UNRAVELLING MECHANISMS OF ASTROCYTIC GDNF EXPRESSION AND SECRETION: RELEVANCE IN GENE THERAPY APPROACHES FOR CNS DISEASES

Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor produced and secreted in the central nervous system by both neurons and glial cells. By binding to the RET receptor, GDNF activates intracellular signalling pathways involved in neuronal development and survival. Under pathological conditions, astrocytes upregulate and secrete GDNF, which may contribute to neuroprotection but also to glial activation. Although GDNF secretion is thought to be calcium-dependent, the mechanisms regulating its release from astrocytes remain poorly characterized. We investigated the regulation of GDNF secretion in primary rat astrocytes under basal conditions and following stimulation with ATP, a signalling molecule released during neuroinflammation or conditions of neuronal hyperactivity, e.g., epileptic seizures. Since astrocytes produce two GDNF isoforms, α and β, predominantly under pathological conditions, we induced their expression using lentiviral vectors encoding each isoform. We compared the two isoforms in terms of expression levels, intracellular localization within the secretory pathway, and secretion efficiency. We further characterized the functional impact of astrocyte-derived GDNF by analysing signalling activation in astrocytes and neuroprotective effects in primary hippocampal neurons. Finally, we evaluated the therapeutic potential of astrocytic GDNF in vivo by inducing its overexpression in hippocampal astrocytes via lentivector delivery, which resulted in secretion of GDNF in the brain parenchyma and conferred protection against recurrent seizures in an experimental model of epilepsy.