Department of Dermatology, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke 329-0498, Tochigi, Japan.
Center for Bioscience Research and Education, Utsunomiya University, 350 Mine, Utsunomiya 321-8505, Tochigi, Japan.
Int J Mol Sci. 2024 Aug 10;25(16):8737. doi: 10.3390/ijms25168737.
We previously reported that a pathogenic abnormality in the barrier and water-holding functions of the stratum corneum (SC) in the skin of patients with atopic dermatitis (AD) is mainly attributable to significantly decreased levels of total ceramides in the SC. That decrease is mediated by the abnormal expression of a novel ceramide-reducing enzyme, sphingomyelin/glucosylceramide deacylase (SGDase), which is the β-subunit (ASAH1b) of acid ceramidase. In this study, we determined whether mice overexpressing ASAH1b in their epidermis develop AD-like skin symptoms. We generated transgenic (TG) mice overexpressing ASAH1b, regulated by the involucrin promoter, to localize its expression in the upper epidermis. After hair removal using a depilatory cream containing glycolic acid, the TG mice without any visible skin inflammation at 8 weeks of age had increased levels of ASAH1b and decreased levels of SC ceramide, with disrupted barrier functions measured by trans-epidermal water loss compared to the wild-type (WT) mice. Interestingly, enzymatic assays revealed that SGDase activity was not detectable in the skin of the TG mice compared to WT mice. Immunological staining revealed that there was an increased expression level of IL-33 in the epidermis and an accumulation of macrophages in the dermis of TG mice compared to WT mice, which are phenotypic characteristics of AD, that were exacerbated by tape-stripping of the skin. In the skin of the TG mice, the mRNA levels of IL-5, CCL11, IL-22, CXCL10, and IFNγ were significantly upregulated compared to the WT mice, and tape-stripping significantly increased the mRNA levels of IL-4, IL-33, CXCL1, CXCL12, TLR9, and CD163 compared to WT mice. These findings strongly indicate that the skin of the depilatory cream-treated TG mice exists in an atopic dry skin condition that is highly sensitive to various environmental stimuli. The sum of our results suggests that ASAH1b itself, even in the absence of its enzymatic activity, is a major etiologic factor for atopic dry skin symptoms via an unknown mechanism.
我们之前报道称，特应性皮炎（AD）患者皮肤的屏障和保水功能障碍的致病异常主要归因于角质层（SC）中总神经酰胺水平显著降低。这种减少是由一种新型神经酰胺还原酶，即神经鞘氨醇/葡萄糖神经酰胺去酰胺酶（SGDase）的异常表达介导的，它是酸性神经酰胺酶的β亚基（ASAH1b）。在这项研究中，我们确定了表皮中过表达 ASAH1b 的小鼠是否会发展出类似 AD 的皮肤症状。我们生成了过表达 ASAH1b 的转基因（TG）小鼠，其表达受 Involucrin 启动子调控，从而使其在上表皮中表达。在用含有甘醇酸的脱毛霜脱毛后，8 周龄时没有明显皮肤炎症的 TG 小鼠的 ASAH1b 水平升高，SC 神经酰胺水平降低，与野生型（WT）小鼠相比，经表皮水分流失测定的屏障功能受损。有趣的是，与 WT 小鼠相比，TG 小鼠皮肤中的 SGDase 活性无法检测到。免疫染色显示，与 WT 小鼠相比，TG 小鼠表皮中 IL-33 的表达水平增加，真皮中巨噬细胞积累，这是 AD 的表型特征，经皮肤胶带剥离后加剧。在 TG 小鼠的皮肤中，与 WT 小鼠相比，IL-5、CCL11、IL-22、CXCL10 和 IFNγ 的 mRNA 水平显著上调，并且胶带剥离显著增加了与 WT 小鼠相比，IL-4、IL-33、CXCL1、CXCL12、TLR9 和 CD163 的 mRNA 水平。这些发现强烈表明，脱毛霜处理的 TG 小鼠的皮肤处于特应性干燥皮肤状态，对各种环境刺激高度敏感。我们的研究结果表明，即使没有酶活性，ASAH1b 本身也是特应性干燥皮肤症状的主要病因因素，其机制未知。
