The role of NECAB2 in mitochondrial stress response

• Applicant: Professor Dr. Axel Methner
• Subject Area: Molecular and Cellular Neurology and Neuropathology ; Molecular Biology and Physiology of Neurons and Glial Cells
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553322568

Neuronal signaling depends on ATP generated by mitochondria. Dysfunctional mitochondria shift the redox balance towards a more oxidative environment. The Neuronal Calcium-binding protein 2 (NECAB2) is strongly expressed in the striatum and spinal motor neurons. NECAB2 increases signaling of G-protein-coupled receptors through direct interaction. High calcium levels result in dissociation of NECAB2 from the receptors and attenuation of receptor signaling in a negative feedback loop. NECAB2 is composed of two calcium-binding EF hands, two coiled coil domains and an evolutionarily conserved enzymatic domain that resembles atypical dimeric prokaryotic heme oxygenases. During the last funding period, we demonstrated that NECAB2 is involved in an endosomal pathway of mitochondrial stress response that involves the Rab5 guanine-exchange factor Alsin. Alsin mutation is a cause of familial amyotrophic lateral sclerosis which affects corticospinal and spinal motor neurons, a site of strong NECAB2 expression. Unpublished own results revealed that in mitochondrial fractions, NECAB2 is mainly present in a dimeric state and that mutation of the EF hands attenuates dimerization. Based on these findings, we hypothesize that calcium-dependent dimerization of NECAB2 at mitochondria triggers its enzymatic function which is important for this novel pathway of endosomal mitochondrial stress response. The physiological calcium signals leading to dimerization and the substrates of this enzymatic function are not known yet. Also unknown is how NECAB2 affects and interacts with Alsin as part of the Rab5-mediated mitochondrial stress response. To fill these gaps in knowledge, we now aim to study the signals that govern dimerization and subcellular localization of NECAB2, investigate changes in iron homeostasis in Necab2-deficient mice and identify proteins that might serve as substrates for the potential heme oxygenase activity of NECAB2, and define NECAB2 and Alsin interaction and interdependence in the Rab5-mediated mitochondrial stress response. This work is of high relevance as it aims to elucidate fundamental aspects of mitochondrial stress response.

• DFG Programme: Research Grants