Analysis of the role of nerve growth factor in promoting cell survival during endoplasmic reticulum stress in PC12 cells

Beyond animal models: revolutionizing neurodegenerative disease modeling using 3D in vitro organoids, microfluidic chips, and bioprinting

Neurodegenerative diseases (NDs) are characterized by uncontrolled loss of neuronal cells leading to a progressive deterioration of brain functions. The transition rate of numerous neuroprotective drugs against Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease, leading to FDA approval, is only 8-14% in the last two decades. Thus, in spite of encouraging preclinical results, these drugs have failed in human clinical trials, demonstrating that traditional cell cultures and animal models cannot accurately replicate human pathophysiology. Hence, in vitro three-dimensional (3D) models have been developed to bridge the gap between human and animal studies. Such technological advancements in 3D culture systems, such as human-induced pluripotent stem cell (iPSC)-derived cells/organoids, organ-on-a-chip technique, and 3D bioprinting, have aided our understanding of the pathophysiology and underlying mechanisms of human NDs. Despite these recent advances, we still lack a 3D model that recapitulates all the key aspects of NDs, thus making it difficult to study the ND's etiology in-depth. Hence in this review, we propose developing a combinatorial approach that allows the integration of patient-derived iPSCs/organoids with 3D bioprinting and organ-on-a-chip technique as it would encompass the neuronal cells along with their niche. Such a 3D combinatorial approach would characterize pathological processes thoroughly, making them better suited for high-throughput drug screening and developing effective novel therapeutics targeting NDs.

Baccharin from Brazilian green propolis induces neurotrophic signaling pathways in PC12 cells: potential for axonal and synaptic regeneration

Neurodegenerative diseases are characterized by progressive loss of the structure and function of specific neuronal populations, and have been associated with reduced neurotrophic support. Neurotrophins, like NGF (nerve growth factor), are endogenous proteins that induce neuritogenesis and modulate axonal growth, branching, and synapsis; however, their therapeutic application is limited mainly by low stability, short half-life, and inability to cross the blood-brain barrier (BBB). Small neurotrophic molecules that have suitable pharmacokinetics and are able to cross the BBB are potential candidates for neuroprotection. Baccharin is a bioactive small molecule isolated from Brazilian green propolis. In the present study, we investigated the neurotrophic and neuroprotective potential of baccharin in the PC12 cell neuronal model. We used pharmacological inhibitors (K252a, LY294002, and U0126), and ELISA (phospho-trkA, phospho-Akt, and phospho-MEK) to investigate the involvement of trkA receptor, PI3k/Akt pathway, and MAPK/Erk pathway, respectively. Additionally, we evaluated the expression of axonal (GAP-43) and synaptic (synapsin I) proteins by western blot. The results showed that baccharin induces neuritogenesis in NGF-deprived PC12 cells, through activation of trkA receptor and the downstream signaling cascades (PI3K/Akt and MAPK/ERK), which is the same neurotrophic pathway activated by NGF in PC12 cells and neurons. Baccharin also induced the expression of GAP-43 and synapsin I, which mediate axonal and synaptic plasticity, respectively. Additionally, in silico predictions of baccharin showed favorable physicochemical properties, pharmacokinetics, drug-likeness, and medicinal chemistry friendliness. Altogether, these findings suggest that baccharin is a promising neurotrophic agent whose therapeutic application in neurodegeneration should be further investigated.

Nerve Growth Factor Protects Against Pyrethroid-Induced Endoplasmic Reticulum (ER) Stress in Primary Hippocampal Neurons

Neurotrophins are a family of growth factors crucial for growth and survival of neurons in the developing and adult brain. Reduction in neurotrophin levels is associated with reduced neurogenesis and cognitive deficits in rodents. Recently, we demonstrated that long-term exposure to low levels of the pyrethroid pesticide deltamethrin causes hippocampal endoplasmic reticulum (ER) stress and learning deficits in mice. Here, we found that nerve growth factor (NGF) mRNA and protein were selectively reduced in the hippocampus of deltamethrin-treated mice. To explore potential mechanisms responsible for this observation, we employed mouse primary hippocampal neurons. Exposure of neurons to deltamethrin (1-5 μM) caused ER stress as indicated by increased levels of C/EBP-homologous protein (CHOP) and glucose-regulated protein 78 (GRP78). These changes were accompanied by increased levels of caspase-12, activated caspase-3, and decreased levels of NGF. Inhibition of ER stress with the eukaryotic initiation factor 2 alpha (eIF2α) inhibitor salubrinal abolished deltamethrin-induced activation of caspase-12 and caspase-3, and restored NGF levels. Furthermore, deltamethrin decreased Akt (protein kinase B) phosphorylation, which was significantly prevented by co-treatment with NGF or SC-79 in cells. Collectively, these results demonstrate that the loss of NGF following ER stress may contribute to deltamethrin-induced apoptosis in the hippocampus through the Akt signaling pathway, and that this may provide a plausible mechanism for impaired learning and memory observed following exposure of mice to deltamethrin.

The Neurotrophic-Like Effect of Carvacrol: Perspective for Axonal and Synaptic Regeneration

Carvacrol (CARV) is a phytochemical widely used as flavoring, preservative, and fragrance in food and cosmetic industries. CARV is able to cross the blood-brain barrier (BBB) and has demonstrated protective potential against neurodegenerative diseases by several mechanisms, including antioxidant, anti-inflammatory, anticholinesterase, and antiapoptotic effects. However, it is not known whether CARV is able to modulate axonal and synaptic plasticity, crucial events in cognition, memory, and learning. Abnormalities in axonal and synaptic plasticity, low levels of neurotrophins, and bioenergetic failure have been associated with the pathogenesis of neurodegenerative diseases, including Parkinson's (PD) and Alzheimer's diseases (ADs). Small lipophilic molecules with neurotrophic activity might be able to restore the axonal and synaptic networks that are lost in neurodegenerative processes. Therefore, this study investigated the neurotrophic potential of CARV in PC12 cell-based neuronal model. Carvacrol induced neurite outgrowth by activating the NGF high-affinity trkA receptor and the downstream PI3K-AKT and MAPK-ERK pathways, without depending on NGF. In addition, CARV increased the expression of proteins involved in neuronal plasticity (β-tubulin III, F-actin, 200-kDa neurofilament, GAP-43 and synapsin-I) and improved bioenergetics (AMPKα, p-AMPKα, and ATP). Our study showed, for the first time, a promising neurotrophic mechanism of CARV that could be beneficial in neurodegenerative and neurological diseases.

Identification and characterization of the Cucurbitacins, a novel class of small-molecule inhibitors of Tropomyosin receptor kinase a

Background

NGF-TrkA is well known to play a key role in propagating and sustaining pruritogenic signals, which form the pathology of chronic pruritus. Inhibition of NGF-TrkA is a known strategy for the treatment of pruritus. In the present paper, we describe the identification, in vitro characterization, structure–activity analysis, and inhibitory evaluation of a novel TrkA inhibitory scaffold exemplified by Cucurbitacins (Cus).

Methods

Cus were identified as TrkA inhibitors in a large-scale kinase library screen. To obtain structural models of Cus as TrkA inhibitors, AutoDock was used to explore their binding to TrkA. Furthermore, PC12 cell culture systems have been used to study the effects of Cus and traditional Chinese medicinal plants (Tian Gua Di and bitter gourd leaf) extracts on the kinase activity of TrkA.

Results

Cus block the phosphorylation of TrkA on several tyrosine sites, including Tyr490, Tyr674/675, and Tyr785, and inhibit downstream Akt and MAPK phosphorylation in response to NGF in PC12 cell model systems. Furthermore, traditional Chinese medicinal plants (Tian Gua Di and bitter gourd leaf) containing Cu extracts were shown to inhibit the phosphorylation of TrkA and Akt. These data reveal mechanisms, at least partly, of the anti-pruritus bioactivity of Cus.

Conclusion

Taken together, with the recent discovery of the important role of TrkA as a therapeutic target, Cus could be the basis for the design of improved TrkA kinase inhibitors, which could someday help treat pruritus.

Acute Ischemia Induced by High-Density Culture Increases Cytokine Expression and Diminishes the Function and Viability of Highly Purified Human Islets of Langerhans

BACKGROUND

Encapsulation devices have the potential to enable cell-based insulin replacement therapies (such as human islet or stem cell-derived β cell transplantation) without immunosuppression. However, reasonably sized encapsulation devices promote ischemia due to high β cell densities creating prohibitively large diffusional distances for nutrients. It is hypothesized that even acute ischemic exposure will compromise the therapeutic potential of cell-based insulin replacement. In this study, the acute effects of high-density ischemia were investigated in human islets to develop a detailed profile of early ischemia induced changes and targets for intervention.

METHODS

Human islets were exposed in a pairwise model simulating high-density encapsulation to normoxic or ischemic culture for 12 hours, after which viability and function were measured. RNA sequencing was conducted to assess transcriptome-wide changes in gene expression.

RESULTS

Islet viability after acute ischemic exposure was reduced compared to normoxic culture conditions (P < 0.01). Insulin secretion was also diminished, with ischemic β cells losing their insulin secretory response to stimulatory glucose levels (P < 0.01). RNA sequencing revealed 657 differentially expressed genes following ischemia, with many that are associated with increased inflammatory and hypoxia-response signaling and decreased nutrient transport and metabolism.

CONCLUSIONS

In order for cell-based insulin replacement to be applied as a treatment for type 1 diabetes, oxygen and nutrient delivery to β cells will need to be maintained. We demonstrate that even brief ischemic exposure such as would be experienced in encapsulation devices damages islet viability and β cell function and leads to increased inflammatory signaling.

The cannabinoid beta-caryophyllene (BCP) induces neuritogenesis in PC12 cells by a cannabinoid-receptor-independent mechanism

Beta-caryophyllene (BCP) is a phytocannabinoid whose neuroprotective activity has been mainly associated with selective activation of cannabinoid-type-2 (CB2) receptors, inhibition of microglial activation and decrease of inflammation. Here, we addressed the potential of BCP to induce neuritogenesis in PC12 cells, a model system for primary neuronal cells that express trkA receptors, respond to NGF and do not express CB2 receptors. We demonstrated that BCP increases the survival and activates the NGF-specific receptor trkA in NGF-deprived PC12 cells, without increasing the expression of NGF itself. The neuritogenic effect of BCP in PC12 cells was abolished by k252a, an inhibitor of the NGF-specific receptor trkA. Accordingly, BCP did not induce neuritogenesis in SH-SY5Y neuroblastoma cells, a neuronal model that does not express trkA receptors and do not respond to NGF. Additionally, we demonstrated that BCP increases the expression of axonal-plasticity-associated proteins (GAP-43, synapsin and synaptophysin) in PC12 cells. It is known that these proteins are up-regulated by NGF in neurons and neuron-like cells, such as PC12 cells. Altogether, these findings suggest that BCP activates trka receptors and induces neuritogenesis by a mechanism independent of NGF or cannabinoid receptors. This is the first study to show such effects of BCP and their beneficial role in neurodegenerative processes should be further investigated.

Memory and PTPIP51--a new protein in hippocampus and cerebellum

Previously the expression of Protein Tyrosine Phosphatase Interacting Protein 51 (PTPIP51) in mouse brain was reported. Here, we investigated PTPIP51 mRNA and protein in two of the brain regions namely the hippocampus and the cerebellum of mouse brains. On a cellular level both the protein and the mRNA were related to the pyramidal cells of the hippocampal formation, the granular cells of the dentate gyrus and the cells of the adjacent strata. In the cerebellum PTPIP51 was traced in Purkinje cells, the cells of the molecular layer and the granular layer. On a subcellular level only partial co-localization was seen for the endoplasmic reticulum, but not with mitochondria. In addition the interactome of PTPIP51 was analysed. In hippocampal cells a strong interaction with PTP1B and vesicle-associated membrane protein-associated protein B (VAPB) was detected. A somewhat differing interaction profile was found in the cerebellum, where high interaction levels were found for 14-3-3, diacylglycerol kinase α (DGKα), NFκB and PTP1B. These interaction partners represent specific signalling pathways linked to building memory. PTPIP51 can be associated with nerve growth factor signalling, dendritic and axonal growth, synaptogenesis, and all processes needed for memory formation. Moreover, in HT-22 mouse hippocampal cells PTPIP51 expression was induced by administrating the fibroblast growth factor 1 (FGF-1), which is known to take part in learning/memory processes. Knocking down p38-MAPK also led to an up-regulation of PTPIP51 probably resembling a compensative mechanism. Thus, a possible connection to the processing of memories can be anticipated. Differences in the interaction profile in both regions may be attributed to the actual/local differences in memory formation.

Neuroprotective effect of novel cognitive enhancer noopept on AD-related cellular model involves the attenuation of apoptosis and tau hyperphosphorylation

Background

Noopept (N-phenyl-acetyl-L-prolylglycine ethyl ester) was constructed as a dipeptide analog of the standard cognition enhancer, piracetam. Our previous experiments have demonstrated the cognition restoring effect of noopept in several animal models of Alzheimer disease (AD). Noopept was also shown to prevent ionic disbalance, excitotoxicity, free radicals and pro-inflammatory cytokines accumulation, and neurotrophine deficit typical for different kinds of brain damages, including AD. In this study, we investigated the neuroprotective action of noopept on cellular model of AD, Aβ_25–35-induced toxicity in PC12 cells and revealed the underlying mechanisms.

Results

The neuroprotective effect of noopept (added to the medium at 10 μM concentration, 72 hours before Аβ_25–35) was studied on Аβ_25–35-induced injury (5 μM for 24 h) in PC12 cells. The ability of drug to protect the impairments of cell viability, calcium homeostasis, ROS level, mitochondrial function, tau phosphorylation and neurite outgrowth caused by Аβ_25–35 were evaluated.

Following the exposure of PC12 cells to Аβ_25–35 an increase of the level of ROS, intracellular calcium, and tau phosphorylation at Ser396 were observed; these changes were accompanied by a decrease in cell viability and an increase of apoptosis. Noopept treatment before the amyloid-beta exposure improved PC12 cells viability, reduced the number of early and late apoptotic cells, the levels of intracellular reactive oxygen species and calcium and enhanced the mitochondrial membrane potential. In addition, pretreatment of PC12 cell with noopept significantly attenuated tau hyperphosphorylation at Ser396 and ameliorated the alterations of neurite outgrowth evoked by Аβ_25–35.

Conclusions

Taken together, these data provide evidence that novel cognitive enhancer noopept protects PC12 cell against deleterious actions of Aβ through inhibiting the oxidative damage and calcium overload as well as suppressing the mitochondrial apoptotic pathway. Moreover, neuroprotective properties of noopept likely include its ability to decrease tau phosphorylation and to restore the altered morphology of PC12 cells. Therefore, this nootropic dipeptide is able to positively affect not only common pathogenic pathways but also disease-specific mechanisms underlying Aβ-related pathology.

ATF4 orchestrates a program of BH3-only protein expression in severe hypoxia

Intratumoral hypoxia is associated with poor prognosis, regardless of the mode of therapy. Cancer cells survive this condition through activating several adaptive signaling pathways, including the integrated stress response (ISR) and autophagy. Activating transcription factor 4 (ATF4) is the major transcriptional mediator of the ISR, which we have shown to be involved in autophagy regulation to protect cells from severe hypoxia. Here we demonstrate that ATF4 orchestrates a program of BH3-only protein expression in severe hypoxia. We find that the BH3-only proteins HRK, PUMA, and NOXA are transcriptionally induced in severe hypoxia and that their expression is abrogated by RNA interference against ATF4. In particular, we show that the BH3-only protein harakiri (HRK) is transactivated by ATF4 in severe hypoxia through direct binding of ATF4 to the promoter region. Furthermore, we demonstrate through siRNA knockdown that HRK induces autophagy and promotes cancer cell survival in severe hypoxia.

Chromaffin cells: the peripheral brain

Chromaffin cells probably are the most intensively studied of the neural crest derivates. They are closely related to the nervous system, share with neurons some fundamental mechanisms and thus were the ideal model to study the basic mechanisms of neurobiology for many years. The lessons we have learned from chromaffin cell biology as a peripheral model for the brain and brain diseases pertain more than ever to the cutting edge research in neurobiology. Here, we highlight how studying this cell model can help unravel the basic mechanisms of cell renewal and regeneration both in the central nervous system (CNS) and neuroendocrine tissue and also can help in designing new strategies for regenerative therapies of the CNS.