Dissection of platelet and myeloid cell defects by conditional targeting of the β3‐integrin subunit

Abstract

The purpose of this work was to determine platelet and myeloid cell-specific requirements for beta3-containing integrins in hemostasis, bone resorption, and tumor growth. LoxP-flanked mice were generated to study the conditional deletion of beta3-integrin in platelets [knockout in platelets (KOP)] and myeloid cells [knockout in myeloid (KOM)]. Using the beta3KOP and beta3KOM strains of mice, we studied the role of beta3-integrin in hemostasis, bone resorption, and subcutaneous tumor growth. Tissue-specific deletion of platelet beta3-integrins in beta3KOP mice did not affect bone mass but resulted in a severe bleeding phenotype. No growth difference of tumor xenografts or in neoangiogenesis were found in beta3KOP mice, in contrast to the defects observed in germline beta3(-/-) mice. Conditional deletion of myeloid beta3-integrins in beta3KOM mice resulted in osteopetrosis but had no effect on hemostasis or mortality. Tumor growth in beta3KOM mice was increased and accompanied by decreased macrophage infiltration, without increase in blood vessel number. Platelet beta3-integrin deficiency was sufficient to disrupt hemostasis but had no effect on bone mass or tumor growth. Myeloid-specific beta3-integrin deletion was sufficient to perturb bone mass and enhance tumor growth due to reduced macrophage infiltration in the tumors. These results suggest that beta3-integrins have cell-specific roles in complex biological processes.-Morgan, E. A., Schneider, J. G., Baroni, T. E., Uluçkan, O., Heller, E., Hurchla, M. A., Deng, H., Floyd, D., Berdy, A., Prior, J. L., Piwnica-Worms, D., Teitelbaum, S. L., Ross, F. P., Weilbaecher, K. N. Dissection of platelet and myeloid cell defects by conditional targeting of the beta3-integrin subunit.

Glanzmann thrombasthenia: a review of ITGA2B and ITGB3 defects with emphasis on variants, phenotypic variability, and mouse models

“…97 Morgan et al, using Cre/loxP technology in mice, showed that conditional depletion of myeloid ␤3-integrins (including from osteoclasts), but not from platelets, resulted in osteopetrosis (with significant increases in trabecular bone volume) but no bleeding. 8 Tumor growth in these mice was also increased and accompanied by decreased macrophage infiltration confirming an earlier study. 8,98 This strongly underlines how ␤3-integrins have cell-specific roles.…”

“…8 Tumor growth in these mice was also increased and accompanied by decreased macrophage infiltration confirming an earlier study. 8,98 This strongly underlines how ␤3-integrins have cell-specific roles. Interestingly, osteopetrosis appears more of a problem in LAD-3 disease, a finding linked to the role for kindlin-3 in activation of 3 integrin classes (␤1, ␤2, and ␤3) expressed on osteoclasts and abrogating the formation of podosomes and sealing zones required for bone resorption.…”

“…Dissection of platelet and myeloid cell defects by conditional targeting of the ␤3-integrin subunit in mice has confirmed that platelet deletion of ␣IIb␤3 alone accounts for the perturbed hemostasis. 8 Yet, the reasons why some patients bleed more frequently than others remain elusive.…”

Acute Depletion of Endothelial β3-Integrin Transiently Inhibits Tumor Growth and Angiogenesis in Mice

“…Furthermore, β3-floxed/ Pf4Cre (a platelet-specific Cre) 27 mice do not show any significant effects on tumor growth. 17 More importantly, Tie1 is expressed by a small proportion (≈20%) of BMD hematopoietic cell lineages 21 (as opposed to other constitutive endothelial-specific Cre models, such as Tie2Cre, which is reportedly expressed in ≈80%). 28 We examined β3-integrin expression in BMDCs from both Cre models.…”

“…The current strategies have proven to be somewhat disappointing with many tumors either not responding to or becoming resistant to β3-integrin-directed therapy. 16 Because this is of such fundamental importance, we have re-evaluated the function of β3-integrin in tumor angiogenesis by crossing β3-floxed mice 17 to 2 different endothelial-specific Cre lines-lines we have used separately in the past to elucidate the role of other endothelial integrins 18,19 and focal adhesion kinase (FAK) 20 in tumor angiogenesis. Tie1Cre 21 constitutively depletes floxed targets in endothelial cells, thereby creating a cell-specific mimic of a global knockout, whereas Pdgfb-iCreER T2 (see Claxton et al 22 ) depletes floxed targets in endothelial cells in a 4-hydroxy-tamoxifen (OHT)-inducible fashion (a model more akin to antagonist administration).…”