Methods: As described below.
Results: MicroCT analyses demonstrated that compared with WT littermates, both Ercc1-/- and Ercc1-/Δ mice display severe, age-dependent progressive osteoporosis in a gender-independent manner. The osteoporosis is caused by reduced bone formation and enhanced osteoclastogenesis, as shown by calcein double-labeling dynamic bone formation assay and TRAP stain, respectively. ERCC1 deficiency leads to atrophy of osteoblastic progenitors in the bone marrow stromal cell population, increased cellular senescence, reduced cell proliferation of osteoblastic cells. Further, ERCC1 deficiency triggers permanent DNA damage and a senescence-associated secretory phenotype (SASP) in bone marrow stromal cells (BMSCs) and osteoblastic cells. The latter leads to enhanced secretion of inflammatory cytokines known to drive osteoclastogenesis, such as IL-6 and RANKL, in BMSCs and osteoblastic cells, and thereby induces an inflammatory bone microenvironment favoring osteoclastogenesis. Furthermore, we found that NF-kB is activated in osteoblastic and osteoclastic cells of the Ercc1 mutant mice. Finally, via employing both genetic deletion of one allele of p65 and pharmacological inhibition of IKK, we demonstrate that NF-kB signaling drives osteoporosis in Ercc1-deficient mice.
Conclusions: These results suggest that DNA damage drives osteoporosis through an NF-kB-dependent mechanism. Therefore, the NF-kB pathway represents a novel therapeutic target to treat ageing-related bone diseases.