Radiation-Induced Loss of Salivary Gland Function Is Driven by Cellular Senescence and Prevented by IL6 Modulation

Abstract

Head and neck cancer patients treated by radiation commonly suffer from a devastating side effect known as dry-mouth syndrome, which results from the irreversible loss of salivary gland function via mechanisms that are not completely understood. In this study, we used a mouse model of radiationinduced salivary hypofunction to investigate the outcomes of DNA damage in the head and neck region. We demonstrate that the loss of salivary function was closely accompanied by cellular senescence, as evidenced by a persistent DNA damage response (gH2AX and 53BP1) and the expression of senescence-associated markers (SA-bgal, p19ARF, and DcR2) and secretory phenotype (SASP) factors (PAI-1 and IL6). Notably, profound apoptosis or necrosis was not observed in irradiated regions. Signs of cellular senescence were also apparent in irradiated salivary glands surgically resected from human patients who underwent radiotherapy. Importantly, using IL6 knockout mice, we found that sustained expression of IL6 in the salivary gland long after initiation of radiation-induced DNA damage was required for both senescence and hypofunction. Additionally, we demonstrate that IL6 pretreatment prevented both senescence and salivary gland hypofunction via a mechanism involving enhanced DNA damage repair. Collectively, these results indicate that cellular senescence is a fundamental mechanism driving radiation-induced damage in the salivary gland and suggest that IL6 pretreatment may represent a promising therapeutic strategy to preserve salivary gland function in head and neck cancer patients undergoing radiotherapy. Cancer Res; 76(5); 1170-80. Ó2016 AACR.

Radiation inhibits salivary gland function by promoting STIM1 cleavage by caspase-3 and loss of SOCE through a TRPM2-dependent pathway

“…Irradiation activates caspase-3 in acinar cells (29, 30), although <20-gray (Gy) radiation results in minimal apoptosis but substantial loss of salivary fluid secretion that is detected soon after the treatment (13, 15). Acinar cells from TRPM2 +/+ and TRPM2 − / − mice had similar amounts of activated caspase-3 before irradiation (control), whereas after irradiation, cells from TRPM2 +/+ mice showed 10-fold higher caspase-3 at 3 and 10 days and about 5-fold at 30 days (Fig.…”

“…The increase in [Ca 2+ ] mt after radiation was due to TRPM2-mediated Ca 2+ influx and contributed to caspase-3 activation and loss of STIM1. Although caspase is activated in salivary glands after irradiation, there is minimal apoptosis after a single dose of radiation (2.5 to 17.5 Gy) (13, 15), which cannot account for the early onset and persistent loss of acinar cell function. Our data suggest a role for caspase-3 in depletion of STIM1, thus linking the activated protease to loss of salivary gland function after irradiation rather than apoptosis.…”

“…Loss of salivary gland fluid secretion was due to decreased STIM1 and SOCE because a gene therapy strategy to express STIM1 in vivo in salivary glands of irradiated mice rescued function. Insulin-like growth factor 1 and interleukin-6 treatments, which protect salivary gland function after irradiation, promote the antiapoptotic factor BCL2 (9, 15). Thus, treatment with these factors would lead to suppression of cytochrome C release from mitochondria, as well as the subsequent activation of caspase-3.…”

Three‐Dimensional Bioprinting Nanotechnologies towards Clinical Application of Stem Cells and Their Secretome in Salivary Gland Regeneration

“…Several secretome components have been studied including specific heparan sulfate peptides [32] and several growth factors and cytokines (see Table 1 for a complete list). The majority of these secretome components (EGF, IGF1, FGF2 [26, 27, 33], FGF7 (or KGF) [28], IL-6 [34], ALDH3 [24], or EDA activators [25]) have similar cellular downstream effects such as the reduction in cell apoptosis and/or the promotion of epithelial proliferation. These secretome-based strategies could be advantageous, although the absolute cell number required for functional regeneration of the human SG is still unknown.…”

Retroductal Nanoparticle Injection to the Murine Submandibular Gland

“…In murine models of RIH, SMG retroductal injection has been used to deliver therapeutics including growth factors, primary cells, adenoviral vectors, cytokines, and antioxidant compounds to modulate the cellular response to injury, and reduce the resulting tissue damage 5,9–16 . The most notable clinical success of retroductal injection is the administration of adenoviral vector to direct expression of a water channel (Aquaporin 1; AQP1) in patients following the radiation for head and neck cancer 17 .…”