Metabolic dysfunction-associated steatohepatitis (MASH), an advanced stage of metabolic dysfunction-associated steatotic liver disease, is characterized by significant hepatic fibrosis and inflammation. The pan-peroxisome proliferator-activated receptor (pan-PPAR) agonist IVA337 (lanifibranor) has shown potential as an anti-MASH therapeutic, although its mechanisms of action remain incompletely understood. This study explores the effects and mechanisms of IVA337 using two distinct MASH models: two-dimensional (2D) primary human hepatic stellate cells (HSCs) stimulated with transforming growth factor β1 (TGF-β1), and three-dimensional (3D) liver spheroids comprising primary hepatocytes, HSCs, and non-parenchymal cells. In TGF-β1-stimulated HSCs, IVA337 effectively suppressed the expression of fibrosis-related genes, including PAI1, COL1A1, and ACAT2, as well as the inflammatory gene IL6. 3D mouse and human liver spheroid models of MASH, characterized by elevated fibrotic gene expression, were established. IVA337 treatment not only attenuated fibrotic gene expression but also restored lipid content in the MASH spheroids, as evidenced by BODIPY staining. Immunostaining further confirmed a reduction in α-smooth muscle actin and collagen 1 levels after IVA337 treatment. Bulk RNA sequencing and Gene Ontology analysis revealed several lipid metabolism-related genes as key effectors downstream of IVA337. In addition, IVA337 modulated multiple signaling pathways, including IL-17, tumor necrosis factor, NF-κB, phosphatidylinositol 3 kinase/protein kinase B, and mitogen-activated protein kinase. Collectively, these findings show that IVA337 effectively mitigates fibrosis development in both 2D and 3D MASH models by restoring lipid homeostasis and regulating crucial fibrotic and inflammatory pathways.

The immune response of the skin to danger signals involves rapid recruitment of neutrophils, but their excessive accumulation leads to inflammatory skin diseases, such as psoriasis; however, the mechanisms governing their initiation and resolution are poorly understood. Here, we revealed a dynamic immunoregulatory role of dermal white adipose tissue (dWAT) in the progression and resolution of neutrophilic skin inflammation in an imiquimod-induced psoriasis mouse model. During inflammation onset, dWAT repopulates PDGFRA+ preadipocytes (pAds), which secrete CXCL1 and SAA3, attracting and activating CXCR2+ neutrophils. These neutrophils further activate pAds through the IL-1R-NFκB-C/EBPδ pathway, establishing a self-sustaining inflammatory loop. Paradoxically, prolonged IL-1β signaling triggers PPARγ-dependent adipogenesis, transitioning pAds into anti-inflammatory early adipocytes that resolve neutrophilic inflammation via lipid mediators. Inhibition of adipogenesis, via pharmacological or genetic inhibition of PPARγ, disrupts the formation of early adipocytes, prevents neutrophil regression, and exacerbates inflammation. Analysis of human psoriatic cells revealed a C/EBPδ+ dermal fibroblast (dFB) subpopulation enriched with preadipocytes, the IL-1 pathway, and inflammatory gene signatures. Furthermore, transcriptomic analyses revealed a negative correlation between the neutrophil-related inflammatory response and the dermal lipogenesis response in generalized pustular psoriasis. Together, our findings reveal the dual role of dWAT: PDGFRA+ pAds initiate inflammation via CXCL1/IL-1β crosstalk with neutrophils, whereas PPARγ-driven adipogenesis resolves this process through lipid mediators. This work establishes dWAT as a critical immunomodulatory hub and proposes adipogenic reprogramming of proinflammatory fibroblasts or topical delivery of early adipocyte lipids as innovative therapies for neutrophil-driven skin diseases, such as psoriasis and ulcers. Our study uncovers a dynamic immunoregulatory role of dermal white adipose tissue (dWAT) in the progression and resolution of neutrophilic skin inflammation in an imiquimod-induced psoriatic mouse model. Initially, dWAT undergoes lipolysis and expands preadipocytes (pAds) secreting CXCL1/SAA3 to recruit neutrophils, which amplify inflammation via IL1β and activate pAds through the IL1-NFκB-C/EBPδ pathway. Prolonged IL1β exposure triggers PPARγ-dependent differentiation of pAds into early adipocytes, producing anti-inflammatory lipids that resolve neutrophilic inflammation. We also observed a negative correlation between neutrophil-related inflammatory response with dermal lipogenesis is also observed in human psoriasis. These findings highlight dWAT as an immunomodulatory hub, suggesting adipogenic reprogramming or lipid delivery as novel psoriasis therapies.

Aberrant activation of dermal fibroblasts during wound healing often leads to debilitating fibrotic changes in the skin, such as scleroderma and keloids. However, the underlying cellular and molecular mechanisms remain elusive. Here, we established a wound-induced skin fibrosis (WISF) mouse model in mature adult mice, characterised by excessive deposition of collagen bundles, loss of dermal adipocytes, and enrichment of DPP4+Ly6A+THY1+ hypodermal interstitial adipocyte progenitors (HI-APs) and pericytes, resembling human fibrotic skin diseases. This WISF model exhibited an age-dependent gain of fibrotic characteristics, contrasting with the wound-induced hair neogenesis observed in younger mice. Through comprehensive analyses of the WISF, we delineated a trajectory of fibroblast differentiation that originates from HI-APs. These progenitors highly expressed several extracellular matrix (ECM) genes and exhibited a TGFβ pathway signature. TGFβ was identified as the key signal to inhibit the adipogenic potential and maintain the fibrogenic potential of dermal APs. Additionally, administering a TGFβ receptor inhibitor to wound scar reduced the abundance of ECM-producing APs. Finally, analysis of human scleroderma skin tissues revealed a negative correlation between the expression of AP-, ECM-, and TGFβ pathway-related genes and PPARG. Overall, this study establishes a wound-induced skin fibrosis mouse model and demonstrates that TGFβ-mediated blockage of HI-AP differentiation is crucial for driving fibrotic pathology. Targeting HI-APs and adipogenesis may provide novel avenues for developing disease-modifying therapies for fibrotic skin diseases.

The skin’s immune response to danger signals involves rapid recruitment of neutrophils, but their excessive accumulation leads to inflammatory skin diseases, such as psoriasis, and how skin resident cells tolerate neutrophilic inflammation is poorly understood. Dermal white adipose tissue (dWAT) is an emerging component of the skin's immune barrier, but its role in controlling skin inflammation remains under-studied. Here, using an imiquimod-induced psoriasis mouse model, we observed a dynamic coupling between dermal adipogenesis, neutrophil infiltration and regression. During the early inflammatory phase, dWAT repopulates with PDGFRA+ preadipocytes that secrete CXCL1 and SAA3, attracting and activating CXCR2+ neutrophils. These neutrophils further activate preadipocytes through IL1β-IL1R signaling, establishing a self-sustaining inflammatory loop. Prolonged activation of pAds triggers PPARγ-dependent adipogenesis, leading to the formation of early adipocytes that secrete lipids exerting potent anti-inflammatory activity against myeloid cells, thereby aiding in inflammation resolution. Inhibition of adipogenesis, via targeted inhibition of PPARγ, through either pharmacological or genetic approaches, disrupts the formation of early adipocytes and prevents neutrophil regression and inflammation resolution. Analysis of human psoriatic cells identified a dFB subpopulation enriched with preadipocyte, IL1-pathway, and inflammatory gene signatures. Furthermore, transcriptomic analyses revealed a negative correlation between neutrophil-related inflammatory response with dermal adipogenesis response in generalized pustular psoriasis. Together, this study highlights the distinct roles of adipogenic fibroblasts and early adipocytes in initiating and resolving skin inflammation and suggests that promoting the differentiation of proinflammatory fibroblasts into anti-inflammatory early adipocytes could open avenues for the treatment of neutrophil-related inflammatory skin diseases, such as psoriasis and ulcers.

Allergic contact dermatitis (ACD), a prevalent inflammatory skin disease, is elicited upon repeated skin contact with protein-reactive chemicals through a complex and poorly characterized cellular network between immune cells and skin resident cells. Here, single-cell transcriptomic analysis of the murine hapten-elicited model of ACD reveals that upon elicitation of ACD, infiltrated CD4 + or CD8 + lymphocytes were primarily the IFNγ-producing type 1 central memory phenotype. In contrast, type 2 cytokines (IL4 and IL13) were dominantly expressed by basophils, IL17A was primarily expressed by δγ T cells, and IL1β was identified as the primary cytokine expressed by activated neutrophils/monocytes and macrophages. Furthermore, analysis of skin resident cells identified a sub-cluster of dermal fibroblasts with preadipocyte signature as a prominent target for IFNγ + lymphocytes and dermal source for key T cell chemokines CXCL9/10. IFNγ treatment shifted dermal fibroblasts from collagen-producing to CXCL9/10-producing, which promoted T cell polarization toward the type-1 phenotype through a CXCR3-dependent mechanism. Furthermore, targeted deletion of Ifngr1 in dermal fibroblasts in mice reduced Cxcl9/10 expression, dermal infiltration of CD8 + T cell, and alleviated ACD inflammation in mice. Finally, we showed that IFNγ + CD8 + T cells and CXCL10-producing dermal fibroblasts co-enriched in the dermis of human ACD skin. Together, our results define the cell type-specific immune responses in ACD, and recognize an indispensable role of dermal fibroblasts in shaping the development of type-1 skin inflammation through the IFNGR-CXCR3 signaling circuit during ACD pathogenesis.

Here, we present a protocol for isolating human hepatocytes and neural progenitor cells from normal and nonalcoholic steatohepatitis livers. We describe steps for perfusion for scaled-up liver cell isolation and optimization of chemical digestion to achieve maximal yield and cell viability. We then detail a liver cell cryopreservation and potential applications, such as the use of human liver cells as a tool to link experimental and translational research.

Dermal adipocyte lineage cells are highly plastic and can undergo reversible differentiation and dedifferentiation in response to various stimuli. Using single-cell RNA sequencing of developing or wounded mouse skin, we classify dermal fibroblasts (dFBs) into distinct non-adipogenic and adipogenic cell states. Cell differentiation trajectory analyses identify IL-1-NF-κB and WNT-β-catenin as top signaling pathways that positively and negatively associate with adipogenesis, respectively. Upon wounding, activation of adipocyte progenitors and wound-induced adipogenesis are mediated in part by neutrophils through the IL-1R-NF-κB-CREB signaling axis. In contrast, WNT activation, by WNT ligand and/or ablation of Gsk3, inhibits the adipogenic potential of dFBs but promotes lipolysis and dedifferentiation of mature adipocytes, contributing to myofibroblast formation. Finally, sustained WNT activation and inhibition of adipogenesis is seen in human keloids. These data reveal molecular mechanisms underlying the plasticity of dermal adipocyte lineage cells, defining potential therapeutic targets for defective wound healing and scar formation.

Infections are a major complication of obesity, but the mechanisms responsible for impaired defense against microbes are not well understood. Here, we found that adipocyte progenitors were lost from the dermis during diet-induced obesity (DIO) in humans and mice. The loss of adipogenic fibroblasts from mice resulted in less antimicrobial peptide production and greatly increased susceptibility to Staphylococcus aureus infection. The decrease in adipocyte progenitors in DIO mice was explained by expression of transforming growth factor-β (TGFβ) by mature adipocytes that then inhibited adipocyte progenitors and the production of cathelicidin in vitro. Administration of a TGFβ receptor inhibitor or a peroxisome proliferator-activated receptor-γ agonist reversed this inhibition in both cultured adipocyte progenitors and in mice and subsequently restored the capacity of obese mice to defend against S. aureus skin infection. Together, these results explain how obesity promotes dysfunction of the antimicrobial function of reactive dermal adipogenesis and identifies potential therapeutic targets to manage skin infection associated with obesity.