THE ROLE OF LYSOSOME REMODELING IN PHAGOCYTOSIS

Lysosomes are mostly vesicular in morphology performing various functions due to their involvement in several signaling mechanisms. Immune response and autophagy can trigger vesicular lysosomes into morphologically distinct tubular lysosomes. Autophagy mediated tubular lysosomes are mTOR independent while immune mediated tubular lysosomes are mTOR dependent. Tubular lysosomes perform antigen presentation in dendritic cells, provide more fluid retention, and aid in enhanced phagocytosis in macrophages while in autophagy, it mediates the biogenesis of lysosomes. But studying the role of tubular lysosomes has been difficult as the stimulants of tubular lysosomes also modify the phenotypes of macrophages making it more activated. Here we describe a DNA nanodevice, Tudor, which tubulates lysosomes in an alternative pathway in macrophages without affecting its polarization states. Tudor binds to cell surface localized Ku70/80 heterodimer proteins and brings about tubulation of lysosomes in various macrophages in TLR independent pathway which was not known before. Further, tubular lysosomes showed lower enzymatic activity as compared to their vesicular counterparts suggesting tubular lysosomal lumenal biochemistry is distinct from vesicular ones. pH correctable calcium sensor, CalipHluor 2.0 imaging showed the presence of pH and calcium gradients within the lumen of tubular lysosomes. In more than 50% of the tubular lysosome population, the part of tubular lysosomes closer to the plasma membrane showed high calcium and hypo-acidic lumenal environment. Tubular lysosomes previously discovered to be delivering V-ATPases to phagosomes needed for their maturation. We found that tubular lysosomes make physical contact with phagosomes and cells with tubular lysosomes showed better phagosome lysosome fusion. Hence Tudor was able to decipher the alternative pathway in which tubular lysosomal formation poises resting macrophages to phagocytosis.