Expression of Cathepsins B, D, and G by the Embryonic Stem Cell–Like Population within Human Keloid Tissues and Keloid-Derived Primary Cell Lines

BACKGROUNDWe have previously shown an embryonic stem cell (ESC)-like population within keloid-associated lymphoid tissues (KALTs) in keloid lesions (KLs) expresses components of the renin-angiotensin system (RAS) which maybe dysregulated. We hypothesized that cathepsin B (cathB), cathepsin D (cathD) and cathepsin G (cathG) are present within the ESC-like population in KLs and contribute to bypass loops of the RAS. METHODS3,3-Diaminobenzidine (DAB) immunohistochemical (IHC) staining for cathB, cathD and cathG was performed on formalin-fixed paraffin-embedded sections in keloid tissue samples (KTS) of 11 patients. Immunofluorescence (IF) IHC staining was performed on three of these KTS, by co-staining with CD34, tryptase, and OCT4. Western blotting (WB), RT-qPCR and enzyme activity assays (EAAs) were performed on five KTS and four keloid-derived primary cell lines (KPCLs) to investigate protein and mRNA expression, and functional activity, respectively. RESULTSDAB IHC staining demonstrated expression of cathB, cathD and cathG in all 15 KTS. IF IHC staining showed localization of cathB and cathD to the endothelium of microvessels within the KALTs, and cathG to the tryptase perivascular cells. WB confirmed semi-quantitative levels of cathB and cathD in KTS and KPCLs. RT-qPCR showed quantitative transcriptional activation of cathB and cathD in KTS and KPCL, and cathG in KTS. EAAs demonstrated functional activity of cathB and cathD. CONCLUSIONCathB, cathD and cathG are expressed by the ESC-like population within the KALTs of KLs and may act to bypass the RAS, suggesting a potential therapeutic target using RAS modulators and cathepsin inhibitors.