Restoration of lysosomal acidification rescues autophagy and metabolic dysfunction in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the world. High levels of free fatty acids in the liver impair hepatic lysosomal acidification and reduce autophagic flux. We investigate whether restoration of lysosomal function in NAFLD recovers autophagic flux, mitochondrial function, and insulin sensitivity. Here, we report the synthesis of novel biodegradable acid-activated acidifying nanoparticles (acNPs) as a lysosome targeting treatment to restore lysosomal acidity and autophagy. The acNPs, composed of fluorinated polyesters, remain inactive at plasma pH, and only become activated in lysosomes after endocytosis. Specifically, they degrade at pH of ~6 characteristic of dysfunctional lysosomes, to further acidify and enhance the function of lysosomes. In established in vivo high fat diet mouse models of NAFLD, re-acidification of lysosomes via acNP treatment restores autophagy and mitochondria function to lean, healthy levels. This restoration, concurrent with reversal of fasting hyperglycemia and hepatic steatosis, indicates the potential use of acNPs as a first-in-kind therapeutic for NAFLD.J.L.Z. and A.M. were supported by a BU Nano Cross-disciplinary fellowship from the BU Nano center at Boston University. J.L.Z. was supported by a Presidential Postdoctoral Fellowship from Nanyang Technological University, Grant/Award Number: 021229-00001. C.H.L. was supported by Dean’s Postdoctoral Fellowship, Nanyang Technological University, Lee Kong Chian School of Medicine, Grant/Award Number: 021207-00001. E.A. was supported by Azrieli Fellowship (The Azrieli Foundation). This work was also supported in part by funding from the National Institutes of Health (R01AA026914, OSS ML; R21AG063373, MWG OSS; and R21AG06045, OSS

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

Brown adipose tissue activation of thermogenesis is accompanied by a sequence of events commonly associated with apoptosis, however they evade cell death. Assali et al. show that NCLX prevents mitochondrial calcium overload and apoptosis. Deletion of NCLX, converts a thermogenic signal into a death pathway

Author Correction: Aberrant activity of mitochondrial NCLX is linked to impaired synaptic transmission and is associated with mental retardation

The original version of this Article contained an error in the spelling of the author Fabiana Perocchi, which was incorrectly given as Fabiana Perrochi. This has now been corrected in both the PDF and HTML versions of the Article

Restoration of lysosomal acidification rescues autophagy and metabolic dysfunction in non-alcoholic fatty liver disease

Abstract Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the world. High levels of free fatty acids in the liver impair hepatic lysosomal acidification and reduce autophagic flux. We investigate whether restoration of lysosomal function in NAFLD recovers autophagic flux, mitochondrial function, and insulin sensitivity. Here, we report the synthesis of novel biodegradable acid-activated acidifying nanoparticles (acNPs) as a lysosome targeting treatment to restore lysosomal acidity and autophagy. The acNPs, composed of fluorinated polyesters, remain inactive at plasma pH, and only become activated in lysosomes after endocytosis. Specifically, they degrade at pH of ~6 characteristic of dysfunctional lysosomes, to further acidify and enhance the function of lysosomes. In established in vivo high fat diet mouse models of NAFLD, re-acidification of lysosomes via acNP treatment restores autophagy and mitochondria function to lean, healthy levels. This restoration, concurrent with reversal of fasting hyperglycemia and hepatic steatosis, indicates the potential use of acNPs as a first-in-kind therapeutic for NAFLD

Restoration of lysosomal acidification rescues autophagy and metabolic dysfunction in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the world. High levels of free fatty acids in the liver impair hepatic lysosomal acidification and reduce autophagic flux. We investigate whether restoration of lysosomal function in NAFLD recovers autophagic flux, mitochondrial function, and insulin sensitivity. Here, we report the synthesis of novel biodegradable acid-activated acidifying nanoparticles (acNPs) as a lysosome targeting treatment to restore lysosomal acidity and autophagy. The acNPs, composed of fluorinated polyesters, remain inactive at plasma pH, and only become activated in lysosomes after endocytosis. Specifically, they degrade at pH of ~6 characteristic of dysfunctional lysosomes, to further acidify and enhance the function of lysosomes. In established in vivo high fat diet mouse models of NAFLD, re-acidification of lysosomes via acNP treatment restores autophagy and mitochondria function to lean, healthy levels. This restoration, concurrent with reversal of fasting hyperglycemia and hepatic steatosis, indicates the potential use of acNPs as a first-in-kind therapeutic for NAFLD

Mitochondria Bound to Lipid Droplets Have Unique Bioenergetics, Composition, and Dynamics that Support Lipid Droplet Expansion

Mitochondria associate with lipid droplets (LDs) in fat-oxidizing tissues, but the functional role of these peridroplet mitochondria (PDM) is unknown. Microscopic observation of interscapular brown adipose tissue reveals that PDM have unique protein composition and cristae structure and remain adherent to the LD in the tissue homogenate. We developed an approach to isolate PDM based on their adherence to LDs. Comparison of purified PDM to cytoplasmic mitochondria reveals that (1) PDM have increased pyruvate oxidation, electron transport, and ATP synthesis capacities; (2) PDM have reduced β-oxidation capacity and depart from LDs upon activation of brown adipose tissue thermogenesis and β-oxidation; (3) PDM support LD expansion as Perilipin5-induced recruitment of mitochondria to LDs increases ATP synthase-dependent triacylglyceride synthesis; and (4) PDM maintain a distinct protein composition due to uniquely low fusion-fission dynamics. We conclude that PDM represent a segregated mitochondrial population with unique structure and function that supports triacylglyceride synthesis

Recruitment and remodeling of peridroplet mitochondria in human adipose tissue.

Beige adipocyte mitochondria contribute to thermogenesis by uncoupling and by ATP-consuming futile cycles. Since uncoupling may inhibit ATP synthesis, it is expected that expenditure through ATP synthesis is segregated to a disparate population of mitochondria. Recent studies in mouse brown adipocytes identified peridroplet mitochondria (PDM) as having greater ATP synthesis and pyruvate oxidation capacities, while cytoplasmic mitochondria have increased fatty acid oxidation and uncoupling capacities. However, the occurrence of PDM in humans and the processes that result in their expansion have not been elucidated. Here, we describe a novel high-throughput assay to quantify PDM that is successfully applied to white adipose tissue from mice and humans. Using this approach, we found that PDM content varies between white and brown fat in both species. We used adipose tissue from pheochromocytoma (Pheo) patients as a model of white adipose tissue browning, which is characterized by an increase in the capacity for energy expenditure. In contrast with control subjects, PDM content was robustly increased in the periadrenal fat of Pheo patients. Remarkably, bioenergetic changes associated with browning were primarily localized to PDM compared to cytoplasmic mitochondria (CM). PDM isolated from periadrenal fat of Pheo patients had increased ATP-linked respiration, Complex IV content and activity, and maximal respiratory capacity. We found similar changes in a mouse model of re-browning where PDM content in whitened brown adipose tissue was increased upon re-browning induced by decreased housing temperature. Taken together, this study demonstrates the existence of PDM as a separate functional entity in humans and that browning in both mice and humans is associated with a robust expansion of peri-droplet mitochondria characterized by increased ATP synthesis linked respiration

Recruitment and remodeling of peridroplet mitochondria in human adipose tissue.

Beige adipocyte mitochondria contribute to thermogenesis by uncoupling and by ATP-consuming futile cycles. Since uncoupling may inhibit ATP synthesis, it is expected that expenditure through ATP synthesis is segregated to a disparate population of mitochondria. Recent studies in mouse brown adipocytes identified peridroplet mitochondria (PDM) as having greater ATP synthesis and pyruvate oxidation capacities, while cytoplasmic mitochondria have increased fatty acid oxidation and uncoupling capacities. However, the occurrence of PDM in humans and the processes that result in their expansion have not been elucidated. Here, we describe a novel high-throughput assay to quantify PDM that is successfully applied to white adipose tissue from mice and humans. Using this approach, we found that PDM content varies between white and brown fat in both species. We used adipose tissue from pheochromocytoma (Pheo) patients as a model of white adipose tissue browning, which is characterized by an increase in the capacity for energy expenditure. In contrast with control subjects, PDM content was robustly increased in the periadrenal fat of Pheo patients. Remarkably, bioenergetic changes associated with browning were primarily localized to PDM compared to cytoplasmic mitochondria (CM). PDM isolated from periadrenal fat of Pheo patients had increased ATP-linked respiration, Complex IV content and activity, and maximal respiratory capacity. We found similar changes in a mouse model of re-browning where PDM content in whitened brown adipose tissue was increased upon re-browning induced by decreased housing temperature. Taken together, this study demonstrates the existence of PDM as a separate functional entity in humans and that browning in both mice and humans is associated with a robust expansion of peri-droplet mitochondria characterized by increased ATP synthesis linked respiration