Depletion of annexin A5, annexin A6, and collagen X causes no gross changes in matrix vesicle–mediated mineralization, but lack of collagen X affects hematopoiesis and the Th1/Th2 response

Abstract

Numerous biochemical studies have pointed to an essential role of annexin A5 (AnxA5), annexin A6 (AnxA6), and collagen X in matrix vesicle-mediated biomineralization during endochondral ossification and in osteoarthritis. By binding to the extracellular matrix protein collagen X and matrix vesicles, annexins were proposed to anchor matrix vesicles in the extracellular space of hypertrophic chondrocytes to initiate the calcification of cartilage. However, mineralization appears to be normal in mice lacking AnxA5 and AnxA6, whereas collagen X-deficient mice show only subtle alterations in the growth plate organization. We hypothesized that the simultaneous lack of AnxA5, AnxA6, and collagen X in vivo induces more pronounced changes in the growth plate development and the initiation of mineralization. In this study, we generated and analyzed mice deficient for AnxA5, AnxA6, and collagen X. Surprisingly, mice were viable, fertile, and showed no obvious abnormalities. Assessment of growth plate development indicated that the hypertrophic zone was expanded in Col10a1 À/À and AnxA5 À/À AnxA6 À/À Col10a1 À/À newborns, whereas endochondral ossification and mineralization were not affected in 13-day-and 1-month-old mutants. In peripheral quantitative computed tomography, no changes in the degree of biomineralization were found in femora of 1-month-and 1-year-old mutants even though the diaphyseal circumference was reduced in Col10a1 À/À and AnxA5 cells and peripheral T-helper cellswere increased in Col10a1 À/À and AnxA5Col10a1 À/À mutants, and activated splenic T cells isolated from Col10a1 À/À mice secreted elevated levels of IL-4 and GM-CSF. Hence, collagen X is needed for hematopoiesis during endochondral ossification and for the immune response, but the interaction of annexin A5, annexin A6, and collagen X is not essential for physiological calcification of growth plate cartilage. Therefore, annexins and collagen X may rather fulfill functions in growth plate cartilage not directly linked to the mineralization process. ß

Label-free quantification proteomics reveals novel calcium binding proteins in matrix vesicles isolated from mineralizing Saos-2 cells

“…Nevertheless, a recent study found that Annexin A5 and Annexin A6-deficient mice developed no abnormal mineralization (34). The same group also found that the depletion of Annexin A5 and Annexin A6 in mice caused no gross changes in MV-mediated mineralization (35). The current results revealed no significant differences in Annexin A1, 2, 4, 5, 6, 7, or 11 expression for MVs from non-stimulated and stimulated cells.…”

Annexins – insights from knockout mice

“…Yet, most important within the context of compensatory effects, upregulation of AnxA2, AnxA6 or AnxA7, all of which with overlapping expression, localization and activity pattern compared to AnxA5, was not observed in the AnxA5 KO mice. Nevertheless, the hypothesis of functional redundancy within the annexin family led to the generation of double KO mice lacking AnxA5 and AnxA6 (Belluoccio et al, 2010;Grskovic et al, 2012), which is described in more detail below (see the section 'AnxA6 KO mice' below; Tables 5 and 6). AnxA5 is believed to be involved in pregnancy loss and thrombosis associated with the antiphospholipid syndrome (Rand et al, 2010).…”

“…It was therefore concluded that AnxA5 and AnxA6 were not essential for mineralization in vivo. As both annexins were speculated to initiate the calcification of cartilage through collagen X-dependent pathways, Grskovic et al generated triple KO mice deficient of AnxA5, AnxA6 and collagen X (Grskovic et al, 2012). However, these mice did not show obvious abnormalities.…”

Bedeutung der extrazellulären Matrix des Knorpels für die Entwicklung und Funktion des Immunsystems

“…Kollagen X wechselwirkt möglicherweise auch mit Annexinen, um Matrixvesikel in der hypertrophen Epiphysenfuge zu platzieren und die Mineralisation zu steuern. In Kollagen-X-defizienten Mäusen ist die Mineralisation allerdings kaum beeinträchtigt ( [5]; . Abb.…”

“…Isolierte T-Zellen waren in vitro nicht zu einer Interleukin(IL)-2-abhängigen Th1-Antwort fähig. Eine starke Th1-Antwort ist aber für die Beseitigung intrazellulärer Infektionen erforderlich; das Ausbleiben einer angemessenen T-Zell-Reaktion in Kollagen-X-defizienten Mäusen könnte entsprechend die erhöhte Mortalität von Mutanten nach einer Infektion mit Toxoplasma gondii erklären [5]. Folglich ruft ein Verlust von Kollagen X, das ausschließlich in hypertrophen Chondrozyten und nicht etwa in Immunzellen exprimiert wird, subtile Defekte in der neonatalen Epiphysenfuge hervor, stört so die Lymphozytendifferenzierung im Knochenmark und beeinträchtigt die T-Zell-Funktion gegen Parasiten in adulten Tieren.…”