Functional analysis of the endocannabinoid system in conditional mouse mutants

Abstract

In the scope of this thesis conditional knockout mice with a cell-specific deletion of Dagla (diacylglycerol lipase alpha) in neurons, astrocytes or microglia cells were generated, in order to identify the cellular source of 2-AG in the brain and to clarify the role of DAGLa in these cells in affective behaviors. <br /> Using the highly sensitive RNAscope technology, we show for the first time that a subpopulation of astrocytes in the mouse brain expresses Dagla, albeit at much lower levels than neurons. <br /> Targeted lipidomics revealed that both, neuronal and astrocytic DAGLa, contribute to the steady-state brain 2-AG levels. However, astrocytic DAGLa only accounts for a small percentage of 2-AG levels, which is in line with the lower expression of DAGLa on astrocytes compared to neurons. Furthermore, our results indicate that deletion of Dagla on one of these cell types, can be at least partly compensated by 2-AG production by the other cell types. Under normal conditions in vivo, microglial DAGLa does not contribute to bulk brain 2-AG levels. <br /> On the behavioral level, neuronal knockout of DAGLa led to clear changes in anxiety-related behaviors, measured in the zero-maze and open field test. These changes were accompanied with highly elevated corticosterone levels, suggesting an extremely important role of neuronal DAGLa in the regulation of stress and anxiety. Furthermore, mice with a neuronal Dagla deletion showed highly decreased body weight and food intake, implicating that neuronal DAGLa controls metabolic functions. <br /> Although astrocytic DAGLa only accounts for a minor percentage of the steady-state brain 2-AG, the deletion of Dagla in adult mouse astrocytes had profound behavioral consequences with significantly increased depressive-like behavioral responses and striking effects on maternal behavior. Our findings therefore indicate that lipids from the DAGLa metabolic axis in astrocytes play a key regulatory role in depressive-like behaviors. The depression-like phenotype was associated with decreased adult hippocampal neurogenesis, suggesting a highly important role of DAGLa in astroglial cells in the regulation of this process. <br /> Conditional knockout mice that were used to investigate DAGLa in microglia, showed slightly increased anxiety-related behaviors and decreased survival of neural progenitor cells in the dentate gyrus. These phenotypes can rather be attributed to the loss of DAGLa on myeloid cells in the periphery than to DAGLa in microglia, based on the characterization of knockout efficacy in our mouse lines <br /> Altogether, data from this thesis suggests that DAGLa in both, neurons and astrocytes, contributes to the steady-state 2-AG levels in the brain. DAGLa in both cell types is involved in the pathology of affective behaviors, with neuronal DAGLa playing a role in anxiety-related behaviors while DAGLa on astrocytes is especially involved in maternal and depressive-like behaviors. Proliferation and survival of progenitor cells during adult hippocampal neurogenesis are regulated by DAGLa on astroglial cells and myeloid cells, respectively.