Abstract
Recent studies have documented that oxidized low-density lipoprotein cholesterol (oxLDL) levels directly impact myocardial structure and function. However, the molecular mechanisms by which oxLDL affects cardiac myocytes are not well established. We addressed the question whether oxLDL modifies load-free cell shortening, a standardized readout of cardiac cellular function, and investigated whether proprotein convertase subtilisin/kexin-9 (PCSK9) is involved on oxLDL-dependent processes. Adult rat ventricular cardiomyocytes were isolated and incubated for 24 h with oxLDL. PCSK9 was silenced by administration of siRNA. Load-free cell shortening was analyzed via a line camera at a beating frequency of 2 Hz. RT-PCR and immunoblots were used to identify molecular pathways. We observed a concentration-dependent reduction of load-free cell shortening that was independent of cell damage (apoptosis, necrosis). The effect of oxLDL was attenuated by silencing of oxLDL receptors (LOX-1), blockade of p38 MAP kinase activation, and silencing of PCSK9. oxLDL increased the expression of PCSK9 and caused oxidative modification of tropomyosin. In conclusion, we found that oxLDL significantly impaired contractile function via induction of PCSK9. This is the first report about the expression of PCSK9 in adult terminal differentiated ventricular cardiomyocytes. The data are important in the light of recent development of PCSK9 inhibitory strategies.
Highlights
Oxidative stress defines a condition in which the formation of reactive oxygen species (ROS) exceeds the oxidant defense capacity of cells
Thereafter, cells were paced at 2 Hz and load-free cell shortening was quantified as percent shortening amplitude normalized to the diastolic cell length of individual cells. oxidized low-density lipoprotein cholesterol (oxLDL) caused a concentration-dependent decrease of cell shortening that reached a maximum at 20 lg/ml (Fig. 1)
In case of oxLDL, shortening of time to peak (TTP) was associated with reduced maximal contraction velocity and prolonged TTP when normalized to shortening amplitudes indicating reduced contraction dynamics
Summary
Oxidative stress defines a condition in which the formation of reactive oxygen species (ROS) exceeds the oxidant defense capacity of cells. Low-density lipoprotein (LDL) particles are susceptible to oxidation and the plasma levels of oxidized LDL (oxLDL) particles increase under conditions of oxidative stress. OxLDL participates in the progression of disease under condition of oxidative stress. In line with these suggestions, plasma oxLDL levels seem to be a predictor for mortality in patients with chronic heart failure suggesting that oxidative stress is causally involved [31]. OxLDL induced the expression of biomarkers associated with heart failure in HL-1 cells, an immortalized cardiac-like cell type [2]. OxLDL increased calcium transients in rabbit cardiomyocytes [15] and it improved L-type currents in rat ventricular cardiomyocytes [5].
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