Functional characterization of starved astrocytes and their potential role in Anorexia nervosa
- Funktionelle Charakterisierung von ausgehungerten Astrozyten und ihre mögliche Rolle bei Anorexia nervosa
Kogel, Vanessa; Marquardt, Till (Thesis advisor); Beyer, Cordian (Thesis advisor); Kampa, Björn M. (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2022
Anorexia nervosa (AN) is a psychiatric disorder characterized by excessive weight loss, disturbed bodyimage and fear of gaining weight. It is the third most common chronic disorder in adolescence with the highest mortality rate of psychiatric disorders. Pathophysiologically, patients suffering from AN exhibit symptoms including hormonal dysregulation, increased inflammatory markers in the blood and brain volume reduction. The activity-based anorexia (ABA) animal model mimics many symptoms of this disease and is therefore well-suited to study AN. In ABA animals, brain volume loss was also found and associated with a reduction of GFAP-positive astrocytes. The pathophysiology of AN and the specific role of the astrocyte loss are still not understood. Cell culture models are valid experimental tools to examine cellular and molecular effects related to diseases in more detail. The aim of this study was to develop an astrocyte culture model that reflects the long-term nutritional undersupply in chronically ill patients with AN. First, the optimal glucose concentration was determined which induces a state of chronic undernutrition but not massive astrocyte cell death. Subsequently, the semi-starved astrocytes were characterized in detail at the protein and gene level with special emphasis on inflammatory and stress-related factors. Additionally, the biosynthetic micro(mi)RNA machinery and miRNA profiles were studied. Starvation-related effects were also tested for reversibility after refeeding with regular glucose concentrations, analogous to nutritional rehabilitation in patients with AN. The optimal glucose concentration to induce semi-starvation was 2 mM and triggered stress responses without impairing cell viability. Astrocytes under semi-starvation developed an increased inflammatory reaction and activation of the unfolded protein response (UPR). In addition, altered morphology as well as induction of markers associated with the pro-inflammatory A1 phenotype and decreased expression of anti-inflammatory A2 phenotype markers indicate an increase in astrocyte reactivity. Taken together, these data show an elevated stress response following glucose deprivation. The absence of cell death and consistent metabolic activity, however, indicates that semi-starved astrocytes are not limited in their basic viability and functions. Elevated expression of genes involved in oxidative phosphorylation as well as a tendency towards a regulation of glucose and glutamate transporters suggest sustained alterations in cell physiology. Further, we found that starvation caused changes in the miRNAbiosynthesis machinery and various miRNAs which may play a critical role in the metabolic transition and inflammatory activity of astrocytes. Refeeding experiments showed that most starvation-induced responses were reversible. The results demonstrate that astrocytes respond to chronic glucose semi-starvation with multiple stress reactions and major changes in cell physiology. With respect to the diverse functions of astrocytes, an association between these elevated stress responses and morphological and functional alterations found in the brains of patients suffering from undernutrition is conceivable.