Elevated mRNA-levels of distinct mitochondrial and plasma membrane Ca2+ transporters in individual hypoglossal motor neurons of endstage SOD1 transgenic mice

Abstract

Disturbances in Ca2+ homeostasis and mitochondrial dysfunction have emerged as major pathogenic features in familial and sporadic forms of Amyotrophic Lateral Sclerosis (ALS), a fatal degenerative motor neuron disease. However, the distinct molecular ALS-pathology remains unclear. Recently, an activity-dependent Ca2+ homeostasis deficit, selectively in highly vulnerable cholinergic motor neurons in the hypoglossal nucleus (hMNs) from a common ALS mouse model, the endstage superoxide dismutase SOD1G93A transgenic mouse, was described. This functional deficit was defined by a reduced hMN mitochondrial Ca2+ uptake capacity and elevated Ca2+ extrusion across the plasma membrane. To address the underlying molecular mechanisms, here we quantified mRNA-levels of respective potential mitochondrial and plasma membrane Ca2+ transporters in individual, choline-acetyltransferase (ChAT) positive hMNs from wildtype (WT) and endstage SOD1G93A mice, by combining UV laser microdissection with RT-qPCR techniques, and specific data normalization. As ChAT cDNA levels as well as cDNA and genomic DNA levels of the mitochondrially encoded NADH dehydrogenase ND1 were not different between hMNs from WT and endstage SOD1G93A mice, these genes were used to normalize hMN-specific mRNA-levels of plasma membrane and mitochondrial Ca2+ transporters, respectively. We detected about 2-fold higher levels of the mitochondrial Ca2+ transporters MCU/MICU1, Letm1, and UCP2 in remaining hMNs from endstage SOD1G93A mice. These higher expression-levels of mitochondrial Ca2+ transporters in individual hMNs were not associated with a respective increase in number of mitochondrial genomes, as evident from hMN specific ND1 DNA quantification. Normalized mRNA-levels for the plasma membrane Na+/Ca2+ exchanger NCX1 were also about 2-fold higher in hMNs from SOD1G93A mice. Thus, pharmacological stimulation of Ca2+ transporters in highly vulnerable hMNs might offer a neuroprotective strategy for ALS.

Preconditioning, induced by sub-toxic dose of the neurotoxin L-BMAA, delays ALS progression in mice and prevents Na+/Ca2+ exchanger 3 downregulation

“…That a protein involved in calcium and sodium homeostasis maintenance could be linked to ALS pathophysiology was clearly conceivable from previous reports 6 , 24 , 25 . In fact, recent evidence suggest that abnormalities in cellular Ca 2+ signaling are common features in the pathogenesis of a range of neurodegenerative disorders, including ALS 6 , 24 , 25 . It is well known that Ca 2+ is one of the most relevant intracellular messengers, being essential in neuronal development, synaptic transmission and plasticity, as well as in the regulation of various transduction pathways in the brain 7 .…”

Metabolic Reprogramming in Amyotrophic Lateral Sclerosis

“…Previous investigations linked the uncoupling protein 2 (UCP2) to mitochondrial dysfunction in ALS 3 , 31 , 32 , so we tested the role of this protein in the bioenergetic alterations of ALS mice motor neurons observed in our study. Pharmacologic UCP2 inhibition with genipin induced a significant increase in the cellular ATP level (Fig.…”

PRMT1-mediated methylation of MICU1 determines the UCP2/3 dependency of mitochondrial Ca2+ uptake in immortalized cells

“…So far, little is known on the modulation of the activity of the MCU complex. On the transcriptional level, the expression patterns of the proteins involved in the mitochondrial Ca 2+ uptake were described to shape the activity of neuronal cell types 57 58 and cancer growth 59 . Hence, MCU expression was found to be under the Ca 2+ -CREB pathway in chicken DT40 B lymphocytes 60 .…”