Intracellular parasites of the genus Leishmania are the causative agents of leishmaniasis. The disease is transmitted by the bite of a sand fly vector, which inoculates the parasite into the skin of mammalian hosts, including humans. During chronic infection the parasite lives and replicates inside phagocytic cells, notably the macrophages. An interesting, but overlooked finding, is that other cell types and even non-phagocytic cells have been found to be infected by Leishmania spp. Nevertheless, the mechanisms by which Leishmania invades such cells had not been previously studied. Here, we show that L. amazonensis can induce their own entry into fibroblasts independently of actin cytoskeleton activity, and, thus, through a mechanism that is distinct from phagocytosis. Invasion involves subversion of host cell functions, such as Ca2+ signaling and recruitment and exocytosis of host cell lysosomes involved in plasma membrane repair. This article has an associated First Person interview with the first author of the paper.

Trypanosoma cruzi enters host cells by subverting the mechanism of cell membrane repair. In this process, the parasite induces small injuries in the host cell membrane leading to calcium entry and lysosomal exocytosis, which are followed by compensatory endocytosis events that drive parasites into host cells. We have previously shown that absence of both LAMP-1 and 2, major components of lysosomal membranes, decreases invasion of T. cruzi into host cells, but the mechanism by which they interfere with parasite invasion has not been described. Here we investigated the role of these proteins in parasitophorous vacuole morphology, host cell lysosomal exocytosis, and membrane repair ability. First, we showed that cells lacking only LAMP-2 present the same invasion phenotype as LAMP1/2^-/- cells, indicating that LAMP-2 is an important player during T. cruzi invasion process. Second, neither vacuole morphology nor lysosomal exocytosis was altered in LAMP-2 lacking cells (LAMP2^-/- and LAMP1/2^-/- cells). We then investigated the ability of LAMP-2 deficient cells to perform compensatory endocytosis upon lysosomal secretion, the mechanism by which cells repair their membrane and T. cruzi ultimately enters cells. We observed that these cells perform less endocytosis upon injury when compared to WT cells. This was a consequence of impaired cholesterol traffic in cells lacking LAMP-2 and its influence in the distribution of caveolin-1 at the cell plasma membrane, which is crucial for plasma membrane repair. The results presented here show the major role of LAMP-2 in caveolin traffic and membrane repair and consequently in T. cruzi invasion. Trypanosoma cruzi is the etiological agent of Chagas disease, a very debilitating illness that has no efficient treatment to date. Better knowledge of the mechanisms involved with host cell infection is important to change this scenario. T. cruzi enters host cells by subverting the mechanism by which cells repair small injuries in their plasma membrane. In this process, parasites interact with host cells causing membrane injuries. These injuries lead to secretion of lysosomal content to the extracellular media, which in turn causes the internalization of plasma membrane wounds via endocytosis. During this endocytic process the parasite is internalized by the host cell. We have previously shown that absence of two proteins located at the lysosomal membrane, LAMP-1 and 2, severely interferes with T. cruzi entry into host cells. In the present manuscript we show that absence of LAMP-2 alone is enough to compromise T. cruzi entry into host cells and it does so by compromising the endocytic events that follow lysosome secretion, which in turn is responsible for driving T. cruzi into the host cell interior.

Impairment of endothelial function under high blood pressure is linked to the loss of inwardly rectifying K⁺ (Kir2.1) channels activity in human resistance arteries, leading to a reduction in flow-induced vasodilation and possibly leading to a vicious cycle between elevation of blood pressure, and further impairment of Kir2.1 function and flow-induced vasodilation.

Shear stress is one of the major hemodynamic forces acting on the endothelium. However, it is not well known how endothelial cells (EC) respond mechanically to these stimuli in vivo. Here we investigated whether changes in biomechanics properties and shear stress could increase cell susceptibility to injury, contributing to vascular fragility. We surgically implanted a shear stress modifier device on the carotid artery of ApoE-knockout mice (ApoE^−/−), which, due to its shape, causes a gradual stenosis in the vessel, resulting in distinct shear stress patterns. Our data show actin fibers accumulation in areas with higher lipid deposition in ApoE^−/−, indicating that dyslipidemia might interfere with EC actin cytoskeleton organization. We also showed that both shear stress and dyslipidemia were important for EC susceptibility to injury. Furthermore, lysosomal distribution, an important organelle for plasma membrane repair, was altered in ApoE^−/−, which could compromise EC’s ability to repair from damage. Therefore, dyslipidemia and variations in shear stress patterns not only affect cellular mechanics by compromising the actin cytoskeleton organization, but also enhance cell susceptibility to injury and alter vesicle trafficking in vascular cells. This may likely contribute to vascular fragility and thus to the initial steps of atherosclerosis development.