In dentistry, orthodontic root resorption is a long-lasting issue with no effective treatment strategy, and its mechanisms, especially those related to senescent cells, remain largely unknown. Here, we used an orthodontic intrusion tooth movement model with an L-loop in rats to demonstrate that mechanical stress-induced senescent cells aggravate apical root resorption, which was prevented by administering senolytics (a dasatinib and quercetin cocktail). Our results indicated that cementoblasts and periodontal ligament cells underwent cellular senescence (p21+ or p16+) and strongly expressed receptor activator of nuclear factor-kappa B (RANKL) from day three, subsequently inducing tartrate-resistant acid phosphatase (TRAP)-positive odontoclasts and provoking apical root resorption. More p21+ senescent cells expressed RANKL than p16+ senescent cells. We observed only minor changes in the number of RANKL+ non-senescent cells, whereas RANKL+ senescent cells markedly increased from day seven. Intriguingly, we also found cathepsin K+p21+p16+ cells in the root resorption fossa, suggesting senescent odontoclasts. Oral administration of dasatinib and quercetin markedly reduced these senescent cells and TRAP+ cells, eventually alleviating root resorption. Altogether, these results unveil those aberrant stimuli in orthodontic intrusive tooth movement induced RANKL+ early senescent cells, which have a pivotal role in odontoclastogenesis and subsequent root resorption. These findings offer a new therapeutic target to prevent root resorption during orthodontic tooth movement.

Senescence-associated secretory phenotype (SASPs) secreted from senescent cells often cause the deleterious damages to the surrounding tissues. Although dedifferentiated fat (DFAT) cells prepared are considered a promising cell source for regenerative therapies, SASPs from DFAT cells undergoing long-term cell culture, which latently induce replicative senescence, have barely been explored. The present study was designed to investigate senescent behaviors in rat-derived DFAT cells at high passage numbers and to analyze the possible types of SASPs. Our data show that DFAT cells undergo senescence during replicative passaging, as determined by multiple senescent hallmarks including morphological changes in cell shape and nucleus. Moreover, RT 2 PCR array analysis indicated that senescent DFAT cells expressed higher levels of 16 inflammatory cytokines (Ccl11,

Procuring a sufficient amount of cells is essential for cell-based regenerative therapy. However, the application of senescent cells replicated using cell culture is limited because the cells have lost their regenerative ability or produce deleterious senescence-associated secretory phenotypes (SASPs). In this study, using a senomorphic (epigallocatechin gallate [EGCG]), which could modulate SASP secretion from senescent cells, nonsenescent and senescent dedifferentiated fat cells from rats (rDFAT cells), and congenital cleft-jaw defects in rats, the authors show that the senomorphic (EGCG)-conjugated cellular scaffold restores the bone regenerative ability of senescent multipotent progenitor cells, even in vivo. In this osteogenic process, the EGCG-conjugated scaffold attenuates the production of representative SASPs (i.e., interleukin [IL]-6 and tumor necrosis factor-𝜶) and reactive oxygen species in vivo and in vitro. In polymerase chain reaction arrays in vitro, the EGCG-conjugated cellular scaffold suppresses the expression of genes associated with deleterious SASP factors for bone formation (e.g., Csf2, IL-1a, and others) from senescent rDFAT cells and elevates the expression of potential osteogenesis-and bone remodelingrelated gene (e.g., Cxcl13 and Spp1). These results provide insights to expand the application of senomorphics and senescent stem/multipotent progenitor cells in cell-based regenerative medicine.