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Glucolipotoxicity diminishes cardiomyocyte TFEB and inhibits lysosomal autophagy during obesity and diabetes.

Biochimica et biophysica acta (2016-10-22)
Purvi C Trivedi, Jordan J Bartlett, Lester J Perez, Keith R Brunt, Jean Francois Legare, Ansar Hassan, Petra C Kienesberger, Thomas Pulinilkunnil
ABSTRACT

Impaired cardiac metabolism in the obese and diabetic heart leads to glucolipotoxicity and ensuing cardiomyopathy. Glucolipotoxicity causes cardiomyocyte injury by increasing energy insufficiency, impairing proteasomal-mediated protein degradation and inducing apoptosis. Proteasome-evading proteins are degraded by autophagy in the lysosome, whose metabolism and function are regulated by master regulator transcription factor EB (TFEB). Limited studies have examined the impact of glucolipotoxicity on intra-lysosomal signaling proteins and their regulators. By utilizing a mouse model of diet-induced obesity, type-1 diabetes (Akita) and ex-vivo model of glucolipotoxicity (H9C2 cells and NRCM, neonatal rat cardiomyocyte), we examined whether glucolipotoxicity negatively targets TFEB and lysosomal proteins to dysregulate autophagy and cause cardiac injury. Despite differential effects of obesity and diabetes on LC3B-II, expression of proteins facilitating autophagosomal clearance such as TFEB, LAMP-2A, Hsc70 and Hsp90 were decreased in the obese and diabetic heart. In-vivo data was recapitulated in H9C2 and NRCM cells, which exhibited impaired autophagic flux and reduced TFEB content when exposed to a glucolipotoxic milieu. Notably, overloading myocytes with a saturated fatty acid (palmitate) but not an unsaturated fatty acid (oleate) depleted cellular TFEB and suppressed autophagy, suggesting a fatty acid specific regulation of TFEB and autophagy in the cardiomyocyte. The effect of glucolipotoxicity to reduce TFEB content was also confirmed in heart tissue from patients with Class-I obesity. Therefore, during glucolipotoxicity, suppression of lysosomal autophagy was associated with reduced lysosomal content, decreased cathepsin-B activity and diminished cellular TFEB content likely rendering myocytes susceptible to cardiac injury.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Protease Inhibitor Cocktail, for use with mammalian cell and tissue extracts, DMSO solution
Sigma-Aldrich
Dulbecco′s Modified Eagle′s Medium/Nutrient Mixture F-12 Ham, With 15 mM HEPES and sodium bicarbonate, without L-glutamine, liquid, sterile-filtered, suitable for cell culture
Sigma-Aldrich
Sodium palmitate, ≥98.5%
Sigma-Aldrich
Medium 199, With Earle′s salts and L-glutamine, without sodium bicarbonate, powder, suitable for cell culture
Sigma-Aldrich
Lysosome Isolation Kit, sufficient for 25 g (tissue), sufficient for 20 mL (packed cells), enrichment of lysosomes from tissues and packed cells