Pesout MiP2010

Pesout C, Garlid AO, Nihei M, Ha A, Gold M, Garlid KD (2010) ) The mechanism of signalling by the adenosine receptor in heart.

Link: Abstracts Session 1

Pesout C, Garlid AO, Nihei M, Ha A, Gold M, Garlid KD (2010)

Event: MiP2010

ATP decreases rapidly during ischemia. It is then degraded to adenosine, which moves to the extracellular space and activates adenosine receptors (ADOR). ADOR play a unique role in cardioprotection against ischemia reperfusion injury, because their activation is responsible for cardioprotection by ischemic preconditioning and ischemic postconditioning.

• O2k-Network Lab: US_OR_Portland_Garlid_KD

Labels:

Stress:Ischemia-Reperfusion; Preservation"Ischemia-Reperfusion; Preservation" is not in the list (Cell death, Cryopreservation, Ischemia-reperfusion, Permeability transition, Oxidative stress;RONS, Temperature, Hypoxia, Mitochondrial disease) of allowed values for the "Stress" property. 

Tissue;cell: Heart 

Full text

ATP decreases rapidly during ischemia. It is then degraded to adenosine, which moves to the extracellular space and activates adenosine receptors (ADOR). ADOR play a unique role in cardioprotection against ischemia reperfusion injury, because their activation is responsible for cardioprotection by ischemic preconditioning and ischemic postconditioning.

Ischemia-reperfusion protocols were used to study cardioprotection in perfused rat hearts. Perfusion of the adenosine analog NECA or 5 min ischemia causes signalosomes to attach loosely to the mitochondrial outer membrane. 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, 2].

The mechanism of ADOR protection has been controversial. ADOR are Gi protein-coupled receptors (GPCR); however, Downey et al. [3] have long held that ADOR bypass the usual GPCR signalling pathway (PI3K - Akt - eNOS - guanylyl cyclase - PKG - mtKATP - ROS). The basis for this conclusion is that inhibitors of this pathway do not block cardioprotection when perfused to bracket the adenosine analogue. Our study of ADOR signalosomes reveals that this result has a different explanation. ADOR activation causes signalosomes to migrate to mitochondria, but, unlike other GPCR signalosomes, the ADOR signalosomes is inactive until it receives an additional signal. Thus, there is nothing to inhibit until this signal is received. The additional signal is ROS, which activates an upstream, signalosomal PKCε that triggers the PI3K-to-PKG pathway (Fig. 1). Thus, ADOR signalling is identical to signalling by other GPCR, but the ADOR signalosome requires both receptor activation and ROS to complete the signal. We also present evidence that ischemia itself causes an ADOR signalosome to attach to mitochondria, and that this signalosome is required for cardioprotection by ischemic preconditioning, ischemic postconditioning, KATP channel openers (e.g., diazoxide), and GSK-3β inhibition.

In vitro functional assays of ADOR signalosomes allowed us to probe the signalling cascade from ADOR to PKG using inhibitors. Signalosomes were activated by brief preincubation with 2 µM H2O2. When provided with the appropriate substrates and cofactors, the signalosome is able to synthesize NO and cGMP. The ADOR inhibitor 8-SPT blocked activity, showing that the receptor itself retains activity in vitro and intracellularly.

1. Quinlan C L, 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. Downey JM, Davis AM, Cohen MV (2007) Signaling pathways in ischemic preconditioning. Heart Fail. Rev. 12: 181-188.