Abstract
Lipid peroxidation produces oxidized phospholipids (OxPL) such as oxidized phosphatidylcholine. These compounds react with amino groups of proteins and lipids to form adducts called oxidation specific epitopes (OSEs), which are proinflammatory moieties present on oxidized low density lipoproteins and on apoptotic cells and, unless removed, cause extensive cell damage. Natural antibodies (NAb) produced by B-1 lymphocytes, bind OxPL and prevent their inflammatory activity. E06 is a NAb that recognizes the phosphocholine moiety of OxPL. We previously showed that transgenic expression of a single chain (scFv) form of the antigen-binding domain of E06 IgM (E06-scFv) increases cancellous and cortical bone mass in both male and female mice by increasing bone formation. Age-related bone loss is characterized by a decline in osteoblast number and bone formation, associated with increased oxidative stress and lipid peroxidation. These findings, together with the evidence that serum anti-OxPL IgM titers decrease with age, suggest that increased OxPL formation and decreased anti-OxPL antibodies may contribute to age-related bone loss. Like humans, mice exhibit an age-dependent worsening in glucose tolerance, mainly due to alteration in body composition and increased fat tissue. Chronic low grade inflammation and oxidative stress are associated with development of diabetes mellitus and B-1 lymphocytes have been shown to be protective against obesity associated inflammation, glucose intolerance, and insulin resistance. We tested the hypothesis that overexpression of E06-scFv could attenuate age-related bone loss and glucose intolerance. Serial BMD measurements by DXA of both female and male C57BL/6 E06-scFv transgenic mice (and their WT littermates) up to 22 and 24 months, respectively, showed that E06-scFv attenuated age-related bone loss at the spine and femur in both sexes. As revealed by microCT analysis, this effect was due to the attenuation of the age-associated decline in cancellous bone in both sexes. Additionally, both male and female E06-scFv transgenic mice accumulated less fat mass than WT littermates during aging. Intraperitoneal glucose tolerance test, at 15 months of age, revealed that glucose tolerance was greater in both male and female E06-ScFv mice than in respective WT littermates and did not differ from the glucose tolerance of young mice, indicating that E06-scFv improves glucose metabolism. These data suggest that OxPL impair both age-related bone loss and age-related glucose intolerance. Therefore, targeting OxPL with a neutralizing antibody such as E06, represents a prototypic therapeutic intervention that may simultaneously ameliorate important age-associated diseases.
The Type 2 Cannabinoid Receptor Regulates Bone Mass and Ovariectomy-Induced Bone Loss by Affecting Osteoblast Differentiation and Bone Formation