DNA damage signaling regulates age-dependent proliferative capacity of quiescent inner ear supporting cells

Abstract

Supporting cells (SCs) of the cochlear (auditory) and vestibular (balance) organs hold promise as a platform for therapeutic regeneration of the sensory hair cells. Prior data have shown proliferative restrictions of adult SCs forced to re-enter the cell cycle. By comparing juvenile and adult SCs in explant cultures, we have here studied how proliferative restrictions are linked with DNA damage signaling. Cyclin D1 overexpression, used to stimulate cell cycle re-entry, triggered higher proliferative activity of juvenile SCs. Phosphorylated form of histone H2AX (γH2AX) and p53 binding protein 1 (53BP1) were induced in a foci-like pattern in SCs of both ages as an indication of DNA double-strand break formation and activated DNA damage response. Compared to juvenile SCs, γH2AX and the repair protein Rad51 were resolved with slower kinetics in adult SCs, accompanied by increased apoptosis. Consistent with the in vitro data, in a Rb mutant mouse model in vivo, cell cycle re-entry of SCs was associated with γH2AX foci induction. In contrast to cell cycle reactivation, pharmacological stimulation of SC-to-hair-cell transdifferentiation in vitro did not trigger γH2AX. Thus, DNA damage and its prolonged resolution are critical barriers in the efforts to stimulate proliferation of the adult inner ear SCs.

Indispensable role of Mdm2/p53 interaction during the embryonic and postnatal inner ear development

“…As also aminoglycoside-induced hair cell death failed to activate SC proliferation in explants from p53 fl / fl ;Pax2-Cre mice, we conclude that p53 loss does not facilitate the capacity of SCs to cell cycle re-entry or transdifferentiation. These findings do not contradict with our previous results showing that p53 is upregulated in the early postnatal SCs forced to re-enter the cell cycle 42 . It is known that unscheduled proliferation and consequent DNA damage trigger p53 upregulation, leading to cell cycle arrest that is often accompanied by apoptosis 43 .…”

Co-regulation of the Notch and Wnt signaling pathways promotes supporting cell proliferation and hair cell regeneration in mouse utricles

“…Previous studies reported that the utricle’s capacity for SC proliferation and HC regeneration decreases with age 59 60 . In this study, we also found that with increased age the SC proliferation and HC mitotic regeneration induced by Notch inhibition and β-catenin up-regulation were significantly decreased.…”

Autophagy and apoptosis in liver injury

“…If mitophagy cannot catch up with the demand for the clearance of old and damaged mitochondria, high levels of ROS would damage cell molecules including proteins, membrane lipids, and nucleus DNA. [102][103][104] A decline of autophagy thus is responsible for cell aging via insufficient turnover of damaged mitochondria; (e) fusion deficiency between autophagosomes and lysosomes. Autophagic vacuoles are accumulated in the liver with age.…”