Contribution of PDGFRα lineage cells in adult mouse hematopoiesis

Single-cell transcriptomic profiling of lung fibroblasts in a bleomycin-induced systemic sclerosis mouse model

Systemic sclerosis (SSc) is a complex autoimmune disease characterized by fibrosis, vascular abnormalities, and immune dysfunction, with no definitive cure. Patients with progressive pulmonary fibrosis face a high mortality risk, underscoring the urgent need for effective treatments. Although fibroblasts are recognized as key drivers of fibrosis, the precise molecular mechanisms remain poorly understood. In this study, we employ single-cell RNA sequencing to explore the role of fibroblasts in pulmonary fibrosis. Using a mouse model induced by subcutaneous bleomycin administration, we identify two distinct fibroblast subpopulations: nephronectin-positive (NPNT) and peptidase inhibitor 16-positive cells(PI16). NPNT-positive fibroblasts, located around the alveoli, exhibit increased extracellular matrix expression following bleomycin treatment. To further understand pulmonary fibrosis, subcutaneous and intratracheal bleomycin-induced mouse models are compared. A comparative gene expression analysis reveals shared and unique features between the models, highlighting the complexity of the fibrotic process. These findings offer valuable insights into the molecular mechanisms of SSc-associated pulmonary fibrosis and may inform the development of therapies targeting specific fibroblast subpopulations or pathways.

High-mobility group box 1 fragment ameliorates chronic pancreatitis induced by caerulein in mice

BACKGROUND

Chronic pancreatitis (CP) is a progressive disease characterized by pancreatic fibrosis for which effective treatment options are lacking. Mesenchymal stem cells (MSCs) have shown potential for fibrosis treatment but face limitations in clinical application. The high-mobility group box 1 (HMGB1) fragment mobilizes MSCs from bone marrow into the blood and has emerged as a promising therapeutic agent for tissue regeneration in various pathological conditions. The aim of this study was to investigate the potential therapeutic effects of systemic administration of the HMGB1 fragment in a mouse model of CP.

METHODS

A caerulein-induced CP mouse model was used, and the HMGB1 fragment was administered by tail vein injection. Parameters such as body weight, pancreatic tissue damage, fibrosis, inflammatory cytokine expression, and collagen-related gene expression were evaluated using various assays, including immunohistochemistry, real-time PCR, serum analysis, and single-cell transcriptome analysis. And the migration of MSCs to the pancreas was evaluated using the parabiosis model.

RESULTS

Administration of the HMGB1 fragment was associated with significant improvements in pancreatic tissue damage and fibrosis. It suppressed the expression of inflammatory cytokines and activated platelet-derived growth factor receptor-α+ MSCs, leading to their accumulation in the pancreas. The HMGB1 fragment also shifted gene expression patterns associated with pancreatic fibrosis toward those of the normal pancreas. Systemic administration of the HMGB1 fragment demonstrated therapeutic efficacy in attenuating pancreatic tissue damage and fibrosis in a CP mouse model.

CONCLUSION

These findings highlight the potential of the HMGB1 fragment as a therapeutic target for the treatment of CP.

Lung fibroblasts facilitate pre-metastatic niche formation by remodeling the local immune microenvironment

Primary tumors are drivers of pre-metastatic niche formation, but the coordination by the secondary organ toward metastatic dissemination is underappreciated. Here, by single-cell RNA sequencing and immunofluorescence, we identified a population of cyclooxygenase 2 (COX-2)-expressing adventitial fibroblasts that remodeled the lung immune microenvironment. At steady state, fibroblasts in the lungs produced prostaglandin E2 (PGE2), which drove dysfunctional dendritic cells (DCs) and suppressive monocytes. This lung-intrinsic stromal program was propagated by tumor-associated inflammation, particularly the pro-inflammatory cytokine interleukin-1β, supporting a pre-metastatic niche. Genetic ablation of Ptgs2 (encoding COX-2) in fibroblasts was sufficient to reverse the immune-suppressive phenotypes of lung-resident myeloid cells, resulting in heightened immune activation and diminished lung metastasis in multiple breast cancer models. Moreover, the anti-metastatic activity of DC-based therapy and PD-1 blockade was improved by fibroblast-specific Ptgs2 deletion or dual inhibition of PGE2 receptors EP2 and EP4. Collectively, lung-resident fibroblasts reshape the local immune landscape to facilitate breast cancer metastasis.

PDGFRα-lineage origin directs monocytes to trafficking proficiency to support peripheral immunity

Multiple embryonic precursors give rise to leukocytes in adults while the lineage‐based functional impacts are underappreciated. Mesodermal precursors expressing PDGFRα appear transiently during E7.5‐8.5 descend to a subset of Lin^–Sca1⁺Kit⁺ hematopoietic progenitors found in adult BM. By analyzing a PDGFRα‐lineage tracing mouse line, we here report that PDGFRα‐lineage BM F4/80⁺SSC^lo monocytes/macrophages are solely Ly6C⁺LFA‐1^hiMac‐1^hi monocytes enriched on the abluminal sinusoidal endothelium while Ly6C^–LFA‐1^loMac‐1^lo macrophages are mostly from non‐PDGFRα‐lineage in vivo. Monocytes with stronger integrin profiles outcompete macrophages for adhesion on an endothelial monolayer or surfaces coated with ICAM‐1‐Fc or VCAM‐1‐Fc. Egress of PDGFRα‐lineage‐rich monocytes and subsequent differentiation to peripheral macrophages spatially segregates them from non‐PDGFRα‐lineage BM‐resident macrophages and allows functional specialization since macrophages derived from these egressing monocytes differ in morphology, phenotype, and functionality from BM‐resident macrophages in culture. Extravasation preference for blood PDGFRα‐lineage monocytes varies by tissues and governs the local lineage composition of macrophages. More PDGFRα‐lineage classical monocytes infiltrated into skin and colon but not into peritoneum. Accordingly, transcriptomic analytics indicated augmented inflammatory cascades in dermatitis skin of BM‐chimeric mice harbouring only PDGFRα‐lineage leukocytes. Thus, the PDGFRα‐lineage origin biasedly generates monocytes predestined for BM exit to support peripheral immunity following extravasation and macrophage differentiation.