Autophagy in chronically ischemic myocardium

Abstract

We tested the hypothesis that chronically ischemic (IS) myocardium induces autophagy, a cellular degradation process responsible for the turnover of unnecessary or dysfunctional organelles and cytoplasmic proteins, which could protect against the consequences of further ischemia. Chronically instrumented pigs were studied with repetitive myocardial ischemia produced by one, three, or six episodes of 90 min of coronary stenosis (30% reduction in baseline coronary flow followed by reperfusion every 12 h) with the non-IS region as control. In this model, wall thickening in the IS region was chronically depressed by Ϸ37%. Using a nonbiased proteomic approach combining 2D gel electrophoresis with in-gel proteolysis, peptide mapping by MS, and sequence database searches for protein identification, we demonstrated increased expression of cathepsin D, a protein known to mediate autophagy. Additional autophagic proteins, cathepsin B, heat shock cognate protein Hsc73 (a key protein marker for chaperone-mediated autophagy), beclin 1 (a mammalian autophagy gene), and the processed form of microtubule-associated protein 1 light chain 3 (a marker for autophagosomes), were also increased. These changes, not evident after one episode, began to appear after two or three episodes and were most marked after six episodes of ischemia, when EM demonstrated autophagic vacuoles in chronically IS myocytes. Conversely, apoptosis, which was most marked after three episodes, decreased strikingly after six episodes, when autophagy had increased. Immunohistochemistry staining for cathepsin B was more intense in areas where apoptosis was absent. Thus, autophagy, triggered by ischemia, could be a homeostatic mechanism, by which apoptosis is inhibited and the deleterious effects of chronic ischemia are limited.proteomics ͉ lyposomal proteins ͉ apoptosis ͉ hibernating myocardium ͉ myocardial protection A utophagy is a cellular degradation process responsible for the turnover of unnecessary or dysfunctional organelles and cytoplasmic proteins and has been studied extensively in lower organisms such as yeast, Caenorhabditis elegans, and Drosophila (1-4). Autophagy has been suggested to be an essential function for cell homeostasis and cell defense and adaptation to an adverse environment (1, 2, 5). Autophagy is typically activated by starvation, when the cytoplasmic proteins or organelles are delivered to the lysosome and degraded (1-4). In autophagy, cytoplasmic proteins or dysfunctional organelles are sequestrated in a doublemembrane-bound vesicle, termed autophagosome, delivered to the lysosome by fusion, and then degraded. Autophagy allows the cell not only to recycle amino acids but also to remove damaged organelles, thereby eliminating oxidative stress and allowing cellular remodeling for survival (2, 6). In fact, autophagy is a cellular mechanism essential for dauer development and lifespan extension in C. elegans (1). It can also prevent accumulation of misfolded and aggregated proteins in Parkinson's, Huntington's, and Alzheimer's disease...

The role of autophagy in the heart

“…[40][41][42] In patients with terminal heart failure, secondary to ischemic cardiomyopathy or dilated cardiomyopathy, cellular degeneration with granular cytoplasmic ubiquitin inclusion is detected in 0.3% of the cardiomyocytes. 38 In human failing hearts with idiopathic dilated cardiomyopathy, the prevalence of autophagic, apoptotic and necrotic cells have also been observed.…”

“…For example, although the myocardium under chronic hypoxia exhibits reduced contractility -the condition termed myocardial hibernation -it can show a full recovery with little evidence of cell death when hypoxia is eased. 40 Hypoxia not only activates a series of cell survival mechanisms but also activates autophagy in the myocardium. 40,58 An earlier study showed a correlation between the suppression of autophagy and the enhancement of myocardial injury in response to acute myocardial ischemia.…”

“…40 Hypoxia not only activates a series of cell survival mechanisms but also activates autophagy in the myocardium. 40,58 An earlier study showed a correlation between the suppression of autophagy and the enhancement of myocardial injury in response to acute myocardial ischemia. 15 An inverse correlation was found between the occurrence of autophagy and apoptosis in the hibernating myocardium.…”

Recycle or die: The role of autophagy in cardioprotection

“…They also reported that the increase in autophagy correlated with functional recovery and salvage of the myocardium after I/R, whereas extended ischemia, which seemed to impair the Atg-Lys pathway, correlated with irreversible damage and contractile dysfunction [8]. In addition, chronic ischemia was reported to induce autophagy and increase lysosomal activity in swine myocardium [37]. The same study found that areas of the heart with increased autophagy displayed fewer apoptotic cells, suggesting that induction of autophagy might have prevented apoptosis.…”

Cisplatin-induced macroautophagy occurs prior to apoptosis in proximal tubules in vivo

“…Mizushima et al confirmed that over-expression of a fusion protein between green fluorescent protein and light chain 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 4 and in other cases induces apoptosis or type-2 programmed cell death [6][7][8]. Chronic myocardial ischemia/reperfusion injury induces autophagy increment and apoptosis decrement [9]. Inhibition of autophagy prevents neuron death after hypoxic-ischemic injury in neonatal mice [10].…”