 21, osteopenia 16 and normal 8) with osteoporotic/traumatic vertebral compression fractures were enrolled and Aβ42 and amyloid precursor protein (APP) levels assessed in the biopsy specimens of vertebral trabecular bone using immunohistochemistry (IHC) staining and semi-quantitative evaluation assays. Spearman rank correlation analysis was applied to explore the association between Aβ42/APP levels and the corresponding bone mineral density (BMD). Moreover, immunofluorescent assays and laser scanning confocal microscopy assays were used to examine the expression patterns of Aβ42/APP in patient bone tissues and osteocytes. Additionally, eight female patients with osteoporotic/traumatic femoral neck fractures, including two control patients were selected and Aβ42 and APP were identified in the femoral necks by RT-PCR and Western blotting (WB) assays. Next, a rat model of ovariectomy-induced osteoporosis was created and we evaluated Aβ42 and APP expression differences in the proximal tibia by IHC and RT-PCR and WB assays in comparison with a sham-operation group. Finally, the RAW264.7 cell line and human bone marrow monocyte (hBMMC) derived osteoclasts and human Aβ42 co-culture assays were performed to investigate the effect of Aβ42 on osteoclasts cell viability, number, differentiation and activation by the Cell Counting Kit-8 assay, tartrate resistant acid phosphatase staining assay, RT-PCR assay measuring the lytic gene expression and hydroxyapatite resorption assay respectively.


RESULTS
The mRNA and protein expression levels of Aβ42 and APP were elevated remarkably in the osteoporotic bone tissues both from human and ovariectomized rats when compared with the age-/sex-matched controls. Moreover, the expression levels had a negative correlation with corresponding BMD in patients (RAβ42=-0.617, p<0.0001; RAPP=-0.531, p=0.0002). In addition, Aβ42 was located mainly in the membrane and cytoplasm of osteocytes and in the extracellular matrix, while APP was largely located in the membrane of the osteocytes. Finally, Aβ42 can potently enhance osteoclasts differentiation and activation but had no effect on osteoclasts cell viability or number (dose- and time-dependency did not exist and oligomerization of Aβ42 was not a prerequisite in the osteoclastogenesis assay).


CONCLUSIONS
Aβ is relevant to human osteoporosis and may have an important role in the pathogenesis of osteoporosis.
Department of Spine Surgery, the Third Affiliated Hospital of Sun Yat-sen University, TianHe Road 600, TianHe District, Guangzhou Guangdong, 510630, PR China. Electronic address: lishangfu2013@163.com.
Shangfu
S
Li
Department of Spine Surgery, the Third Affiliated Hospital of Sun Yat-sen University, TianHe Road 600, TianHe District, Guangzhou Guangdong, 510630, PR China. Electronic address: johnliu2001@sina.com.
Bin
B
Liu
Department of Spine Surgery, the Third Affiliated Hospital of Sun Yat-sen University, TianHe Road 600, TianHe District, Guangzhou Guangdong, 510630, PR China. Electronic address: leven_zhang@163.com.
Liangming
L
Zhang
Department of Spine Surgery, the Third Affiliated Hospital of Sun Yat-sen University, TianHe Road 600, TianHe District, Guangzhou Guangdong, 510630, PR China. Electronic address: ronglimin@21cn.com.
Limin
L
Rong
D000368:Aged; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D015519:Bone Density; D002454:Cell Differentiation / Q000502:physiology; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D008875:Middle Aged; D010010:Osteoclasts / Q000166:cytology / Q000378:metabolism*; D010024:Osteoporosis / Q000378:metabolism*; D058866:Osteoporotic Fractures / Q000378:metabolism; D051381:Rats; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016103:Spinal Fractures / Q000378:metabolism
D016229:Amyloid beta-Peptides
Amyloid beta peptide; Amyloid precursor protein; Bone mineral density; Osteoclast; Osteocyte; Osteoporosis