Basement membrane of mouse bone marrow sinusoids shows distinctive structure and proteoglycan composition: A high resolution ultrastructural study

Abstract

Venous sinusoids in bone marrow are the site of a large-scale traffic of cells between the extravascular hemopoietic compartment and the blood stream. The wall of the sinusoids consists solely of a basement membrane interposed between a layer of endothelial cells and an incomplete covering of adventitial cells. To examine its possible structural specialization, the basement membrane of bone marrow sinusoids has now been examined by high resolution electron microscopy of perfusion-fixed mouse bone marrow. The basement membrane layer was discontinuous, consisting of irregular masses of amorphous material within a uniform 60-nm-wide space between apposing endothelial cells and adventitial cell processes. At maximal magnifications, the material was resolved as a random arrangement of components lacking the "cord network" formation seen in basement membranes elsewhere. Individual components exhibited distinctive ultrastructural features whose molecular identity has previously been established. By these morphological criteria, the basement membrane contained unusually abundant chondroitin sulfate proteoglycan (CSPG) revealed by 3-nm-wide "double tracks," and moderate amounts of both laminin as dense irregular coils and type IV collagen as 1-1.5-nm-wide filaments, together with less conspicuous amounts of amyloid P forming pentagonal frames. In contrast, 4.5-5-nm-wide "double tracks" characteristic of heparan sulfate proteoglycan (HSPG) were absent. The findings demonstrate that, in comparison with "typical" basement membranes in other tissues, the bone marrow sinusoidal basement membrane is uniquely specialized in several respects. Its discontinuous nature, lack of network organization, and absence of HSPG, a molecule that normally helps to maintain membrane integrity, may facilitate disassembly and reassembly of basement membrane material in concert with movements of adventitial cell processes as maturing hemopoietic cells pass through the sinusoidal wall: the exceptionally large quantity of CSPG may represent a reservoir of CD44 receptor for use in hemopoiesis. Anat Rec 264: 294 -304, 2001.

Leukocyte extravasation: chemokine transport and presentation by the endothelium

“…However, this can vary since mouse bone marrow venous sinusoids show unusually abundant chondroitin sulfate proteoglycan and an absence of heparan sulfate proteoglycan. 47 Altered expression in the type of blood vessel GAG has been observed in several pathological and physiological situations, such as atherosclerosis, inflammatory bowel disease, and wound healing. 48,49 For example, in the intima of atherosclerotic human aortas, there is a decrease in the proportion of heparan sulfate and an increase in the proportions of chondoitin and dermatan sulfate, which are produced by smooth muscle cells.…”

CXCR2 and CXCR4 antagonistically regulate neutrophil trafficking from murine bone marrow

“…Neutrophil homeostasis is maintained through a balance of neutrophil production, release from the bone marrow, and clearance from the circulation (1). The bone marrow is the primary site of neutrophil production, requiring that mature neutrophils transmigrate through an endothelial cell barrier to enter the circulation (2)(3)(4). Under basal conditions, less than 2% of the total body of mature neutrophils is in the circulation (5).…”

Programmable 3D silk bone marrow niche for platelet generation ex vivo and modeling of megakaryopoiesis pathologies

“…The walls of the sinusoids consist solely of a layer of endothelial cells on a discontinuous basement membrane. 8 Endothelial cells and extracellular matrix (ECM) components are important for the maintenance of correct hematopoiesis. [9][10][11] In the bone marrow, platelets are generated by megakaryocytes (Mks) that associate with the bone marrow vasculature, where they convert their cytoplasm into proplatelets that protrude through the vascular endothelium and release platelets into the lumen.…”