APP-CD74 axis mediates endothelial cell-macrophage communication to promote kidney injury and fibrosis

The crucial role of metabolic reprogramming in driving macrophage conversion in kidney disease

Interstitial fibrosis after acute kidney injury is an ongoing pathological process of chronic inflammatory injury and repair. Macrophages participate in renal inflammation, repair and fibrosis by continuously changing their phenotype and function. The tissue microenvironment of kidney injury induces changes in key metabolic enzymes, pathways and metabolites in macrophages, leading to phenotypic and functional conversions, but the detailed mechanisms are unclear. However, in the early phase of acute kidney injury, macrophages shift to a pro-inflammatory role relying on glycolysis and pentose phosphate pathways. The tissue microenvironment regulates the suppression of glycolysis-related genes and the up-regulation of oxidative phosphorylation and tricarboxylic acid cycle genes in macrophages, resulting in a gradual shift to an anti-inflammatory phenotype, which is involved in tissue repair and remodelling. In the late stage of injury, if macrophages continue to be overactive, they will be involved in renal fibrosis. The concomitant enhancement of nucleotide and amino acid metabolism, especially arginine and glutamine metabolism, is critical for the macrophage function and phenotypic transition during the above injury process. Macrophage metabolic reprogramming therefore provides new therapeutic targets for intervention in inflammatory injury and interstitial fibrosis in kidney disease.

Single-cell RNA-seq uncovers lineage-specific regulatory alterations of fibroblasts and endothelial cells in ligamentum flavum hypertrophy

Background

Lumbar spinal stenosis (LSS) represents a major global healthcare burden resulting in back pain and disorders of the limbs among the elderly population. The hypertrophy of ligamentum flavum (HLF), marked by fibrosis and inflammation, significantly contributes to LSS. Fibroblasts and endothelial cells are two important cells in the pathological process of ligamentum flavum (LF) fibrosis and inflammation. These two cells exhibit heterogeneity in various fibrotic diseases, yet their heterogeneity in LF fibrosis remains poorly defined.

Methods

Using single-cell RNA-seq, we examined the alterations of fibroblasts, endothelial cells, and key genes in the hypertrophic LF, aiming to establish a comprehensive single-cell atlas of LF to identify high-priority targets for pharmaceutical treatment of LSS.

Results

Here, we find there are five distinct subpopulations of LF fibroblasts: secretory-papillary, secretory-reticular, mesenchymal, pro-inflammatory, and unknown. Importantly, in HLF, the proportion of mesenchymal fibroblast subpopulations increases significantly compared to normal LF (NLF), reflecting their close association with the pathogenesis of HLF. Furthermore, critical target genes that might be involved in HLF and fibrosis, such as MGP, ASPN, OGN, LUM, and CTSK, are identified. In addition, we also investigate the heterogeneity of endothelial cells and highlight the critical role of AECs subpopulation in LF fibrosis.

Conclusion

This study will contribute to our understanding of the pathogenesis of HLF and offer possible targets for the treatment of fibrotic diseases.

CD47-amyloid-β-CD74 signaling triggers adaptive immunosuppression in sepsis

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. However, how this dysregulation occurs remains to be elucidated. In this study, we use single-cell RNA sequencing (scRNA-seq) and conventional RNA-seq to analyze the immune landscape of sepsis and observe that adaptive immunity is acutely and strongly suppressed. This systemic immunosuppression occurs not only in the peripheral blood but also in all other immune compartments, including the spleen, lymph nodes, and bone marrow. Clinical data show that these adaptive immunity-related genes may have the potential to be used to distinguish patients with sepsis from those with common infections. CD47 is found to play a pivotal role in this immunosuppression by inducing the production of amyloid-β (Aβ), which interacts with CD74 on B cells, leading to B-cell suppression and subsequent adaptive immunosuppression. Blocking CD47-Aβ signaling significantly reduces organ injury and improves the survival rate of septic mice by restoring phagocytic cell functions and alleviating B-cell suppression and adaptive immunosuppression.

Dynamic single-cell transcriptomic reveals the cellular heterogeneity and a novel fibroblast subpopulation in laryngotracheal stenosis

BACKGROUND

Laryngotracheal stenosis (LTS), a pathological narrowing of the upper airway caused by excessive extracellular matrix (ECM) deposition, often leads to dyspnea and even respiratory failure. However, systematic studies addressing the specific subpopulations and their contribution to LTS development still remain underexplored.

RESULTS

We collected laryngotracheal tissue at multiple time points of LTS rat model, established by injuring their laryngotracheal lining, and performed dynamic single-cell RNA sequencing (scRNA-seq) to elucidate the transcriptomic atlas of LTS development. The results showed, from the inflammatory state to the repair/fibrotic state, infiltration of immune cells such as monocyte macrophages decreased and fibroblast increased. We delineated the markers and functional status of different fibroblasts subsets and identified that fibrotic fibroblasts may originate from multiple fibroblast subpopulations, including a new subpopulation characterized by the expression of chondrogenic markers such as Ucma and Col2a1, we designated this subcluster as chondrocyte injury-related fibroblasts (CIRF). Furthermore, we categorized monocytes/macrophages into several subtypes and identified that SPP1 high macrophages represented the largest macrophage subpopulation in LTS, providing evidence to clarify the importance of SPP1 macrophages in fibrosis disease. Our findings also revealed the interactions among these cells to explore the molecular mechanism associated with LTS pathogenesis.

CONCLUSIONS

Our study, for the first time, conducted dynamic scRNA-seq on LTS, revealing the cellular heterogeneity and providing a valuable resource for exploring the intricate molecular landscape of LTS. We propose CIRF may represent a tissue-specific fibroblast lineage in LTS and potentially originate from cells in the perichondrium of the trachea and transform into fibrotic fibroblasts. Integration of our study with those of other respiratory fibrotic diseases will allow for a comprehensive understanding of airway remodeling in respiratory diseases and exploring potential new therapeutic targets for their treatment.