A disproportionate increase in activated nuclear factor-kappa B (NF-κB) has been shown to drive the Aβ deposition, neuroinflammation and neurodegeneration in Alzheimer’s disease (AD). Hence, selective targeting of activated p65 represents an attractive therapeutic approach for AD. Glucocorticoid induced leucine zipper (GILZ) is a NF-κB interactant that binds and sequesters the activated p65 in the cytoplasm. The p65 binding domain of GILZ adopts a polyproline type II helical conformation, a motif that acts as an adaptable glove in the interface with the binding partner and constitutes an excellent template for drug design. Previously, peptide analogs of the p65 binding domain of GILZ, referred to as GA have been shown to suppress pathology in the lipopolysaccharide induced model of neuroinflammation. In this study, we investigated the CNS delivery of labeled GA administered intraperitoneally in adult mice for a period of upto 24 h. Further, we evaluated the suppressive potential of GA in 5xFAD mice, an aggressive model with five genetic mutations closely associated with human AD. Groups of 5xFAD mice administered GA or control peptide intraperitoneally on alternate days for six weeks were evaluated for Aβ deposition, microglia, inflammation and innate immune responses by immunohistochemistry and real time polymerase reaction. GA was observed in proximity with NeuN positive neurons suggesting that the compound crossed the blood brain barrier to reach the brain parenchyma. Further, GA treatment decreased Aβ load, reduced Iba1 + microglia and glial fibrillary acidic protein (GFAP)+ astrocytes, inhibited inflammatory cytokines and suppressed toll like receptor (TLR-2, TLR-4) expressions in 5xFAD mice.

Schematic representation of selective inhibition of NF-κB p65 by glucocorticoid induced leucine zipper (GILZ) or GILZ analog (GA).

In resting cells, the NF-κB p65:p50 dimers remain in an active complex by the IκB complex. Activation of neuron or glial cells by various stimuli such as accumulating amyloid-β plaques or reactive active species phosphorylate the IκB proteins, this releases the p65:p50 dimer from the inhibitory complex, which then translocate to the nucleus and induce transactivation of pathological mediators. Structurally, the p65 protein includes an amino terminal Rel homology domain for dimerization and a transactivation domain (TAD), which facilitates transactivation of target genes. Glucocorticoid induced glucine zipper (GILZ) or GILZ analog (GA) bind the exposed p65-TAD blocking its nuclear translocation and thereby modulate transactivation of pathological mediators including pro-inflammatory cytokines, innate immune receptors such as toll like receptor (TLR), pro-apoptotic molecules and neurotoxic molecules.