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Published on: August 15, 2012
Substrate Elasticity Exerts Functional Effects on Primary Microglia
Stefan J Blaschke1,2, Seda Demir1, Anna König1
1Department of Neurology, Faculty of Medicine and University Hospital, The University of Cologne, Cologne, Germany.
Abstract:
Microglia-the brain's primary immune cells-exert a tightly regulated cascade of pro- and anti-inflammatory effects upon brain pathology, either promoting regeneration or neurodegeneration. Therefore, harnessing microglia emerges as a potential therapeutic concept in neurological research. Recent studies suggest that-besides being affected by chemokines and cytokines-various cell entities in the brain relevantly respond to the mechanical properties of their microenvironment. For example, we lately reported considerable effects of elasticity on neural stem cells, regarding quiescence and differentiation potential. However, the effects of elasticity on microglia remain to be explored.Under the hypothesis that the elasticity of the microenvironment affects key characteristics and functions of microglia, we established an in vitro model of primary rat microglia grown in a polydimethylsiloxane (PDMS) elastomer-based cell culture system. This way, we simulated the brain's physiological elasticity range and compared it to supraphysiological stiffer PDMS controls. We assessed functional parameters of microglia under "resting" conditions, as well as when polarized towards a pro-inflammatory phenotype (M1) by lipopolysaccharide (LPS), or an anti-inflammatory phenotype (M2) by interleukin-4 (IL-4). Microglia viability was unimpaired on soft substrates, but we found various significant effects with a more than two-fold increase in microglia proliferation on soft substrate elasticities mimicking the brain (relative to PDMS controls). Furthermore, soft substrates promoted the expression of the activation marker vimentin in microglia. Moreover, the M2-marker CD206 was upregulated in parallel to an increase in the secretion of Insulin-Like Growth Factor-1 (IGF-1). The upregulation of CD206 was abolished by blockage of stretch-dependent chloride channels. Our data suggest that the cultivation of microglia on substrates of brain-like elasticity promotes a basic anti-inflammatory activation state via stretch-dependent chloride channels. The results highlight the significance of the omnipresent but mostly overlooked mechanobiological effects exerted on microglia and contribute to a better understanding of the complex spatial and temporal interactions between microglia, neural stem cells, and glia, in health and disease.
Insights
Brain elasticity influences microglia function. Soft, brain-like substrates increase microglia proliferation and promote an anti-inflammatory state via stretch-dependent channels, offering therapeutic insights.
Area of Science:
- Neuroscience
- Immunology
- Biomaterials Science
Background:
- Microglia are key immune cells in the brain, influencing both regeneration and neurodegeneration.
- Emerging evidence suggests that the mechanical properties of the brain microenvironment, such as elasticity, impact neural cell behavior.
- The specific effects of microenvironmental elasticity on microglia remain largely unexplored.
Purpose of the Study:
- To investigate the hypothesis that microenvironmental elasticity affects microglia characteristics and functions.
- To explore the role of mechanobiology in regulating microglia activation states.
- To understand how substrate stiffness influences microglia proliferation, activation markers, and cytokine secretion.
Main Methods:
- Developed an in vitro model using primary rat microglia cultured on polydimethylsiloxane (PDMS) elastomers with varying elasticity.
- Simulated physiological brain elasticity and compared it to stiffer, supraphysiological controls.
- Assessed microglia functional parameters under resting, M1 (pro-inflammatory), and M2 (anti-inflammatory) polarized conditions.
Main Results:
- Microglia viability was unaffected by substrate elasticity.
- Soft, brain-like elastic substrates significantly increased microglia proliferation (over two-fold) compared to stiffer controls.
- Soft substrates promoted vimentin expression and upregulated the M2 marker CD206, alongside increased Insulin-Like Growth Factor-1 (IGF-1) secretion.
- CD206 upregulation was dependent on stretch-activated chloride channels.
Conclusions:
- Cultivating microglia on substrates mimicking brain elasticity promotes a baseline anti-inflammatory activation state.
- This effect is mediated through stretch-dependent chloride channels, highlighting the importance of mechanobiology.
- These findings contribute to understanding glia-neuron interactions and offer potential therapeutic avenues for neurological diseases by modulating the brain's mechanical properties.
