Aresearcher who studies neurodegenerative diseases has found that dying neurons contains a high concentration of miss-folded proteins in their cytoplasm. further experiments demonstrated that the lysosomes are working properly in these neurons. according to this information, which cellular structure is responsible for this disease?

The cellular structure responsible for this disease is THE ENDOPLASMIC RETICULUM. 
In eurkaryotic cells, endoplasmic reticulum is very essential for the folding and trafficking of proteins. Increased protein synthesis and environmental insults usually leads to the misfolding of proteins by endoplasmic reticulum. The accumulation of misfolded proteins inside the cell is called endoplasmic reticulum stress.