Telomerase in kinetoplastid parasitic protozoa

We have identified telomerase activity in extracts of three evolutionarily diverse kinetoplastid species: Trypanosoma brucei, Leishmania major, and Leishmania tarentolae. Telomerase activity was initially detected in extracts from insect form cells of all three kinetoplastid species by using a modification of the one-tube telomere repeat amplification protocol [Kim, N., et al. (1994) Science 266, 2011–2015], although better results were subsequently achieved with the two-tube telomere repeat amplification protocol [Autexier, C., Pruzan, R., Funk, W. & Greider, C. (1996) EMBO J. 15, 5928–5935]. The activity in T. brucei extracts was sufficiently robust to enable its detection in a direct assay of telomerase; enzyme processivity was found to be relatively low. The in vitro properties of telomerase suggest a possible templating domain sequence for the telomerase RNA of T. brucei. Telomerase activity is likely to contribute to telomere maintenance in these parasitic organisms and provides a new target for chemotherapeutic intervention.

IL-4 inhibits osteoclast formation through a direct action on osteoclast precursors via peroxisome proliferator-activated receptor γ1

IL-4 is a pleiotropic immune cytokine secreted by activated TH2 cells that inhibits bone resorption both in vitro and in vivo. The cellular targets of IL-4 action as well as its intracellular mechanism of action remain to be determined. We show here that IL-4 inhibits receptor activator of NF-κB ligand-induced osteoclast differentiation through an action on osteoclast precursors that is independent of stromal cells. Interestingly, this inhibitory effect can be mimicked by both natural as well as synthetic peroxisome proliferator-activated receptor γ1 (PPARγ1) ligands and can be blocked by the irreversible PPARγ antagonist GW 9662. These findings suggest that the actions of IL-4 on osteoclast differentiation are mediated by PPARγ1, an interpretation strengthened by the observation that IL-4 can activate a PPARγ1-sensitive luciferase reporter gene in RAW264.7 cells. We also show that inhibitors of enzymes such as 12/15-lipoxygenase and the cyclooxygenases that produce known PPARγ1 ligands do not abrogate the IL-4 effect. These findings, together with the observation that bone marrow cells from 12/15-lipoxygenase-deficient mice retain sensitivity to IL-4, suggest that the cytokine may induce novel PPARγ1 ligands. Our results reveal that PPARγ1 plays an important role in the suppression of osteoclast formation by IL-4 and may explain the beneficial effects of the thiazolidinedione class of PPARγ1 ligands on bone loss in diabetic patients.