PKC delta and cell renewal in irradiated taste epithelium

描述(申请人提供)：味觉障碍，即感觉丧失或改变，是头颈癌放射治疗过程中常见的情况。然而，除了抗肿瘤作用外，电离辐射还经常对周围的口腔粘膜(水泡/粘膜炎)和唾液腺(口干/口干)造成显著的副作用。虽然已经开发了一些方案来减少一些口腔后遗症，但减轻辐射对味觉功能的影响仍然难以捉摸。重要的是，味觉减退的患者往往没有食欲，吃得更少，导致体重减轻，以及生活质量显著下降。虽然放射治疗引起的味觉丧失是癌症治疗的一个众所周知的副作用，但确切的靶点(S)还没有确定。已经提出了合理的解释，包括间接影响，即减少唾液和口腔起泡，以及直接机制，如味蕾神经支配中断，特定味觉感受器细胞类型的丧失(S)，以及味觉前体细胞的丧失。我们的初步数据支持这样的假设，即增殖的味蕾前体细胞是辐射损伤的直接目标。因此，在这项提议的目标1中，我们将确定味蕾前体细胞味觉细胞更新的动力学，并研究辐射如何影响这一活跃的循环前体种群。我们还将确定辐射诱导的细胞周期停滞、DNA修复和凋亡对损伤后味觉细胞更新的贡献。在目标2中，我们将研究新的蛋白激酶C增量异构体(PKC4)在辐射诱导的味觉上皮损伤中的作用。PKC4是辐射诱导细胞凋亡的关键调节因子，即抑制PKC4可以保护受辐射的唾液腺细胞免于死亡。PKC4还与维持紫外线损伤的角质形成细胞DNA修复所需的细胞周期停滞有关。因此，我们将检验这一假设，即PKC4的丢失保护味觉前体细胞免于死亡，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，虽然PKC4KO小鼠拥有正常的味觉上皮，但对辐射的反应，它们的味蕾前体细胞群体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感受器细胞是不同的，很容易识别，将使我们更好地理解头颈部辐射所针对的精确细胞群(S)。此外，味觉上皮明确的细胞组织结构将使我们能够梳理出味觉上皮中PKC4的功能，并有可能导致PKC4的特异性药物抑制剂的开发，以保护口腔组织免受辐射损伤。 公共卫生相关性：头颈部癌症的放射治疗经常会对口腔附近的组织造成损害。特别是，大多数患者将经历味觉改变或减少，导致食欲不振、体重减轻和生活质量显著下降。这项提案中的研究将解决有关头颈癌患者接受放射治疗后味觉丧失的细胞和分子基础的新的和重要的问题。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，并改善接受头颈部放射治疗的患者的生活质量。

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.