Neuronal cell death in neurodegenerative diseases: recurring themes around protein handling

Cellular stress responses: cell survival and cell death

Cells can respond to stress in various ways ranging from the activation of survival pathways to the initiation of cell death that eventually eliminates damaged cells. Whether cells mount a protective or destructive stress response depends to a large extent on the nature and duration of the stress as well as the cell type. Also, there is often the interplay between these responses that ultimately determines the fate of the stressed cell. The mechanism by which a cell dies (i.e., apoptosis, necrosis, pyroptosis, or autophagic cell death) depends on various exogenous factors as well as the cell's ability to handle the stress to which it is exposed. The implications of cellular stress responses to human physiology and diseases are manifold and will be discussed in this review in the context of some major world health issues such as diabetes, Parkinson's disease, myocardial infarction, and cancer.

The neuronal cell cycle as a mechanism of pathogenesis in Alzheimer's disease

Differentiated neurons display specific biochemical, physiological and morphological properties that apparently prevent them from further cell division. Nevertheless, expression of cell cycle modulators persists after neuronal differentiation and is upregulated under stress conditions, such as trophic factor deprivation, oxidative stress and the presence of DNA damaging agents. This apparent reactivation of the cell cycle has been postulated as a sine qua non for neuronal death in response to those stress conditions, particularly in Alzheimer's disease. However, the physiological and pathogenic implications of a putative neuronal cell cycle are far from clear. Here, we discuss the notion of the neuronal cell cycle as a mediator of cell death, with particular emphasis on Alzheimer's disease.

Heat shock protein 27 in neuronal survival and neurite outgrowth

The small heat shock protein 27 (Hsp27) is well documented to promote neuronal survival in neurodegenerative diseases and following nerve injury. It can directly inhibit apoptotic pathways, and as a chaperone it can ameliorate the toxic effects of misfolded proteins. More recently, Hsp27 has been implicated to also play a role in neurite outgrowth. Thus, Hsp27 is situated at the intersection of neuronal survival and differentiation and, as such, it has dual potential as a key therapeutic target for neuroregeneration.