Hippocampal protein kinase D1 is necessary for DHPG-induced learning and memory impairments in rats

Small Molecule Inhibitors of Protein Kinase D: Early Development, Current Approaches, and Future Directions

Now entering its fourth decade, research on the biological function, small molecule inhibition, and disease relevance of the three known isoforms of protein kinase D, PKD1, PKD2, and PKD3, has entered a mature development stage. This mini-perspective focuses on the medicinal chemistry that provided a structurally diverse set of mainly active site inhibitors, which, for a brief time period, moved through preclinical development stages but have yet to be tested in clinical trials. In particular, between 2006 and 2012, a rapid expansion of synthetic efforts led to several moderately to highly PKD-selective chemotypes but did not yet achieve PKD subtype selectivity or resolve general toxicity and pharmacokinetic challenges. In addition to cancer, other unresolved medical needs in cardiovascular, inflammatory, and metabolic diseases would, however, benefit from a renewed focus on potent and selective PKD modulators.

High glucose-mediated PICALM and mTORC1 modulate processing of amyloid precursor protein via endosomal abnormalities

BACKGROUND AND PURPOSE

Although diabetes mellitus (DM) is an important risk factor for Alzheimer's disease (AD), the detailed mechanism(s) by which DM regulates amyloid β (Aβ) processing is still unclear. The longer residence time of amyloid precursor protein (APP) in endosomes is critical for Aβ production and DM is known to cause endosomal dysregulation. Here we have examined the effects of high glucose on APP-producing endosomes and related signaling pathways.

EXPERIMENTAL APPROACH

To identify the underlying mechanisms, we investigated the effects of high glucose on abnormalities in early endosomes and related signalling pathways in human neuroblastoma cells. In vivo, diabetic mice treated with pharmacological inhibitors were used to examine endosomal dysfunction.

KEY RESULTS

The hippocampus of diabetic animals presented endosomal abnormalities and Aβ up-regulation. High glucose increased Aβ production through early endosomal enlargement achieved by increased lipid raft-mediated APP endocytosis. High glucose induced ROS-stimulated Sp1 activation, up-regulating phosphatidylinositol binding clathrin assembly protein (PICALM), clathrin heavy chain, and adaptor-related protein complex 2 alpha 1. PICALM facilitated clathrin-mediated APP endocytosis resulting in early endosomal enlargement. Meanwhile, AMPK/mTORC1-mediated autophagy defect and ROS- and mTORC1-mediated lysosomal dysfunction aggravated early endosomal enlargement under high glucose. Moreover, the increased Aβ production and cognitive deficits in diabetic mice were reversed by inhibition of early endosomal enlargement.

CONCLUSION AND IMPLICATIONS

High glucose induces early endosomal abnormalities through PICALM-induced APP endocytosis and mTORC1-inhibited endosomal clearance, up-regulating Aβ production. Thus, targeting PICALM and mTORC1 to prevent endosomal disorders is a promising strategy for managing diabetes-induced AD.

Central cholinergic neuronal degeneration promotes the development of postoperative cognitive dysfunction

Postoperative cognitive dysfunction (POCD) is consistently associated with increased morbidity and mortality. However, its mechanism remains poorly understood. We hypothesized that central cholinergic neuronal degeneration facilitates the development of POCD. The impact of anesthesia/surgery (appendectomy) on learning and memory and the levels of choline acetyltransferase (ChAT), acetylcholinesterase (AChE), vesicular acetylcholine transporter (VAChT), and choline transporter (CHT) in adult and aged mice were measured. Separate cohorts were analyzed after pretreatment with donepezil, an AChE inhibitor, in aged mice or with murine-p75-saporin (mu-p75-sap), a cholinergic-specific immunotoxin, in adult mice. Morris Water Maze was used to measure the learning and memory changes after anesthesia/surgery. Western blot was used to measure the changes in the protein levels of the biomarkers of the central cholinergic system. We found that anesthesia/surgery-induced memory decline and attenuation of central cholinergic biomarkers (ChAT and VAChT) in aged mice but not in adult mice. Donepezil pretreatment reduced central cholinergic impairment in the aged mice and prevented learning and memory declines after anesthesia/surgery. In contrast, when central cholinergic neurons were pre-injured with mu-p75-sap, cognitive dysfunction developed in the adult mice after anesthesia/surgery. These data suggest that central cholinergic neuronal degeneration facilitates the development of POCD.