Research articleAmelioration of scopolamine-induced learning and memory impairment by the TRPV4 inhibitor HC067047 in ICR mice
Introduction
Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that causes severe cognitive decline and an inability to function in daily life [1]. The hallmark features of AD include the loss of neurons and synapses [2], deleterious senile plaques that develop in the brain [3], and the presence of intracellular neurofibrillary tangles (NFTs) [4]. To date, AD affects 50 million people worldwide, and this number will more than triple to 152 million by 2050 [5]. AD has a complex multifactorial etiology that, despite years of research, remains quite elusive.
Some studies noted that damage to basal forebrain cholinergic neurons seems to be one of the most important characteristics in AD [6]. Dysfunction of the cholinergic system has been regarded as a marker of neurological pathology that is associated with deterioration of learning and memory functions [7]. Therefore, recuperating the cholinergic role remains an effective treatment strategy for improving the symptoms of AD. Scopolamine (SCP) is a muscarinic acetylcholine receptor (mAChR) antagonist [8]. Some studies suggest that it can disrupt learning and memory function in animals and humans by promoting acetylcholinesterase (AChE) and upregulating levels of brain iron [9]. These conditions are similar to those observed in patients with AD. Therefore, SCP has been widely used to establish an AD-like model to evaluate the effects of potential therapeutics and the benefits of drug candidates in dementia.
Recently, some studies have suggested that cation channels are involved in synaptic plasticity and memory [10]. Transient receptor potential vanilloid 4 (TRPV4) channels are members of the vanilloid TRP subfamily forming, a large group of related cell membrane proteins known as TRP channels [11]. Various stimuli, including hypotonicity, warm temperature, and lipids downstream of arachidonic acid metabolism, can activate TRPV4 channels [12]. As a calcium-selective cation channel, TRPV4 can lead to inward currents (primarily Ca2+ influx) when it is activated. TRPV4 is also widely expressed in the central nervous system, including, the hippocampus and cortex, thalamus and cerebellum, and is located in neurons, astrocytes and microglia [13]. Activated TRPV4 channels have been suggested to participate in multiple pathophysiological processes, such as amyloid-β (Aβ) 40-induced hippocampal cell death [14]. The role of TRPV4 in neurotoxicology has been elaborated in detail. However, the role of TRPV4 in AD-like model pathogenesis remains largely elusive.
The aim of this study was to assess whether SCP-induced cognitive dysfunction is associated with TRPV4 in the hippocampus and to explore the possible mechanism underlying these associations. In this study, we investigated the memory enhancing effects of HC067047 on SCP-induced memory deficits in ICR mice using NPRT, NORT, and Y-maze tests. It has been reported that the activation of TRPV4 leads to the disturbance of Ca2+ homeostasis, which might increase cellular excitability and lead to apoptosis [15]. Thus, the expression of hippocampal CamkIIα/p-CamkⅡα was examined. Furthermore, to elucidate the molecular mechanisms underlying the neuroprotective effect of HC067047, the expression of proteins involved in apoptosis and neuronal markers including the neurogenesis marker DCX and the mature neuronal marker NeuN, was also examined.
Section snippets
Materials
HC067047 was purchased from Target Molecule Co. (T4680). HC067047 was dissolved in vehicle (8% DMSO (Sigma)) and 2% Tween 80 (Solarbio) in saline solution). SCP was purchased from MedChem Express Co. (St. New Jersey, US), was dissolved in saline, for use in experiments.
Animals
Eight-week-old ICR male mice were purchased from the Hunan SJA Lab Animal Center of Changsha (Hunan, China). The mice were randomly divided into vehicle, SCP and HC067047 + SCP groups (n = 15 mice each). Mice were maintained at
Induction of cognitive dysfunction in mice using SCP
To investigate the effects of SCP on animal behavior, we performed a series of behavioral tests (Fig. 1). Compared NS mice, SCP mice exhibited a significantly reduced discrimination ratio as measured by NPRT (t = 3.986, P = 0.0008) (Fig. 1A). In the NORT, SCP mice displayed an impaired discrimination ratio compared to NS mice. (t = 12.75, P < 0.01) (Fig. 1B). In the Y-maze, the time spent in the novel arm was also reduced in the model group compared to the NS group (t = 2.873, P = 0.0152) (Fig.
Discussion
The basic pathological features of Aβ plaques and NFTs in AD are considered to be involved in the pathogenesis of AD [18]. However, drug candidates targeting Aβ or tau protein have not passed a phase III clinical trial [19], as the precise molecular mechanisms of AD still remain to be further explored. Meanwhile, there is a lack of effective and relatively safe therapeutic drugs for clinical treatment of AD. Hence, effective agents acting on other molecular targets involved in the pathogenesis
Conclusions
SCP triggering of TRPV4-CamkIIα-apoptosis proteins might participate in the development of cognitive dysfunctions. The Present results demonstrate that the TRPV4 inhibitor HC067047 ameliorates the scopolamine-induced behavioral changes in learning- and memory- impaired mice. Therefore, the TRPV4 inhibitor HC067047 could be a potential therapeutic and a neuroprotective agent against progressive AD.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Support was provided by research grants from the Hunan Provincial Education Department Foundation of China (2019JJ40257). and the Undergraduate Innovation and Entrepreneurship Training Program of Hunan Province (S202010555252).
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These authors contributed equally to this work.