Role of heat shock protein 47 in platelet glycoprotein VI dimerisation and signaling

AlOuda, S. K., Sasikumar, P., AlThunayan, T., Alaajam, F., Khan, S., Sahli, K. A., Abohassan, M. S., Pollitt, A. ORCID: https://orcid.org/0000-0001-8706-5154, Jung, S. M. and Gibbins, J. M. ORCID: https://orcid.org/0000-0002-0372-5352 (2023) Role of heat shock protein 47 in platelet glycoprotein VI dimerisation and signaling. Research and Practice in Thrombosis and Haemostasis, 7 (6). 102177. ISSN 2475-0379 doi: 10.1016/j.rpth.2023.102177

Abstract/Summary

Background: Heat shock protein 47 (HSP47) is an intracellular chaperone protein with an indispensable role in collagen biosynthesis in collagen-secreting cells. This chaperone has also been shown to be released and present on the surface of platelets. The inhibition of HSP47 in human platelets or its ablation in mouse platelets reduces platelet function in response to collagen and the glycoprotein (GP) VI collagen receptor agonist CRP-XL. Aims: In this study we sought, through experiments to explore cellular distribution, trafficking and influence on GPVI interactions, to understand how HSP47 modulates collagen receptor signaling. Results: Using subcellular fractionation analysis and immunofluorescence microscopy HSP47 was found to be localised to the platelet dense tubular system. Following platelet stimulation, HSP47 mobilisation to the cell surface was shown to be dependent on actin polymerisation, a feature in common with other dense tubular system resident platelet proteins that are released to the cell surface during activation. In this location HSP47 was found to contribute to platelet adhesion to collagen or CRP-XL, but not to GFOGER peptide (an integrin α2β1- binding sequence within collagens), indicating selective effects of HSP47 on GPVI function. Dimerization of GPVI on the platelet surface increases its affinity for collagen. GPVI dimerization was reduced following HSP47 inhibition, as was collagen and CRP-XL-mediated signalling. Conclusions: The present study identifies a role for cell surface-localised HSP47 in modulating platelet responses to collagen through dimerization of GPVI, thereby enhancing platelet signalling and activation.