Staphylococcus aureus phagocytosis is affected by senescence.

Senescent cells accumulate in multicellular animals with aging, resulting in organ or tissue dysfunction. These alterations increase the incidence of a variety of illnesses, including infectious diseases, and, in certain instances, its severity. In search of a rationale for this phenomenon, we focused on the endophagocytic pathway in senescent cells. We first described the endocytic vesicle populations at different stages of maturation using confocal microscopy. There was an increase in the number of vacuoles per cell, which was partially explained by an increase in cell size. No changes in vesicle maturation or degradation capacities were determined by microscopy or Western blot assays. Also, we studied the internalization of various endophagocytic cargoes in senescent cells and observed only a decrease in the intracellular recovery of bacteria such as Staphylococcus aureus. Afterwards, we studied the intracellular traffic of S. aureus, and observed no differences in the infection between control and senescent cells. In addition we quantified the recovery of bacteria from control and senescent cells infected in the presence of several inhibitors of endophagosomal maturation, and no changes were observed. These results suggest that bacterial internalization is affected in senescent cells. Indeed, we confirmed this hypothesis by determining minor bacterial adherence and internalization by confocal microscopy. Furthermore, it is important to highlight that we found very similar results with cells from aged animals, specifically BMDMs. This alteration in senescent cells enlightens the diminished bacterial clearance and may be a factor that increases the propensity to suffer severe infectious conditions in the elderly.

FKBP8 is a novel molecule that participates in the regulation of the autophagic pathway.

Autophagy is a homeostatic process by which misfolded proteins, organelles and cytoplasmic material are engulfed in autophagosomal vesicles and degraded through a lisosomal pathway. FKBP8 is a member of the FK506-binding proteins family (FKBP) usually found in mitochondria and the endoplasmic reticulum. This protein plays a critical role in cell functions such as protein trafficking and folding. In the present report we demonstrate that the depletion of FKBP8 abrogated autophagy activation induced by starvation, whereas the overexpression of this protein triggered the autophagy cascade. We found that FKBP8 co-localizes with ATG14L and BECN1, both members of the VPS34 lipid kinase complex, which regulates the initial steps in the autophagosome formation process. We have also demonstrated that FKBP8 is necessary for VPS34 activity. Our findings indicate that the regulatory function of FKBP8 in the autophagy process depends of its transmembrane domain. Surprisingly, this protein was not found in autophagosomal vesicles, which reinforces the notion that the FKBP8 only participates in the initial steps of the autophagosome formation process. Taken together, our data provide evidence that FKBP8 modulates the early steps of the autophagosome formation event by interacting with the VPS34 lipid kinase complex. SUMMARY: In this article, the protein FKBP38 is reported to be a novel modulator of the initial steps of the autophagic pathway, specifically in starvation-induced autophagy. FKBP38 interacts with the VPS34 lipid kinase complex, with the transmembrane domain of FKBP38 being critical for its biological function.

The cAMP effectors, Rap2b and EPAC, are involved in the regulation of the development of the Coxiella burnetii containing vacuole by altering the fusogenic capacity of the vacuole.

Cyclic Adenosine 3',5'-monophosphate (cAMP) is a key second messenger known to directly regulate not only the protein kinase A (PKA) activity but also other important molecules such as the exchange protein activated by cAMP (EPAC), which is as a guanine nucleotide exchange factor (GEF) of the low molecular weight GTPase, Rap2. Coxiella burnetii is a Gram negative bacterium that survives and grows in a large Coxiella replicative vacuole (CRV), which displays lysosomal and autophagic features. In this report, we present evidence that both, EPAC and its downstream effector Rap2b, were recruited to the CRV. The transient over-expression of the Rap2b wt protein, but not its inactive mutant Rap2b ΔAAX, markedly inhibited the development of the large CRV. Additionally, Rap2b wtinhibited the fusion of early Coxiella phagosomes with the fully developed CRV, indicating that homotypic fusion events are altered in the presence of high levels of Rap2b wt. Likewise, the fusion of endosome/lysosomal compartments (heterotypic fusions) with the large CRV was also affected by the over-expression of this GTPase. Interestingly, cell overexpression of Rap2b wt markedly decreased the levels of the v-SNARE, Vamp7, suggesting that this down-regulation impairs the homotypic and heterotypic fusions events of the Coxiella vacuole.