Delannoy, C. | bioRxiv Science

bioRxiv2022

Structural and functional analysis of natural capsid variants reveals sialic-acid independent entry of BK polyomavirus

BK Polyomavirus (BKPyV) is an opportunistic pathogen that causes nephropathy in kidney transplant recipients. The BKPyV major capsid protein, VP1, engages gangliosides, lipid-linked sialylated glycans at the cell surface, to gain entry into cells. Here, we characterise the influence of VP1 mutations observed in patients with persistent post-transplant BKPyV replication on ganglioside binding, VP1 protein structure, and the tropism of the virus in two renal cell lines: 293TT and immortalised renal tubular epithelial (RS) cells. Infectious entry of single mutants E73Q, E73A and the triple mutant A72V-E73Q-E82Q (VQQ) remained sialic acid-dependent. These three variants acquired binding to a-series gangliosides, including GD1a, although only E73Q was able to infect GD1a-supplemented LNCaP or GM95 cells. Crystal structures of the three mutants showed a clear shift of the BC2 loop in mutants E73A and VQQ that correlated with the inability of these VP1 variants to infect ganglioside complemented cells. On the other hand, the double mutant K69N-E82Q lost the ability to bind sialic acid, with the K69N mutation leading to a steric clash which precludes sialic acid binding. Nevertheless, this mutant retained significant infectivity in 293TT cells that was not dependent on heparan sulphate proteoglycans, implying that an unknown sialic acid-independent entry receptor for BKPyV exists.

microbiology↗

bioRxiv2021

A ganglioside-based senescence-associated immune checkpoint

Senescent cells accumulate in aging tissues, and their elimination can favor healthy aging1-4. Therefore, therapeutic interventions targeting cellular senescence may be promising strategies for delaying or reversing a vast range of age-related diseases5. As cells of the immune system are responsible for senescent cell elimination6-11, a possible anti-aging and pro-healthspan treatment is the specific activation of the immune system to induce senescent cell clearance. However, whether this elimination is limited by an immune checkpoint leading to tolerance of senescence cells is currently unknown. Here, we show that cellular senescence, elicited by various stressors other than oncogenic activation, triggers immune escape toward natural killer (NK) cells, which may thus limit the use of anti-senescence immunotherapies. Moreover, using mass spectrometry, we reveal that senescent cells reshuffle their glycosphingosine composition, toward a marked increase in the ganglioside content, including the appearance of disialylated ganglioside GD3. This senescence associated GD3 overexpression results from transcriptional upregulation of the gene encoding the enzyme ST8SIA1, which is responsible for GD3 synthesis. The high level of GD3 leads to a strong immunosuppressive signal affecting NK cell-mediated immunosurveillance. In a mouse model of lung fibrosis, senescent cell-dependent NK cell immunosuppression is blunted by in vivo administration of anti-GD3 monoclonal antibodies leading to a clear anti-fibrotic effect. These results demonstrate that GD3 upregulation in senescent cells drives a switch from immune clearance toward immune tolerance of senescent cells. Therefore, we propose that GD3 level acts as a senescence-associated immune checkpoint (SIC) that regulates NK cell functions toward senescent cells. Thus, targeting GD3 with specific antibodies may be a promising strategy for the development of effective anti-senescence immunotherapies.

immunology↗