Streicher, Anna
[Verfasser:in]
;
Lausch, Ekkehart
[Akademische:r Betreuer:in]Albert-Ludwigs-Universität Freiburg Fakultät für Biologie,
Professur für Entwicklungsbiologie der Tiere
Potassium channel Kir6.1 is associated with the progression of hereditary multiple osteochondromas
Hochschulschrift:
Dissertation, Universität Freiburg, 2022
Anmerkungen:
Beschreibung:
Abstract: Multiple osteochondromas (MO) are benign cartilage-capped tumors believed to originate from the perichondrium of long bones. The most severe complication of MO is malignant transformation of an osteochondroma into a radiation-resistant secondary peripheral chondrosarcoma. Most MO patients harbor heterozygous mutations in either exostosin-1 (EXT1) or exostosin-2 (EXT2). Both genes code for glycosyltransferases catalyzing heparan sulfate (HS) proteoglycan biosynthesis. A defect in either of these two enzymes results in loss of HS molecules in the extracellular matrix of chondrocytes and bone cells. This reduction of HS chains alters binding of numerous extracellular signaling molecules which in turn leads to disruption of key downstream signaling pathways. Whereas in MO mouse models it has already been shown that tumor formation is caused by enhanced BMP signaling and altered differentiation of cells in the perichondrium, the underlying mechanism of malignant progression is still unknown. There is evidence for both EXT-dependent signaling alterations and involvement of genes alternative to EXT forcing tumor progression. This study was aimed to unravel the molecular mechanism driving malignant transformation of osteochondroma into chondrosarcoma. <br>To this end, human dermal fibroblasts isolated from MO patients and selected controls were trans-differentiated into chondrocyte-like cells. Studying this in vitro model, aberrant BMP signaling and altered chondrogenesis was confirmed in patient cells and was efficiently rescued by the RARγ selective agonist palovarotene. This result was consistent with previous findings in EXT-deficient mice. To unravel candidate genes involved in malignant transformation, RNA-seq was performed on total RNA isolated from human benign and malignant tumor tissues. Differential expression analysis revealed that both KCNJ8 (coding for Kir6.1 proteins) and ABCC9 (coding for SUR2 subunits of Kir6.1 potassium channel) were strongly induced in chondrosarcomas. In addition, upregulation of both KCNJ8 and ABCC9 was confirmed in tumor samples and in our in vitro chondrogenesis model by real-time quantitative PCR. Using the SUR2 potassium channel inhibitor glibenclamide, upregulated BMP signaling could be reversed in patient-derived chondrogenic cells suggesting an involvement of Kir6.1 in maintaining BMP signal transduction. Interestingly, TGF-ß/BMP signaling was capable to induce KCNJ8 expression in patient cells. This may in turn lead to accumulation of Kir6.1 protein and enhanced channel activity. Finally, patient cells displayed normal proliferation but elevated wound healing capacity. Since alterations in wound healing of patient cells were also rescued by glibenclamide we hypothesized that Kir6.1 may play a role in epithelial-mesenchymal transformation (EMT) and thus contribute to MO progression.<br>For the first time, current findings from MO mouse models were confirmed in a human primary cell model. Furthermore, the results indicated that ATP-sensitive K+ channel Kir6.1 is a potential therapeutic target in MO progression. Since Kir6.1 channel activity may be involved in the regulation of BMP signaling and TGF-ß/BMP signaling seems to promote KCNJ8 expression, we postulated that TGF-ß/BMP signaling and Kir6.1 may be part of a feedback loop which is highly dysregulated in MO. This work thus did not only provide novel insights into MO pathogenesis but also into potassium channel function and bone development. In addition, potassium channel inhibitors such as glibenclamide may be promising for MO tumor treatment