Biomedical subjects

Jon Kosek

Publications and source records attributed to Jon Kosek.

5 recordsLinked to original sources

PubMed2007

PAR-1 kinase phosphorylates Dlg and regulates its postsynaptic targeting at the Drosophila neuromuscular junction.

Targeting of synaptic molecules to their proper location is essential for synaptic differentiation and plasticity. PSD-95/Dlg proteins have been established as key components of the postsynapse. However, the molecular mechanisms regulating the synaptic targeting, assembly, and disassembly of PSD-95/Dlg are not well understood. Here we show that PAR-1 kinase, a conserved cell polarity regulator, is critically involved in controlling the postsynaptic localization of Dlg. PAR-1 is prominently localized at the Drosophila neuromuscular junction (NMJ). Loss of PAR-1 function leads to increased synapse formation and synaptic transmission, whereas overexpression of PAR-1 has the opposite effects. PAR-1 directly phosphorylates Dlg at a conserved site and negatively regulates its mobility and targeting to the postsynapse. The ability of a nonphosphorylatable Dlg to largely rescue PAR-1-induced synaptic defects supports the idea that Dlg is a major synaptic substrate of PAR-1. Control of Dlg synaptic targeting by PAR-1-mediated phosphorylation thus constitutes a critical event in synaptogenesis.

Animals↗

PubMed2005

Inactivation of Drosophila DJ-1 leads to impairments of oxidative stress response and phosphatidylinositol 3-kinase/Akt signaling.

Parkinson's disease (PD) is the most common movement disorder characterized by dopaminergic dysfunction and degeneration. The cause of most PD cases is unknown, although postmortem studies have implicated the involvement of oxidative stress. The identification of familial PD-associated genes offers the opportunity to study mechanisms of PD pathogenesis in model organisms. Here, we show that DJ-1A, a Drosophila homologue of the familial PD-associated gene DJ-1, plays an essential role in oxidative stress response and neuronal maintenance. Inhibition of DJ-1A function through RNA interference (RNAi) results in cellular accumulation of reactive oxygen species, organismal hypersensitivity to oxidative stress, and dysfunction and degeneration of dopaminergic and photoreceptor neurons. To identify other genes that may interact with DJ-1A in regulating cell survival, we performed genetic interaction studies and identified components of the phosphatidylinositol 3-kinase (PI3K)/Akt-signaling pathway as specific modulators of DJ-1A RNAi-induced neurodegeneration. PI3K signaling suppresses DJ-1A RNAi phenotypes at least in part by reducing cellular reactive oxygen species levels. Consistent with the genetic interaction results, we also found reduced phosphorylation of Akt in DJ-1A RNAi animals, indicating an impairment of PI3K/Akt signaling by DJ-1A down-regulation. Together with recent findings in mammalian systems, these results implicate impairments of PI3K/Akt signaling and oxidative stress response in DJ-1-associated disease pathogenesis. We also observed impairment of PI3K/Akt signaling in the fly parkin model of PD, hinting at a common molecular event in the pathogenesis of PD. Manipulation of PI3K/Akt signaling may therefore offer therapeutic benefits for the treatment of PD.

Animals↗

PubMed2004

Protecting the myocardium: a role for the beta2 adrenergic receptor in the heart.

OBJECTIVE: The sympathetic nervous system enhances cardiac muscle function by activating beta adrenergic receptors (betaARs). Recent studies suggest that chronic betaAR stimulation is detrimental, however, and that it may play a role in the clinical deterioration of patients with congestive heart failure. To examine the impact of chronic beta1AR and beta2AR subtype stimulation individually, we studied the cardiovascular effects of catecholamine infusions in betaAR subtype knockout mice (beta1KO, beta2KO). DESIGN: Prospective, randomized, experimental study. SETTING: Animal research laboratory. SUBJECTS: beta1KO and beta2KO mice and wild-type controls. INTERVENTIONS: The animals were subjected to 2 wks of continuous infusion of the betaAR agonist isoproterenol. Analyses of cardiac function and structure were performed during and 3 days after completion of the infusions. Functional studies included graded exercise treadmill testing, in vivo assessments of left ventricular function using Mikro-Tip catheter transducers, right ventricular pressure measurements, and analyses of organ weight to body weight ratios. Structural studies included heart weight measurements, assessments of myocyte ultrastructure using electron microscopy, and in situ terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick-end labeling staining to quantitate myocyte apoptosis. MEASUREMENTS AND MAIN RESULTS: We found that isoproterenol-treated beta2KO mice experienced greater mortality rates (p =.001, chi-square test using Fisher's exact method) and increased myocyte apoptosis at 3- and 7-day time points (p =.04 and p =.0007, respectively, two-way analysis of variance). CONCLUSION: The results of this study suggest that in vivo beta2AR activation is antiapoptotic and contributes to myocardial protection.

Adrenergic beta-Agonists↗

PubMed2003

Cartilage tissue engineering using cryogenic chondrocytes.

OBJECTIVE: To generate in vitro hyaline cartilage from cryogenically preserved human septal chondrocytes in a simulated microgravity environment on a 3-dimensional biodegradable scaffolding material. METHODS: In this experiment, cryogenically frozen chondrocytes were thawed and cultured in a monolayer in serum-based chondrocyte media. They were seeded onto 3-dimensional biopolymer scaffolds in a spinner flask. The seeded constructs were then transferred to a bioreactor (an environment of solid-body rotation) for 6 weeks. Chondrocyte growth and extracellular matrix production in the constructs were confirmed by cell count, cell viability, and histologic analysis and by electron microscopy. RESULTS: Histologic sections stained with hematoxylin-eosin and Alcian blue (for acidic proteoglycans) confirmed the presence of hyaline cartilage in the cartilage constructs. Ultrastructural examination using transmission electron microscopy demonstrated matrix formation and chondrocyte viability. CONCLUSIONS: This study proves that chondrocytes that are cryogenically stored for extended periods can be used to grow cartilage in vitro. Cryogenically preserved chondrocytes retain their ability to grow in tissue culture, redifferentiate, and produce extracellular matrix.

Bioreactors↗

PubMed2002

Abnormal cardiac function associated with sympathetic nervous system hyperactivity in mice.

alpha(2A)-Adrenergic receptors (ARs) in the midbrain regulate sympathetic nervous system activity, and both alpha(2A)-ARs and alpha(2C)-ARs regulate catecholamine release from sympathetic nerve terminals in cardiac tissue. Disruption of both alpha(2A)- and alpha(2C)-ARs in mice leads to chronically elevated sympathetic tone and decreased cardiac function by 4 mo of age. These knockout mice have increased mortality, reduced exercise capacity, decreased peak oxygen uptake, and decreased cardiac contractility relative to wild-type controls. Moreover, we observed significant abnormalities in the ultrastructure of cardiac myocytes from alpha(2A)/alpha(2C)-AR knockout mice by electron microscopy. Our results demonstrate that chronic elevation of sympathetic tone can lead to abnormal cardiac function in the absence of prior myocardial injury or genetically induced alterations in myocardial structural or functional proteins. These mice provide a physiologically relevant animal model for investigating the role of the sympathetic nervous system in the development and progression of heart failure.

Animals↗