Keratinocyte-derived S100A9 modulates neutrophil infiltration and affects psoriasis-like skin and joint disease.

OBJECTIVES: S100A9, an alarmin that can form calprotectin (CP) heterodimers with S100A8, is mainly produced by keratinocytes and innate immune cells. The contribution of keratinocyte-derived S100A9 to psoriasis (Ps) and psoriatic arthritis (PsA) was evaluated using mouse models, and the potential usefulness of S100A9 as a Ps/PsA biomarker was assessed in patient samples. METHODS: Conditional S100A9 mice were crossed with DKO* mice, an established psoriasis-like mouse model based on inducible epidermal deletion of c-Jun and JunB to achieve additional epidermal deletion of S100A9 (TKO* mice). Psoriatic skin and joint disease were evaluated in DKO* and TKO* by histology, microCT, RNA and proteomic analyses. Furthermore, S100A9 expression was analysed in skin, serum and synovial fluid samples of patients with Ps and PsA. RESULTS: Compared with DKO* littermates, TKO* mice displayed enhanced skin disease severity, PsA incidence and neutrophil infiltration. Altered epidermal expression of selective pro-inflammatory genes and pathways, increased epidermal phosphorylation of STAT3 and higher circulating TNFα were observed in TKO* mice. In humans, synovial S100A9 levels were higher than the respective serum levels. Importantly, patients with PsA had significantly higher serum concentrations of S100A9, CP, VEGF, IL-6 and TNFα compared with patients with only Ps, but only S100A9 and CP could efficiently discriminate healthy individuals, patients with Ps and patients with PsA. CONCLUSIONS: Keratinocyte-derived S100A9 plays a regulatory role in psoriatic skin and joint disease. In humans, S100A9/CP is a promising marker that could help in identifying patients with Ps at risk of developing PsA.

Topical application of an amygdalin analogue reduces inflammation and keratinocyte proliferation in a psoriasis mouse model.

Psoriasis is a chronic inflammatory skin disease without cure. Systemic and biological therapies are the most effective treatments for patients with severe psoriasis. However, these drugs can cause serious side effects from extended use. Safe and effective topical drugs are needed to decrease psoriatic plaques and reduce the risk of adverse effects. Amygdalin analogues are stable small molecules that showed benefits in psoriasis xenografts to immune-deficient mice by systemic application. However, whether topical application of these amygdalin analogues could reduce the progression of the psoriatic phenotype in an immune-competent organism is unknown. Here, we analyse the efficiency of topical application of an amygdalin analogue cream on a well-established genetic and immune-competent mouse model of psoriasis. Topical application of an amygdalin analogue cream ameliorates psoriasis-like disease in mice, reduces epidermal hyperplasia and skin inflammation. Amygdalin analogue treatment leads to reduced expression of local pro-inflammatory cytokines, but systemic pro-inflammatory cytokines that are highly expressed in psoriasis patients such as IL-17A, IL6 or G-CSF are also decreased. Furthermore, expression of important mediators of psoriasis initiation and epidermal hyperplasia, such as TNFa, S100A9 and TSLP, is decreased in lesional epidermis after amygdalin analogue treatment. In conclusion, we show that amygdalin analogue reduces the proliferative capacity of psoriasis-like stimulated keratinocytes and their inflammatory response in vivo and in vitro. These results suggest that topical application of amygdalin analogues may represent a safe and effective treatment for psoriasis.

Role of bulge epidermal stem cells and TSLP signaling in psoriasis.

Psoriasis is a common inflammatory skin disease involving a cross-talk between epidermal and immune cells. The role of specific epidermal stem cell populations, including hair follicle stem cells (HF-SCs) in psoriasis is not well defined. Here, we show reduced expression of c-JUN and JUNB in bulge HF-SCs in patients with scalp psoriasis. Using lineage tracing in mouse models of skin inflammation with inducible deletion of c-Jun and JunB, we found that mutant bulge HF-SCs initiate epidermal hyperplasia and skin inflammation. Mechanistically, thymic stromal lymphopoietin (TSLP) was identified in mutant cells as a paracrine factor stimulating proliferation of neighboring non-mutant epidermal cells, while mutant inter-follicular epidermal (IFE) cells are lost over time. Blocking TSLP in psoriasis-like mice reduced skin inflammation and decreased epidermal proliferation, VEGFα expression, and STAT5 activation. These findings unravel distinct roles of HF-SCs and IFE cells in inflammatory skin disease and provide novel mechanistic insights into epidermal cell interactions in inflammation.

Single-cell imaging and transcriptomic analyses of endogenous cardiomyocyte dedifferentiation and cycling.

While it is recognized that there are low levels of new cardiomyocyte (CM) formation throughout life, the source of these new CM generates much debate. One hypothesis is that these new CMs arise from the proliferation of existing CMs potentially after dedifferentiation although direct evidence for this is lacking. Here we explore the mechanisms responsible for CM renewal in vivo using multi-reporter transgenic mouse models featuring efficient adult CM (ACM) genetic cell fate mapping and real-time cardiomyocyte lineage and dedifferentiation reporting. Our results demonstrate that non-myocytes (e.g., cardiac progenitor cells) contribute negligibly to new ACM formation at baseline or after cardiac injury. In contrast, we found a significant increase in dedifferentiated, cycling CMs in post-infarct hearts. ACM cell cycling was enhanced within the dedifferentiated CM population. Single-nucleus transcriptomic analysis demonstrated that CMs identified with dedifferentiation reporters had significant down-regulation in gene networks for cardiac hypertrophy, contractile, and electrical function, with shifts in metabolic pathways, but up-regulation in signaling pathways and gene sets for active cell cycle, proliferation, and cell survival. The results demonstrate that dedifferentiation may be an important prerequisite for CM proliferation and explain the limited but measurable cardiac myogenesis seen after myocardial infarction (MI).

Neural-competent cells of adult human dermis belong to the Schwann lineage.

Resident neural precursor cells (NPCs) have been reported for a number of adult tissues. Understanding their physiological function or, alternatively, their activation after tissue damage or in vitro manipulation remains an unsolved issue. Here, we investigated the source of human dermal NPCs in adult tissue. By following an unbiased, comprehensive approach employing cell-surface marker screening, cell separation, transcriptomic characterization, and in vivo fate analyses, we found that p75NTR(+) precursors of human foreskin can be ascribed to the Schwann (CD56(+)) and perivascular (CD56(-)) cell lineages. Moreover, neural differentiation potential was restricted to the p75NTR(+)CD56(+) Schwann cells and mediated by SOX2 expression levels. Double-positive NPCs were similarly obtained from human cardiospheres, indicating that this phenomenon might be widespread.

THY-1 receptor expression differentiates cardiosphere-derived cells with divergent cardiogenic differentiation potential.

Despite over a decade of intense research, the identity and differentiation potential of human adult cardiac progenitor cells (aCPC) remains controversial. Cardiospheres have been proposed as a means to expand aCPCs in vitro, but the identity of the progenitor cell within these 3D structures is unknown. We show that clones derived from cardiospheres could be subdivided based on expression of thymocyte differentiation antigen 1 (THY-1/CD90) into two distinct populations that exhibit divergent cardiac differentiation potential. One population, which is CD90(+), expressed markers consistent with a mesenchymal/myofibroblast cell. The second clone type was CD90(-) and could form mature, functional myocytes with sarcomeres albeit at a very low rate. These two populations of cardiogenic clones displayed distinct cell surface markers and unique transcriptomes. Our study suggests that a rare aCPC exists in cardiospheres along with a mesenchymal/myofibroblast cell, which demonstrates incomplete cardiac myocyte differentiation.

Characterization and therapeutic potential of induced pluripotent stem cell-derived cardiovascular progenitor cells.

BACKGROUND: Cardiovascular progenitor cells (CPCs) have been identified within the developing mouse heart and differentiating pluripotent stem cells by intracellular transcription factors Nkx2.5 and Islet 1 (Isl1). Study of endogenous and induced pluripotent stem cell (iPSC)-derived CPCs has been limited due to the lack of specific cell surface markers to isolate them and conditions for their in vitro expansion that maintain their multipotency. METHODOLOGY/PRINCIPAL FINDINGS: We sought to identify specific cell surface markers that label endogenous embryonic CPCs and validated these markers in iPSC-derived Isl1(+)/Nkx2.5(+) CPCs. We developed conditions that allow propagation and characterization of endogenous and iPSC-derived Isl1(+)/Nkx2.5(+) CPCs and protocols for their clonal expansion in vitro and transplantation in vivo. Transcriptome analysis of CPCs from differentiating mouse embryonic stem cells identified a panel of surface markers. Comparison of these markers as well as previously described surface markers revealed the combination of Flt1(+)/Flt4(+) best identified and facilitated enrichment for Isl1(+)/Nkx2.5(+) CPCs from embryonic hearts and differentiating iPSCs. Endogenous mouse and iPSC-derived Flt1(+)/Flt4(+) CPCs differentiated into all three cardiovascular lineages in vitro. Flt1(+)/Flt4(+) CPCs transplanted into left ventricles demonstrated robust engraftment and differentiation into mature cardiomyocytes (CMs). CONCLUSION/SIGNIFICANCE: The cell surface marker combination of Flt1 and Flt4 specifically identify and enrich for an endogenous and iPSC-derived Isl1(+)/Nkx2.5(+) CPC with trilineage cardiovascular potential in vitro and robust ability for engraftment and differentiation into morphologically and electrophysiologically mature adult CMs in vivo post transplantation into adult hearts.