Osmotic and hypoxic induction of osteopontin in retinal pigment epithelial cells: Involvement of purinergic receptor signaling

Purpose

Osteopontin (OPN) is a neuroprotective factor in the retina that improves photoreceptor survival. The aim of the present study was to investigate whether human RPE cells express and respond to OPN.

Methods

Hypoxia and chemical hypoxia were induced by cell culture in 0.25% O₂ and the addition of CoCl₂, respectively. Hyperosmolarity was produced by the addition of 100 mM NaCl or 200 mM sucrose. Gene expression was quantified with real-time reverse transcription (RT)-PCR, and protein secretion was investigated with enzyme-linked immunosorbent assay (ELISA). Nuclear factor of activated T cell 5 (NFAT5) was depleted with siRNA.

Results

The acutely isolated RPE cells and the cultured RPE cells expressed OPN. OPN gene expression was induced by hypoxia and hyperosmotic media, as well as by exogenous bFGF. High extracellular NaCl and hypoxia induced secretion of OPN. Hyperosmotic expression of the OPN gene was mediated by the p38 MAPK and ERK1/2 signal transduction pathways, and the transcriptional activities of CREB and NFAT5. The hypoxic expression of the OPN gene was mediated by the PI3K signal transduction pathway and caspase-mediated, necrosis-related pathways. Phospholipases A₂ were involved in mediating hyperosmotic and hypoxic OPN gene expression. Autocrine or paracrine P2Y₂ receptor signaling induced by extracellular ATP contributed to hyperosmotic expression of the OPN gene whereas activation of A₁ receptors by extracellularly formed adenosine contributed to thypoxic OPN gene expression. Autocrine or paracrine VEGF signaling exerted an inhibitory effect on expression of the OPN gene. Exogenous OPN induced expression and secretion of bFGF, but not of VEGF.

Conclusions

The data indicated that RPE cells produce and respond to OPN; OPN expression is, in part, induced by the cellular danger signal ATP. RPE-derived neuroprotective factors such as bFGF may contribute to the prosurvival effect of OPN on photoreceptor cells.

Finding the ideal place for a psychotherapeutic intervention in a stepped care approach--a brief overview of the literature and preliminary results from the Project PREDICT

AIMS

To provide an overview over empirical evidence regarding stepped care approaches that include psychotherapies. To present own preliminary study results in alcohol dependent patients.

METHODS

Publications were searched in the databases Medline, PsycINFO and the internet search engine Google Scholar. Inclusion criteria were psychosocial treatment and psychiatric disorders. Our own study consists of two steps. In step 1 patients receive anti-craving medication or placebo and Medical Management (MM). After a relapse to heavy drinking patients can step up and after randomization they either continue with the same treatment or they receive additional alcoholism specific psychotherapy (ASP).

RESULTS

Evidence suggests that stepped care might be efficacious in patients with obsessive-compulsive behavior and depression. There is no evidence for efficacy in problem drinkers. Results of our own study show that the completer rate in MM alone is higher than in ASP with MM, but there are no significant differences concerning age, sex and disease severity between completer and non-completer in both study arms.

CONCLUSIONS

Further research with regard to stepped care in alcohol dependent patients is needed. An introduction of the psychotherapy at earlier stages might be sensible.