Long-term functional regeneration of radiation-damaged salivary glands through delivery of a neurogenic hydrogel

Abstract

Salivary gland acinar cells are severely depleted after radiotherapy for head and neck cancer, leading to loss of saliva and extensive oro-digestive complications. With no regenerative therapies available, organ dysfunction is irreversible. Here, using the adult murine system, we demonstrate that radiation-damaged salivary glands can be functionally regenerated via sustained delivery of the neurogenic muscarinic receptor agonist cevimeline. We show that endogenous gland repair coincides with increased nerve activity and acinar cell division that is limited to the first week after radiation, with extensive acinar cell degeneration, dysfunction, and cholinergic denervation occurring thereafter. However, we found that mimicking cholinergic muscarinic input via sustained local delivery of a cevimeline–alginate hydrogel was sufficient to regenerate innervated acini and retain physiological saliva secretion at nonirradiated levels over the long term (>3 months). Thus, we reveal a previously unknown regenerative approach for restoring epithelial organ structure and function that has extensive implications for human patients.

CSF1R-dependent macrophages in the salivary gland are essential for epithelial regeneration after radiation-induced injury

“…4A), to characterize how these cells respond after irradiation. This regime is a well-established model of irradiation injury (36)(37)(38)(39)(40) and recapitulates the damage experienced by radiotherapy patients (41). As previously reported in the murine sublingual gland (42), transcriptional analysis of whole SMG tissue confirmed early cellular apoptosis and epithelial damage, with a significant increase in proapoptotic Bax expression at days 1 and 3 after irradiation, which had returned to baseline levels by day 7 (Fig.…”

FGFR2 is essential for salivary gland duct homeostasis and MAPK-dependent seromucous acinar cell differentiation

“…It is not clear whether disruption of FGFR2 signaling is directly involved in acinar pathogenesis in a setting of gland dysfunction post irradiation. Also, additional factors are likely involved in acinar regeneration post-irradiation damage, which was increased by neuronal stimulation that induced acinar cell proliferation 56 . It was also recently shown that irradiation of human SGs leads to MEC-specific upregulation of neurotrophin receptors, which potentially hinder acinar regeneration 57 .…”

Chronic Phenotypes Underlying Radiation-Induced Salivary Gland Dysfunction

“…Further, they report increased nerve activity and regeneration of innervated acini as evidenced by a significant increase in GFRa2 + filaments (Li et al 2022). Interestingly, mice treated weekly with this hydrogel had significantly improved saliva output at days 49, 63, 77, and 91 post-IR (Li et al 2022). Another study used NRTN transfer via adeno-associated serotype 2 (AAV2) vector 10 d prior to 5 × 6 Gy radiation to further understand NRTN involvement in glandular damage (Lombaert et al 2020).…”

“…The P2X7 receptor is activated by extracellular ATP and is involved in multiple inflammatory conditions; P2X7R −/− knockout mice or mice treated with a P2X7R antagonist have significantly improved saliva flow at 30 d post-IR when compared with WT IR-only controls (Gilman et al 2019). Interestingly, a study using a cevimeline-alginate hydrogel to mimic cholinergic muscarinic stimulation in mice found a significant increase in CD206+CD68+ macrophages and a significant decrease in CD3+ T cells at day 70 when compared with control mice (Li et al 2022). Finally, a study treating mice with therapeutic IGF-1 injections at days 4 to 6 following 5 Gy IR reported attenuation of the increase observed in F4/80+CD11b+ macrophages, Ly-6G+CD11b+ neutrophils, and CD3+/CD4+CD8+ double-positive T cells (Gunning et al 2024).…”

“…In mice treated with 1 dose of a cevimeline-alginate hydrogel that acts as a muscarinic-cholinergic receptor agonist, researchers reported glandular repair at day 70 as measured by increased AQP5, pHH3 + SOX2 + , and pHH3 + SOX2 − cells and significant improvements in saliva flow at days 49 and 56 but not day 63 post-IR (Li et al 2022). Further, they report increased nerve activity and regeneration of innervated acini as evidenced by a significant increase in GFRa2 + filaments (Li et al 2022). Interestingly, mice treated weekly with this hydrogel had significantly improved saliva output at days 49, 63, 77, and 91 post-IR (Li et al 2022).…”