p27kip1 and TRPV4: molecular regulators for microglial motion

Abstract

Microglia, the resident macrophages of the central nervous system (CNS), are the first glial cells to be present in the brain and are important regulators of brain development, inflammation, homeostasis and plasticity (1, 2). They interact with various cell types in the brain, thereby driving synaptic pruning and modulating neurogenesis, neuronal activity and synaptogenesis (3). Microglia invade the developing brain where they adopt a highly ramified phenotype and continuously screen their environment to build and later maintain normal brain function (1, 3, 4). Malfunction of microglia is often correlated with brain malformation, brain dysfunction and both neurodegenerative and neurodevelopmental disorders including autism spectrum disorder (ASD), schizophrenia or Alzheimer’s disease (2, 5). Moreover, developmental deficits can lead to long-term changes in microglial movement affecting the adult brain response to infections or cognitive information processing, emphasizing the importance of proper microglial function and regulation (2, 6, 7). Despite recent breakthroughs regarding the various and critical roles of microglia in brain development and homeostasis, many aspects of the cellular and molecular mechanisms underlying their function remain unresolved. In this thesis, focus has specifically been laid on studying microglial motion as many aspects regarding the mechanism underlying microglial movement remain unresolved. After all, microglia require proper dynamics to fulfil their plethora of functions in both the developing and adult brain. Therefore, in this dissertation, two plausible candidates that might be involved in the cellular and molecular mechanisms regulating microglial functioning were explored. In chapter 3 we investigated whether p27kip1, a cell cycle and microtubule-associated protein is involved in microglial immune activation (Section 3.4.2), morphology (Section 3.4.3), migration (Section 3.4.4 & 3.4.5), branch motility (Section 3.4.4 & 3.4.6) and phagocytosis (Section 3.4.7). On the other hand, in chapter 4, we investigated a possible role for the mechanosensitive cation channel TRPV4 in cytoskeleton remodelling necessary for microglial movement. Some emphasis was put on the following questions: does TRPV4 influence morphology and motility in vitro (Section 4.4.1)? How does TRPV4 influence actin and tubulin dynamics in microglial cells (Section 4.4.2)? Finally, the question to whether TRPV4 is involved in regulating microglial motility in situ is briefly evaluated (Section 4.4.3).