GSE161946
Skeletal Stem Cell Aging
Skeletal aging and disease are associated with a misbalance in the opposing actions of osteoblasts and osteoclasts that are responsible for maintaining the integrity of bone tissues. Here, we show through detailed functional and single-cell genomic studies that intrinsic aging of bona fide mouse skeletal stem cells (SSCs) alters bone marrow niche signaling and skews bone and blood lineage differentiation leading to fragile bones that regenerate poorly. Aged SSCs have diminished bone and cartilage forming potential but produce higher frequencies of stromal lineages that express high levels of pro-inflammatory and pro-resorptive cytokines. Single-cell transcriptomic studies reveal a distinct population of SSCs in aged mice that gradually outcompete their younger counterparts in the bone marrow niche. While systemic exposure to a youthful circulation through heterochronic parabiosis reduced local expression of inflammatory cytokines, it did not reverse the diminished osteochondrogenic activity of aged SSCs and was insufficient to improve bone mass and skeletal-healing parameters in aged mice. Hematopoietic reconstitution of aged mice with young hematopoietic stem cells (HSC) also did not improve bone integrity and repair. We find that deficient bone regeneration in aged mice could only be reversed by the local application of a combinatorial treatment that re-activates aged SSCs and simultaneously abates crosstalk to hematopoietic cells favoring an inflammatory milieu. This treatment expanded aged SSC pools, reduced osteoclast activity, and enhanced bone healing to youthful levels. Our findings provide mechanistic insight into the complex, multifactorial mechanisms underlying skeletal aging and offer new prospects for rejuvenating the aged skeletal system. Overall design: SmartSeq2 single cell RNA sequencing of flow cytometrically purified single skeletal stem cells from adult mouse long bones.