PKC delta and cell renewal in irradiated taste epithelium

描述（由申请人提供）：味觉功能障碍，感觉丧失或改变，是头颈癌放疗期间常见的情况。然而，除了抗肿瘤作用外，电离辐射还经常在周围口腔粘膜（起泡/粘膜炎）和唾液腺（口干/口干）中引起显著的副作用。虽然已经制定了一些方案，以尽量减少一些口腔后遗症，减轻辐射对味觉功能的影响仍然难以捉摸。重要的是，味觉降低的患者往往缺乏食欲，吃得少得多，导致体重减轻，生活质量显著降低。 虽然放疗引起的味觉丧失是癌症治疗的一种有据可查的副作用，但尚未确定确切的靶点。已经提出了一些合理的解释，包括间接影响，即，减少流涎和口腔起泡，以及直接机制如味蕾神经支配的破坏、特定味觉受体细胞类型的损失以及味觉祖细胞的损失。我们的初步数据支持增殖的味蕾祖细胞是辐射损伤的直接目标的假设。因此，在本提案的目标1中，我们将确定味蕾祖细胞的味觉细胞更新动力学，并检查照射如何影响这种活跃的循环祖细胞群。我们还将确定辐射诱导的细胞周期停滞，DNA修复和凋亡的味觉细胞更新损伤后的贡献。在目标2中，我们将研究新的蛋白激酶C δ亚型（PKC 4）在辐射诱导的味觉上皮损伤中的作用。PKC 4是辐射诱导的细胞凋亡的关键调节因子，即，PKC 4的抑制保护照射的唾液腺细胞免于死亡。PKC 4还涉及维持UV损伤的人角质形成细胞中DNA修复所需的细胞周期停滞。因此，我们将测试这一假设，即PKC 4的损失保护味觉祖细胞免于死亡，和/或促进它们在辐射损伤后继续有丝分裂。我们的初步数据表明，该模型表明，虽然PKC 4 KO小鼠具有正常的味觉上皮细胞，但响应于辐射，它们的味蕾祖细胞群似乎受到保护并继续增殖。总之，我们的味觉模型，其中祖细胞和分化的味觉受体细胞是不同的，易于识别，将使我们能够更好地了解头部和颈部辐射靶向的精确细胞群。此外，味觉上皮细胞的明确组织结构将使我们能够梳理味觉上皮中PKC 4的功能，并可能导致开发PKC 4的特异性药理学抑制剂，以保护口腔组织免受辐射诱导的损伤。 公共卫生相关性：头颈癌的放射治疗经常会对口腔附近的组织造成损伤。特别是大多数患者会经历味觉的改变或降低，导致食欲不振，体重减轻和生活质量显著受损。这项提案中的研究将解决有关头颈癌放射治疗患者味觉丧失的细胞和分子基础的新的重要问题。了解味觉丧失是如何发生的，将有助于制定治疗策略，以逆转或预防味觉丧失，并改善接受头颈部照射的患者的生活质量。

DESCRIPTION (provided by applicant): Taste dysfunction, either loss or alteration in sensation, is a common occurrence during radiotherapy for head and neck cancer. In addition to anti-tumor effects, however, ionizing irradiation frequently causes significant side effects in the surrounding oral mucosa (blistering/mucositis) and salivary glands (dry mouth/xerostomia). Although protocols have been developed to minimize some oral sequelae, mitigation of the impact of irradiation on taste function has remained elusive. Importantly, patients with reduced taste sensation tend to lack appetite and eat far less, leading to weight loss, as well as a significantly compromised quality of life. While radiotherapy induced taste loss is a well-documented side effect of cancer treatment, the precise target(s) responsible have not been determined. Plausible explanations have been put forth, including indirect effects, i.e., reduced salivation and oral blistering, and direct mechanisms such as disruption of taste bud innervation, loss of particular taste receptor cell type(s), as well as loss of taste progenitor cells. Our preliminary data favor the hypothesis that proliferating taste bud progenitor cells are the direct targets of radiation damage. Accordingly, in Aim 1 of this proposal, we will determine the kinetics of taste cell renewal by taste bud progenitors, and examine how irradiation affects this actively cycling progenitor population. We will also define the contribution of radiation-induced cell cycle arrest, DNA repair and apoptosis to taste cell renewal following injury. In Aim 2 we will investigate the role of the novel protein kinase C delta isoform (PKC4) in irradiation-induced taste epithelial injury. PKC4 is a key regulator of irradiation-induced apoptosis, i.e., suppression of PKC4 protects irradiated salivary gland cells from death. PKC4 has also been implicated in maintenance of cell cycle arrest required for DNA repair in UV damaged human keratinocytes. Thus, we will test the hypothesis that loss of PKC4 protects taste progenitor cells from death, and/or promotes their continued mitosis following irradiation injury. This model is suggested by our preliminary data, which indicate that, while PKC4 KO mice possess normal taste epithelia, in response to irradiation, their taste bud progenitor cell population appears to be protected and continues to proliferate. In sum, our taste model, where progenitors and differentiated taste receptor cells are distinct and readily identifiable, will allow us to better understand the precise cell population(s) targeted by head and neck radiation. Further, the defined cellular organization of taste epithelium will allow us to tease apart the functions of PKC4 in taste epithelium, and lead potentially to development of specific pharmacological inhibitors of PKC4 to protect oral tissues from irradiation-induced damage. PUBLIC HEALTH RELEVANCE: Radiation therapy of head and neck cancer frequently causes damage to nearby tissues in the oral cavity. In particular the majority of patients will experience an altered or reduced sense of taste, resulting in loss of appetite, weight loss, and a significantly compromised quality of life. Studies in this proposal will address novel and important questions regarding the cellular and molecular basis of taste loss in patients treated with irradiation for head and neck cancer. Understanding how taste loss occurs will enable the development of therapeutic strategies to reverse or prevent taste loss and improve the quality of life of patients undergoing head and neck irradiation.