Endoplasmic reticulum–mitochondria crosstalk in NIX-mediated murine cell death

Abstract

Transcriptional upregulation of the proapoptotic BCL2 family protein NIX limits red blood cell formation and can cause heart failure by inducing cell death, but the requisite molecular events are poorly defined. Here, we show complementary mechanisms for NIX-mediated cell death involving direct and ER/sarcoplasmic reticulum-mediated (ER/SR-mediated) mitochondria disruption. Endogenous cardiac NIX and recombinant NIX localize both to the mitochondria and to the ER/SR. In genetic mouse models, cardiomyocyte ER/SR calcium stores are proportional to the level of expressed NIX. Whereas Nix ablation was protective in a mouse model of apoptotic cardiomyopathy, genetic correction of the decreased SR calcium content of Nix-null mice restored sensitivity to cell death and reestablished cardiomyopathy. Nix mutants specific to ER/SR or mitochondria activated caspases and were equally lethal, but only ER/SR-Nix caused loss of the mitochondrial membrane potential. These results establish a new function for NIX as an integrator of transcriptional and calcium-mediated signals for programmed cell death.

TRPV1 activation improves exercise endurance and energy metabolism through PGC-1α upregulation in mice

“…Mitochondria in cultured myotubes were stained with a mitochondrial probe, MitoFluor Red 589, which was reported to accumulate in mitochondria regardless of mitochondrial membrane potential, according to the manufacturer's protocol and previously reported methods [46]. Briefly, C2C12 myotubes were incubated in the prewarmed (37 °C) growth medium containing 200 nM MitoFluor Red 589 for 30 min, and then washed with prewarmed PBS.…”

Cardiac reanimation: targeting cardiomyocyte death by BNIP3 and NIX/BNIP3L

“…A cellular mechanism for the putative stress-sensing function of NIX/BNIP3L was recently delineated, based on the observation that only B80% of transfected NIX/ BNIP3L localize to mitochondria in neonatal rat cardiomyocytes or HEK293 cells, with the remainder localizing to the endoplasmic reticulum/sarcoplasmic reticulum (ER/SR) (Diwan et al, 2008a). These organelles are the predominant sites for intracellular calcium stores, and the highly organized subcellular architecture of adult cardiac myocytes enforces close proximity between SR and mitochondria, making it possible for calcium to transfer from SR to mitochondria through junctional microdomains referred to as 'calcium hot-spots' (Rizzuto and Pozzan, 2006).…”

“…However, it was recognized early on that BNIP3 can cause programmed cell death in a manner that does not require caspase activation and involve MPT (type 3 cell death). Our recent studies with organelle-specific NIX/BNIP3L mutants have more clearly defined a likely mechanism for NIX/BNIP3L-and BNIP3-mediated programmed necrosis via opening of mitochondrial permeability transition pores (MPTP, see above) (Diwan et al, 2008a). Because MPTPmediated cardiomyocyte death appears to have a major function in various forms of heart injury associated with increased cytosolic or sarcoplasmic reticular calcium levels (Nakayama et al, 2007;Diwan et al, 2008a), the mechanism is reviewed (see Figure 2).…”

“…Our recent studies with organelle-specific NIX/BNIP3L mutants have more clearly defined a likely mechanism for NIX/BNIP3L-and BNIP3-mediated programmed necrosis via opening of mitochondrial permeability transition pores (MPTP, see above) (Diwan et al, 2008a). Because MPTPmediated cardiomyocyte death appears to have a major function in various forms of heart injury associated with increased cytosolic or sarcoplasmic reticular calcium levels (Nakayama et al, 2007;Diwan et al, 2008a), the mechanism is reviewed (see Figure 2). Mitochondria are normally the major source of cellular ATP stores, which is needed to sustain the normal electrochemical gradient (Dc m ) across mitochondrial inner membranes.…”

Dual autonomous mitochondrial cell death pathways are activated by Nix/BNip3L and induce cardiomyopathy

“…One of these proteins, Nix/BNip3L (Nix), limits survival of, and mediates mitochondrial clearance from, erythroid cells (8)(9)(10) and is responsible for cardiomyocyte dropout and heart failure after chronic pressure overload (11,12). We have postulated that functional diversity of Nix may relate to dual localization at mitochondria and endoplasmic reticulum (13).…”