Calcium is essential in the fusion of mouse alveolar macrophages induced by 1 alpha,25-dihydroxyvitamin D3

Calcium-modulated chloride pathways contribute to chloride flux in murine cystic fibrosis-affected macrophages

Cystic fibrosis (CF), a common lethal inherited disorder defined by ion transport abnormalities, chronic infection, and robust inflammation, is the result of mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein, a cAMP-activated chloride (Cl-) channel. Macrophages are reported to have impaired activity in CF. Previous studies suggest that Cl- transport is important for macrophage function; therefore, impaired Cl- secretion may underlie CF macrophage dysfunction. To determine whether alterations in Cl- transport exist in CF macrophages, Cl- efflux was measured using N-[ethoxycarbonylmethyl]- 6-methoxy-quinolinium bromide (MQAE), a fluorescent indicator dye. The contribution of CFTR was assessed by calculating Cl- flux in the presence and absence of cftr(inh)-172. The contribution of calcium (Ca(2+))-modulated Cl- pathways was assessed by examining Cl- flux with varied extracellular Ca(2+) concentrations or after treatment with carbachol or thapsigargin, agents that increase intracellular Ca(2+) levels. Our data demonstrate that CFTR contributed to Cl- efflux only in WT macrophages, while Ca(2+)-mediated pathways contributed to Cl- transport in CF and WT macrophages. Furthermore, CF macrophages demonstrated augmented Cl- efflux with increases in extracellular Ca(2+). Taken together, this suggests that Ca(2+)-mediated Cl- pathways are enhanced in CF macrophages compared with WT macrophages.

Partial characterization of rat marrow stromal cells

Fibroblast-like rat marrow stromal cell (CFU-F) cultures have been characterized in terms of their responsiveness to calciotropic hormones, metal ions, the nonsteroidal antiinflammatory drug, and by their putative paracrine role in the maintenance of active populations of osteoblasts at the marrow-bone interface. These studies indicate that CFU-Fs lack a complete osteoblast signature. Subconfluent CFU-Fs grown in the presence or absence of 10(-7) M dexamethasone lack receptors for PTH and calcitonin, and fail to show enhanced cAMP or cGMP responses to 10(-7) M 1-34 PTH (rat), or any evidence of osteocalcin production [+/- 10(-9) M 1,25-(OH)2D3]. Low concentrations of fluoride [10(-12) and 10(-9) M] stimulated CFU-F grown in vitro in serum-free media, though higher levels (10(-7) and 10(-6) M), inhibited growth in vivo and in vitro. Aluminum (10(-12)-10(-7) M) and ibuprofen (10(-7) M) did not alter normal growth patterns, indicating an action on bone cells more differentiated than CFU-Fs. Serum-free conditioned medium (CM) from control and ovariectomized (OVX)/OVX+ dihydrotachysterol-Rx rat CFU-F cultures was mitogenic for neonatal rat calvarial osteoblasts in vitro, but not for ROS 17/2.8 cells. The studies affirm the mesenchymal-like character of CFU-Fs and project their significant role in sustaining functional endosteal osteogenic cell populations.

Transglutaminase is involved in the fusion of mouse alveolar macrophages induced by 1 alpha, 25-dihydroxyvitamin D3

We have reported that 1 alpha,25-dihydroxyvitamin D3 [1 alpha, 25(OH)2D3] induces fusion of mouse alveolar macrophages directly by a mechanism involving spermidine-dependent protein synthesis (Tanaka, H. et. al., 1989, Exp. Cell Res. 180, 72-83). The macrophage fusion induced by 1 alpha,25(OH)2D3 occurred in a calcium-dependent manner (Jin, C.H. et al., 1988, J. Cell. Physiol. 137, 110-116). In the present study, we examined the possibility that transglutaminase, a calcium-dependent enzyme, is involved in the fusion of macrophages induced by 1 alpha,25(OH)2D3. The activity of transglutaminase increased greatly 12 h after 1 alpha,25(OH)2D3 was ended and reached a maximum at 48 h. Western blot analysis of the cell lysate using an anti-transglutaminase antibody showed that 1 alpha,25(OH)2D3 induced a 77-kDa protein corresponding to transglutaminase. When spermidine synthesis was inhibited by adding methylglyoxal bis(guanylhydrazone) (MGBG), an inhibitor of S-adenosylmethionine decarboxylase, the increase in the transglutaminase synthesis by 1 alpha,25(OH)2D3 was markedly inhibited with concomitant inhibition of fusion. Adding more spermidine restored both the synthesis of transglutaminase and the fusion. The treatment of macrophages with cystamine, an inhibitor of transglutaminase, inhibited the fusion in parallel with the suppression of transglutaminase activity, both induced by 1 alpha,25(OH)2D3. These results clearly indicate that 1 alpha,25(OH)2D3 induces transglutaminase by a spermidine-dependent mechanism and that this enzyme is involved in a biological reaction(s) essential for inducing macrophage fusion.

Fusion of mouse alveolar macrophages induced by 1 alpha,25-dihydroxyvitamin D3 involves extracellular, but not intracellular, calcium

We have reported that the active form of vitamin D3, 1 alpha, 25-dihydroxy-vitamin D3 [1 alpha, 25(OH)2D3], directly induces the fusion of mouse alveolar macrophages (Abe et al: Proc. Natl. Acad. Sci. USA 80:5583-5587, 1983). The fusion process can be divided into two phases: the 1 alpha,25(OH)2D3-dependent priming phase (0-18 hr) and the calcium-dependent progression phase (18-72 hr) (Jin et al: J. Cell. Physiol. 137:110-116, 1988). In the present study, we examined the role of calcium in the progression phase of macrophage fusion induced by 1 alpha,25(OH)2D3. Macrophages pretreated with 1 alpha,25(OH)2D3 for 48 hr in a low-calcium (0.13 mM) medium began to fuse quickly 30 min after the culture medium was switched to a normal calcium (1.85 mM) medium. Of various cations tested, calcium was the most effective in inducing fusion, followed by strontium and manganese. Magnesium, potassium, and sodium had no effect. Calcium ionophores such as A23187 and ionomycin did not induce fusion in the low-calcium medium, nor did they potentiate fusion in the media containing higher concentrations of calcium. The intracellular concentration of free Ca2+, measured by a fluorescent method using fura-2 AM, was 116 +/- 1 nM in the macrophages pretreated with 1 alpha,25(OH)2D3 for 48 hr in the low-calcium medium. When calcium chloride was added to the assay system at a final concentration of 1.85 mM, the cytosolic free Ca2+ concentration did not increase appreciably (from 116 to 144 nM). But the macrophages began to fuse quickly when CaCl2 was added. In contrast, adding ionomycin increased cytosolic free Ca2+ from 116 to 440 nM, but no fusion occurred. These results clearly indicate that the extracellular, but not the intracellular, calcium is involved in the progression phase of the fusion of mouse alveolar macrophages primed by 1 alpha,25(OH)2D3.

Synergistic activation of 2-deoxy-D-glucose uptake in rat and murine peritoneal macrophages by human macrophage colony-stimulating factor-stimulated coupling between transport and hexokinase activity and phorbol-dependent stimulation of pentose phosphate-shunt activity

1. Transport and accumulation of 2-deoxy-D-glucose (2dGlc) in rat and murine peritoneal macrophages were investigated by using C-1-3H-labelled and C-2,6-3H-labelled 2dGlc. 2. There was active accumulation of both C-1- and C-2,6-labelled 2dGlc by quiescent rat and murine macrophages via a phloretin-inhibitable transport system. 3. The rate of uptake and accumulation of 2dGlc (C-1 label) was increased by exposure to human macrophage colony-stimulating factor (mCSF-1) (1000 units/ml) in both murine and rat macrophages. This indicates that mCSF-1 enhances coupling between hexokinase activity and glucose transport at the endofacial surface of the transporter. 4. Phorbol 12-myristate 13-acetate ('phorbol') at 40 nM stimulated 2dGlc in rat macrophages entirely by increasing the C-2,6 label uptake. This indicates that phorbol stimulates 2dGlc uptake mainly by increasing the activity of the pentose phosphate pathway. 5. Simultaneous exposure to phorbol and mCSF-1 stimulates 2dGlc uptake to a greater extent than found with either phorbol or mCSF-1 alone. This result is explained by a simultaneous enhancement of pentose phosphate-pathway activity and of hexokinase activity acting at the endofacial surface of the cell membrane. The dual activation of these serial processes coupled to the loss of the reaction products of the pentose phosphate-shunt pathway from the cells in the form of reactive oxygen intermediates, protons and CO2 could explain the synergistic action of phorbol and mCSF-1 in activation of sugar transport in macrophages.