NCLX prevents cell death during adrenergic activation of the brown adipose tissue

Essam Assali ^1,2,3,4 Anthony E. Jones ³ Michaela Veliova ³ Rebeca Acín-Pérez ² Mahmoud Taha ⁴ Nathanael Miller ² Michaël Shum ² Marcus F. Oliveira ⁵ Guy Las ¹ Marc Liesa ² Israel Sekler ⁴ Orian S. Shirihai ^1,2,3

¹Department of Clinical Biochemistry, Faculty of Health Sciences, Ben-Gurion University, Israel
²Division of Endocrinology, Department of Medicine, David Geffen School of Medicine, University of California Los Angeles, USA
³Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California Los Angeles, USA
⁴Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University, Israel
⁵Institute of Medical Biochemistry Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Brazil

Uncoupling, mitochondrial network fragmentation and depolarization are signs of bioenergetic crisis leading to autophagic removal of dysfunctional mitochondria, and ultimately, to apoptosis. Remarkably, brown adipose tissue (BAT) undergoes this scenario whenever the animal is cold exposed, yet no cell death occurs during thermogenesis. In this study we show that adrenergic stimulation of BAT activates a PKA-dependent mitochondrial Ca²⁺extrusion via the mitochondrial Na⁺/Ca²⁺exchanger, NCLX. Adrenergic stimulation of brown adipocytes (BA) from the NCLX-null mice induces profound mitochondrial Ca²⁺ overload and impaired uncoupled respiration. Core body temperature, PET-CT imaging of glucose uptake and VO2 measurements confirm a BAT specific thermogenic defect in NCLX-null mice.
We show that mitochondrial Ca²⁺ overload induced by adrenergic stimulation of NCLX KO BAT, triggers the opening of the mitochondrial permeability transition pore (mPTP), leading to Cytochrome c release, remarkable mitochondrial swelling and cell death in BAT. However, treatment with a novel mPTP inhibitor, NIM811, rescue mitochondrial respiratory function and thermogenesis in NCLX-null BA in vitro and in vivo. Our findings identify a novel pathway enabling non-lethal mitochondrial Ca²⁺ elevation during adrenergic stimulation of uncoupled respiration. Deletion of NCLX transforms the adrenergic pathway responsible for the stimulation of thermogenesis into a death pathway.