Targeting the neuronal calcium sensor DREAM with small-molecules for Huntington's disease treatment.

DREAM, a neuronal calcium sensor protein, has multiple cellular roles including the regulation of Ca2+ and protein homeostasis. We recently showed that reduced DREAM expression or blockade of DREAM activity by repaglinide is neuroprotective in Huntington's disease (HD). Here we used structure-based drug design to guide the identification of IQM-PC330, which was more potent and had longer lasting effects than repaglinide to inhibit DREAM in cellular and in vivo HD models. We disclosed and validated an unexplored ligand binding site, showing Tyr118 and Tyr130 as critical residues for binding and modulation of DREAM activity. IQM-PC330 binding de-repressed c-fos gene expression, silenced the DREAM effect on KV4.3 channel gating and blocked the ATF6/DREAM interaction. Our results validate DREAM as a valuable target and propose more effective molecules for HD treatment.

Identification of IQM-266, a Novel DREAM Ligand That Modulates KV4 Currents.

Downstream Regulatory Element Antagonist Modulator (DREAM)/KChIP3/calsenilin is a neuronal calcium sensor (NCS) with multiple functions, including the regulation of A-type outward potassium currents (I A). This effect is mediated by the interaction between DREAM and KV4 potassium channels and it has been shown that small molecules that bind to DREAM modify channel function. A-type outward potassium current (I A) is responsible of the fast repolarization of neuron action potentials and frequency of firing. Using surface plasmon resonance (SPR) assays and electrophysiological recordings of KV4.3/DREAM channels, we have identified IQM-266 as a DREAM ligand. IQM-266 inhibited the KV4.3/DREAM current in a concentration-, voltage-, and time-dependent-manner. By decreasing the peak current and slowing the inactivation kinetics, IQM-266 led to an increase in the transmembrane charge ( Q K V 4.3 / DREAM ) at a certain range of concentrations. The slowing of the recovery process and the increase of the inactivation from the closed-state inactivation degree are consistent with a preferential binding of IQM-266 to a pre-activated closed state of KV4.3/DREAM channels. Finally, in rat dorsal root ganglion neurons, IQM-266 inhibited the peak amplitude and slowed the inactivation of I A. Overall, the results presented here identify IQM-266 as a new chemical tool that might allow a better understanding of DREAM physiological role as well as modulation of neuronal I A in pathological processes.

Inhibition of the Neuronal Calcium Sensor DREAM Modulates Presenilin-2 Endoproteolysis.

Deregulated intracellular Ca2+ and protein homeostasis underlie synaptic dysfunction and are common features in neurodegenerative diseases. DREAM, also known as calsenilin or KChIP-3, is a multifunctional Ca2+ binding protein of the neuronal calcium sensor superfamily with specific functions through protein-DNA and protein-protein interactions. Small-molecules able to bind DREAM, like the anti-diabetic drug repaglinide, disrupt some of the interactions with other proteins and modulate DREAM activity on Kv4 channels or on the processing of activating transcription factor 6 (ATF6). Here, we show the interaction of endogenous DREAM and presenilin-2 (PS2) in mouse brain and, using DREAM deficient mice or transgenic mice overexpressing a dominant active DREAM (daDREAM) mutant in the brain, we provide genetic evidence of the role of DREAM in the endoproteolysis of endogenous PS2. We show that repaglinide disrupts the interaction between DREAM and the C-terminal PS2 fragment (Ct-PS2) by coimmunoprecipitation assays. Exposure to sub-micromolar concentrations of repaglinide reduces the levels of Ct-PS2 fragment in N2a neuroblastoma cells. These results suggest that the interaction between DREAM and PS2 may represent a new target for modulation of PS2 processing, which could have therapeutic potential in Alzheimer's disease (AD) treatment.

Inhibition of DREAM-ATF6 interaction delays onset of cognition deficit in a mouse model of Huntington's disease.

The transcriptional repressor DREAM (downstream regulatory element antagonist modulator) is a multifunctional neuronal calcium sensor (NCS) that controls Ca2+ and protein homeostasis through gene regulation and protein-protein interactions. Downregulation of DREAM is part of an endogenous neuroprotective mechanism that improves ATF6 (activating transcription factor 6) processing, neuronal survival in the striatum, and motor coordination in R6/2 mice, a model of Huntington's disease (HD). Whether modulation of DREAM activity can also ameliorate cognition deficits in HD mice has not been studied. Moreover, it is not known whether DREAM downregulation in HD is unique, or also occurs for other NCS family members. Using the novel object recognition test, we show that chronic administration of the DREAM-binding molecule repaglinide, or induced DREAM haplodeficiency delays onset of cognitive impairment in R6/1 mice, another HD model. The mechanism involves a notable rise in the levels of transcriptionally active ATF6 protein in the hippocampus after repaglinide administration. In addition, we show that reduction in DREAM protein in the hippocampus of HD patients was not accompanied by downregulation of other NCS family members. Our results indicate that DREAM inhibition markedly improves ATF6 processing in the hippocampus and that it might contribute to a delay in memory decline in HD mice. The mechanism of neuroprotection through DREAM silencing in HD does not apply to other NCS family members.