Alzheimer's disease therapeutic candidate SAK3 is an enhancer of T-type calcium channels

The impact of chelating compounds on Cu2+, Fe2+/3+, and Zn2+ ions in Alzheimer's disease treatment

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid - β extracellular plaques and tau interfibrillar tangles, leading to memory loss, cognitive decline, and behavioral changes. With dementia posing a growing global health concern, there is an urgent need for comprehensive strategies to address its challenges. The economic burden of dementia is projected to rise significantly, emphasizing the necessity for collaborative efforts in research and healthcare. In the United States alone, millions are affected by AD, with prevalence increasing with age and even affecting younger individuals. The complexity of AD involves intricate biological processes, including the aggregation of amyloid beta, oxidative stress, and metal ion dysregulation. Metal ions, particularly those from copper, iron, and zinc, play pivotal roles in AD pathology, influencing Aβ deposition and tau protein accumulation. Current treatments offer symptomatic relief but do not address the underlying disease mechanisms. This paper explores the potential of various chelating compounds to target metal ions involved in AD pathology. N-acylhydrazones, morpholine, chrysin, quinoline, oxindole, cyclam, catechol-based, and quinazolinone-based derivatives show promising chelation activity and therapeutic effects. Metal chelation therapy offers a targeted approach to AD treatment by addressing the core pathology. By selectively binding to metal ions implicated in disease progression, chelators may minimize side effects associated with broad-spectrum treatments. Additionally, chelators may offer neuroprotective effects beyond metal binding, further enhancing their therapeutic potential. Overall, metal chelation therapy presents a promising strategy in combating AD, with the potential to significantly impact disease progression and improve patient outcomes.

SAK3 confers neuroprotection in the neurodegeneration model of X-linked Dystonia-Parkinsonism

Background X-linked Dystonia-Parkinsonism(XDP) is an adult-onset neurodegenerative disorder that results in the loss of striatal medium spiny neurons (MSNs). XDP is associated with disease-specific mutations in and around the TAF1 gene. This study highlights the utility of directly reprogrammed MSNs from fibroblasts of affected XDP individuals as a platform that captures cellular and epigenetic phenotypes associated with XDP-related neurodegeneration. In addition, the current study demonstrates the neuroprotective effect of SAK3 currently tested in other neurodegenerative diseases. Methods XDP fibroblasts from three independent patients as well as age- and sex-matched control fibroblasts were used to generate MSNs by direct neuronal reprogramming using miRNA-9/9*-124 and thetranscription factors CTIP2 , DLX1 -P2A- DLX2 , and MYT1L . Neuronal death, DNA damage, and mitochondrial health assays were carried out to assess the neurodegenerative state of directly reprogrammed MSNs from XDP patients (XDP-MSNs). RNA sequencing and ATAC sequencing were performed to infer changes in the transcriptomic and chromatin landscapesof XDP-MSNs compared to those of control MSNs (Ctrl-MSNs). Results Our results show that XDP patient fibroblasts can be successfully reprogrammed into MSNs and XDP-MSNs display several degenerative phenotypes, including neuronal death, DNA damage, and mitochondrial dysfunction, compared to Ctrl-MSNs reprogrammed from age- and sex-matched control individuals' fibroblasts. In addition, XDP-MSNs showed increased vulnerability to TNFα -toxicity compared to Ctrl-MSNs. To dissect the altered cellular state in XDP-MSNs, we conducted transcriptomic and chromatin accessibility analyses using RNA- and ATAC-seq. Our results indicate that pathways related to neuronal function, calcium signaling, and genes related to other neurodegenerative diseases are commonly altered in XDP-MSNs from multiple patients. Interestingly, we found that SAK3, a T-type calcium channel activator, that may have therapeutic values in other neurodegenerative disorders, protected XDP-MSNs from neuronal death. Notably, we found that SAK3-mediated alleviation of neurodegeneration in XDP-MSNs was accompanied by gene expression changes toward Ctrl-MSNs.

Misfolded protein oligomers: mechanisms of formation, cytotoxic effects, and pharmacological approaches against protein misfolding diseases

The conversion of native peptides and proteins into amyloid aggregates is a hallmark of over 50 human disorders, including Alzheimer's and Parkinson's diseases. Increasing evidence implicates misfolded protein oligomers produced during the amyloid formation process as the primary cytotoxic agents in many of these devastating conditions. In this review, we analyze the processes by which oligomers are formed, their structures, physicochemical properties, population dynamics, and the mechanisms of their cytotoxicity. We then focus on drug discovery strategies that target the formation of oligomers and their ability to disrupt cell physiology and trigger degenerative processes.

Mammalian neurotoxins, Blarina paralytic peptides, cause hyperpolarization of human T-type Ca channel hCav3.2 activation

Among the rare venomous mammals, the short-tailed shrew Blarina brevicauda has been suggested to produce potent neurotoxins in its saliva to effectively capture prey. Several kallikrein-like lethal proteases have been identified, but the active substances of B. brevicauda remained unclear. Here, we report Blarina paralytic peptides (BPPs) 1 and 2 isolated from its submaxillary glands. Synthetic BPP2 showed mealworm paralysis and a hyperpolarization shift (-11 mV) of a human T-type Ca2+ channel (hCav3.2) activation. The amino acid sequences of BPPs were similar to those of synenkephalins, which are precursors of brain opioid peptide hormones that are highly conserved among mammals. However, BPPs rather resembled centipede neurotoxic peptides SLPTXs in terms of disulfide bond connectivity and stereostructure. Our results suggested that the neurotoxin BPPs were the result of convergent evolution as homologs of nontoxic endogenous peptides that are widely conserved in mammals. This finding is of great interest from the viewpoint of the chemical evolution of vertebrate venoms.

[Mibefradil improves skeletal muscle mass, function and structure in obese mice]

OBJECTIVE

To observe the effect of mibefradil on skeletal muscle mass, function and structure in obese mice.

METHODS

Fifteen 6-week-old C57BL/6 mice were randomized equally into normal diet group (control group), high-fat diet (HFD) group and high-fat diet +mibefradil intervention group (HFD +Mibe group). The grip strength of the mice was measured using an electronic grip strength meter, and the muscle content of the hindlimb was analyzed by X-ray absorptiometry (DXA). Triglyceride (TG) and total cholesterol (TC) levels of the mice were measured with GPO-PAP method. The cross-sectional area of the muscle fibers was observed with HE staining. The changes in the level of autophagy in the muscles were detected by Western blotting and immunofluorescence assay, and the activation of the Akt/mTOR signaling pathway was detected with Western blotting.

RESULTS

Compared with those in the control group, the mice in HFD group had a significantly greater body weight, lower relative grip strength, smaller average cross sectional area of the muscle fibers, and a lower hindlimb muscle ratio (P < 0.05). Immunofluorescence assay revealed a homogenous distribution of LC3 emitting light red fluorescence in the cytoplasm in the muscle cells in HFD group and HFD+Mibe group, while bright spots of red fluorescence were detected in HFD group. In HFD group, the muscular tissues of the mice showed an increased expression level of LC3 II protein with lowered expressions of p62 protein and phosphorylated AKT and mTOR (P < 0.05). Mibefradil treatment significantly reduced body weight of the mice, lowered the expression level of p62 protein, and increased forelimb grip strength, hindlimb muscle ratio, cross-sectional area of the muscle fibers, and the expression levels of LC3 II protein and phosphorylated AKT and mTOR (P < 0.05).

CONCLUSION

Mibefradil treatment can moderate high-fat diet-induced weight gain and improve muscle mass and function in obese mice possibly by activating AKT/mTOR signal pathway to improve lipid metabolism and inhibit obesityinduced autophagy.

Cav3 T-Type Voltage-Gated Ca2+ Channels and the Amyloidogenic Environment: Pathophysiology and Implications on Pharmacotherapy and Pharmacovigilance

Voltage-gated Ca2+ channels (VGCCs) were reported to play a crucial role in neurotransmitter release, dendritic resonance phenomena and integration, and the regulation of gene expression. In the septohippocampal system, high- and low-voltage-activated (HVA, LVA) Ca2+ channels were shown to be involved in theta genesis, learning, and memory processes. In particular, HVA Cav2.3 R-type and LVA Cav3 T-type Ca2+ channels are expressed in the medial septum-diagonal band of Broca (MS-DBB), hippocampal interneurons, and pyramidal cells, and ablation of both channels was proven to severely modulate theta activity. Importantly, Cav3 Ca2+ channels contribute to rebound burst firing in septal interneurons. Consequently, functional impairment of T-type Ca2+ channels, e.g., in null mutant mouse models, caused tonic disinhibition of the septohippocampal pathway and subsequent enhancement of hippocampal theta activity. In addition, impairment of GABA A/B receptor transcription, trafficking, and membrane translocation was observed within the septohippocampal system. Given the recent findings that amyloid precursor protein (APP) forms complexes with GABA B receptors (GBRs), it is hypothesized that T-type Ca2+ current reduction, decrease in GABA receptors, and APP destabilization generate complex functional interdependence that can constitute a sophisticated proamyloidogenic environment, which could be of potential relevance in the etiopathogenesis of Alzheimer's disease (AD). The age-related downregulation of T-type Ca2+ channels in humans goes together with increased Aβ levels that could further inhibit T-type channels and aggravate the proamyloidogenic environment. The mechanistic model presented here sheds new light on recent reports about the potential risks of T-type Ca2+ channel blockers (CCBs) in dementia, as observed upon antiepileptic drug application in the elderly.

Role of Cholinergic Signaling in Alzheimer's Disease

Acetylcholine, a neurotransmitter secreted by cholinergic neurons, is involved in signal transduction related to memory and learning ability. Alzheimer’s disease (AD), a progressive and commonly diagnosed neurodegenerative disease, is characterized by memory and cognitive decline and behavioral disorders. The pathogenesis of AD is complex and remains unclear, being affected by various factors. The cholinergic hypothesis is the earliest theory about the pathogenesis of AD. Cholinergic atrophy and cognitive decline are accelerated in age-related neurodegenerative diseases such as AD. In addition, abnormal central cholinergic changes can also induce abnormal phosphorylation of ttau protein, nerve cell inflammation, cell apoptosis, and other pathological phenomena, but the exact mechanism of action is still unclear. Due to the complex and unclear pathogenesis, effective methods to prevent and treat AD are unavailable, and research to explore novel therapeutic drugs is various and active in the world. This review summaries the role of cholinergic signaling and the correlation between the cholinergic signaling pathway with other risk factors in AD and provides the latest research about the efficient therapeutic drugs and treatment of AD.

Regulation of Hippocampal Gamma Oscillations by Modulation of Intrinsic Neuronal Excitability

Ion channels activated around the subthreshold membrane potential determine the likelihood of neuronal firing in response to synaptic inputs, a process described as intrinsic neuronal excitability. Long-term plasticity of chemical synaptic transmission is traditionally considered the main cellular mechanism of information storage in the brain; however, voltage- and calcium-activated channels modulating the inputs or outputs of neurons are also subjects of plastic changes and play a major role in learning and memory formation. Gamma oscillations are associated with numerous higher cognitive functions such as learning and memory, but our knowledge of their dependence on intrinsic plasticity is by far limited. Here we investigated the roles of potassium and calcium channels activated at near subthreshold membrane potentials in cholinergically induced persistent gamma oscillations measured in the CA3 area of rat hippocampal slices. Among potassium channels, which are responsible for the afterhyperpolarization in CA3 pyramidal cells, we found that blockers of SK (K_Ca2) and K_V7.2/7.3 (KCNQ2/3), but not the BK (K_Ca1.1) and IK (K_Ca3.1) channels, increased the power of gamma oscillations. On the contrary, activators of these channels had an attenuating effect without affecting the frequency. Pharmacological blockade of the low voltage-activated T-type calcium channels (Ca_V3.1–3.3) reduced gamma power and increased the oscillation peak frequency. Enhancement of these channels also inhibited the peak power without altering the frequency of the oscillations. The presented data suggest that voltage- and calcium-activated ion channels involved in intrinsic excitability strongly regulate the power of hippocampal gamma oscillations. Targeting these channels could represent a valuable pharmacological strategy against cognitive impairment.

Emerging potential of cannabidiol in reversing proteinopathies

The aberrant accumulation of disease-specific protein aggregates accompanying cognitive decline is a pathological hallmark of age-associated neurological disorders, also termed as proteinopathies, including Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and multiple sclerosis. Along with oxidative stress and neuroinflammation, disruption in protein homeostasis (proteostasis), a network that constitutes protein surveillance system, plays a pivotal role in the pathobiology of these dementia disorders. Cannabidiol (CBD), a non-psychotropic phytocannabinoid of Cannabis sativa, is known for its pleiotropic neuropharmacological effects on the central nervous system, including the ability to abate oxidative stress, neuroinflammation, and protein misfolding. Over the past years, compelling evidence has documented disease-modifying role of CBD in various preclinical and clinical models of neurological disorders, suggesting the potential therapeutic implications of CBD in these disorders. Because of its putative role in the proteostasis network in particular, CBD could be a potent modulator for reversing not only age-associated neurodegeneration but also other protein misfolding disorders. However, the current understanding is insufficient to underpin this proposition. In this review, we discuss the potentiality of CBD as a pharmacological modulator of the proteostasis network, highlighting its neuroprotective and aggregates clearing roles in the neurodegenerative disorders. We anticipate that the current effort will advance our knowledge on the implication of CBD in proteostasis network, opening up a new therapeutic window for aging proteinopathies.

SAK3 Administration Improves Spine Abnormalities and Cognitive Deficits in AppNL-G-F/NL-G-F Knock-in Mice by Increasing Proteasome Activity through CaMKII/Rpt6 Signaling

Alzheimer's disease (AD) is the most common form of dementia and is characterized by neuropathological hallmarks consisting of accumulation of extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles (NFT). Recently, we have identified a new AD therapeutic candidate, ethyl-8'-methyl-2',4-dioxo-2-(piperidin-1-yl)-2'H-spiro[cyclopentane-1,3'-imidazo [1,2-a] pyridin]-2-ene-3-carboxylate (SAK3), which ameliorates the AD-like pathology in AppNL-F/NL-F knock-in mice. However, the detailed mechanism underlying the therapeutic effects of SAK3 remains unclear. In this study, we found that SAK3 administration improved the reduced proteasome activity through the activation of CaMKII/Rpt6 signaling in AppNL-F/NL-F knock-in (NL-G-F) mice. Moreover, spine abnormalities observed in NL-G-F mice were significantly reversed by SAK3 administration. Along with this, cognitive impairments found in NL-G-F mice were markedly ameliorated by SAK3. In summary, our data suggest that SAK3 administration increases the activity of the proteasome via activation of the CaMKII/Rpt6 signaling pathway, contributing to improvements in spine abnormalities and cognitive deficits in NL-G-F mice. Overall, our findings suggest that SAK3 might be a new attractive drug candidate, representing a new mechanism for the treatment of AD pathology.

Congenetic Hybrids Derived from Dearomatized Isoprenylated Acylphloroglucinol with Opposite Effects on Cav3.1 Low Voltage-Gated Ca2+ Channel

A hybrid of dearomatized isoprenylated acylphloroglucinol (DIAP) and monoterpenoid, hypatone A (1), together with its biosynthetic analogues 2-4 is characterized from Hypericum patulum. Structurally, 1 possesses an unprecedented spiro[bicyclo[3.2.1]octane-6,1'-cyclohexan]-2',4',6'-trione core as elucidated by extensive spectroscopic and X-ray crystallographic analyses. Biological studies reveal that compounds 1 and 2-4 produce opposite effects on Ca_v3.1 low voltage-gated Ca²⁺ channel, with 1 and 4, respectively, being the most potent Ca_v3.1 agonist and antagonist from natural products. Further studies suggest that compound 1 and its biogenetical precursor, 2, have the same binding site on Ca_v3.1 and that the rigid cagelike moiety at C-5 and C-6 is a key structural feature responsible for 1 being an agonist. Furthermore, 1 can normalize the pathological gating of a mutant Ca_v3.1 channel found in spinocerebellar ataxia 42 (SCA42), a hereditary neurodegenerative disorder with no available therapy. Collectively, our findings provide valuable tools for future studies on Ca_v3.1 physiology and pathophysiology, as well as afford possible leads for developing new drugs against SCA42, epilepsy, and pain.

Cognitive enhancer ST101 improves schizophrenia-like behaviors in neonatal ventral hippocampus-lesioned rats in association with improved CaMKII/PKC pathway

Atypical antipsychotics improve positive and negative symptoms but are not effective for treating cognitive impairments in patients with schizophrenia. We previously reported that cognitive impairments in neonatal ventral hippocampus (NVH)-lesioned rats show resistance to atypical antipsychotics risperidone and are associated with reduced calcium/calmodulin-dependent protein kinase II (CaMKII) and protein kinase C (PKC) signaling in memory-related regions. The cognitive enhancer ST101 (spiro[imi-dazo[1,2-a]pyridine-3,2-indan]-2(3H)-one) stimulates CaMKII activity in the hippocampus and medial prefrontal cortex (mPFC). We thus tested ST101 on cognitive impairments in NVH-lesioned rats. Chronic ST101 administration (0.1 and/or 0.5 mg/kg, p.o.) significantly improved deficits in prepulse inhibition (PPI), social interaction, and cognitive function in NVH-lesioned rats. ST101 administration (0.5 mg/kg, p.o.) significantly restored the decreased CaMKII autophosphorylation (Thr-286) in the mPFC and hippocampal CA1 regions of NVH-lesioned rats when assessed by immunohistochemistry. Chronic ST101 administration (0.1 mg/kg, p.o.) improved the decline in phosphorylation levels of CaMKII (Thr-286), PKCα (Ser-657), α-amino-3-hydroxy-5-methyl-4-isoxazol- propionic acid (AMPA)-type glutamate receptor subunit 1 (GluA1: Ser-831), and N-methyl-d-aspartate (NMDA) receptor subunit 1 (GluN1: Ser-896) in the mPFC and hippocampal CA1 regions. Taken together, these results suggest that ST101 improves schizophrenia-like behaviors and cognitive impairment by enhancing CaMKII/PKCα signaling in the mPFC and hippocampus in NVH-lesioned rats.

T-Type Channel Druggability at a Crossroads

Low-voltage activated T-type calcium channels mediate essential functions in the nervous system, and alteration of channel activity is causally linked to a number of neurological conditions. Therefore, T-type channels hold great promise as pharmacological targets for new medicines. In this Viewpoint, we discuss the potential of T-type channels as druggable targets and reevaluate the strategies available for developing therapeutically efficient and specific modulators of this channel.