Psoriasis is a common, immune-mediated genetic disorder of the skin and is associated with arthritis in approximately 30% of cases. Previously, we localized PSORS2 (psoriasis susceptibility locus 2) to chromosomal region 17q25.3-qter after a genome-wide linkage scan in a family of European ancestry with multiple cases of psoriasis and psoriatic arthritis. Linkage to PSORS2 was also observed in a Taiwanese family with multiple psoriasis-affected members. In caspase recruitment domain family, member 14 (CARD14), we identified unique gain-of-function mutations that segregated with psoriasis by using genomic capture and DNA sequencing. The mutations c.349G>A (p.Gly117Ser) (in the family of European descent) and c.349+5G>A (in the Taiwanese family) altered splicing between CARD14 exons 3 and 4. A de novo CARD14 mutation, c.413A>C (p.Glu138Ala), was detected in a child with sporadic, early-onset, generalized pustular psoriasis. CARD14 activates nuclear factor kappa B (NF-kB), and compared with wild-type CARD14, the p.Gly117Ser and p.Glu138Ala substitutions were shown to lead to enhanced NF-kB activation and upregulation of a subset of psoriasis-associated genes in keratinocytes. These genes included chemokine (C-C motif) ligand 20 (CCL20) and interleukin 8 (IL8). CARD14 is localized mainly in the basal and suprabasal layers of healthy skin epidermis, whereas in lesional psoriatic skin, it is reduced in the basal layer and more diffusely upregulated in the suprabasal layers of the epidermis. We propose that, after a triggering event that can include epidermal injury, rare gain-of-function mutations in CARD14 initiate a process that includes inflammatory cell recruitment by keratinocytes. This perpetuates a vicious cycle of epidermal inflammation and regeneration, a cycle which is the hallmark of psoriasis.

Psoriasis is a chronic and complex inflammatory skin disease with lesions displaying dramatically altered mRNA expression profiles. However, much less is known about the expression of small RNAs. Here, we describe a comprehensive analysis of the normal and psoriatic skin miRNAome with next-generation sequencing in a large patient cohort. We generated 6.7 3 10 8 small RNA reads representing 717 known and 284 putative novel microRNAs (miRNAs). We also observed widespread expression of isomiRs and miRNA * s derived from known and novel miRNA loci, and a low frequency of miRNA editing in normal and psoriatic skin. The expression and processing of selected novel miRNAs were confirmed with qRT-PCR in skin and other human tissues or cell lines. Eighty known and 18 novel miRNAs were 2-42-fold differentially expressed in psoriatic skin. Of particular significance was the 2.7-fold upregulation of a validated novel miRNA derived from the antisense strand of the miR-203 locus, which plays a role in epithelial differentiation. Other differentially expressed miRNAs included hematopoietic-specific miRNAs such as miR-142-3p and miR-223/223 * , and angiogenic miRNAs such as miR-21, miR-378, miR-100 and miR-31, which was the most highly upregulated miRNA in psoriatic skin. The functions of these miRNAs are consistent with the inflammatory and hyperproliferative phenotype of psoriatic lesions. In situ hybridization of differentially expressed miRNAs revealed stratified epidermal expression of an uncharacterized keratinocyte-derived miRNA, miR-135b, as well as the epidermal infiltration of the hematopoietic-specific miRNA, miR-142-3p, in psoriatic lesions. This study lays a critical framework for functional characterization of miRNAs in healthy and diseased skin.

Heterozygous deletion of RPS14 occurs in del(5q) MDS and has been linked to impaired erythropoiesis, characteristic of this disease subtype. We generated a murine model with conditional inactivation of Rps14 and demonstrated a p53-dependent erythroid differentiation defect with apoptosis at the transition from polychromatic to orthochromatic erythroblasts resulting in age-dependent progressive anemia, megakaryocyte dysplasia, and loss of hematopoietic stem cell (HSC) quiescence. Using quantitative proteomics, we identified significantly increased expression of proteins involved in innate immune signaling, particularly the heterodimeric S100a8/S100a9 proteins in purified erythroblasts. S100a8 expression was significantly increased in erythroblasts, monocytes and macrophages and recombinant S100a8 was sufficient to induce an erythroid differentiation defect in wild-type cells. We rescued the erythroid differentiation defect in Rps14 haploinsufficient HSCs by genetic inactivation of S100a8 expression. Our data link Rps14 haploinsufficiency to activation of the innate immune system via induction of S100A8/A9 and the p53-dependant erythroid differentiation defect in del(5q) MDS.

The inaccessibility of living bone marrow hampers the study of its pathophysiology under myelotoxic stress induced by drugs, radiation or genetic mutations. Here, we show that a vascularized human bone-marrow-on-a-chip supports the differentiation and maturation of multiple blood-cell lineages over 4 weeks while improving CD34+ cell maintenance, and that it recapitulates aspects of marrow injury, including myeloerythroid toxicity after clinically relevant exposures to chemotherapeutic drugs and ionizing radiation as well as marrow recovery after drug-induced myelosuppression. The chip comprises a fluidic channel filled with a fibrin gel in which CD34 + cells and bone-marrow-derived stromal cells are co-cultured, a parallel channel lined by human vascular endothelium and perfused with culture medium, and a porous membrane separating the two channels. We also show that bone-marrow chips containing cells from patients with the rare genetic disorder Shwachman–Diamond syndrome reproduced key haematopoietic defects and led to the discovery of a neutrophil-maturation abnormality. As an in vitro model of haematopoietic dysfunction, the bone-marrow-on-a-chip may serve as a human-specific alternative to animal testing for the study of bone-marrow pathophysiology.