Medizinische Universität Graz - Research portal
Selected Publication:
Khan, M.
Molecular mechanisms of lipotoxicity in endothelial cells
[ Dissertation ] Medical University of Graz; 2013. pp. 99
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- Authors Med Uni Graz:
- Khan Muhammad Jadoon
- Advisor:
- Graier Wolfgang
- Malli Roland
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- Abstract:
- Accumulation of palmitic acid (PA) in cells from non-adipose tissues is known to induce lipotoxicity resulting in cellular dysfunction and death. A number of different molecular pathways have been proposed to mediate the process of cellular dysfunction and death in different tissues which mainly focus on apoptosis as a major cell death pathway. Recent developments have provided strong evidence on the contribution of necrosis as a programmed cell death pathway (necroptosis) which was otherwise considered as a random or accidental phenomenon. The exact molecular pathways of PA-induced cell death are still mysterious and one or a combination of different signaling cascades may be involved. Here, we show that PA triggers autophagy and lysosomal dysfunction simultaneously leading to endothelial cell death. The PA-induced cell death was predominantly necrotic as indicated by annexin V and propidium iodide (PI) staining, absence of caspase activity, low levels of DNA hypoploidy, and an early ATP depletion. In addition PA induced a strong elevation of mRNA levels of ubiquitin carboxyl-terminal hydrolase (CYLD), a known mediator of necroptosis. Moreover, siRNA-mediated knockdown of CYLD significantly antagonized PA-induced necrosis of endothelial cells. In contrast, inhibition and knockdown of receptor interacting protein kinase 1 (RIPK1) had no effect on PA-induced necrosis, indicating the induction of a CYLD-dependent but RIPK1-independent cell death pathway. PA was recognized as a strong and early inducer of autophagy. The inhibition of autophagy by both pharmacological inhibitors and genetic knockdown of the autophagy-specific genes, vacuolar protein sorting 34 (VPS34), and autophagy-related protein 7 (ATG7), could rescue the PA-induced death of endothelial cells. Moreover, the initiation of autophagy and cell death by PA was reduced in endothelial cells loaded with the Ca(2+) chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-(acetoxymethyl) ester (BAPTA-AM), indicating that Ca(2+) triggered the fatal signaling of PA. At the same time PA was found to activate calpain 1 and induces lysosomal dysfunction. A siRNA-mediated knock down of calpain 1 inhibited the PA-induced cell death significantly. To summarize PA induces autophagy and lysosomal dysfunction simultaneously leading to ATP depletion which further activates necroptosis in endothelial cells.