Venue : Centre Broca Nouvelle-Aquitaine
Thesis defended in English
Sarah Bou Sader Nehme
IMN
Thesis directed by Marc Landry and Walid Hleihel
Title
Cortical mechanisms of comorbidity between pain sensitization and attention-deficit/hyperactivity disorder (ADHD) in a mouse model
Abstract
Attention deficit/hyperactivity disorder (ADHD) and chronic pain are two complex conditions of multifactorial origins. Clinical and preclinical studies support an association between these two syndromes. However, the mechanisms underlying their comorbidity are not well understood. Previous findings from our team demonstrated a hyperactivity of the neurons of the anterior cingulate cortex (ACC) and a deregulation of the ACC-posterior insula (PI) pathway in ADHD-like conditions. Growing evidence also suggests a role for neuroinflammation in this concomitance. Our hypothesis thus suggests that neuroinflammation triggers an enhanced neuronal activity in the ACC that sensitizes pathways involved in ADHD symptoms and pain perception. Therefore, this Ph.D. work aims to elucidate the inflammatory mechanisms that may underlie ADHD and its associated pain sensitization, with an interest in the role of the purinergic P2X4 receptor.
To address this question, we generated an ADHD-like mouse model through the unilateral intracerebroventricular injection of 6-hydroxydopamine (6-OHDA) at P5. Two-month-old wild-type male and female mice were sacrificed, their brains were extracted, and their ACC and PI were dissected. Fixed tissues were used to study microglial and astrocytic morphology while fresh tissues were utilized for transcriptomic, proteomic, and phosphoproteomic investigations. Moreover, mice with a total knock-out of the P2X4 receptor were tested for thermal and mechanical pain sensitization, in addition to hyperactivity. Fixed tissues of the ACC were used to study changes in microglial morphology while fresh tissues of the ACC and PI were utilized for transcriptomic analyses.
Regarding the identification of inflammatory mechanisms in our ADHD-like mouse model, our results report (i) changes in microglial and astrocytic morphology, associated with cellular reactivity, in the ACC of 6-OHDA mice, (ii) the presence of a pro-inflammatory environment in the ACC and PI of 6-OHDA mice, (iii) modifications in protein expression and kinase (serine-threonine and tyrosine) activity in the ACC and PI of 6-OHDA mice, and correlated with impairments in axon guidance, apoptosis, cytoskeleton dynamics, signaling cascades, neurotrophins, and neurotransmitter systems, and (iv) alterations in protein interactions and, therefore, neuronal-astrocytic communication in the ACC of 6-OHDA mice. Finally, data integration identified four processes impaired in the ACC and PI of 6-OHDA males and females: apoptosis, axon guidance, synaptic plasticity (long-term potentiation), and growth of neuronal components. Interestingly, alterations in these processes were not only linked to ADHD and chronic pain conditions but also associated with Eph/ephrin bidirectional signaling cascades. Our findings also indicate a role for the P2X4 receptor in the worsening of ADHD hyperactivity symptom and the induction of morphological changes in microglial cells that correlate with cellular reactivity. However, it exerts a protective effect by limiting the expression of pro-inflammatory molecules, possibly from non-microglial cells.
In conclusion, our work provides interesting insights into the inflammatory mechanisms that may underpin the comorbidity between ADHD and pain sensitization. A mild and sustained pro-inflammatory environment in the ACC and PI drives changes in synaptic-related (long-term potentiation, axon guidance, outgrowth of neuronal components) and apoptotic processes. These impairments alter cell-cell connectivity and neuronal activity, thus participating in ADHD and chronic pain pathogenesis.
Key words
Cortical mechanisms, ADHD, pain sensitization, neuroinflammation, anterior cingulate cortex, insular cortex
Jury
Mme NADJAR Agnès, Professeure, Université de Bordeaux, Présidente du jury
M. GLENNON Jeffrey, Docteur, University College Dublin, Rapporteur
Mme SÁNCHEZ-PÉREZ Ana-María, Professeure, University Jaume I, Rapportrice
Mme BITAR Tania, Docteure, Université Saint-Esprit Kaslik, Examinatrice
M. GALINEAU Laurent, Docteur, Université de Tours, Examinateur
Mme RÉAUX-LE-GOAZIGO Annabelle, Directrice de recherche INSERM, Examinatrice
M. LANDRY Marc, Professeur, Université de Bordeaux, Directeur de thèse
M. HLEIHEL Walid, Professeur, Université Saint-Esprit Kaslik, Directeur de thèse
Publications
- Bou Sader Nehme, S., Sanchez-Sarasua, S., Adel, R., Tuifua, M., Ali, A., Essawy, A. E., Abdel Salam, S., Hleihel, W., Boué-Grabot, E., & Landry, M. (2024). P2X4 signalling contributes to hyperactivity but not pain sensitization comorbidity in a mouse model of attention deficit/hyperactivity disorder. Frontiers in pharmacology, 14, 1288994. https://doi.org/10.3389/fphar.2023.1288994
- Assaf, M., Rouphael, M., Bou Sader Nehme, S., Soufia, M., Alameddine, A., Hallit, S., Landry, M., Bitar, T., & Hleihel, W. (2024). Correlational Insights into Attention-Deficit/Hyperactivity Disorder in Lebanon. Int. J. Environ. Res. Public Health, 21, 1027. https://doi.org/10.3390/ijerph21081027
- Bou Sader Nehme, S., Sanchez-Sarasua, S., Dhellemmes, T., Tuifua, M., Hleihel, W., Landry, M. (2024). Neuroinflammation et mécanismes spinaux de la douleur (under review)