Glycerophosphodiesters inhibit lysosomal phospholipid catabolism in Batten disease.

Batten disease, the most prevalent form of neurodegeneration in children, is caused by mutations in the CLN3 gene, which encodes a lysosomal transmembrane protein. CLN3 loss leads to significant accumulation of glycerophosphodiesters (GPDs), the end products of glycerophospholipid catabolism in the lysosome. Despite GPD storage being robustly observed upon CLN3 loss, the role of GPDs in neuropathology remains unclear. Here, we demonstrate that GPDs act as potent inhibitors of glycerophospholipid catabolism in the lysosome using human cell lines and mouse models. Mechanistically, GPDs bind and competitively inhibit the lysosomal phospholipases PLA2G15 and PLBD2, which we establish to possess phospholipase B activity. GPDs effectively inhibit the rate-limiting lysophospholipase activity of these phospholipases. Consistently, lysosomes of CLN3-deficient cells and tissues accumulate toxic lysophospholipids. Our work establishes that the storage material in Batten disease directly disrupts lysosomal lipid homeostasis, suggesting GPD clearance as a potential therapeutic approach to this fatal disease.

Putative Phospholipase B-Like 2 is Not Responsible for Polysorbate Degradation in Monoclonal Antibody Drug Products.

Polysorbates (PS) are surfactants commonly added in a therapeutic protein drug product as excipients to protect proteins from denaturation and aggregation during storage, transportation, and delivery. Significant degradation of PS in drug products could lead to shortened drug shelf lives and PS-degrading activity in drug products must be minimized. Identification of lipases that degrade PS could lead to better process control in drug manufacturing. In 2016, phospholipase B-like 2 (PLBD2) was proposed as a residual host cell protein responsible for degrading PS20 in a drug formulation. We have carried out a series of studies to verify the role of PLBD2 in degrading polysorbates in drug products purified from recombinant Chinese Hamster Ovary (CHO) cells. Genetic knock-out and immuno-depletion results showed that when PLBD2 was removed or depleted, the degradation of PS20 or PS80 was neither diminished nor reduced. In addition, a quantitative analysis of PLBD2 and PS20 degradation in multiple formulated mAb products did not establish a correlation between the amount of PLBD2 and the level of PS20 degradation. Collectively these results suggest that PLBD2 is not the primary cause of polysorbate degradation in formulated drug products purified using standard Protein A and ion exchange chromatography.