除毛雷射對生長期毛囊的影響: 傷害反應與毛囊再生

Effect of depilatory laser on anagen hair follicles: damage response and regeneration

邱顯鎰(Hsien-Yi Chiu)

指導教授 ： 林頌然

國立臺灣大學/工學院/醫學工程學研究所/博士(2017年)

https://doi.org/10.6342/NTU201702568

摘要

毛囊總是終其一生不斷進行著不斷的衰退與再生；而且常常毛囊在遭受傷害時，也總是能有效率的修復再生。除毛雷射現已廣泛應用於臨床，一般相信此雷射是藉由引起對毛囊的熱效應來達到除毛的效果。然而即使如此，過去的臨床文獻也指出在經過雷射治療3個月後，約有40~80%的毛髮有再重新長回來的現象。雖然臨床上有觀察到上述現象，但除毛雷射是對毛囊造成怎樣的熱傷害，我們仍所知有限；另一方面，有些毛髮是如何再修復雷射所引起的熱傷害而再生依然沒有被研究過，我們對此仍一無所知。
故而本研究旨在研究除毛雷射是對毛囊造成怎樣的熱傷害及探究毛囊在經歷除毛雷射的傷害後是利用何種的細胞及分子機轉來進行修復的過程。在此研究中我們利用7週大(休止期)的C57BL/6小鼠當做研究模型，此外，我們也用蜜蠟拔毛的方法誘導小鼠背部皮膚的毛囊同步進入生長期。2週後當毛囊已在生長期時，我們在小鼠背部皮膚施予不同能量密度(fluence: 8, 10, 12, 14 J/cm2 , pulse duration: 3 ms)的除毛雷射(亞歷山大雷射，波長: 755 nm，脈衝期間: 3 ms)，觀察毛囊後續產生的變化。
此研究發現除毛雷射會引起隨使用能量密度升高而增加的熱傷害，造成毛囊多部位的熱傷害引起細胞死亡，而這些受傷害的部位包含: 內外根鞘(outer and inner root sheath cells)，毛囊皮質(hair cortex)，毛囊球部(hair bulb)，毛囊前皮質(precortex areas)，毛間上皮(interfollicular epithelium)等。且在受傷的毛囊，毛囊往內分化為內根鞘及毛囊皮質的過程會被迫暫時性地中止待毛囊修復。另一方面，我們發現，毛囊細胞受傷後很快地於毛囊球部、外根鞘及毛囊隆起部位(bulge)的毛囊幹細胞(bulge stem cell)，都出現了BrdU陽性的複製修復反應。更進一步我們使用基因轉殖鼠子代追蹤技術(K19CreER/+; R26tdTomato/+)，發現被雷射傷害活化的毛囊幹細胞會離開他的棲位(niche)，並分別往下及往上位移分化至受傷的外根鞘及毛間上皮來修復再生這些受傷害的毛囊表皮細胞。然而我們卻發現雷射後大量降低的毛囊幹細胞表面標記(Lhx2, Sox9 and keratin 15)，進而得知毛囊幹細胞的數目明顯減少，了解到這雷射傷害過程會消耗毛囊幹細胞的儲備量，導致後續再生的毛囊變細及變短。而我們也發現hedgehog signaling是主宰毛囊受到除毛雷射熱傷害，幹細胞複製離開棲位修復毀損的毛囊細胞過程中，重要的分子訊號機轉之一。
此研究發現除毛雷射會對生長期的毛囊造成依使用能量密度高低不同的熱傷害，而毛囊為了修復這熱傷害，在hedgehog訊號的趨使下，將導致毛囊幹細胞不合時宜過度的活化離開他們的棲位，進而犧牲幹細胞的儲備量導致毛囊幹細胞的耗竭及後續毛囊的萎縮微小化。

關鍵字

毛囊 ； 幹細胞 ； 亞歷山大雷射 ； 熱傷害 ； 修復 ； 再生 ； 耗竭

並列摘要

Throughout adult life, hair follicles cyclically degenerate and regenerate. After injury, adult HFs can often efficiently “rebuild” themselves. Depilatory laser has been widely used clinically and its clinical effect is believed to be mediated by a selective photothermolytic effect. Nevertheless, variable regrowth rates have been reported, ranging from 40% to 80% 12 weeks after depilatory laser treatment. The thermal damage to HFs after laser irradiation has not been well characterized. How the thermally damaged HFs are repaired or regenerated remains to be explored.
This study is aimed at characterizing the damage to the hair follicles induced by depilatory laser treatment and exploring the cellular and molecular mechanisms governing the subsequent regenerative process.
We used 7-week-old adult C57BL/6 mice as a model in which synchronized anagen entry was induced by waxing during telogen. Two weeks after waxing when anagen has been initiated, alexandrite laser (755 nm) with various fluence ( 8, 10, 12, 14 J/cm2 , pulse duration: 3 ms) was administered on the dorsal skin. We found that alexandrite laser induced fluence-dependent thermal injury, resulting in cell death of multiple HF subpopulations, including precortex areas, outer and inner root sheath cells, hair cortex, and hair bulb cells. In the damaged hair follicles, the differentiation toward inner root sheath and hair cortex was also disrupted. Rapidly responding to laser irradiation, the proliferative reparative activity, indicated by pulse BrdU labeling, was revealed in the hair bulb, outer root sheath and hair follicle bulge stem cells. Through lineage tracing in K19CreER/+; R26tdTomato/+mice, we demonstrated that aberrantly activated bulge stem cells migrated out of the bulge niche and moved downward and upward to the outer root sheath and interfollicular epidermis, respectively. The progeny of bulge stem cells contributed to the regenerated hair bulbs and occasionally the interfollicular epidermis. However, this process was accompanied by decrease in bulge stem cell numbers, evidenced by decreased cells expressing of bulge stem cell markers of Lhx2, Sox9 and keratin 15. It resulted in significant reduction in the diameter and length of the regrowing hairs. We also found that hedgehog signaling was activated in bulge stem cells after laser injury and its activation was required to activate bulge stem cells to repair the damaged hair bulb. Inhibition of hedgehog signaling after laser treatment lead to failed repair and premature catagen entry.
Our study showed that depilatory laser induces fluence-dependent thermal injury to anagen hair follicles. The thermal damage causes mistimed activation of bulge stem cells by enhancing hedgehog signaling. Mobilization of bulge stem cells out their niche might lead to their exhaustion and hair follicle miniaturization.

並列關鍵字

hair follicle ； stem cell ； alexandrite laser ； thermal injury ； repair ； regeneration ； exhaustion

參考文獻

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