Analysis of the mechanisms that regulate autophagy in astrocytes and their role in the clearance of the amyloid-b peptide

• Autores: Marta García Juan
• Directores de la Tesis: Francisco Wandosell (dir. tes.), Lara Ordóñez Gutiérrez (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2024
• Idioma: inglés
• Número de páginas: 152
• Títulos paralelos:
  • Análisis de los mecanismos que regulan la autofagia en astrocitos y su papel en la eliminación del péptido beta amiloide
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • The imbalance of mechanisms such as autophagy/ macroautophagy is a hallmark of Alzheimer Disease (AD), where the production of amyloid beta (Ab) disturbs the neuronal/glial proteostasis. The MTORC1 and AMPK pathways present therapeutical potential through autophagy regulation. Previously, we described that rapamycin, a well-known MTORC1 inhibitor, reduces Ab in the brain of the APP/PSEN1 AD mouse model. In primary neurons treated with rapamycin, Ab reduction also occurred but in a moderate fashion.

    In this Doctoral Thesis project, we focused on the mechanisms that regulate autophagy in astrocytes, essential for the maintenance of brain homeostasis. We hypothesize that the modulation of these molecular processes in this cell type could mitigate the pathological accumulation of Ab.

    First, we found a higher MTORC1 activity in the brain of 6-months-old APP/PSEN1 mice, primarily localized to neurons. In a model of organotypic brain slices, we described that MTORC1 inhibition produced a higher accumulation of autophagosomes/ lysosomes in neurons. These results suggest a differential regulation of MTORC1 that promotes a higher autophagic flux in astrocytes.

    Subsequent studies in primary astrocytes revealed a decreased activity of the MTORC1 pathway in APP/PSEN1 versus WT, without differences in the AMPK pathway. This was correlated with a higher autophagic flux, without changes in the energy metabolism. Notably, specific inhibition of MTORC1 with rapamycin in primary astrocytes increased autophagy and produced an autophagy-dependent anti-amyloid effect. In contrast, only the overexpression of the constitutively active AMPK mutant form increased autophagy, failing to replicate this through its pharmacological activation. Surprisingly, AMPK activation did not modify Ab secretion and the overexpression of mutant isoforms even exacerbated it. Finally, we found a differential effect of leucine, arginine and glutamine deprivation in primary astrocytes in terms of MTORC1 regulation, which did not reflect in an increment of macroautophagy. Surprisingly, the recovery of these amino acids in the media of amino acid deprived astrocytes suggested that another catabolic process, that remains to be fully elucidated, is being activated.

    Together, our findings underscore the significant role of astrocytes to the brain homeostasis and the importance of studying autophagy mechanisms in this cell type. In fact, we demonstrate that their contribution to the Ab burden could be rescued through autophagy mediated mechanisms. In addition, these results shed light on the controversy about the possible therapeutic effect of AMPK activation and MTORC1 on autophagy induction