Protein kinase C -activating isophthalate derivatives mitigate Alzheimer's disease-related cellular alterations

Abstract

Abnormal protein kinase C (PKC) function contributes to many pathophysiological processes relevant for Alzheimer's disease (AD), such as amyloid precursor protein (APP) processing. Phorbol esters and other PKC activators have been demonstrated to enhance the secretion of soluble APPα (sAPPα), reduce the levels of β-amyloid (Aβ), induce synaptogenesis, and promote neuroprotection. We have previously described isophthalate derivatives as a structurally simple family of PKC activators. Here, we characterised the effects of isophthalate derivatives HMI-1a3 and HMI-1b11 on neuronal viability, neuroinflammatory response, processing of APP and dendritic spine density and morphology in in vitro. HMI-1a3 increased the viability of embryonic primary cortical neurons and decreased the production of the pro-inflammatory mediator TNFα, but not that of nitric oxide, in mouse neuron-BV2 microglia co-cultures upon LPS- and IFN-γ-induced neuroinflammation. Furthermore, both HMI-1a3 and HMI-1b11 increased the levels of sAPPα relative to total sAPP and the ratio of Aβ42/Aβ40 in human SH-SY5Y neuroblastoma cells. Finally, bryostatin-1, but not HMI-1a3, increased the number of mushroom spines in proportion to total spine density in mature mouse hippocampal neuron cultures. These results suggest that the PKC activator HMI-1a3 exerts neuroprotective functions in the in vitro models relevant for AD by reducing the production of TNFα and increasing the secretion of neuroprotective sAPPα.

Distinct regulation of cardiac fibroblast proliferation and transdifferentiation by classical and novel protein kinase C isoforms: possible implications for new antifibrotic therapies

“…after a 24-h exposure to 10 µM HMI-1b11, but not as noticeable as in SH-SY5Y cells or cardiomyocytes treated with 100 nM PMA (Johnson et al, 1995;Sarajärvi et al, 2018). This together with our data demonstrating nPKC-mediated ERK1/2 activation in response to PMA or HMI-1b11 further supports the conclusion that the observed effects are due to PKC activation and not inhibition by downregulation.…”

“…PMA and the PKC inhibitors induced less than 10% increase in cytotoxicity even with the highest concentrations. Concentrations for the proliferation and transdifferentiation experiments were selected based on the present results regarding toxicity and previous reports regarding in vitro efficacy of the compounds (Sarajärvi et al, 2018;Talman et al, 2013). Furthermore, as PMA induces down-regulation of several PKC isoforms at 100 nM (Johnson et al, 1995), the 10 nM concentration was chosen to avoid down-regulation.…”

Pharmacological Protein Kinase C Modulators Reveal a Pro-hypertrophic Role for Novel Protein Kinase C Isoforms in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

“…The PKC activator bryostatin-1 was purchased from Sigma-Aldrich (Steinheim, Germany), the cPKC inhibitor Gö6976 from Merck Millipore (Burlington, MA, United States), the pan-PKC inhibitor Gö6983 from Stemcell Technologies (Vancouver, Canada), and the mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor U0126 from Tocris Bioscience (Bristol, United Kingdom). The concentrations of the commercially available PKC and MEK1/2 modulators were chosen based on reported K i values and our previous work (Boije af Gennäs et al, 2009;Talman et al, 2013;Sarajärvi et al, 2018). Endothelin-1 (ET-1), purchased from Sigma-Aldrich, was dissolved in 1% bovine serum albumin (BSA) in Dulbecco's modified Eagle medium (DMEM), while all other compounds were dissolved in dimethyl sulfoxide (DMSO).…”

“…While the isophthalates, such as HMI-1b11, activate PKC in cellular context and induce PKC-dependent extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, they seem to act as partial agonists instead of full activators (Boije af Gennäs et al, 2009;Talman et al, 2011;Talman et al, 2013). Together with their easy synthesis, partial agonism can be considered an advantage for the isophthalates, as they do not induce PKC downregulation (Sarajärvi et al, 2018) and thus more closely mimic physiological activation by DAG.…”

Evaluation of Toxic Amyloid β42 Oligomers in Rat Primary Cerebral Cortex Cells and Human iPS-derived Neurons Treated with 10-Me-Aplog-1, a New PKC Activator

“…After a 24 h incubation, 1 did not reduce Aβ42/Aβ40 as expected above, because the amounts of both Aβ42 and Aβ40 were lowered ( Figure 2a). 12-O-Tetradecanoylphorbol 13-acetate (TPA) is a PKC ligand that exerts a similar effect [34]. Because the extracellular levels of toxic oligomers after a 24 h incubation were under the detection limit for specific ELISA (#27709 Human Amyloid β Toxic Oligomer Assay Kit-IBL) and Aβ42 easily aggregates to form amyloid fibrils after a 24 h incubation in vitro [35,36], we sampled at an earlier time point, 6 h, to determine the formation of toxic Aβ oligomers.…”