Probes for LONG

Psoriasis is a common immune-mediated skin disease characterized by epidermal hyperproliferation and chronic skin inflammation. Long non-coding RNAs (lncRNAs) are >200 nucleotide long transcripts, which possess important regulatory functions. To date, little is known about the contribution of lncRNAs to psoriasis. Here, we identify LINC00958 as a lncRNA overexpressed in keratinocytes from psoriasis skin lesions, in a transcriptomic screen performed on keratinocytes sorted from psoriasis and healthy skin. Increased levels of LINC00958 in psoriasis keratinocytes were confirmed by RT-qPCR and single molecule in situ hybridization. Confocal microscopy and analysis of subcellular fractions showed that LINC00958 is mainly localized in the cytoplasm of keratinocytes. IL-17A, a key psoriasis cytokine, induced LINC00958 in keratinocytes through C/EBP-β and the p38 pathway. Inhibition of LINC00958 led to decreased proliferation as measured by Ki67 expression, IncuCyte imaging and EdU assays. Transcriptomic analysis of LINC00958-depleted keratinocytes revealed enrichment of proliferation and cell cycle-related genes among differentially expressed transcripts. Moreover, LINC00958-depletion led to decreased basal and IL-17A-induced phosphorylation of p38. Furthermore, IL-17A-induced keratinocyte proliferation was counteracted by the inhibition of LINC00958. In summary, our data support a role for the IL-17A-induced lncRNA, LINC00958, in the pathological circuits in psoriasis by reinforcing IL-17A-induced epidermal hyperproliferation.

Genetic mutations in the Xylt1 gene are associated with Desbuquois dysplasia type II syndrome characterized by sever prenatal and postnatal short stature. However, the specific role of XylT-I in the growth plate is not completely understood. Here, we show that XylT-I is expressed and critical for the synthesis of proteoglycans in resting and proliferative but not in hypertrophic chondrocytes in the growth plate. We found that loss of XylT-I induces hypertrophic phenotype-like of chondrocytes associated with reduced interterritorial matrix. Mechanistically, deletion of XylT-I impairs the synthesis of long glycosaminoglycan chains leading to the formation of proteoglycans with shorter glycosaminoglycan chains. Histological and Second Harmonic Generation microscopy analysis revealed that deletion of XylT-I accelerated chondrocyte maturation and prevents chondrocytes columnar organization and arrangement in parallel of collagen fibers in the growth plate, suggesting that XylT-I controls chondrocyte maturation and matrix organization. Intriguingly, loss of XylT-I induced at embryonic stage E18.5 the migration of progenitor cells from the perichondrium next to the groove of Ranvier into the central part of epiphysis of E18.5 embryos. These cells characterized by higher expression of glycosaminoglycans exhibit circular organization then undergo hypertrophy and death creating a circular structure at the secondary ossification center location. Our study revealed an uncovered role of XylT-I in the synthesis of proteoglycans and provides evidence that the structure of glycosaminoglycan chains of proteoglycans controls chondrocyte maturation and matrix organization.

Abstract Unavailable

Skeletal stem cells regulate bone growth and homeostasis by generating diverse cell types, including chondrocytes, osteoblasts and marrow stromal cells. The emerging concept postulates that there exists a distinct type of skeletal stem cell that is closely associated with the growth plate1–4, which is a type of cartilaginous tissue that has critical roles in bone elongation5. The resting zone maintains the growth plate by expressing parathyroid hormone-related protein (PTHrP), which interacts with Indian hedgehog (Ihh) that is released from the hypertrophic zone6–10, and provides a source of other chondrocytes11. However, the identity of skeletal stem cells and how they are maintained in the growth plate are unknown. Here we show, in a mouse model, that skeletal stem cells are formed among PTHrP-positive chondrocytes within the resting zone of the postnatal growth plate. PTHrP-positive chondrocytes expressed a panel of markers for skeletal stem and progenitor cells, and uniquely possessed the properties of skeletal stem cells in cultured conditions. Cell-lineage analysis revealed that PTHrP-positive chondrocytes in the resting zone continued to form columnar chondrocytes in the long term; these chondrocytes underwent hypertrophy, and became osteoblasts and marrow stromal cells beneath the growth plate. Transit-amplifying chondrocytes in the proliferating zone—which was concertedly maintained by a forward signal from undifferentiated cells (PTHrP) and a reverse signal from hypertrophic cells (Ihh)—provided instructive cues to maintain the cell fates of PTHrP-positive chondrocytes in the resting zone. Our findings unravel a type of somatic stem cell that is initially unipotent and acquires multipotency at the post-mitotic stage, underscoring the malleable nature of the skeletal cell lineage. This system provides a model in which functionally dedicated stem cells and their niches are specified postnatally, and maintained throughout tissue growth by a tight feedback regulation system.