Abnormal Lymphatic Sphingosine-1-Phosphate Signaling Aggravates Lymphatic Dysfunction and Tissue Inflammation

Insulin regulates lymphatic endothelial integrity via palmitoylation

Lipid metabolism plays a critical role in lymphatic endothelial cell (LEC) development and vessel maintenance. Altered lipid metabolism is associated with loss of lymphatic vessel integrity, which compromises organ function, protective immunity, and metabolic health. Thus, understanding how lipid metabolism affects LECs is critical for uncovering the mechanisms underlying lymphatic dysfunction. Protein palmitoylation, a lipid-based post-translational modification, has emerged as a critical regulator of protein function, stability, and interaction networks. Insulin, a master regulator of systemic lipid metabolism, also regulates protein palmitoylation. However, the role of insulin-driven palmitoylation in LEC biology remains unexplored. To examine the role of palmitoylation in LEC function, we generated the first palmitoylation proteomics profile in human LECs, validated insulin-regulated targets, and determined the role of palmitoylation in LEC barrier function. In unstimulated conditions, palmitoylation occurred primarily on proteins involved in vesicular and membrane trafficking, and in translation initiation. Insulin treatment, instead, enriched palmitoylation of proteins involved in LEC integrity, namely junctional proteins such as claudin 5, along with small GTPases and ubiquitination enzymes. We also investigated the role of the long-chain fatty acid transporter CD36, a major mediator of palmitate uptake into cells, in regulating optimal lymphatic protein palmitoylation. CD36 silencing in LECs increased by 2-fold palmitoylation of proteins involved in inflammation and immune cell activation. Overall, our findings provide novel insights into the intricate relationship between lipid modification and LEC function, suggesting that insulin and palmitoylation play a critical role in lymphatic endothelial function.

Exploring the molecular mechanisms by which secretory phospholipase a2 regulates lymphatic endothelial cell dysfunction by activating macrophages

This study offers new insights into the dual role of secretory phospholipase A2 (sPLA2) in lymphedema, highlighting its impact on lymphatic endothelial cell (LEC) functionality. Through transcriptomic analyses and co-culture experiments, we observed that sPLA2 has both protective and detrimental effects on human LECs (HLECs), mediated by macrophage activation. Our findings reveal that while low levels of sPLA2 promote LEC health, excessive sPLA2 leads to dysfunction, emphasizing the significance of the sPLA2/PLA2R axis and arachidonic acid metabolism (AA) in lymphedema pathology. The study suggests targeting sPLA2 and its downstream pathways as a novel therapeutic strategy for lymphedema, aiming to mitigate its progression by safeguarding HLEC integrity. This research underscores the importance of balanced sPLA2 activity in maintaining lymphatic vessel health and presents a new avenue for lymphedema management and treatment.

Leukocyte-lymphatic intersections during cardiac inflammation

Advances in genetic, pharmacologic, and sequencing technology have led to new insight into the role of lymphatics in health and disease. This includes fundamental aspects of the crosstalk between immune cells with cardiac lymphatics. At the interface between leukocytes and lymphatic endothelial cells, myeloid populations are sources of lymphatic growth factors during inflammation. Lymphatic endothelial cells also secrete signals that activate leukocytes, including to antigen presenting cells. Taken together, a view of the lymphatic vasculature as a supplemental cardiac immune hub is emerging. Herein, we discuss reciprocal cell and molecular crosstalk between leukocytes and lymphatics in the myocardium, with implications for health and cardiac inflammation.

The emerging importance of lymphangiogenesis in aging and aging-associated diseases

Lymphatic aging represented by cellular and functional changes, is involved in increased geriatric disorders, but the intersection between aging and lymphatic modulation is less clear. Lymphatic vessels play an essential role in maintaining tissue fluid homeostasis, regulating immune function, and promoting macromolecular transport. Lymphangiogenesis and lymphatic remodeling following cellular senescence and organ deterioration are crosslinked with the progression of some lymphatic-associated diseases, e.g., atherosclerosis, inflammation, lymphoedema, and cancer. Age-related detrimental tissue changes may occur in lymphatic vessels with diverse etiologies, and gradually shift towards chronic low-grade inflammation, so-called inflammaging, and lead to decreased immune response. The investigation of the relationship between advanced age and organ deterioration is becoming an area of rapidly increasing significance in lymphatic biology and medicine. Here we highlight the emerging importance of lymphangiogenesis and lymphatic remodeling in the regulation of aging-related pathological processes, which will help to find new avenues for effective intervention to promote healthy aging.

Bioactive sphingolipids as emerging targets for signal transduction in cancer development

Sphingolipids, crucial components of cellular membranes, play a vital role in maintaining cellular structure and signaling integrity. Disruptions in sphingolipid metabolism are increasingly implicated in cancer development. Key bioactive sphingolipids, such as ceramides, sphingosine-1-phosphate (S1P), ceramide-1-phosphate (C1P), and glycosphingolipids, profoundly impact tumor biology. They influence the behavior of tumor cells, stromal cells, and immune cells, affecting tumor aggressiveness, angiogenesis, immune modulation, and extracellular matrix remodeling. Furthermore, abnormal expression of sphingolipids and their metabolizing enzymes modulates the secretion of tumor-derived extracellular vesicles (TDEs), which are key players in creating an immunosuppressive tumor microenvironment, remodeling the extracellular matrix, and facilitating oncogenic signaling within in situ tumors and distant pre-metastatic niches (PMNs). Understanding the role of sphingolipids in the biogenesis of tumor-derived extracellular vesicles (TDEs) and their bioactive contents can pave the way for new biomarkers in cancer diagnosis and prognosis, ultimately enhancing comprehensive tumor treatment strategies.