Biology subjects

Fahim, S. A.

Publications and source records attributed to Fahim, S. A..

2 recordsLinked to original sources

bioRxiv2019

Aggregatibacter actinomycetemcomitans LtxA hijacks endocytic trafficking pathways in human lymphocytes

Leukotoxin (LtxA) from oral pathogen Aggregatibacter actinomycetemcomitans is a secreted membrane-damaging protein. LtxA is internalized by {beta}2 integrin LFA-1 (CD11a/CD18) expressing leukocytes and ultimately causes cell death; however toxin localization in the host cell is poorly understood and these studies fill this void. We investigated LtxA trafficking using multi-fluor confocal imaging, flow cytometry and Rab5 knockdown in human T lymphocyte Jurkat cells. Planar lipid bilayers were used to characterize LtxA pore-forming activity at different pH. Our results demonstrate that LtxA/LFA-1 complex gains an access to the cytosol of Jurkat cells without evidence of plasma membrane damage utilizing dynamin-dependent and clathrin-independent mechanism. Upon internalization LtxA follows the LFA-1 endocytic trafficking pathways as identified by co-localization experiments with endosomal and lysosomal markers (Rab5, Rab11A, Rab7, and Lamp2) and CD11a. Knockdown of Rab5a resulted in loss of susceptibility of Jurkat cells to LtxA cytotoxicity suggesting that late events of LtxA endocytic trafficking are required for toxicity. The toxin trafficking via the degradation endocytic pathway may culminate in delivery of the protein to lysosomes or its accumulation in Rab11A-dependent recycling endosomes. The ability of LtxA to form pores at acidic pH may result in permeabilization of the endosomal and lysosomal membranes.

microbiology↗

bioRxiv2019

Asparagine endopeptidase cleaves tau at N167 after uptake into microglia

BackgroundTau cleavage by different proteolytic enzymes generates short, aggregation-prone fragments that have been implicated in the pathogenesis of Alzheimers disease (AD). Asparagine endopeptidase (AEP) activity in particular has been associated with tau dysfunction and aggregation, and the activity of the protease is increased in both aging and AD. Methods and ResultsUsing a mass spectrometry approach we identified a novel tau cleavage site at N167 and confirmed its processing by AEP. In combination with the previously known site at N368, we show that AEP cleavage yields a tau fragment that is present in both control and AD brains at similar levels. AEP is a lysosomal enzyme, and our data suggest that it is expressed in microglia rather than in neurons. Accordingly, we observe tau cleavage at N167 and N368 after endocytotic uptake into microglia, but not neurons. However, tau168-368 does not accumulate in microglia and we thus conclude that the fragment is part of a proteolytic cascade leading to tau degradation. ConclusionsWhile we confirm previous studies showing increased overall AEP activity in AD brains, our data suggests that AEP-mediated cleavage of tau is a physiological event occurring during microglial degradation of the secreted neuronal protein. The disease-associated increase in active AEP may thus be related to pro-inflammatory conditions in AD brains, and our findings argue against AEP inhibition as a therapeutic approach in AD.

neuroscience↗