Impaired TNF-alpha control of IP3R-mediated Ca2+ release in Alzheimer's disease mouse neurons

ALPK1 Expressed in IB4-Positive Neurons of Mice Trigeminal Ganglions Promotes MIA-Induced TMJ pain

Pain is one of the main reasons for patients with temporomandibular joint (TMJ) disorders seeking medical care. However, there is no effective treatment yet as its mechanism remains unclear. Herein, we found that the injection of monoiodoacetate (MIA) into mice TMJs can induce typical joint pain as early as 3 days, accompanied by an increased percentage of calcitonin gene-related peptide positive (CGRP+) neurons and isolectin B4 positive (IB4+) in the trigeminal ganglions (TGs). Our previous study has discovered that alpha-kinase 1 (ALPK1) may be involved in joint pain. Here, we detected the expression of ALPK1 in neurons of TGs in wild-type (WT) mice, and it was upregulated after intra-TMJ injection of MIA. Meanwhile, the increased percentage of neurons in TGs expressing ALPK1 and CGRP or ALPK1 and IB4 was also demonstrated by the immunofluorescent double staining. Furthermore, after the MIA injection, ALPK1-/- mice exhibited attenuated pain behavior, as well as a remarkably decreased percentage of IB4+ neurons and an unchanged percentage of CGRP+ neurons, as compared with WT mice. In vitro assay showed that the value of calcium intensity was weakened in Dil+ neurons from ALPK1-/- mice of TMJ pain induced by the MIA injection, in relation to those from WT mice, while it was significantly enhanced with the incubation of recombinant human ALPK1 (rhA). Taken together, these results suggest that ALPK1 promotes mice TMJ pain induced by MIA through upregulation of the sensitization of IB4+ neurons in TGs. This study will provide a new potential therapeutic target for the treatment of TMJ pain.

Spatial and temporal crosstalk between the cAMP and Ca2+ signaling systems

The ubiquitous secondary messengers, Ca²⁺ and cAMP, play a vital role in shaping a diverse array of physiological processes. More significantly, accumulating evidence over the past several decades underpin extensive crosstalk between these two canonical messengers in discrete sub-cellular nanodomains across various cell types. Within such specialized nanodomains, each messenger fine-tunes signaling to maintain homeostasis by manipulating the activities of cellular machinery accountable for the metabolism or activity of the complementary pathway. Interaction between these messengers is ensured by scaffolding proteins which tether components of the signaling machinery in close proximity. Disruption of dynamic communications between Ca²⁺ and cAMP at these loci consequently is linked to several pathological conditions. This review summarizes recent novel mechanisms underlying effective crosstalk between Ca²⁺ and cAMP in such nanodomains.

Calcium Ions Aggravate Alzheimer's Disease Through the Aberrant Activation of Neuronal Networks, Leading to Synaptic and Cognitive Deficits

Alzheimer’s disease (AD) is a neurodegenerative disease that is characterized by the production and deposition of β-amyloid protein (Aβ) and hyperphosphorylated tau, leading to the formation of β-amyloid plaques (APs) and neurofibrillary tangles (NFTs). Although calcium ions (Ca²⁺) promote the formation of APs and NFTs, no systematic review of the mechanisms by which Ca²⁺ affects the development and progression of AD has been published. Therefore, the current review aimed to fill the gaps between elevated Ca²⁺ levels and the pathogenesis of AD. Specifically, we mainly focus on the molecular mechanisms by which Ca²⁺ affects the neuronal networks of neuroinflammation, neuronal injury, neurogenesis, neurotoxicity, neuroprotection, and autophagy. Furthermore, the roles of Ca²⁺ transporters located in the cell membrane, endoplasmic reticulum (ER), mitochondria and lysosome in mediating the effects of Ca²⁺ on activating neuronal networks that ultimately contribute to the development and progression of AD are discussed. Finally, the drug candidates derived from herbs used as food or seasoning in Chinese daily life are summarized to provide a theoretical basis for improving the clinical treatment of AD.

The Ca(2+) channel inhibitor 2-APB reverses β-amyloid-induced LTP deficit in hippocampus by blocking BAX and caspase-3 hyperactivation

BACKGROUND AND PURPOSE

At the early stage of Alzheimer's disease (AD), the accumulation of β-amyloid (Aβ) oligomers disturbs intracellular Ca(2+) homeostasis and disrupts synaptic plasticity of brain neurons. Prevention of Aβ-induced synaptic failure remains an unsolved problem for the treatment of AD. Here, the effects of 2-aminoethoxydiphenyl borate (2-APB), a non-specific, but moderately potent Ca(2+) channel inhibitor, on Aβ-induced deficit of synaptic long-term potentiation (LTP) and the underlying molecular mechanisms were explored.

EXPERIMENTAL APPROACH

We used hippocampal slices and primary cultures of hippocampal neurons from C57BL/6 mice. Methods applied in our study included electrophysiological recording, membrane protein extraction, Western blot assay and Ca(2+) imaging.

KEY RESULTS

2-APB at 10 μM effectively reversed suppression by oligomeric Aβ1-42 (500 nM) of LTP in hippocampal slices. 2-APB also restored phosphorylation and trafficking of the glutamate receptor subunit GluA1 in Aβ-treated hippocampal slices, supporting its protective action on synaptic function. Aβ-mediated abnormal neuronal [Ca(2+) ]i elevation and hyperactivation of the mitochondrial apoptotic proteins BAX, caspase-3, and glycogen synthase kinase-3β, were blocked by 2-APB pretreatment. Moreover, the defict in long term potentiation deficit in hippocampal slices from APPswe /PS1ΔE 9 gene mutant mice was rescued by 2-APB at 10 μM.

CONCLUSIONS AND IMPLICATION

These data demonstrate that 2-APB is a potentially useful chemical to protect synaptic plasticity against neurotoxic effects of Aβ in AD.

Integration of modeling with experimental and clinical findings synthesizes and refines the central role of inositol 1,4,5-trisphosphate receptor 1 in spinocerebellar ataxia

A suite of models was developed to study the role of inositol 1,4,5-trisphosphate receptor 1 (IP3R1) in spinocerebellar ataxias (SCAs). Several SCAs are linked to reduced abundance of IP3R1 or to supranormal sensitivity of the receptor to activation by its ligand inositol 1,4,5-trisphosphate (IP3). Detailed multidimensional models have been created to simulate biochemical calcium signaling and membrane electrophysiology in cerebellar Purkinje neurons. In these models, IP3R1-mediated calcium release is allowed to interact with ion channel response on the cell membrane. Experimental findings in mice and clinical observations in humans provide data input for the models. The SCA modeling suite helps interpret experimental results and provides suggestions to guide experiments. The models predict IP3R1 supersensitivity in SCA1 and compensatory mechanisms in SCA1, SCA2, and SCA3. Simulations explain the impact of calcium buffer proteins. Results show that IP3R1-mediated calcium release activates voltage-gated calcium-activated potassium channels in the plasma membrane. The SCA modeling suite unifies observations from experiments in a number of SCAs. The cadre of simulations demonstrates the central role of IP3R1.

PKCα signaling pathway involves in TNF-α-induced IP3R1 expression in human mesangial cells

BACKGROUND

This study aimed to explore the effects of TNF-α on the expression of IP3R1 mRNA and protein in human mesangial cells (HMCs), and to elucidate the mechanism of TNF-α relating to IP3R1 expression in the occurrence of hepatorenal syndrome (HRS).

METHODS

HMCs were stimulated by tumor (TNF-α) with 100 ng/mL for different hours (2, 4, 8, and 24 hours). The expression changes of IP3R1 mRNA and protein were detected by quantitative real-time polymerase chain reaction and immunoblotting. Several inhibitors including D609, U73122, PP1, safingol, rottlerin and non-radioactive protein kinase C (PKC) were used to examine the mechanism of signal transduction of TNF-α-regulated IP3R1 in HMCs.

RESULTS

The levels of IP3R1 mRNA at 2 hours after TNF-α exposure were significantly enhanced and peaked at 8 hours in HMCs (P<0.01), then descended at 24 hours (P<0.01). The levels of IP3R1 protein at 4 hours after TNF-α exposure were obviously increased and peaked at 24 hours after TNF-α exposure (P<0.01). Compared to the control group, safingol (PKCα inhibitor) and D609 (phosphatidylcholine-specific phospholipase C inhibitor) significantly blocked the TNF-αinduced expression of IP3R1 mRNA (3.30±0.81 vs. 1.95±0.13, P<0.05; 2.10±0.49, P<0.01) and IP3R1 protein (3.09±0.13 vs. 1.86+0.39, P<0.01; 1.98±0.02, P<0.01). TNF-α promoted PKCα activation with maximal PKCα phosphorylation that occurred 8 hours after stimulation measured by non-radioactive PKC assay, and the effect was markedly attenuated by pretreatment with D609 or safingol.

CONCLUSION

TNF-α increased the expression of IP3R1 and this was mediated, at least in part, through the PC-PLC/PKCα signaling pathways in HMCs.

Tumor necrosis factor alpha maintains denervation-induced homeostatic synaptic plasticity of mouse dentate granule cells

Neurons which lose part of their input respond with a compensatory increase in excitatory synaptic strength. This observation is of particular interest in the context of neurological diseases, which are accompanied by the loss of neurons and subsequent denervation of connected brain regions. However, while the cellular and molecular mechanisms of pharmacologically induced homeostatic synaptic plasticity have been identified to a certain degree, denervation-induced homeostatic synaptic plasticity remains not well understood. Here, we employed the entorhinal denervation in vitro model to study the role of tumor necrosis factor alpha (TNFα) on changes in excitatory synaptic strength of mouse dentate granule cells following partial deafferentation. Our experiments disclose that TNFα is required for the maintenance of a compensatory increase in excitatory synaptic strength at 3-4 days post lesion (dpl), but not for the induction of synaptic scaling at 1-2 dpl. Furthermore, laser capture microdissection combined with quantitative PCR demonstrates an increase in TNFα-mRNA levels in the denervated zone, which is consistent with our previous finding on a local, i.e., layer-specific increase in excitatory synaptic strength at 3-4 dpl. Immunostainings for the glial fibrillary acidic protein and TNFα suggest that astrocytes are a source of TNFα in our experimental setting. We conclude that TNFα-signaling is a major regulatory system that aims at maintaining the homeostatic synaptic response of denervated neurons.

Anti-aggregating effect of the naturally occurring dipeptide carnosine on aβ1-42 fibril formation

Carnosine is an endogenous dipeptide abundant in the central nervous system, where by acting as intracellular pH buffering molecule, Zn/Cu ion chelator, antioxidant and anti-crosslinking agent, it exerts a well-recognized multi-protective homeostatic function for neuronal and non-neuronal cells. Carnosine seems to counteract proteotoxicity and protein accumulation in neurodegenerative conditions, such as Alzheimer's Disease (AD). However, its direct impact on the dynamics of AD-related fibril formation remains uninvestigated. We considered the effects of carnosine on the formation of fibrils/aggregates of the amyloidogenic peptide fragment Aβ1-42, a major hallmark of AD injury. Atomic force microscopy and thioflavin T assays showed inhibition of Aβ1-42 fibrillogenesis in vitro and differences in the aggregation state of Aβ1-42 small pre-fibrillar structures (monomers and small oligomers) in the presence of carnosine. in silico molecular docking supported the experimental data, calculating possible conformational carnosine/Aβ1-42 interactions. Overall, our results suggest an effective role of carnosine against Aβ1-42 aggregation.

TNFα induces IP3R1 expression via TNFR1/PKCα and TNFR2 signaling pathways in human mesangial cells

AIM: To investigate the role of PKC and TNFR in TNFα-induced expression of IP₃R1 in human mesangial cells (HMCs).

METHODS: Quantitative real-time polymerase chain reaction and immunoblot assay were used to examine the effect of TNFα treatment on IP₃R1 mRNA and protein expression. Depletion of PKC with PMA, treatment with PKC kinase inhibitors, and overexpression of dominant negative mutant of PKCα were used to examine the role of PKC in TNFα-induced expression of IP₃R1 in HMCs. The expression of total PKCα and p-PKCα was assayed by Western blot. The contribution of TNFR1 and TNFR2 to PKCα activation and TNFα-induced IP₃R1 expression was also detected by Western blot.

RESULTS: Treatment with TNFα increased IP₃R1 mRNA and protein expression in HMCs, and this effect could be blocked by prolonged incubation with PMA, Safingol treatment and transfection with domain negative PKCα construct. TNFα could promote PKCα autophosphorylation. Both anti-TNFR1 and TNFR2 antibodies attenuated TNFα-induced IP₃R1 expression, while only anti-TNFR1 antibody attenuated TNFα-induced PKCα activity.

CONCLUSION: TNFα increases the expression of IP₃R1 through the TNFR1/PKCα and TNFR2 signaling pathways in HMCs.

IP3, a small molecule with a powerful message

Research conducted over the past two decades has provided convincing evidence that cell death, and more specifically apoptosis, can exceed single cell boundaries and can be strongly influenced by intercellular communication networks. We recently reported that gap junctions (i.e. channels directly connecting the cytoplasm of neighboring cells) composed of connexin43 or connexin26 provide a direct pathway to promote and expand cell death, and that inositol 1,4,5-trisphosphate (IP3) diffusion via these channels is crucial to provoke apoptosis in adjacent healthy cells. However, IP3 itself is not sufficient to induce cell death and additional factors appear to be necessary to create conditions in which IP3 will exert proapoptotic effects. Although IP3-evoked Ca(2+) signaling is known to be required for normal cell survival, it is also actively involved in apoptosis induction and progression. As such, it is evident that an accurate fine-tuning of this signaling mechanism is crucial for normal cell physiology, while a malfunction can lead to cell death. Here, we review the role of IP3 as an intracellular and intercellular cell death messenger, focusing on the endoplasmic reticulum-mitochondrial synapse, followed by a discussion of plausible elements that can convert IP3 from a physiological molecule to a killer substance. Finally, we highlight several pathological conditions in which anomalous intercellular IP3/Ca(2+) signaling might play a role. This article is part of a Special Issue entitled:12th European Symposium on Calcium.