Biomedical subjects

Michael K Ahlijanian

Publications and source records attributed to Michael K Ahlijanian.

4 recordsLinked to original sources

PubMed2004

Discovery and SAR of 2-aminothiazole inhibitors of cyclin-dependent kinase 5/p25 as a potential treatment for Alzheimer's disease.

High-throughput screening with cyclin-dependent kinase 5 (cdk5)/p25 led to the discovery of N-(5-isopropyl-thiazol-2-yl)isobutyramide (1). This compound is an equipotent inhibitor of cdk5 and cyclin-dependent kinase 2 (cdk2)/cyclin E (IC(50)=ca. 320nM). Parallel and directed synthesis techniques were utilized to explore the SAR of this series. Up to 60-fold improvements in potency at cdk5 and 12-fold selectivity over cdk2 were achieved.

Alzheimer Disease↗

PubMed2003

APP processing is regulated by cytoplasmic phosphorylation.

Amyloid-beta peptide (Abeta) aggregate in senile plaque is a key characteristic of Alzheimer's disease (AD). Here, we show that phosphorylation of amyloid precursor protein (APP) on threonine 668 (P-APP) may play a role in APP metabolism. In AD brains, P-APP accumulates in large vesicular structures in afflicted hippocampal pyramidal neurons that costain with antibodies against endosome markers and the beta-secretase, BACE1. Western blot analysis reveals increased levels of T668-phosphorylated APP COOH-terminal fragments in hippocampal lysates from many AD but not control subjects. Importantly, P-APP cofractionates with endosome markers and BACE1 in an iodixanol gradient and displays extensive colocalization with BACE1 in rat primary cortical neurons. Furthermore, APP COOH-terminal fragments generated by BACE1 are preferentially phosphorylated on T668 verses those produced by alpha-secretase. The production of Abeta is significantly reduced when phosphorylation of T668 is either abolished by mutation or inhibited by T668 kinase inhibitors. Together, these results suggest that T668 phosphorylation may facilitate the BACE1 cleavage of APP to increase Abeta generation.

Alzheimer Disease↗

PubMed2003

Partial rescue of the p35-/- brain phenotype by low expression of a neuronal-specific enolase p25 transgene.

Cyclin-dependent kinase 5 (Cdk5) is activated on binding of activator proteins p35 and p39. A N-terminally truncated p35, termed p25, is generated through cleavage by the Ca(2+)-dependent protease calpain after induction of ischemia in rat brain. p25 has been shown to accumulate in brains of patients with Alzheimer's disease and may contribute to A-beta peptide-mediated toxicity. Studies from transfected neurons as well as p35 and p25 transgenic mice have indicated that Cdk5, when activated by p25, gains some toxic function compared with p35/Cdk5. It remains unclear, however, whether p25/Cdk5 signaling additionally channels into pathways usually used by p35/Cdk5 and whether p25 is associated with a loss of p35 function. To clarify these issues, we have generated p25-transgenic mice in a p35-null background. We find that low levels of p25 during development induce a partial rescue of the p35-/- phenotype in several brain regions analyzed, including a rescue of cell positioning of a subset of neurons in the neocortex. In accordance with the partial rescue of brain anatomy, phosphorylation of the Cdk5 substrate mouse disabled 1 is partially restored during development. Besides this, p25/Cdk5 fails to phosphorylate other substrates that are normally phosphorylated by p35/Cdk5. Our results show that p25 can substitute for p35/Cdk5 under certain circumstances during development. In addition, they suggest that p25 may have lost some functions of p35.

Aging↗

PubMedDate not supplied

Role of cdk5 in the pathogenesis of Alzheimer's disease.

Alzheimer's disease (AD) is characterized by two pathological hallmarks, namely, senile plaques and neurofibrillary tangles (NFTs). The former are mainly composed of amyloid-beta peptides (Abeta) while the latter consists mainly of filaments of hyperphosphorylated tau. Cyclin-dependent kinase 5 (cdk5) has been implicated not only in the tangle pathology, but recent data also implicate cdk5 in the generation of Abeta peptides. Since both Abeta peptides and NFTs are believed to play a role in neurodegeneration in AD, this proline-directed serine/threonine protein kinase is likely to contribute to the pathogenesis of AD. In vitro and in vivo animal data demonstrate the ability of cdk5 to induce phosphorylation and aggregation of tau, and NFT deposition and neurodegeneration. Findings from AD brain samples also show an elevated cdk5 activity and conditions that support the activation of cdk5. Evidence for the role of cdk5 in regulating Abeta production is just emerging. The mechanisms for this potentially damaging activity of cdk5 are largely unknown although amyloid precursor protein and presenilin-1 are both cdk5 substrates.

Alzheimer Disease↗