Mitophagy induction improves salivary gland stem/progenitor cell function by reducing senescence after irradiation.

BACKGROUND AND PURPOSE: Patients undergoing radiotherapy for head and neck cancer often experience a decline in their quality of life due to the co-irradiation of salivary glands. Radiation-induced cellular senescence is a key factor contributing to salivary gland dysfunction. Interestingly, mitochondrial dysfunction and cellular senescence have been reported to be strongly interconnected and thus implicated in several aging-related diseases. This study aims to investigate the role of mitochondrial dysfunction in senescence induction in salivary gland stem/progenitor cells after irradiation. MATERIALS AND METHODS: A dose of 7 Gy photons was used to irradiate mouse salivary gland organoids. Senescent markers and mitochondrial function were assessed using rt-qPCR, western blot analysis, SA-ß-Gal staining and flow cytometry analysis. Mitochondrial dynamics-related proteins were detected by western blot analysis while Mdivi-1 and MFI8 were used to modulate the mitochondrial fission process. To induce mitophagy, organoids were treated with Urolithin A and PMI and subsequently stem/progenitor cell self-renewal capacity was assessed as organoid forming efficiency. RESULTS: Irradiation led to increased senescence and accumulation of dysfunctional mitochondria. This was accompanied by a strong downregulation of mitochondrial fission-related proteins and mitophagy-related genes. After irradiation, treatment with the mitophagy inducer Urolithin A attenuated the senescent phenotype and improved organoid growth and stem/progenitor cell self-renewal capacity. CONCLUSION: This study shows the important interplay between senescence and mitochondrial dysfunction after irradiation. Importantly, activation of mitophagy improved salivary gland stem/progenitor cell function thereby providing a novel therapeutic strategy to restore the regenerative capacity of salivary glands following irradiation.

Role of immediate early genes in the development of salivary gland organoids in polyisocyanopeptide hydrogels.

Human salivary gland organoids have opened tremendous possibilities for regenerative medicine in patients undergoing radiotherapy for the treatment of head and neck cancer. However, their clinical translation is greatly limited by the current use of Matrigel for organoid derivation and expansion. Here, we envisage that the use of a fully, synthetic hydrogel based on the oligo (-ethylene glycol) functionalized polymer polyisocyanopeptides (PICs) can provide an environment suitable for the generation and expansion of salivary gland organoids (SGOs) after optimization of PIC polymer properties. We demonstrate that PIC hydrogels decorated with the cell-binding peptide RGD allow SGO formation from salivary gland (SG)-derived stem cells. This self-renewal potential is preserved for only 4 passages. It was found that SGOs differentiated prematurely in PIC hydrogels affecting their self-renewal capacity. Similarly, SGOs show decreased expression of immediate early genes (IEGs) after culture in PIC hydrogels. Activation of multiple signalling pathways involved in IEG expression by ß-adrenergic agonist isoproterenol, led to increased stem cell self-renewal capacity as measured by organoid forming efficiency (OFE). These results indicate that PIC hydrogels are promising 3D matrices for SGOs, with the option to be used clinically, after further optimization of the hydrogel and culture conditions.