Bhar, S. | bioRxiv Science

bioRxiv2025

Tissue Kallikrein 1 cleaves complement factor C3 and activates the alternative complement pathway

Hematopoietic stem cell transplant-associated thrombotic microangiopathy (HSCT-TMA), characterized by microvascular endothelial damage and severe renal injury, negatively affects HSCT survivorship with high mortality and long-term renal morbidity. After HSCT, innate immunity and inflammation are often dysregulated. The alternative complement pathway (AP) of the innate immune system is overactivated in HSCT-TMA, but the mechanisms of its initiation are poorly described. Complement component C3 of the AP can be cleaved by proteases outside of the AP. Because mRNA expression of tissue kallikrein 1 (KLK1), an inflammatory serine protease that produces kinins, has been found to be markedly elevated in the renal endothelium of inflamed mice, we hypothesized that increased KLK1 activity during inflammation contributes to AP overactivation and endothelial injury in HSCT-TMA. We assessed AP activation, KLK1 activity, endothelial injury, and renal function in HSCT-TMA experimental models and disease settings and investigated C3 cleavage and AP activation by KLK1. We found that patients with HSCT-TMA had significantly increased AP activation and decreased KLK1 inactivation at TMA diagnosis compared to pre-HSCT. Mice challenged with HSCT-TMA triggers cyclosporine A (CsA) and lipopolysaccharide (LPS) exhibited increased AP activation, renal endothelial injury, and impaired renal function in the setting of decreased KLK1 inactivation. We further demonstrated that KLK1 cleaved AP component C3 to C3b that functionally activated the AP. Our data indicate a noncanonical mechanism for AP activation by KLK1 in settings of HSCT-TMA. Key PointsO_LITissue kallikrein (KLK1) functionally cleaves complement factor C3. C_LIO_LIReduced KLK1 inhibition is associated with activation of the alternative pathway of complement. C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=111 SRC="FIGDIR/small/674260v1_ufig1.gif" ALT="Figure 1"> View larger version (13K): org.highwire.dtl.DTLVardef@8f260aorg.highwire.dtl.DTLVardef@a6511org.highwire.dtl.DTLVardef@7160f6org.highwire.dtl.DTLVardef@194d36d_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical Abstract.C_FLOATNO HSCT-TMA triggers (e.g. inflammation, immunosuppression) upregulate expression of the inflammatory serine protease KLK1, which cleaves C3 to initiate AP activation and amplification, leading to renal endothelial injury. Created with BioRender.com under its Academic License Terms with Baylor College of Medicine. C_FIG

molecular biology↗

bioRxiv2024

Evidence from metagenomic study indicate that subclinical mastitis may have a different pathological origin than clinical mastitis

Bovine mastitis is one of the main causes of low milk production, resulting in significant economic losses for the dairy industry. Therefore, the industry will benefit from the development of strategies for the timely diagnosis of bovine mastitis, especially the sub-clinical sub-type. Here, we analysed the milk metagenome of healthy cows and cows suffering from various forms of mastitis, viz. clinical, sub-clinical and chronic/ recurrent sub-types. We identified Neisseria, Eubacterium and Streptococcus as the key drivers of the change in microbial community structure from a healthy state to a clinical mastitis state. Our results also indicate that the microbiota composition and the probable cause of clinical and recurrent bovine mastitis may not be the same as that of sub-clinical mastitis. Further, the sensory protein load in the sub-clinical mastitis sub-group differed significantly from the other studied categories, wherein Achromobacter, Dickeya, Pectobacterium and Raoultella were identified as the discriminatory features. We also propose ML-based classifiers to screen for bovine mastitis using milk metagenomic samples. The principles elucidated here through the study of mastitis in cows can be applied to other animals and hopefully will benefit the entire dairy industry.

microbiology↗