Complex sentence: Increased levels of one of these initiation factors often trigger a cascade of events that leads to increased levels of other initiation factors meaning that neuronal apoptosis is being induced by multiple things at any given time.
Split into simpler sentences: Increased levels of one of these initiation factors often trigger a cascade of events that leads to increased levels of other initiation factors. This means that neuronal apoptosis is being induced by multiple things at any given time.