Estrogen and cytokines production - The possible cause of gender differences in neurological diseases

Naturally occurring sexual dimorphism has been implicated in the risk, progression and recovery front numerous neurological disorders. These include head injury, multiple sclerosis (MS), stroke, and neurodegenerative diseases (Parkinson's disease (PD), Alzheimer's disease (AD) or amyotrophic lateral sclerosis (ALS). Accumulating evidence suggests that observed differences between men and women could result from estrogen's wide range of effects within the mammalian central nervous system (CNS), with it's neuroprotective effect being one of the most important. It seems possible that neuroprotective activity of estrogen could be partially a result of it's anti-inflammatory action. It has been well established that inflammation plays an important role in the etiopathogenesis and manifestation of brain pathological changes. In this regard, an important role has been Suggested for pro-inflammatory cytokines produced by activated glial cells, neurons and immune cells that invade brain tissue. Within the CNS, cytokines stimulate inflammatory processes that may impair blood-brain barrier permeability as well as promote apoptosis of neurons, oligodendrocytes and induce myelin damage. Given that estrogen may modulate cytokine expression, coupled with the fact that gender differences of cytokine production are apparent in animal models of PD and MS, suggests an important connection between hormonal-cytokine link in neurodegeneration. Indeed, while MS patients and mice subjected to experimental autoimmune encephalomyelitis (EAE) display gender specific alterations of IFN-gamma and IL-12, variations of TNF and IL-6 were associated with PD. Also in case of more acute neurodegenerative conditions, such as stroke, the effect of IL-6 gene G-174C polymorphism was different in males and females. Given that our understanding of the role of estrogen on cytokine production and accompanying CNS pathological conditions is limited, the present reviews aims to present some of our recent findings in this area and further evaluate the evidence that may be relevant to the design of new hormonal anti-inflammatory treatment strategies for neurodegenerative diseases.