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Recent studies suggest that the lipid mediator platelet-activating factor (PAF) is involved in keratinocyte function and skin inflammation. Indeed, PAF is found in association with inflammatory skin diseases, intradermal injections of PAF induce inflammation, and keratinocytes express functional PAF receptors (PAF-R). One mechanism by which the keratinocyte PAF-R could contribute to epidermal functions and inflammatory states would be through the synthesis of inflammatory regulators, such as PAF, PGs, and cytokines. The ability of the epidermal PAF-R to induce the synthesis of these immunomodulators was tested using a model system created by transduction of the PAF-R-negative human epidermal cell line KB with the PAF-R. Activation of this epidermal PAF-R resulted in arachidonic acid release, and the biosynthesis of PAF and PGE2. In addition, the KB PAF-R triggered increased levels of mRNA and protein for the inducible isozyme of cyclooxygenase (COX-2) as well as IL-6 and IL-8, both of which have been implicated in skin inflammatory processes. Studies with the human keratinocyte-derived epidermal cell line HaCaT revealed that activation of the endogenous PAF-R led to the increased accumulation of COX-2, IL-6, and IL-8 mRNA similar to that seen with the KB PAF-R model system. Finally, treatment of HaCaT keratinocytes with IL-8 resulted in PAF biosynthesis, indicating the existence of a positive feedback loop between IL-8 and PAF in epidermal cells. These studies suggest involvement of PAF and the PAF-R in the epidermal cytokine network.

Inorganic phosphate (Pi) plays a vital role in intracellular energy metabolism. Its many effects include stimulation of glucose use, enhancement of high-energy phosphate concentrations, and modulation of cytosolic free [Ca2+]. Cultured fetal rat cortical neurons constitutively import Pi, and cytosolic levels positively correlate with [ATP], [NADPH], and energy charge. In the present study, we demonstrate that the concentration of intracellular Pi is an important determinant of acute neuronal survival after an excitotoxic or oxidative insult to cultured fetal rat cortical neurons. Extracellular Pi dose-dependently enhanced survival of cortical neurons after exposure to NMDA at early (< or = 6 h) time points after termination of the insult. Pi similarly increased neuronal survival after exposure to kainic acid or H2O2. Pi-exposed neurons had higher basal intracellular [Pi], [ATP], and [GSH], and slightly lower cytosolic free [Ca2+], compared with Pi-deprived neurons. Pi-exposed neurons maintained increased [ATP] after exposure to NMDA and displayed reduced formation of reactive oxygen species after exposure to kainic acid or H2O2, compared with Pi-deprived neurons. These findings demonstrate that changes in extracellular and intracellular Pi can affect neuronal survival after excitotoxic or oxidative insults.

Cardiac hypertrophy was produced in embryonic chicks by decreasing the incubation temperature from 38 degrees C to 32 degrees C on day 11. Increases in ventricular protein, RNA, and DNA support the cardiac enlargement. Cytochrome-c oxidase activity and citrate synthase activity were depressed in hypothermic ventricles by 63% and 56%, respectively. No significant differences were seen in enzyme activities in pectoralis muscles. The involvement of mitochondrial gene replication and transcription was evaluated using a cDNA clone for the mitochondrially encoded subunit III of cytochrome-c oxidase (CO III). Quantitative slot-blot analysis demonstrated that the relative CO III mRNA concentration was reduced in hypothermic ventricles. In contrast, the relative mitochondrial DNA concentration was increased in hypothermic ventricles. Taken together, these data indicate that a hypothermia-induced decrease in cytochrome-c oxidase activity is associated with a decrease in CO III mRNA, which is not coupled to a decrease in the mitochondrial DNA copy number. This dissociation of mitochondrial gene replication and transcription may provide a useful model for examining the regulation of mitochondrial biogenesis.