Expansion of myeloid-derived suppressor cells with aging in the bone marrow of mice through a NF-κB-dependent mechanism

With aging, there is progressive loss of tissue homeostasis and functional reserve, leading to an impaired response to stress and an increased risk of morbidity and mortality. A key mediator of the cellular response to damage and stress is the transcription factor NF-kappa B. We demonstrated previously that NF-kappa B transcriptional activity is upregulated in tissues from both natural aged mice and in a mouse model of a human progeroid syndrome caused by defective repair of DNA damage (ERCC1-deficient mice). We also demonstrated that genetic reduction in the level of the NF-kappa B subunit p65(RelA) in the Ercc1(-1 Delta) progeroid mouse model of accelerated aging delayed the onset of age-related pathology including muscle wasting, osteoporosis, and intervertebral disk degeneration. Here, we report that the largest fraction of NF-kappa B -expressing cells in the bone marrow (BM) of aged (> 2 year old) mice (C57BL/6-NF-kappa B-EGFP reporter mice) are Gr-1(+)CD11b(+) myeloid-derived suppressor cells (MDSCs). There was a significant increase in the overall percentage of MDSC present in the BM of aged animals compared with young, a trend also observed in the spleen. However, the function of these cells appears not to be compromised in aged mice. A similar increase of MDSC was observed in BM of progeroid Ercc1(-1 Delta) and BubR1(H/H) mice. The increase in MDSC in Ercc1(-1 Delta) mice was abrogated by heterozygosity in the p65/RelA subunit of NF-kappa B. These results suggest that NF-kappa B activation with aging, at least in part, drives an increase in the percentage of MDSCs, a cell type able to suppress immune cell responses.