Abnormal keratinocyte differentiation in the nasal planum of Labrador Retrievers with hereditary nasal parakeratosis (HNPK)

Abstract

Hereditary nasal parakeratosis (HNPK) is an inherited disorder described in Labrador Retrievers and Greyhounds. It has been associated with breed-specific variants in the SUV39H2 gene encoding a histone 3 methyltransferase involved in epigenetic silencing. Formalin-fixed biopsies of the nasal planum of Labrador Retrievers were screened by immunofluorescence microscopy for the presence and distribution of epidermal proliferation and differentiation markers. Gene expression of these markers was further analysed using RNA sequencing (RNA-seq) and ultrastructural epidermal differences were investigated by electron microscopy. Differentiation of the nasal planum in the basal and suprabasal epidermal layers of HNPK-affected dogs (n = 6) was similar compared to control dogs (n = 6). In the upper epidermal layers, clear modifications were noticed. Loricrin protein was absent in HNPK-affected nasal planum sections in contrast to sections of the same location of control dogs. However, loricrin was present in the epidermis of paw pads and abdominal skin from HNPK dogs and healthy control dogs. The patterns of keratins K1, K10 and K14, were not markedly altered in the nasal planum of HNPK-affected dogs while the expression of the terminal differentiation marker involucrin appeared less regular. Based on RNA-seq, LOR and IVL expression levels were significantly decreased, while KRT1, KRT10 and KRT14 levels were up-regulated (log2fold-changes of 2.67, 3.19 and 1.71, respectively) in HNPK-affected nasal planum (n = 3) compared to control dogs (n = 3). Electron microscopical analysis revealed structural alterations in keratinocytes and stratum corneum, and disrupted keratinocyte adhesions and distended intercellular spaces in lesional samples (n = 3) compared

SUV39H2 epigenetic silencing controls fate conversion of epidermal stem and progenitor cells

“…Up-regulation of stress-induced p53 targets further highlights that the premature exit from the cell cycle occurs on a background of progressive genomic instability and a senescence-like state. This collective phenotype agrees with the severe histological alterations in HNPK nasal epidermis (Bannoehr et al, 2020;Bauer et al, 2018;Jagannathan et al, 2013;Pagé et al, 2003).…”

“…Given that the HNPK phenotype develops in young dogs ( Bannoehr et al, 2020 ; Pagé et al, 2003 ), it can be assumed that keratinocytes, which have undergone a number of cell divisions, start to enter a metastable state. Cells of passage 15 were therefore chosen for subsequent analyses that are healthy and nonapoptotic but might be prone to phenotypic alterations.…”

“…Lack of an HNPK phenotype in skin correlates with low SUV39H2 and high SUV39H1 levels Finally, we addressed the conundrum of why the SUV39H2 variant severely affects homeostasis of the glabrous nasal epidermis but spares hairy skin (Bannoehr et al, 2020;Jagannathan et al, 2013). We first questioned whether repressive H3K9me3 marks are present in hairy skin biopsies of one of the HNPK dogs used in the nose study (HNPK 1; Fig.…”

“…RNA-seq and pathway analysis RNA-seq data were obtained from nasal planum biopsies of three HNPK-affected dogs and three control dogs (European Nucleotide Archive and GenBank accession no. PRJEB32103; Bannoehr et al, 2020). The nasal epidermis (including the rete ridges) was manually separated from the dermis using a stereo microscope.…”

Effect of SUV39H1 Histone Methyltransferase Knockout on Expression of Differentiation-Associated Genes in HaCaT Keratinocytes

“…Enhancement in the expression of only some of the studied differentiation-associated genes points to a defined topology of the H3K9me3 mark imposed by SUV39H1. Interestingly, changes in the expression of epidermal genes were also noted in the nasal epidermis of dogs with loss-of-function mutation in SUV39H2 [39,40]. Namely, INV and LOR expression was slightly diminished and that of K10 increased, similar to SUV39H1-KO HaCaT cells, but the expression of DSG1 was not affected.…”