Rapid repair of plasma membrane wounds is critical for cellular survival. Muscle fibers are particularly susceptible to injury, and defective sarcolemma resealing causes muscular dystrophy. Caveolae accumulate in dystrophic muscle fibers and caveolin and cavin mutations cause muscle pathology, but the underlying mechanism is unknown. Here we show that muscle fibers and other cell types repair membrane wounds by a mechanism involving Ca2+-triggered exocytosis of lysosomes, release of acid sphingomyelinase, and rapid lesion removal by caveolar endocytosis. Wounding or exposure to sphingomyelinase triggered endocytosis and intracellular accumulation of caveolar vesicles, which gradually merged into larger compartments. The pore-forming toxin SLO was directly visualized entering cells within caveolar vesicles, and depletion of caveolin inhibited plasma membrane resealing. Our findings directly link lesion removal by caveolar endocytosis to the maintenance of plasma membrane and muscle fiber integrity, providing a mechanistic explanation for the muscle pathology associated with mutations in caveolae proteins.DOI: http://dx.doi.org/10.7554/eLife.00926.001

Trypanosoma cruzi takes advantage of a sphingomyelinase-dependent plasma membrane repair pathway to gain access to host cells.

Iron uptake promotes hydrogen peroxide–dependent differentiation of Leishmania promastigotes into infective amastigotes.

Mammalian cell invasion by Trypanosoma cruzi is a complex process in which various parasite and host cell components interact, triggering the activation of signaling cascades and Ca^^ mobilization in both cells. Using metacyclic trypomastigotes (MT) generated in vitro and tissue culture-derived trypomastigotes (TCT), as counterparts of insect-borne and bloodstream parasites, respectively, the mechanisms of host cell invasion by X cruzi have been partially elucidated. Distinct sets of molecules are engaged by MT and TCT to enter target cells. MT make use of surface glycoproteins with dual Qo?^ signaling activity, in a manner dependent of 77 cruzi isolate. In highly infective MT, the binding of gp82 to its receptor triggers a signaling cascade involving protein tyrosine kinase, phospholipase C and production of inositol 1,4,5-triphosphate, whereas in poorly invasive MT, the mucin-like gp35/50 induces the activation of a signaling route in which adenylate cyclase, generation of cAMP and Ca^^ mobilization from acidocalcisomes are implicated. The host cell signaling pathways activated by MT remain to be determined. Differently from MT, the TCT surface molecules that bind to host cells as a prelude to invasion, such as the glycopro› teins of gp85 family, appear to be devoid of signaling properties, but they may induce TCT enzymes, such as oligopeptidase B and cruzipain, to generate Ca ^ signaling factors of para› site or host cell origin. Host cell responses mediated by TGF-p receptor or integrin family member may also be triggered by TCT. A more complete and detailed picture of T. cruzi invasion needs further investigations.

Summary Leishmania parasites infect macrophages, cells normally involved in innate defense against pathogens. L. amazonensis and L. major cause severe or mild disease, respectively, consistent with each parasite’s ability to survive within activated macrophages. The mechanisms underlying increased virulence of L. amazonensis are mostly unknown. We show that L. amazonensis promotes its own survival by inducing expression of CD200, an immunoregulatory molecule that inhibits macrophage activation. L. amazonensis does not form typical non-healing lesions in CD200−/− mice and cannot replicate in CD200−/− macrophages, an effect reversed by exogenous administration of soluble CD200-Fc. The less virulent L. major does not induce CD200 expression and forms small, self-healing lesions in both wild type and CD200−/− mice. Notably, CD200-Fc injection transforms the course of L. major infection to one resembling L. amazonensis, with large, non-healing lesions. CD200-dependent iNOS inhibition allows parasite growth in macrophages, identifying a mechanism for the increased virulence of L. amazonensis.

The disassembly of host cell actin cytoskeleton as a facilitator of Trypanosoma cruzi invasion has been reported by some authors, while other workers claim that it instead inhibits internalization of the parasite. In this study we aimed at elucidating the basis of this discrepancy. We performed experiments with metacyclic trypomastigotes of T. cruzi strains G and CL, which differ markedly in infectivity and enter target cells by engaging the surface molecules gp35/50 and gp82, respectively, which have signaling activity. Treatment of HeLa cells with the F-actin-disrupting drug cytochalasin D or latrunculin B inhibited the invasion by strain G but not the invasion by strain CL. In contrast to cells penetrated by strain CL, which were previously shown to have a disrupted actin cytoskeleton architecture, no such alteration was observed in HeLa cells invaded by strain G, and parasites were found to be closely associated with target cell actin. Coinfection with enteroinvasive Escherichia coli (EIEC), which recruits host cell actin for internalization, drastically reduced entry of strain CL into HeLa cells but not entry of strain G. In contrast to gp82 in its recombinant form, which induces disruption of F-actin and inhibits EIEC invasion, purified mucin-like gp35/50 molecules promoted an increase in EIEC uptake by HeLa cells. These data, plus the finding that drugs that interfere with mammalian cell signaling differentially affect the internalization of metacyclic forms of strains G and CL, indicate that the host cell invasion mediated by gp35/50 is associated with signaling events that favor actin recruitment, in contrast to gp82-dependent invasion, which triggers the signaling pathways leading to disassembly of F-actin.

Upon oral infection, Trypanosoma cruzi metacyclic trypomastigotes invade and replicate in the gastric mucosal epithelium, being apparently uniquely specialized for adhesion to mucin and mucosal invasion. Here we investigated the involvement of gp82, the metacyclic-stage-specific surface glycoprotein implicated in host cell entry, in both adhesion to gastric mucin and invasion of the mucosal epithelium upon oral challenge. Metacyclic forms, preincubated with a control monoclonal antibody (MAb) or with MAb 3F6 directed to gp82, were administered orally to BALB/c mice, and parasitemia was monitored. Mice that received parasites treated with MAb 3F6 had greatly reduced parasitemia, displaying at the peak a mean number of blood parasites more than 100-fold lower than that of the control group. MAbs directed to other T. cruzi surface glycoproteins had no such effect. gp82, as either a native or a recombinant molecule, but not the metacyclic trypomastigote surface molecule gp90 or gp35/50, bound to gastric mucin in enzyme-linked immunosorbent assays. MAb 3F6 significantly inhibited the penetration of cultured epithelial HeLa cells by metacyclic forms in the absence or in the presence of gastric mucin. Mucin alone did not affect parasite internalization. Parasite infectivity was not altered by treatment of metacyclic forms with pepsin, to which gp82 was resistant, or with proteinase K, which removed the N-terminal portion of gp82 but preserved its host cell binding site. Taken together, these findings suggest that gp82 mediates the interaction of metacyclic trypomastigotes with gastric mucin and the subsequent penetration of underlying epithelial cells.Trypanosoma cruzi, the protozoan parasite that causes Chagas' disease and is transmitted by bloodsucking triatomine insects, can also infect people orally and by blood transfusion. More than half of the acute cases of Chagas' disease recorded between 1968 and 2000 in the Brazilian Amazon were attributable to microepidemics of orally transmitted infection from contaminated food (3). Potential sources of food contamination are whole triatomine insects or their feces containing infective metacyclic trypomastigotes and possibly the anal gland secretion of T. cruzi-infected opossums (3), which are important wild reservoirs of the parasite. Metacyclic trypomastigotes, typically present in the intestinal lumen of the insect vector, are also found in the lumen of the marsupial anal glands, where the parasite goes through an extracellular cycle corresponding to that in the triatomines (4). Oral transmission through contaminated food in a region with a high rate of T. cruzi-infected opossums has been reported (15).Metacyclic trypomastigotes can invade and replicate in the gastric mucosal epithelium, and it appears that gastric mucosal invasion is the unique portal of entry for systemic T. cruzi infection after oral challenge (7). It has been shown that insectderived metacyclic trypomastigotes delivered orally were sufficient for consistent infection of 100% of BALB/c mice, whereas ...

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