Profibrotic subsets of SPP1+ macrophages and POSTN+ fibroblasts contribute to fibrotic scarring in acne keloidalis

Acne keloidalis (AK) is a primary scarring alopecia characterized by longstanding inflammation in the scalp leading to keloid-like scar formation and hair loss. Histologically, AK is characterized by mixed leukocytic infiltrates in the acute stage followed by a granulomatous reaction and extensive fibrosis in later stages. To further explore its pathogenesis, bulk RNA-sequencing and single-cell RNA sequencing were applied to scalp biopsy specimens of lesional and adjacent non-lesional skin in patients with clinically active disease. Unbiased clustering revealed 18 distinct cell populations, including two notable populations, POSTN+ fibroblasts with enriched extracellular matrix signatures, and SPP1+ myeloid cells M2 macrophages. Cell communication analyses indicate that fibroblasts and myeloid cells communicate by collagen and SPP1 signaling networks in lesional skin. Tissue immunofluorescence staining demonstrated SPP1+ myeloid cells and POSTN+ fibroblasts at the upper segment of outer root sheath of the hair follicle in the subacute stage, confirming micro-anatomic specificity with relevant disease activity. Therapy with intralesional corticosteroids reduced SPP1 and POSTN expression, and lessened AK progression. In summary, the communication between POSTN+ fibroblasts and SPP1+ myeloid cells by collagen and SPP1 axis may contribute to the pathogenesis of AK. We conducted droplet-based scRNA-seq (10X Genomics, California, USA) on paired 6 mm punch biopsies of AK lesional skin (n = 1) and adjacent healthy non-lesional skin (n = 1) from an individual patient Please note that raw data are not available due to patient privacy concerns.

瘢痕疙瘩性痤疮（Acne keloidalis, AK）是一类原发性瘢痕性秃发，以头皮长期存在的炎症为核心特征，可进展为瘢痕疙瘩样瘢痕并引发秃发。组织病理学层面，AK急性期以混合性白细胞浸润为特征，后续会出现肉芽肿性反应，晚期则进展为广泛纤维化。为深入解析AK的发病机制，本研究针对临床活动期患者的病变头皮活检组织及邻近非病变皮肤标本，开展了批量RNA测序（bulk RNA-sequencing）与单细胞RNA测序（single-cell RNA sequencing）。无偏聚类分析共鉴定出18种独立的细胞群，其中两类特征尤为显著：一类是POSTN+成纤维细胞，其细胞外基质相关基因特征显著富集；另一类是SPP1+髓系细胞（即M2型巨噬细胞）。细胞通讯分析结果显示，在病变皮肤中，成纤维细胞与髓系细胞可通过胶原蛋白及SPP1信号通路实现相互通讯。组织免疫荧光染色实验证实，在亚急性期病变组织的毛囊外根鞘上段，存在SPP1+髓系细胞与POSTN+成纤维细胞的富集，这一结果确认了该细胞分布的微观解剖特异性与疾病活动度的相关性。病灶内注射糖皮质激素治疗可下调SPP1与POSTN的表达水平，并延缓AK的病情进展。综上，POSTN+成纤维细胞与SPP1+髓系细胞通过胶原蛋白及SPP1轴介导的相互通讯，可能参与了AK的发病过程。本研究对1名AK患者的配对活检标本开展了基于微滴的单细胞RNA测序（droplet-based scRNA-seq），所用平台为美国加利福尼亚州10X Genomics公司产品；标本包含1份AK病变皮肤的6mm钻孔活检样本与1份邻近健康非病变皮肤的6mm钻孔活检样本。请注意，受患者隐私保护相关要求限制，本研究的原始数据暂不对外公开。