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Control of mitochondrial motility and distribution by the calcium signal: a homeostatic circuit.

Yi M, Weaver D, Hajnóczky G - J. Cell Biol. (2004)

Bottom Line: By clamping cytoplasmic [Ca2+] ([Ca2+]c) at various levels, mitochondrial motility was found to be regulated by Ca2+ in the physiological range.The inositol 1,4,5-trisphosphate- or ryanodine receptor-mediated [Ca2+]c signal also induced a decrease in mitochondrial motility.This decrease followed the spatial and temporal pattern of the [Ca2+]c signal.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA.

ABSTRACT
Mitochondria are dynamic organelles in cells. The control of mitochondrial motility by signaling mechanisms and the significance of rapid changes in motility remains elusive. In cardiac myoblasts, mitochondria were observed close to the microtubular array and displayed both short- and long-range movements along microtubules. By clamping cytoplasmic [Ca2+] ([Ca2+]c) at various levels, mitochondrial motility was found to be regulated by Ca2+ in the physiological range. Maximal movement was obtained at resting [Ca2+]c with complete arrest at 1-2 microM. Movement was fully recovered by returning to resting [Ca2+]c, and inhibition could be repeated with no apparent desensitization. The inositol 1,4,5-trisphosphate- or ryanodine receptor-mediated [Ca2+]c signal also induced a decrease in mitochondrial motility. This decrease followed the spatial and temporal pattern of the [Ca2+]c signal. Diminished mitochondrial motility in the region of the [Ca2+]c rise promotes recruitment of mitochondria to enhance local Ca2+ buffering and energy supply. This mechanism may provide a novel homeostatic circuit in calcium signaling.

Show MeSH
Control of mitochondrial motility by [Ca2+]c oscillations and waves. Mitochondrial motility was evaluated simultaneously with [Ca2+]c in cells cotransfected with constructs encoding mitoYFP and RyR1 and loaded with fura2. To promote RyR-mediated Ca2+ mobilization, the cells were exposed to 10 mM of caffeine (Caff). (A) In the image series, mitochondrial movements are visualized in a cell that showed [Ca2+]c oscillations in response to stimulation by Caff (arrow) and in a cell that did not show a Caff-induced [Ca2+]c rise (top left corner) as described for Fig. 1. Also shown is the effect of 100 nM VP that elicited a [Ca2+]c signal in both cells. The time course of [Ca2+]c (black trace) and mitochondrial motility (red trace) for the Caff-sensitive cell is plotted. (B) Sustained inhibition of mitochondrial motility in a cell that displayed a relatively high frequency [Ca2+]c oscillation in response to stimulation by Caff. (C) Calcium waves were induced in mitoYFP-expressing cells by treatment with 75 μM thimerosal (TM) and 0.1 nM VP. The image series shows the mitoYFP fluorescence (i) and the first two calcium waves after addition of VP and TM (t = 60 s; ii–ix). The first wave begins simultaneously at the ends of the cell and converges in the center as indicated by the arrows (iv). The second wave begins at the lower end of the cell and weakens as it propagates to the top (vi–viii, arrow marks the direction of the wave propagation in vii). Measurement of [Ca2+]c (x) and mitochondrial movement (ix) in three distinct regions of the cell, labeled 1–3 in panel ii, reveals spatio-temporal heterogeneity in the inhibition of movement corresponding to the local calcium concentration.
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fig4: Control of mitochondrial motility by [Ca2+]c oscillations and waves. Mitochondrial motility was evaluated simultaneously with [Ca2+]c in cells cotransfected with constructs encoding mitoYFP and RyR1 and loaded with fura2. To promote RyR-mediated Ca2+ mobilization, the cells were exposed to 10 mM of caffeine (Caff). (A) In the image series, mitochondrial movements are visualized in a cell that showed [Ca2+]c oscillations in response to stimulation by Caff (arrow) and in a cell that did not show a Caff-induced [Ca2+]c rise (top left corner) as described for Fig. 1. Also shown is the effect of 100 nM VP that elicited a [Ca2+]c signal in both cells. The time course of [Ca2+]c (black trace) and mitochondrial motility (red trace) for the Caff-sensitive cell is plotted. (B) Sustained inhibition of mitochondrial motility in a cell that displayed a relatively high frequency [Ca2+]c oscillation in response to stimulation by Caff. (C) Calcium waves were induced in mitoYFP-expressing cells by treatment with 75 μM thimerosal (TM) and 0.1 nM VP. The image series shows the mitoYFP fluorescence (i) and the first two calcium waves after addition of VP and TM (t = 60 s; ii–ix). The first wave begins simultaneously at the ends of the cell and converges in the center as indicated by the arrows (iv). The second wave begins at the lower end of the cell and weakens as it propagates to the top (vi–viii, arrow marks the direction of the wave propagation in vii). Measurement of [Ca2+]c (x) and mitochondrial movement (ix) in three distinct regions of the cell, labeled 1–3 in panel ii, reveals spatio-temporal heterogeneity in the inhibition of movement corresponding to the local calcium concentration.

Mentions: Our data have shown that the control of mitochondrial motility can respond to repetitive stimulation by an IP3-linked agonist (Fig. 2 C). Along this line, Fig. 3 B shows that the [Ca2+]c rise-induced inhibition of mitochondrial movement can be reversed by termination of the [Ca2+]c elevation and subsequently, reproduced by a second step of [Ca2+]c elevation. This suggests that no desensitization of the Ca2+ regulation of mitochondrial motility occurred. If there is no desensitization and the reversal of the movement inhibition is slower than the decay of the [Ca2+]c spike, [Ca2+]c oscillations may be able to cause a prolonged depression of mitochondrial motility. In differentiated H9c2 myotubes, RyR-mediated [Ca2+]c oscillations have been demonstrated (Szalai et al., 2000). As shown in Fig. 4, [Ca2+]c oscillations were also observed in H9c2 myoblasts transfected with RyR1 (Bhat et al., 1997) and stimulated with caffeine (Caff). Similar to the IP3-linked [Ca2+]c spikes, the RyR-mediated [Ca2+]c spikes also triggered inhibition of mitochondrial motility and the oscillations of [Ca2+]c were often associated with oscillations in movement activity (Fig. 4 A, cell marked by an arrow). Each burst of RyR1-mediated Ca2+ release could result in maximal inhibition of mitochondrial motility (Fig. 4, A and B). Isolated spikes of mitochondrial movement inhibition were observed during low frequency [Ca2+]c oscillations (unpublished data). However, if the frequency of [Ca2+]c spiking was higher and the recovery of motility was slow, [Ca2+]c oscillations could produce an essentially sustained maximal inhibition in movement activity (Fig. 4 B). Thus the frequency-modulated [Ca2+]c signals are translated into a time-averaged motility response. Notably, at supramaximal stimulation the [Ca2+]c oscillations run together and fuse into a large and slowly decaying single [Ca2+]c spike (Szalai et al., 2000), but this [Ca2+]c signal could not provide for sustained inhibition of the mitochondrial motility (e.g., Fig. 1 B). In this way, the control of mitochondrial motility may serve as a model whereby [Ca2+]c oscillations are an effective signal for long-term modulation, but a nonoscillatory [Ca2+]c signal is unable to maintain inhibition.


Control of mitochondrial motility and distribution by the calcium signal: a homeostatic circuit.

Yi M, Weaver D, Hajnóczky G - J. Cell Biol. (2004)

Control of mitochondrial motility by [Ca2+]c oscillations and waves. Mitochondrial motility was evaluated simultaneously with [Ca2+]c in cells cotransfected with constructs encoding mitoYFP and RyR1 and loaded with fura2. To promote RyR-mediated Ca2+ mobilization, the cells were exposed to 10 mM of caffeine (Caff). (A) In the image series, mitochondrial movements are visualized in a cell that showed [Ca2+]c oscillations in response to stimulation by Caff (arrow) and in a cell that did not show a Caff-induced [Ca2+]c rise (top left corner) as described for Fig. 1. Also shown is the effect of 100 nM VP that elicited a [Ca2+]c signal in both cells. The time course of [Ca2+]c (black trace) and mitochondrial motility (red trace) for the Caff-sensitive cell is plotted. (B) Sustained inhibition of mitochondrial motility in a cell that displayed a relatively high frequency [Ca2+]c oscillation in response to stimulation by Caff. (C) Calcium waves were induced in mitoYFP-expressing cells by treatment with 75 μM thimerosal (TM) and 0.1 nM VP. The image series shows the mitoYFP fluorescence (i) and the first two calcium waves after addition of VP and TM (t = 60 s; ii–ix). The first wave begins simultaneously at the ends of the cell and converges in the center as indicated by the arrows (iv). The second wave begins at the lower end of the cell and weakens as it propagates to the top (vi–viii, arrow marks the direction of the wave propagation in vii). Measurement of [Ca2+]c (x) and mitochondrial movement (ix) in three distinct regions of the cell, labeled 1–3 in panel ii, reveals spatio-temporal heterogeneity in the inhibition of movement corresponding to the local calcium concentration.
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Related In: Results  -  Collection

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fig4: Control of mitochondrial motility by [Ca2+]c oscillations and waves. Mitochondrial motility was evaluated simultaneously with [Ca2+]c in cells cotransfected with constructs encoding mitoYFP and RyR1 and loaded with fura2. To promote RyR-mediated Ca2+ mobilization, the cells were exposed to 10 mM of caffeine (Caff). (A) In the image series, mitochondrial movements are visualized in a cell that showed [Ca2+]c oscillations in response to stimulation by Caff (arrow) and in a cell that did not show a Caff-induced [Ca2+]c rise (top left corner) as described for Fig. 1. Also shown is the effect of 100 nM VP that elicited a [Ca2+]c signal in both cells. The time course of [Ca2+]c (black trace) and mitochondrial motility (red trace) for the Caff-sensitive cell is plotted. (B) Sustained inhibition of mitochondrial motility in a cell that displayed a relatively high frequency [Ca2+]c oscillation in response to stimulation by Caff. (C) Calcium waves were induced in mitoYFP-expressing cells by treatment with 75 μM thimerosal (TM) and 0.1 nM VP. The image series shows the mitoYFP fluorescence (i) and the first two calcium waves after addition of VP and TM (t = 60 s; ii–ix). The first wave begins simultaneously at the ends of the cell and converges in the center as indicated by the arrows (iv). The second wave begins at the lower end of the cell and weakens as it propagates to the top (vi–viii, arrow marks the direction of the wave propagation in vii). Measurement of [Ca2+]c (x) and mitochondrial movement (ix) in three distinct regions of the cell, labeled 1–3 in panel ii, reveals spatio-temporal heterogeneity in the inhibition of movement corresponding to the local calcium concentration.
Mentions: Our data have shown that the control of mitochondrial motility can respond to repetitive stimulation by an IP3-linked agonist (Fig. 2 C). Along this line, Fig. 3 B shows that the [Ca2+]c rise-induced inhibition of mitochondrial movement can be reversed by termination of the [Ca2+]c elevation and subsequently, reproduced by a second step of [Ca2+]c elevation. This suggests that no desensitization of the Ca2+ regulation of mitochondrial motility occurred. If there is no desensitization and the reversal of the movement inhibition is slower than the decay of the [Ca2+]c spike, [Ca2+]c oscillations may be able to cause a prolonged depression of mitochondrial motility. In differentiated H9c2 myotubes, RyR-mediated [Ca2+]c oscillations have been demonstrated (Szalai et al., 2000). As shown in Fig. 4, [Ca2+]c oscillations were also observed in H9c2 myoblasts transfected with RyR1 (Bhat et al., 1997) and stimulated with caffeine (Caff). Similar to the IP3-linked [Ca2+]c spikes, the RyR-mediated [Ca2+]c spikes also triggered inhibition of mitochondrial motility and the oscillations of [Ca2+]c were often associated with oscillations in movement activity (Fig. 4 A, cell marked by an arrow). Each burst of RyR1-mediated Ca2+ release could result in maximal inhibition of mitochondrial motility (Fig. 4, A and B). Isolated spikes of mitochondrial movement inhibition were observed during low frequency [Ca2+]c oscillations (unpublished data). However, if the frequency of [Ca2+]c spiking was higher and the recovery of motility was slow, [Ca2+]c oscillations could produce an essentially sustained maximal inhibition in movement activity (Fig. 4 B). Thus the frequency-modulated [Ca2+]c signals are translated into a time-averaged motility response. Notably, at supramaximal stimulation the [Ca2+]c oscillations run together and fuse into a large and slowly decaying single [Ca2+]c spike (Szalai et al., 2000), but this [Ca2+]c signal could not provide for sustained inhibition of the mitochondrial motility (e.g., Fig. 1 B). In this way, the control of mitochondrial motility may serve as a model whereby [Ca2+]c oscillations are an effective signal for long-term modulation, but a nonoscillatory [Ca2+]c signal is unable to maintain inhibition.

Bottom Line: By clamping cytoplasmic [Ca2+] ([Ca2+]c) at various levels, mitochondrial motility was found to be regulated by Ca2+ in the physiological range.The inositol 1,4,5-trisphosphate- or ryanodine receptor-mediated [Ca2+]c signal also induced a decrease in mitochondrial motility.This decrease followed the spatial and temporal pattern of the [Ca2+]c signal.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA.

ABSTRACT
Mitochondria are dynamic organelles in cells. The control of mitochondrial motility by signaling mechanisms and the significance of rapid changes in motility remains elusive. In cardiac myoblasts, mitochondria were observed close to the microtubular array and displayed both short- and long-range movements along microtubules. By clamping cytoplasmic [Ca2+] ([Ca2+]c) at various levels, mitochondrial motility was found to be regulated by Ca2+ in the physiological range. Maximal movement was obtained at resting [Ca2+]c with complete arrest at 1-2 microM. Movement was fully recovered by returning to resting [Ca2+]c, and inhibition could be repeated with no apparent desensitization. The inositol 1,4,5-trisphosphate- or ryanodine receptor-mediated [Ca2+]c signal also induced a decrease in mitochondrial motility. This decrease followed the spatial and temporal pattern of the [Ca2+]c signal. Diminished mitochondrial motility in the region of the [Ca2+]c rise promotes recruitment of mitochondria to enhance local Ca2+ buffering and energy supply. This mechanism may provide a novel homeostatic circuit in calcium signaling.

Show MeSH