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Garlid MiP2010 1-01

From Bioblast
Garlid KD, Quinlan C, Pesout C, Garlid AO (2010) Signalosomes - a general signalling mechanism to and from mitochondria. MiP2010.

Link: Abstracts Session 1

Garlid KD, Quinlan C, Pesout C, Garlid AO (2010)

Event: MiP2010

Information transfer from plasma membrane receptors to intracellular organelles regulates metabolism, gene transcription, and other cellular processes. Cardioprotection against ischemia-reperfusion injury is known to require signalling from plasma membrane to mitochondria. It is a useful model for studying cell signalling for this reason, and also because hypotheses can readily be tested in the ex vivo perfused rat heart.

โ€ข Keywords: Signalling


Labels: MiParea: mtDNA;mt-genetics 


Organism: Rat  Tissue;cell: Heart 

Enzyme: Complex I, Inner mt-membrane transporter  Regulation: Ion;substrate transport, pH 




Full text

Information transfer from plasma membrane receptors to intracellular organelles regulates metabolism, gene transcription, and other cellular processes. Cardioprotection against ischemia-reperfusion injury is known to require signalling from plasma membrane to mitochondria. It is a useful model for studying cell signalling for this reason, and also because hypotheses can readily be tested in the ex vivo perfused rat heart.

Ischemia-reperfusion protocols were used to study cardioprotection in perfused rat hearts. Perfusion of a receptor agonist, such as bradykinin or adenosine, causes signalosomes to attach loosely to the mitochondrial outer membrane, and they remain attached when mitochondria are isolated in low ionic strength medium. Signalosomes were separated from mitochondria in a Percoll gradient and further purified to remove mitochondrial debris using Triton X-100 at 4 oC. Signalosomes were assayed by Western blot and electron microscopy. They were assayed for functional activity by adding them to respiring, isolated mitochondria from untreated heart or liver. Functionally active signalosomes induced opening of the mitochondrial ATP-sensitive K+ channel (mtKATP) and inhibition of the mitochondrial permeability transition (MPT) [1].

Cardioprotective signalling to mitochondria is mediated by signalosomes, which are assembled in caveolae and contain the receptor and all of the enzymes and components of the receptor-specific signalling cascade [2]. The diagram in Fig. 1 describes some of these features for the signalosomes obtained after perfusion of the heart with bradykinin. The bradykinin receptor B2R is uniquely observed in signalosomes obtained from bradykinin-treated hearts. All of the enzymes known to be contained in the GPCR signalling pathway were identified by Western blot. All signalosomes we have studied are dissolved by methyl-b-cyclodextrin and resistant to Triton X-100, characteristic of a caveolar origin. They are also highly decorated with caveolin. These 140 nm organelles migrate to the mitochondrial outer membrane, where they phosphorylate receptors using PKG, the terminal kinase of the cascade. This activates the mitochondrial signalling pathway described in Fig. 2. First, an endogenous inner membrane PKCฮต that is closely associated with mtKATP is activated, causing it to phosphorylate and open mtKATP. This causes increases in matrix K+, volume, and pH. The increased pH inhibits Complex I, leading to an increase in ROS production [3]. This ROS activates a second endogenous PKCฮต, which inhibits MPT opening, leading to protection against necrotic cell death [4].

Signalosomes can readily be isolated and purified from the perfused heart, and they demonstrate activity in vitro. That is, they cause mtKATP opening and MPT inhibition in mitochondria isolated from untreated hearts. This permits study of a signalling unit in its naturally organized state with preserved functionality. The signalosome mechanism is a general mechanism of cell signalling that is probably utilized by all receptors and all cell types.

1. Quinlan CL, Costa ADT, Costa CL, Pierre SV, Dos Santos P, Garlid KD (2008) Conditioning the heart induces formation of signalosomes that interact with mitochondria to open mitoKATP. Am. J. Physiol. 295: H953-961.

2. Garlid KD, Costa ADT, Quinlan CL, Pierre SV, Dos Santos P (2009) Cardioprotective signaling to mitochondria. J. Mol. Cell Cardiol. 46: 858-866.

3. Andrukhiv A, Costa AD, West IC, Garlid KD (2006) Opening mitoKATP increases superoxide generation from Complex I of the electron transport chain. Am. J. Physiol. 291: H2067-2074.

4. Costa AD, Jakob R, Costa CL, Andrukhiv K, West IC, Garlid KD (2006) The mechanism by which mitoKATP opening and H2O2 inhibit the mitochondrial permeability transition. J. Biol. Chem. 281: 20801-20808.