探討毛囊間質細胞於輻射造成毛囊微小化的角色

Abstract

癌症患者逐年增加且約有60%的患者接受過放射線治療，透過放射線造成癌細胞死亡，然而除了癌細胞被影響，周邊健康組織的細胞也受放射線傷害影響，而落髮是放射線治療常見的副作用之一。然而頭髮是不可或缺的，失去頭髮對於患者來說不僅會產生心理壓力、負面情緒，還會影響生活品質。 放射線治療導致的落髮可分為暫時性落髮和永久性落髮，暫時性落髮的患者約在放射線療程結束二至六個月後頭髮恢復，永久性落髮的患者則是在放射線療程結束六個月後頭髮仍無法恢復。此外，不管是暫時性還是永久性落髮的患者，他們再生的頭髮發生一定程度變細的情況，代表毛囊發生微小化的問題，而毛囊微小化這個現象只會日趨嚴重，最終導致毛囊消失無法再生，且目前臨床上並沒有有效的治療方法，因此本研究致力於探討放射線造成毛囊微小化的原因以及提出改善方法。 為了模擬臨床上經放射線治療後造成毛囊微小化的現象，於實驗中以銫-137作為射源，給予不同輻射劑量以建立動物模型，最後以20Gy作為探討毛囊微小化的輻射劑量。臨床上以頭髮變細這個現象作為認定毛囊微小化的依據，而從本研究發現毛髮的寬度及長度都有減少的現象，意即毛髮變細及變短，毛囊發生微小化。 追究造成毛囊微小化的原因為毛囊間質細胞中的真皮乳突細胞數量減少，且細胞減少的時間點落在退化性衰退期，因為於退化性休止期和下個生長期 (輻射後再生) 毛囊真皮乳突細胞數量已經減少。而真皮乳突細胞數量減少的原因目前可以排除細胞凋亡，因為透過cleaved caspase 3的染色並沒有觀察到真皮乳突細胞凋亡的情形，至於詳細真皮乳突細胞數量減少的原因還有待釐清。 同時透過aSMACreER:R26LSL-tdtomato轉基因鼠追蹤毛囊翹幹細胞補充至真皮乳突的毛囊比例，發現毛囊鞘幹細胞補充至真皮乳突的毛囊比例減少，代表毛囊鞘幹細胞特化為真皮乳突細胞的能被抑制，所以經高劑量輻射傷害後無法藉由毛囊鞘幹細胞的補充來增加真皮乳突細胞數量。 另外，為了促進毛囊鞘幹細胞特化為真皮乳突細胞的能力，我們觀察真皮鞘細胞與毛囊鞘幹細胞的生長動態，從實驗結果瞭解真皮鞘細胞在生長期第一期就開始增生，且持續增生至生長期第三、四期，而毛囊鞘幹細胞則是在生長期第三期就補充至真皮乳突，所以未來若要促進毛囊鞘幹細胞的能力，必須在生長期早期開始實施。

The number of cancer patients has been increasing year by year, with approximately 60% of patients receiving radiation therapy. Radiation therapy causes the death of cancer cells, but it also affects the surrounding healthy tissue cells, resulting in a common side effect known as alopecia. However, hair is essential, and losing it not only generates psychological stress and negative emotions for patients but also affects their quality of life. Radiation-induced alopecia can be categorized into temporary alopecia and persistent alopecia. Patients with temporary alopecia usually experience hair regrowth within two to six months after the completion of radiation therapy, while patients with persistent alopecia are unable to restore their hair even six months after the completion of radiation therapy. Furthermore, regardless of temporary or persistent alopecia, the regrown hair tends to be thinner, indicating the problem of hair follicle miniaturization. This phenomenon of hair follicle miniaturization worsens over time, eventually leading to the disappearance of hair follicles and the inability to regenerate hair. Currently, there are no effective treatment methods for this issue in clinical practice. Therefore, this study aims to investigate the causes of radiation-induced hair follicle miniaturization and propose improvement methods. To simulate the phenomenon of radiation-induced hair follicle miniaturization observed in clinical practice, the experiment utilized cesium-137 (Cs-137) as the radiation source and administered different radiation doses to establish an animal model. Ultimately, a radiation dose of 20Gy was selected to investigate hair follicle miniaturization. In clinical practice, the thinning of hair serves as the basis for identifying hair follicle miniaturization. This study discovered a decrease in both the width and length of hair, indicating hair thinning and shortening, as well as hair follicle miniaturization. The investigation into the causes of hair follicle miniaturization led to the observation of a decrease in the number of dermal papilla cells. The reduction in cell numbers occurred during the dystrophic catagen, as the number of dermal papilla cells had already decreased during the dystrophic catagen and subsequent anagen (post-radiation regenerated anagen). However, cell apoptosis can be ruled out as the cause of the reduction in dermal papilla cell numbers, as no apoptosis of dermal papilla cells was observed through staining with cleaved caspase 3. The specific reasons for the decrease in dermal papilla cell numbers remain to be clarified. Additionally, tracking the proportion of hair follicle dermal stem cells (hfDSCs) replenishing the dermal papilla in aSMACreER:R26LSL-tdtomato transgenic mice revealed a decrease in this ratio. This indicates that the specialization of hfDSCs into dermal papilla cells is inhibited. Therefore, after high-dose radiation injury, the replenishment of dermal papilla cells cannot be achieved through the supplementation of hfDSCs. The Wnt signaling family plays a crucial role in hair follicle regeneration and the maintenance of hair follicle stem cells. In addition, to enhance the specialization ability of hfDSCs into dermal papilla cells, we observed the growth dynamics of dermal sheath cells and hfDSCs. From the experimental results, we found that dermal sheath cells begin to proliferate during the anagen phase and continue to proliferate until anagen III or IV. On the other hand, hfDSCs replenish the dermal papilla during anagen III. Therefore, if we aim to promote the ability of hfDSCs, it is crucial to implement interventions during early anagen.