Transferrin uptake by bone marrow macrophages is independent of the degree of iron saturation

Abstract

The uptake of transferrin by macrophages was studied in relation to the degree of iron saturation. Rat bone marrow derived macrophages were incubated with transferrin labelled with 59Fe and 3H. At 37 degrees C the amount of 59Fe incorporated by macrophages was dependent on the time of incubation. 3H labelled transferrin was found degraded in the supernatants of the cell culture (material not precipitated by trichloroacetic acid) in a time dependent fashion. Taking into account the specific activity of 59Fe-3H labelled transferrin, we found that 95% of the transferrin uptake was degraded. This suggests that most of the uptake of transferrin was not mediated by a receptor-dependent mechanism, but by a phase fluid endocytosis. 3H-labelled apotransferrin appears in the supernatant of the cell culture at the same rate as 59Fe-3H labelled diferric transferrin, showing an identical uptake for the two types of transferrin. Uptake of apo- or diferric transferrin by macrophages was identical in relation to time of incubation and the amount of transferrin used. These studies suggest that most of the transferrin uptake by bone marrow macrophages (non-activated or non-elicited cells) is mediated by a non-receptor mechanism that is independent of the degree of transferrin saturation.

Minimizing Laboratory-Induced Decay in Bone Proteomics

“…87 In addition to apolipoproteins (APOA1, APOA2) involved in the plasma transport of lipoproteins, transferrin (TF) and fetuin (AHSG) were also part of this cluster. TF is a plasma protein able to deliver iron to the bone marrow to load newly formed erythrocytes, 88 whereas AHSG is a plasma protein bound to the bone matrix with important functions in regulating bone turnover. 39 The cluster of plasma proteins with coagulation-related functions includes prothrombin (F2), coagulation factors (F9 and F10), fibrinogen alpha and beta chains (FGA and FGB), vitamin K-dependent protein C (PROC), vitamin K-dependent protein S (PROS1), and antithrombin-III (SERPIN C1).…”

Apotransferrin is internalized and distributed in the same way as holotransferrin in K562 cells

“…The inconsistency suggests the existence of different mechanisms involved in the endocytic cycles of apo‐Tf and Fe 2 ‐Tf in different types of cells. Rama and Sanchez (1992) investigated the effect of iron saturation on Tf uptake by rat bone‐marrow‐derived macrophages. They found that the uptake of apo‐Tf or Fe 2 ‐Tf by macrophages is identical in relation to time of incubation and the amount of Tf used.…”

Secretion of growth factors from macrophages when cultured with microparticles

“…Primary murine macrophages from bone marrow are expanded in vitro either by using L929 supernatants or recombinant macrophages–colony stimulating factor (rM‐CSF) or by thioglycolate elicitation from the peritoneum . This study utilized expansion of macrophages from murine bone marrow using L929 supernatants, as this method has been shown to consistently produce high yields of pure macrophage cultures with properties that are similar to those produced using rM‐CSF, which is more expensive . L929 supernatants were obtained using previously established protocols .…”

“…30 This study utilized expansion of macrophages from murine bone marrow using L929 supernatants, as this method has been shown to consistently produce high yields of pure macrophage cultures with properties that are similar to those produced using rM-CSF, which is more expensive. 31,32 L929 supernatants were obtained using previously established ORIGINAL ARTICLE JOURNAL OF BIOMEDICAL MATERIALS RESEARCH A | NOV 2013 VOL 101A, ISSUE 11 protocols. 30 Briefly, L929 cells were cultured in 5 mL RPMI supplemented with 10% FBS, using a T-25 flask.…”