Effect of intracellular lipid droplets on cytosolic Ca²⁺ and cell death during ischaemia–reperfusion injury in cardiomyocytes

Abstract

Lipid droplets (LD) consist of accumulations of triacylglycerols and have been proposed to be markers of ischaemic but viable tissue. Previous studies have described the presence of LD in myocardium surviving an acute coronary occlusion. We investigated whether LD may be protective against cell death secondary to ischaemia-reperfusion injury. The addition of oleate-bovine serum albumin complex to freshly isolated adult rat cardiomyocytes or to HL-1 cells resulted in the accumulation of intracellular LD detectable by fluorescence microscopy, flow cytometry and 1 H-nuclear magnetic resonance spectroscopy. Simulated ischaemia-reperfusion of HL-1 cells (respiratory inhibition at pH 6.4 followed by 30 min of reperfusion) resulted in significant cell death (29.7 ± 2.6% of total lactate dehydrogenase release). However, cell death was significantly attenuated in cells containing LD (40% reduction in LDH release compared with control cells, P = 0.02). The magnitude of LD accumulation was inversely correlated (r 2 = 0.68, P = 0.0003) with cell death. The protection associated with intracellular LD was not a direct effect of the fatty acids used to induce their formation, because oleate added 30 min before ischaemia, during ischaemia or during reperfusion did not form LD and did not protect against cell death. Increasing the concentration of free oleate during reperfusion progressively decreased the protection afforded by LD. HL-1 cells labelled with fluo-4, a Ca 2+ -sensitive fluorochrome, fluorescence within LD areas increased more throughout simulated ischaemia and reperfusion than in the cytosolic LD-free areas of the same cells. As a consequence, cells with LD showed less cytosolic Ca 2+ overload than control cells. These results suggest that LD exert a protective effect during ischaemia-reperfusion by sequestering free fatty acids and Ca 2+ .

Empagliflozin normalizes the size and number of mitochondria and prevents reduction in mitochondrial size after myocardial infarction in diabetic hearts

“…), by buffering cytosolic Ca 2+ overload during ischemia‐reperfusion (Barba et al. ) and by preventing the production of ROS via sequestration of fatty acids from excess oxidation (Kuramoto et al. ).…”

Lipid body accumulation alters calcium signaling dynamics in immune cells

“…Long term sinks of calcium have been previously characterised as mitochondria and Golgi vesicles, and LB may now be added to that group [50-52]. Barba et al examined cardiomyocytes in which ectopic lipid deposition was induced and the subsequent effects upon myocyte calcium signals and contractility [35]. Interestingly, they noted that after ischemia-reperfusion, there was a net accumulation of calcium in lipid droplet positive regions, supporting the idea of these structures as sinks [35].…”

“…A relationship between calcium signalling and steatosis has only been marginally explored in the literature, with one study suggesting altered calcium-dependent contractile signalling in skeletal myocytes with ectopic lipid deposition (ELD), and a study in the porcine system suggesting that ovarian follicle LB act as reservoirs of stored calcium [35, 36]. Moreover, intriguing recent data in the eosinophil system demonstrate that there are ER lamellae within LB, which may imply that the calcium storage functionality of the ER may be transferred, along with the physical structures, to the LB [37].…”

Not Just Fat: The Structure and Function of the Lipid Droplet

“…Unsaturated fatty acids help cells to circumvent the toxicity of saturated fatty acid in mammalian cells by promoting TG production (Listenberger et al 2003). This function is also important in cardiomyocytes that are exposed to ischemia and reperfusion (Barba et al 2009), neurons during nutrient deprivation (Du et al (Gubern et al 2009). In Saccharomyces cerevisiae, a mutant lacking all lipid ester synthesis is viable under the normal conditions (Sandager et al 2002), but excess unsaturated fatty acids causes massive membrane proliferation and cell death ).…”