Abstract
The study of microglia, the immune cells of the brain, has experienced a renaissance after the discovery of microglia polarization. In fact, the concept that activated microglia can shift into the M1 pro-inflammatory or M2 neuroprotective phenotypes, depending on brain microenvironment, has completely changed the understanding of microglia in brain aging and neurodegenerative diseases. Microglia polarization is particularly important in aging since an increased inflammatory status of body compartments, including the brain, has been reported in elderly people. In addition, inflammatory markers, mainly derived from activated microglia, are widely present in neurodegenerative diseases. Microglial inflammatory dysfunction, also linked to microglial senescence, has been extensively demonstrated and associated with cognitive impairment in neuropathological conditions related to aging. In fact, microglia polarization is known to influence cognitive function and has therefore become a main player in neurodegenerative diseases leading to dementia. As the life span of human beings increases, so does the prevalence of cognitive dysfunction. Thus, therapeutic strategies aimed to modify microglia polarization are currently being developed. Pharmacological approaches able to shift microglia from M1 pro-inflammatory to M2 neuroprotective phenotype are actually being studied, by acting on many different molecular targets, such as glycogen synthase kinase-3 (GSK3) β, AMP-activated protein kinase (AMPK), histone deacetylases (HDACs), etc. Furthermore, nutritional approaches can also modify microglia polarization and, consequently, impact cognitive function. Several bioactive compounds normally present in foods, such as polyphenols, can have anti-inflammatory effects on microglia. Both pharmacological and nutritional approaches seem to be promising, but still need further development. Here we review recent data on these approaches and propose that their combination could have a synergistic effect to counteract cognitive aging impairment and Alzheimer’s disease (AD) through immunomodulation of microglia polarization, i.e., by driving the shift of activated microglia from the pro-inflammatory M1 to the neuroprotective M2 phenotype.
Highlights
Reviewed by: Björn Spittau, Albert Ludwig University of Freiburg, Germany Rubem C
Pharmacological and nutritional strategies aimed at modulating microglial activation (Figure 2) offer much potential for future brain aging and Alzheimer’s disease (AD) therapy
Clinical trials focused on immunomodulation targets performed so far, have not resulted in AD patient improvement, it has to be considered that immunomodulatory strategies may have preventive rather than protective effects
Summary
Microglia are the resident mononuclear phagocytes of the central nervous system and constitute about 5%–20% of total brain cells displaying regional differences in density (Lawson et al, 1990) These cells are known for their plastic capability and the functional characteristic depending on their activation state; it is not difficult to find morphological changes these cells undergo depending on their function (Szabo and Gulya, 2013). Under conditions of stress, inflammation, injury or upon the effect of certain signals, microglia change their morphology and activation state, from a non-activated to an activated state (Stence et al, 2001) Microglial cells enlarge their cell body and their ramifications become shorter and less arborized. In vitro studies in cell cultures have shown the ambivalent role of microglial cells on neurons; neuroprotective, and neurotoxic, while in vivo studies mainly support the neuroprotective potential of activated microglia (Streit, 2002)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
