Endocrine Abstracts

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the formation of amyloid-β (Aβ) plaques and Tau neurofibrillary tangles, leading to neuronal loss, inflammation, reduced neurogenesis, and cognitive impairment. Currently, there is no effective cure for AD, highlighting the urgent need for novel therapeutic strategies. Growth hormone-releasing hormone (GHRH), besides promoting the release of pituitary growth hormone (GH), exerts many peripheral functions, such as the stimulation of cell survival and proliferation. Notably, both GHRH and its agonistic analog MR-409 exert antinflammatory, cardioprotective, and neuroprotective effects, and protect against skeletal muscle atrophy. However, the role of GHRH in AD remains to be elucidated. Thus, in the present study we explored the neuroprotective functions of GHRH in vitro, in rat hippocampal neural stem cells (NSCs) and human neuroblastoma SH-SY5Y cell line, and in vivo, in transgenic 5xFAD mouse model of AD. In vitro, GHRH(1-44)NH₂increased cell survival and proliferation, and reduced apoptosis in NSCs and SH-SY5Y cells, under both growth factor deprivation and exposure to amyoid-β 1-42 (Aβ_1-42) peptide. The underlying mechanisms included stimulation of Gβ_αSβ/cAMP/PKA/CREB pathway, as well as ERK1/2 and PI3K/Akt, and inactivation of GSK-3β. Furthermore, GHRH showed neurogenic effects by promoting the differentiation of NSCs into neurons and astrocytes, and SH-SY5Y cells into neurons. Importantly, GHRH counteracted the Aβ_1-42-induced phosphorylation of Tau and activation of GSK-3β while suppressing the expression of inflammatory cytokines and phosphorylation of NF-κB. In vivo, 3-month-old male mice were assigned to the following groups: wild type (WT)-vehicle (VH) (n=7); WT-MR-409 (n=7); 5xFAD-VH (n=10); 5xFAD-MR-409 (n=10). Mice were subcutaneously treated daily with 0.8 mg/kg MR-409 or VH for 3 months. Compared with untreated, 5xFAD-MR-409 mice showed increased body weight. Importantly, we observed that treatment with MR-409 strongly reduced brain amyloid-β deposits and astrogliosis, as well as mRNA expression of inflammatory cytokines and phosphorylation of NF-κB in brain tissues of 5xFAD mice. Moreover, MR-409 reduced neuron loss, evaluated by neuronal marker NeuN, and increased brain-derived neurotrophic factor (BDNF) expression in brain lysates of 5xFAD mice. MR-409 also reduced the phosphorylation of Tau protein and inhibited the activation of GSK-3β in brain tissues of AD mice. Finally, AD mice treated with MR-409 showed attenuated expression of the atrophy-related markers atrogin and MurF1 in the skeletal muscle. Overall, these results, combined with our previous in vitro findings, suggest a protective role for MR-409 in AD.