Epigenetic changes associated with Cutibacteriam acnes-induced innate immune memory events in human keratinocytes

Summary: Abstract Body: Cutaneous microbiota can transiently activate keratinocytes, leading to innate immune and inflammatory responses that may persist beyond the initial trigger. This phenomenon is referred to as trained immunity or innate immune memory (IIM). We investigated whether Cutibacterium acnes can induce IIM in keratinocytes and to analyze the underlying epigenetic changes. Normal human epidermal keratinocytes from mammoplasty (NHEK-B) or abdominoplasty (NHEK-A) were trained with C. acnes and induced with Pam3CSK4 after five days of rest. The contribution of epigenetic regulation to IIM events was analyzed using pharmacological inhibitors during training, and whole-genome methylation changes were assessed by ELISA. Our results revealed the formation of region-specific immune training(NHEK-B) vs. tolerance(NHEK-A) events, as judged by the significant mRNA expression differences of selected immune effectors (TNFα, IL-8) in trained cells after Pam3CSK4 induction, compared to the untrained ones. Pargyline HCL, a histone deacetylase inhibitor, during training did not modulate the immune effectors. The histone deacetylase inhibitor SAHA resulted in altered mRNA expressions, increased levels in NHEK-B and decreased in NHEK-A, following induction, regardless of training. 5-Aza-dC, a DNA methyltransferase inhibitor, resulted in altered TNFα and IL-8 expression regulation, but only in the untrained cells. The global 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) reduced in both levels in the genomic DNA of trained NHEK-B compared to NHEK-A cells. These epigenetic differences were supported by region-specific changes in mRNA expression of TET and DNMT genes. Our findings suggest that the cutaneous microbiota induces skin region-specific IIM changes in keratinocytes and that altered epigenetic regulation may be involved in these processes. Fanni Balogh^{1, 2, 3}, Anett Magyari³, Lilla Erdei^{1, 2}, Blanka Toldi^{1, 3}, Katalin Burián⁴, Rolland Gyulai³, Lajos Kemény^{1, 2, 3}, Kornélia Szabó^{1, 2, 3} 1. HUN-REN-SZTE Dermatological Research Group, Szeged, Hungary. 2. HCEMM-USZ Skin Research Group, Szeged, Hungary. 3. Department of Dermatology and Allergology, University of Szeged, Szeged, Hungary. 4. Institute of Clinical Microbiology, University of Szeged, Szeged, Hungary. Innate Immunity, Microbiology, and Microbiome