The T. cruzi trans-sialidase induces PC12 cell differentiation via MAPK/ERK pathway.

The trans-sialidase (TS) of Trypanosoma cruzi induces survival and differentiation of neuronal and glial cells. This mechanism underlying survival is via phosphatidylinositol 3-kinase (PI3K) but how TS promotes neuronal differentiation remained to be determined. Here we show that TS-induced neurite outgrowth in PC12 cells is through sustained activation of the mitogen-activated protein kinase or ERK cascade and, therefore, by a signaling mechanism distinct from the one it uses to induce cell survival. Such differential activation of signal pathways in neuronal cells to effectuate diverse biological activities is analogous to the action of authentic neurotrophins and other growth factors, thereby reinforcing the novel concept of T. cruzi mimicry of host neurotrophic factor(s).

Trypanosoma cruzi trans-sialidase: a potent and specific survival factor for human Schwann cells by means of phosphatidylinositol 3-kinase/Akt signaling.

Patients infected with Trypanosoma cruzi may remain asymptomatic for decades and show signs of neuroregeneration in the peripheral nervous system (PNS). In the absence of such neuroregeneration, patients may die in part by extensive neuronal destruction in the gastrointestinal tract. Thus, T. cruzi may, despite their invasion of the PNS, directly prevent cell death to keep nerve destruction in check. Indeed, T. cruzi invasion of Schwann cells, their prime target in PNS, suppressed host-cell apoptosis caused by growth-factor deprivation. The trans-sialidase (TS) of T. cruzi and the Cys-rich domain of TS reproduced the antiapoptotic activity of the parasites at doses (> or =3.0 nM) comparable or lower than those of bona fide mammalian growth factors. This effect was blocked by LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3K). TS also activated Akt, a downstream effector of PI3K. Ectopic expression of TS in an unrelated parasite, Leishmania major, turned those parasites into activators of Akt in Schwann cells. In contrast, the Cys-rich domain of TS did not block apoptosis in Schwann cells overexpressing dominant-negative Akt or constitutively active PTEN, a negative regulator of PI3K/Akt signaling. The results demonstrate that T. cruzi, through its TS, triggers the survival of host Schwann cells via the PI3K/Akt pathway, suggesting a role for PI3K/Akt in the pathogenesis of Chagas' disease.

A trypanosomal protein synergizes with the cytokines ciliary neurotrophic factor and leukemia inhibitory factor to prevent apoptosis of neuronal cells.

Despite the neuronal degeneration in the chronic stage of Chagas' disease, neuron counts actually increase in the preceding, asymptomatic stage, in contrast to the age-related decrease in neuron counts in age-matched normal individuals. Relevant to this observation, we found that the trans-sialidase (TS) of Trypanosoma cruzi, the etiologic agent of Chagas' disease, induces neurite outgrowth and rescues PC12 cells from apoptotic death caused by growth factor deprivation. These properties, novel for a parasite protein, were independent of catalytic activity and were mapped to the C terminus of the catalytic domain of TS. TS activated protein kinase Akt in a phosphoinositide-3 kinase-inhibitable manner, suggesting a molecular mechanism for the TS-induced neuroprotection. TS also triggered bcl-2 gene expression in growth factor-deprived cells, an effect consistent with TS protecting against apoptosis. Ciliary neurotrophic factor and leukemia inhibitory factor, two cytokines critical to the repair of injured motor neurons, specifically potentiated the TS action. The results suggest that TS acts in synergy with host ciliary neurotrophic factor or leukemia inhibitory factor to promote neuronal survival in T. cruzi-infected individuals.

[Effect of levorin and its combination with a modifying factor on lipid peroxidation in Crithidia oncopelti]. / Vliianie levorina i ego sochetaniia s modifitsiruiushchim faktorom na perekisnoe okislenie lipidov u Crithidia oncopelti.

It was shown earlier by the authors that in the presence of sodium acetate as a modifier of C. oncopelti reaction to levorin, a polyenic antibiotic sensitivity of this organism to the antibiotic increased. At the same time there were observed changes in the ratio of the lipids and fatty acids of the total lipid fraction of C. oncopelti. The changes in the lipid composition of the biological membranes influenced lipid peroxidation (LPO). The present paper deals with investigation of interrelation between increasing of C. oncopelti sensitivity to levorin in the presence of sodium acetate and LPO levels. Accumulation of the primary, secondary and final LPO products in C. oncopelti under the effect of sodium acetate, levorin (1 microgram/ml) added simultaneously with the modifier and levorin in a concentration of 10 micrograms/ml was investigated. It was shown that sodium acetate did not induce accumulation of LPO products as compared to the initial culture. Levorin added simultaneously with sodium acetate and levorin in a concentration of 10 micrograms/ml induced an increase in the content of LPO products in the C. oncopelti lipids. The causes of the LPO rate increase in the presence of the polyenic antibiotic are discussed.

[Effect of levorin and its combination with a modifying factor on the fatty acid composition of Crithidia oncopelti lipids]. / Vliianie levorina i ego kombinatsii s modifitsiruiushchim faktorom na zhirnokislotnyi sostav lipidov Crithidia oncopelti.

It was shown by us earlier that the sensitivity of Crithidia oncopelti to levorin, a polyene antibiotic, increased in the presence of sodium acetate as a modifying factor. A simultaneous change in the ratio of C. oncopelti structural lipids was also observed. The present paper deals with investigation of the effect of levorin and its combination with the modifying factor on the fatty acid composition of C. oncopelti lipids. The study showed that addition of sodium acetate in a concentration of 40 mg/ml to the medium for cultivation of C. oncopelti resulted in an increase in the total level of fatty acid unsaturation at the expense of a significant increase in the content of linoleic acid and polyunsaturated acids. The content of monoene fatty acids simultaneously decreased. In a concentration of 1 microgram/ml levorin had no effect on the growth of C. oncopelti and did not practically change the relative content of its fatty acids. Combined addition of levorin (1 microgram/ml) and sodium acetate (40 mg/ml) to the medium resulted in inhibition of the culture growth by 60-80 per cent and a marked increase in the total content of saturated acids with a decrease in the level of monounsaturated and polyunsaturated acids. The trypanostatic concentration of levorin (10 micrograms/ml) had the same effect and also lowered the total level of unsaturated fatty acids of C. oncopelti.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of a modifying factor on the sensitivity of Crithidia oncopelti to levorin]. / Vliianie modifitsiruiushchego faktora na chuvstvitel'nosti Crithidia oncopelti k levorinu.

The paper deals with possible discovery of ways for increasing sensitivity of trypanosomides to polyenic antibiotics. The following substances were tested: sodium pyruvate and acetate, calcium salts, ascorbic acid and 1-valine. The total number of the cells and the number of the viable cells in the culture and their morphological characteristics were used as the criteria for estimation of the C. oncopelti sensitivity. It was shown that sodium acetate most actively modified the levorin effect on C. oncopelti. Its addition in a concentration of 40 mg/ml to the cultivation medium with levorin in a concentration of 1 microgram/ml induced a trypanocidal effect. With the use of levorin alone such an effect was observed when the antibiotic was used in a concentration of 10 micrograms/ml. The growth rate of the protozoon was decreased by 60-80 per cent as compared to the control. The number of the viable cells was lowered 4 times. The morphology of the culture markedly changed. This indicates that the presence of sodium acetate as a modifier in the culture medium allowed one to decrease 10 times the dose of levorin and to preserve the trypanocidal effect.

[Trypanosome sensitivity to polyene antibiotics]. / Izuchenie chuvstvitel'nosti tripanosomid k polienovym antibiotikam.

Swelling of the plasma membrane is one of the mechanisms of resistance to damages in pathogenic Protozoa. Polyenic antibiotics induce reconstruction of the cytoplasma membrane of unicellular eukaryotic organisms, i. e. fungi and Protozoa by binding the membrane lipids. The effect of 5 heptaene polyenic antibiotics, such as amphotericin B, mycoheptin, levorin, its sodium salt and levoridone on the growth of trypanosomides of Trypanosoma lewisi and Crithidia oncopelti was studied. The MIC and IC50 of these antibiotics were determined. It was found that these antibiotics were inhibitors of the trypanosomide growth and development. Levorin and amphotericin were most active with respect to C. oncopelti and levorin was most active with respect to T. lewisi. Physiological and morphological changes in the trypanosomides induced by the polyenic antibiotics were noted. The effect of levorin and amphotericin B on the content of lipids in the trypanosomide cells was studied. A decrease in the total content of the intracellular lipids due to the effect of the polyenes was shown. Differences in the rate of the inhibitory effect as dependent on the structure of the hydrophile part of the lactone ring of the heptaene polyenic antibiotics were found.