C3 rho-inhibitor for targeted pharmacological manipulation of osteoclast-like cells.

The C3 toxins from Clostridium botulinum (C3bot) and Clostridium limosum (C3lim) as well as C3-derived fusion proteins are selectively taken up into the cytosol of monocytes/macrophages where the C3-catalyzed ADP-ribosylation of Rho results in inhibition of Rho-signalling and characteristic morphological changes. Since the fusion toxin C2IN-C3lim was efficiently taken up into and inhibited proliferation of murine macrophage-like RAW 264.7 cells, its effects on RAW 264.7-derived osteoclasts were investigated. C2IN-C3lim was taken up into differentiated osteoclasts and decreased their resorption activity. In undifferentiated RAW 264.7 cells, C2IN-C3lim-treatment significantly decreased their differentiation into osteoclasts as determined by counting the multi-nucleated, TRAP-positive cells. This inhibitory effect was concentration- and time-dependent and most efficient when C2IN-C3lim was applied in the early stage of osteoclast-formation. A single-dose application of C2IN-C3lim at day 0 and its subsequent removal at day 1 reduced the number of osteoclasts in a comparable manner while C2IN-C3lim-application at later time points did not reduce the number of osteoclasts to a comparable degree. Control experiments with an enzymatically inactive C3 protein revealed that the ADP-ribosylation of Rho was essential for the observed effects. In conclusion, the results indicate that Rho-activity is crucial during the early phase of osteoclast-differentiation. Other bone cell types such as pre-osteoblastic cells were not affected by C2IN-C3lim. Due to their cell-type selective and specific mode of action, C3 proteins and C3-fusions might be valuable tools for targeted pharmacological manipulation of osteoclast formation and activity, which could lead to development of novel therapeutic strategies against osteoclast-associated diseases

Application of C2IN-C3lim in the early stage of differentiation inhibits osteoclast-formation.

<p>C2IN-C3lim (0.5 and 2µg/mL) was added from day 0 on (A), from day 1 on (B), from day 2 on (C) or at day 0 only with subsequent medium change on day 1 (D). The number of multi-nucleated (at least three nuclei) and TRAP-positive osteoclasts per well (96 well plate) were determined at day 5. </p

Specific and selective uptake of C2IN-C3lim into macrophage-like RAW 264.7 cells.

<p><i>A</i>. ADP-ribosylation status of Rho in RAW 264.7 cells treated with C2IN-C3lim. Cells were incubated with 0.5 or 2 µg/mL of C2IN-C3lim or left untreated for control. The cells were lysed after 6 and 24 h and equal amounts of lysate proteins incubated with fresh C3bot1 and biotin-labelled NAD⁺. The biotinylated, i.e. ADP-ribosylated Rho is shown. Equal amounts of loaded protein were confirmed by Ponceau S staining of the blotted proteins (not shown). <i>B</i>. C2I alone is not taken up into RAW 264.7 cells. Cells were incubated with C2I (2 µg/mL) alone or with C2I (0.4 µg/mL) + C2IIa (0.8 µg/mL) or left untreated for control. After 6 h cells were lysed and equal amounts of lysate proteins incubated with fresh C2I and biotin-labelled NAD⁺. The biotinylated, i.e. ADP-ribosylated actin is shown. Equal amounts of loaded protein were confirmed by Ponceau S staining of the blotted proteins (not shown). <i>C</i>. C2IN-C3lim is not taken up into pre-osteoblastic MC3T3 cells under comparable conditions. Cells were incubated with C2IN-C3lim (5 µg/mL) or with C2IN-C3lim (1 µg/mL) + C2IIa (2 µg/mL) or left untreated for control. After 6 h the cells were lysed and the ADP-ribosylation status of Rho determined as described in A. The biotinylated, i.e. ADP-ribosylated Rho is shown. Equal amounts of loaded protein were confirmed by Ponceau S staining of the blotted proteins (not shown).</p

Effect of C3bot1, C3lim and C2IN-C3lim on RAW 264.7 cells.

<p><i>A</i>. Effect of C3bot1, C3lim and C2IN-C3lim on the morphology of RAW 264.7 cells grown in 12 well plates. Each of the proteins were added in final concentrations of 0.2 µg/mL (= 4 nM C2IN-C3lim, 8 nM C3bot1 or C3lim), 0.6 µg/mL (= 12 nM C2IN-C3lim, 24 nM C3bot1 or C3lim), 2 µg/mL (= 40 nM C2IN-C3lim, 80 nM C3bot1 or C3lim), and 6 µg/mL (= 120 nM C2IN-C3lim, 240 nM C3bot1 or C3lim) into the medium and cells were incubated in the presence of the proteins and pictures were taken from the cells after 24 h. For control, cells were left untreated. The morphology of control cells and C2IN-C3lim-treated cells is shown in the left panel. The percentages of cells displaying the typical “C3-morphology” were calculated from six individual pictures (right panel). The values were given as mean ± S.D. (n = 6). <i>B</i>. Effect of C2IN-C3lim on the proliferation of RAW 264.7 cells. Cells were incubated in 96 well plates with 0.6 and 2 µg/mL C2IN-C3lim or left untreated for control. After 24, 48 and 72 h pictures from the cells were taken and the total number of cells determined from 3 different pictures (left panel). The values were given as mean ± S.D. (n = 3). Significance was determined by student’s t-test for cells treated with the respective C3 protein against untreated (*** = p<0.001; ** = p<0.01; * = p<0. 1; n.s. = not significant). Alternatively, RAW 264.7 cells grown in 96 well plates were incubated with 0.6 and 2 µg/mL C2IN-C3lim or left untreated for control. After 24, 48 and 72 h the amount of viable cells was determined by MTT test (mid panel). The values are given in percent from control cells as mean ± S.D. (n = 3). Right panel: The values for 72 h C2IN-C3lim are given in percent from the values after 24 h C2IN-C3lim-treatment with the respective concentration of C2IN-C3lim. <i>C</i>. Effect of C3bot1E174Q on the morphology of RAW 264.7 cells. RAW 264.7 cells grown in 96 well plates were incubated for up to 72 h with 20 µg/mL (= 800 nM) C3bot1E174Q or left untreated for control. Pictures from the cells were taken and the percentages of cells displaying “C3-morphology” calculated from three individual pictures. The values were given as mean ± S.D. (n = 3). Significance was determined by student’s t-test for cells treated with C3bot1E174Q against untreated (n.s. = not significant).</p

Uptake of C2IN-C3lim into differentiating osteoclasts and morhophological changes caused by C2IN-C3lim.

<p>RAW264.7 cells which were grown in the presence of RANKL to induce differentiation to osteoclasts. Cells were left untreated for control (A) or treated with C2IN-C3lim (2 µg/mL) at day 0 and 2 (B and C). At day 5, osteoclasts were stained for actin (red), nuclei (blue) and C3 (green) and cells analyzed by phase contrast microscopy (left row) and fluorescence microscopy. </p

Effect of C2IN-C3lim on osteoclast-formation.

<p>C2IN-C3lim (0.5 and 2µg/mL) was added to RAW264.7 cells from day 0 on and cells were treated with RANKL. For control, cells were treated with RANKL in the absence of C2IN-C3lim. At day 5, osteoclasts were stained for tartrate-resistant acid phosphatase. Osteoclasts formed in the absence (A) and presence of increasing concentration of C2IN-C3lim (B: 0.5 µg/mL; C: 2 µg/mL) are shown.</p