Biology subjects

Stutzmann, G. E.

Publications and source records attributed to Stutzmann, G. E..

2 recordsLinked to original sources

bioRxiv2024

NCLX controls hepatic mitochondrial Ca2+ extrusion and couples hormone-mediated mitochondrial Ca2+ oscillations with gluconeogenesis

Hepatic Ca2+ signaling is emerging as a key factor in mediating gluconeogenesis. However, the identity of the hepatic mitochondrial Ca2+ transporter is controversial and the role of mitochondria in controlling hormonal Ca2+ signaling and linking them to metabolic activity is poorly understood. We first interrogated the role of the mitochondrial Na+/Ca2+ exchanger NCLX by triggering cytosolic Ca2+ purinergic signaling in primary hepatocytes, and Ca2+ responses in isolated mitochondria from WT, global NCLX KO, and conditional hepatic NCLX KO mice models. We monitored a higher rate of Na+-dependent mitochondrial Ca2+ efflux in NCLX-expressing hepatocytes, indicating that it constitutes the major Ca2+ efflux pathway. We then asked if NCLX is controlling the hormone-dependent mitochondrial Ca2+ oscillations by employing physiological concentrations of glucagon and vasopressin. Consistent with previous studies, hormone applications triggered mitochondrial Ca2+ oscillations in WT hepatocytes. In NCLX KO hepatocytes the cytosolic oscillations persisted, however, the mitochondrial Ca2+ oscillations were suppressed. To further understand the metabolic role of NCLX in the hepatic system, we examined gluconeogenic function in vivo and ex vitro by monitoring hepatic glucose production. We found that blood glucose dropped faster in the conditional KO mice and their hepatic glucagon-dependent glucose production was reduced, indicating that gluconeogenesis was impaired in hepatic conditional NCLX KO mice. Taken together, our results indicate that NCLX is the primary Ca2+ extruder in hepatocytes and is required for mediating the hormone-dependent mitochondrial Ca2+ oscillations and gluconeogenesis. SignificanceHepatic Ca2+ signaling is crucial for gluconeogenesis, but the mitochondrial control of this process is not resolved. This study identifies the mitochondrial transporter, NCLX, as a critical link between hormonal-dependent mitochondrial Ca2+ oscillations and gluconeogenesis. We first show that NCLX is the major hepatic mitochondrial efflux pathway. We then demonstrate that NCLX is required for glucagon-dependent mitochondrial Ca2+ oscillations and the acceleration of mitochondrial oxidative function. Using a conditional hepatic NCLX-null mouse model, we show that NCLX is required for maintaining hepatic glucose production during fasting and in response to glucagon stimulation. Overall, the study identifies NCLX as the integrator of hepatic mitochondrial Ca2+ signaling, required for gluconeogenesis.

physiology↗

bioRxiv2022

Protein mishandling and impaired lysosomal proteolysis generated through calcium dysregulation in Alzheimer's disease

Impairments in neural lysosomal- and autophagic-mediated degradation of cellular debris contribute to neuritic dystrophy and synaptic loss. While these are well-characterized features of neurodegenerative disorders such as Alzheimers disease (AD), the upstream cellular processes driving deficits in pathogenic protein mishandling are less understood. Using a series of fluorescent biosensors and optical imaging in model cells, AD mouse models and human neurons derived from AD patients, we reveal a novel cellular signaling cascade underlying protein mishandling mediated by intracellular calcium dysregulation, an early component of AD pathogenesis. Increased Ca2+ release via the endoplasmic reticulum (ER) resident ryanodine receptor (RyR) is associated with reduced expression of the lysosome proton pump vATPase subunits (V1B2 and V0a1), resulting in lysosome deacidification and disrupted proteolytic activity in AD mouse models and human induced neurons (HiN). As a result of impaired lysosome digestive capacity, mature autophagosomes with hyperphosphorylated tau accumulated in AD murine neurons and AD HiN, exacerbating proteinopathy. Normalizing AD-associated aberrant RyR-Ca2+ signaling with the negative allosteric modulator, dantrolene (Ryanodex), restored vATPase levels, lysosomal acidification and proteolytic activity, and autophagic clearance of intracellular protein aggregates in AD neurons. These results highlight that prior to overt AD histopathology or cognitive deficits, aberrant upstream Ca2+ signaling disrupts lysosomal acidification and contributes to pathological accumulation of intracellular protein aggregates. Importantly, this is demonstrated in animal models of AD, and in human iPSC-derived neurons from AD patients. Furthermore, pharmacological suppression of RyR-Ca2+ release rescued proteolytic function, revealing a target for therapeutic intervention that has demonstrated effects in clinically-relevant assays. Significance StatementWe demonstrate in model cells, murine neuronal cultures, and iPSC-derived human neurons, that AD associated RyR-Ca2+ dyshomeostasis impairs lysosomal acidification, lysosomal proteolytic activity and hinders autophagic-mediated protein aggregate clearance, which are processes vital to neuronal survival. These deficits were reversed by restoring intracellular Ca2+ homeostasis. Notably, this provides a therapeutic target and emphasizes the pathogenic relationship between ER-Ca2+ handling, that is known to be altered in AD, to pathogenic protein accumulation as a critical turning point in early stages of Alzheimers disease.

neuroscience↗