Study of two analogues of pituitary adenylate cyclase-activating polypeptide as novel therapeutic compounds for Huntington’s disease

Huntington’s disease (HD) is a neurodegenerative genetic disorder with no effective treatment characterized by motor discoordination, deficits in cognitive function (acquiring new knowledges, memory, understanding…), and psychiatric alterations. The cause of HD is the expression of the mutant huntingtin (mHTT) which leads to the malfunctioning and degeneration of different brain regions. The loss of neurons in the striatum (striatal neurons) is a key feature in the development and progression of motor discoordination, whereas the malfunction of hippocampus has been associated with cognitive deficits in HD. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide widely distributed throughout the central nervous system considered a potential therapeutic agent for protecting neurons through the activation of three receptors: PAC1R, VPAC1R, and VPAC2R. However, the pharmacological use of PACAP is limited because the molecule is rapidly metabolized and because the activation of peripheral VPACRs has been associated to cardiovascular and respiratory secondary effects. As PAC1R is suggested to be the main effector of the neuroprotective effect of PACAP, more stable analogues of PACAP with higher affinity for PAC1R have been proposed as promising therapeutic tools. In this thesis we first showed that PACAP protects striatal cells against mHTT-induced toxicity and that although all PACAP receptors take part in neuroprotection, PAC1R plays a key role. Additionally, we demonstrated for the first time that the intranasal administration of metabolically stable analogues of PACAP displaying higher affinity for PAC1R improves cognitive and motor functions in a HD mouse model promoting beneficial actions in the hippocampus and the striatumLa malaltia de Huntington (MH) és una malaltia neurodegenerativa d’origen genètic sense un tractament efectiu que es caracteritza per provocar símptomes motors, cognitius (habilitat d’adquirir nous aprenentatges, memòria, comprensió...) i alteracions psiquiàtriques. La MH és causada per l’expressió de la huntingtina mutada (mHTT), la qual porta al mal funcionament i degeneració de diferents regions cerebrals. La pèrdua de neurones de l’estriat (neurones estriatals) és una característica en el desenvolupament i progressió de la descoordinació motora, mentre que el mal funcionament de l’hipocamp s’ha associat amb els dèficits cognitius de la MH. El polipèptid activador de l’adenilat ciclasa (PACAP) és un neuropèptid present al sistema nerviós central considerat un potencial agent terapèutic per ser capaç de protegir les neurones a través de l’activació dels seus receptors anomenats PAC1R, VPAC1R i VPAC2R. Tanmateix, el seu ús farmacològic es veu limitat perquè la molècula és ràpidament degradada i perquè s’ha detectat que causa efectes secundaris al sistema cardiovascular i respiratori quan activa els VPACs de forma perifèrica. Com que l’activació del PAC1R s’ha vist que promou la majoria d’efectes neuroprotectors de PACAP, s’ha proposat que anàlegs sintètics de PACAP més estables i amb una major afinitat pel PAC1R podrien ser eines terapèutiques prometedores. En aquesta tesi hem observat, en primer lloc, que el PACAP protegeix les neurones estriatals de la toxicitat induïda per la mHTT i, tot i que tots els receptors participen en la neuroprotecció, el PAC1R hi té una implicació clau. A més, hem demostrat per primera vegada que l’administració intranasal de dos anàlegs sintètics de PACAP més estables i amb més afinitat per PAC1R millora els símptomes motors i cognitius d’un model de ratolí de la MH, promovent accions beneficioses en l’hipocamp i l’estriatPrograma de Doctorat en Biologia Molecular, Biomedicina i Salu

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Protects Striatal Cells and Improves Motor Function in Huntington’s Disease Models: Role of PAC1 Receptor

International audienceHuntington’s disease (HD) is a hereditary neurodegenerative disorder caused by the expression of mutant huntingtin (mHtt). One of the main features of HD is the degeneration of the striatum that leads to motor discoordination. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that acts through three receptors named PAC1R, VPAC1R, and VPAC2R. In the present study, we first investigated the effect of PACAP on STHdhQ7/Q7 and STHdhQ111/Q111 cells that express wild-type Htt with 7 and mHtt with 111 glutamines, respectively. Then we explored the capacity of PACAP to rescue motor symptoms in the R6/1, a murine model of HD. We found that PACAP treatment (10 –7 M) for 24 h protects STHdhQ111/Q111 cells from mHtt-induced apoptosis. This effect is associated with an increase in PAC1R transcription, phosphorylation of ERK and Akt, and an increase of intracellular c-fos, egr1, CBP, and BDNF protein content. Moreover, the use of pharmacological inhibitors revealed that activation of ERK and Akt mediates these antiapoptotic and neurotrophic effects of PACAP. To find out PAC1R implication, we treated STHdh cells with vasoactive intestinal peptide (VIP), which exhibits equal affinity for VPAC1R and VPAC2R, but lower affinity for PAC1R, in contrast to PACAP which has same affinity for the three receptors. VIP reduced cleaved caspase-3 protein level, without promoting the expression of c-fos, egr1, CBP, and the neurotrophin BDNF. We next measured the protein level of PACAP receptors in the striatum and cortex of R6/1 mice. We observed a specific reduction of PAC1R at the onset of motor symptoms. Importantly, the intranasal administration of PACAP to R6/1 animals restored the motor function and increased the striatal levels of PAC1R, CBP, and BDNF. In conclusion, PACAP exerts antiapoptotic and neurotrophic effects in striatal neurons mainly through PAC1R. This effect in HD striatum allows the recovery of motor function and point out PAC1R as a therapeutic target for treatment of HD

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Protects Striatal Cells and Improves Motor Function in Huntington's Disease Models: Role of PAC1 Receptor.

Huntington's disease (HD) is a hereditary neurodegenerative disorder caused by the expression of mutant huntingtin (mHtt). One of the main features of HD is the degeneration of the striatum that leads to motor discoordination. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that acts through three receptors named PAC1R, VPAC1R, and VPAC2R. In the present study, we first investigated the effect of PACAP on STHdhQ7/Q7 and STHdhQ111/Q111 cells that express wild-type Htt with 7 and mHtt with 111 glutamines, respectively. Then we explored the capacity of PACAP to rescue motor symptoms in the R6/1, a murine model of HD. We found that PACAP treatment (10-7 M) for 24 h protects STHdhQ111/Q111 cells from mHtt-induced apoptosis. This effect is associated with an increase in PAC1R transcription, phosphorylation of ERK and Akt, and an increase of intracellular c-fos, egr1, CBP, and BDNF protein content. Moreover, the use of pharmacological inhibitors revealed that activation of ERK and Akt mediates these antiapoptotic and neurotrophic effects of PACAP. To find out PAC1R implication, we treated STHdh cells with vasoactive intestinal peptide (VIP), which exhibits equal affinity for VPAC1R and VPAC2R, but lower affinity for PAC1R, in contrast to PACAP which has same affinity for the three receptors. VIP reduced cleaved caspase-3 protein level, without promoting the expression of c-fos, egr1, CBP, and the neurotrophin BDNF. We next measured the protein level of PACAP receptors in the striatum and cortex of R6/1 mice. We observed a specific reduction of PAC1R at the onset of motor symptoms. Importantly, the intranasal administration of PACAP to R6/1 animals restored the motor function and increased the striatal levels of PAC1R, CBP, and BDNF. In conclusion, PACAP exerts antiapoptotic and neurotrophic effects in striatal neurons mainly through PAC1R. This effect in HD striatum allows the recovery of motor function and point out PAC1R as a therapeutic target for treatment of HD