title: Processing of CXCL12 by different osteoblast-secreted cathepsins.
abstract: Hematopoietic stem and progenitor cells (HSPCs) are known to reside in specialized niches at the endosteum in the trabecular bone. Osteoblasts are the major cell type of the endosteal niche. It is well established that secreted proteases are involved in cytokine-induced mobilization processes that release stem cell from their niches. However, migratory processes such as the regular trafficking of HSPCs between their niches and the periphery are not fully understood. In the current study we analyzed whether osteoblast-secreted cysteine cathepsins are able to reduce the direct interaction of HSPCs with bone-forming osteoblasts. Isolated human osteoblasts were shown to secrete proteolytically active cysteine cathepsins, such as cathepsins B, K, L, and X. All of these cathepsins were able to digest, although with different efficacy, the chemokine CXCL12, which is known to be important for retaining HSPCs in their niches. Of the 4 identified cathepsins, only cathepsin X was able to reduce binding of HSPCs to osteoblasts. Interestingly, nonactivated pro-cathepsin X and mature cathepsin X did not interfere with HSPC-osteoblast interactions. Only pro-cathepsin X treated with dithiothreitol, which unfolds but does not lead to full maturation of cathepsin X, significantly reduced HSPC adhesion to osteoblasts. These observations argue for a role of the accessible cathepsin X prodomain in diminishing cell binding. Our findings strongly suggest that the cysteine cathepsins B, K, and L constitutively secreted by osteoblasts are part of the fine-tuned regulation of CXCL12 in the bone marrow, whereas pro-cathepsin X with its prodomain can affect HSPC trafficking in the niche.
authors: Section for Transplantation Immunology and Immunohematology, Center for Medical Research, University Medical Clinic, University of Tübingen, Tübingen, Germany.
authors: Nicole D
authors: ND
authors: Staudt
authors: Andreas
authors: A
authors: Maurer
authors: Bärbel
authors: B
authors: Spring
authors: Hubert
authors: H
authors: Kalbacher
authors: Wilhelm K
authors: WK
authors: Aicher
authors: Gerd
authors: G
authors: Klein
mesh_terms: D018952:Antigens, CD34 / Q000737:chemistry; D002401:Cathepsin B / Q000737:chemistry / Q000494:pharmacology; D056657:Cathepsin K / Q000737:chemistry / Q000494:pharmacology; D002403:Cathepsins / Q000737:chemistry* / Q000494:pharmacology; D002448:Cell Adhesion / Q000187:drug effects; D002465:Cell Movement; D060833:Cellular Microenvironment; D054377:Chemokine CXCL12 / Q000737:chemistry*; D017077:Culture Media, Conditioned / Q000737:chemistry; D004229:Dithiothreitol / Q000494:pharmacology; D004789:Enzyme Activation; D057075:Enzyme Assays; D006412:Hematopoietic Stem Cells / Q000737:chemistry / Q000166:cytology / Q000187:drug effects; D006801:Humans; D010006:Osteoblasts / Q000737:chemistry* / Q000166:cytology / Q000187:drug effects; D061251:Primary Cell Culture; D011498:Protein Precursors / Q000737:chemistry* / Q000494:pharmacology; D059748:Proteolysis; D011994:Recombinant Proteins / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013997:Time Factors
chemical_list: D018952:Antigens, CD34; C515255:CXCL12 protein, human; D054377:Chemokine CXCL12; D017077:Culture Media, Conditioned; D011498:Protein Precursors; D011994:Recombinant Proteins; D002403:Cathepsins; C516795:procathepsin X, human; C533912:CTSB protein, human; D002401:Cathepsin B; C534130:CTSK protein, human; D056657:Cathepsin K; D004229:Dithiothreitol