During inflammatory, demyelinating diseases such as multiple sclerosis (MS), inflammation and axonal damage are prevalent early in the course. Axonal damage includes swelling, defects in transport, and failure to clear damaged intracellular proteins, all of which affect recovery and compromise neuronal integrity. The clearance of damaged cell components is important to maintain normal turnover and restore homeostasis. In this study, we used mass spectrometry to identify insoluble proteins within high-speed/mercaptoethanol/sarcosyl-insoluble pellets from purified white matter plaques isolated from the brains of individuals with relapsing–remitting MS (RRMS). We determined that the transmembrane protein 106B (TMEM106B), normally lysosome-associated, is insoluble in RRMS plaques relative to normal-appearing white matter from individuals with Alzheimer’s disease and non-neurologic controls. Relative to wild-type mice, hypomorphic mice with a reduction in TMEM106B have increased axonal damage and lipid droplet accumulation in the spinal cord following myelin-oligodendrocyte-glycoprotein-induced experimental autoimmune encephalomyelitis. Additionally, the corpora callosa from cuprizone-challenged hypomorphic mice fail to clear lipid droplets efficiently during remyelination, suggesting that when TMEM106B is compromised, protein and lipid clearance by the lysosome is delayed. As TMEM106B contains putative lipid- and LC3-binding sites, further exploration of these sites is warranted.
Introduction To prevent and treat thrombotic complications in patients hospitalized with severe COVID-19 infection, anticoagulation treatments primarily with heparin and low molecular weight heparin have been recommended. Heparin-induced thrombocytopenia (HIT) is a rare but conceivably fatal reaction to heparin that is characterized by a sudden drop in platelet count accompanied by new onset of thrombosis 4-10 days after heparin exposure. The purpose of this retrospective study was to investigate the prevalence of thrombocytopenia and HIT in hospitalized COVID-19 patients, as well as their association with mortality. Methods 3,672 plasma samples were collected from patients admitted to the first wave of COVID-19 in our institution at New York City (March to May 2020). All patients admitted with a platelet count of less than 150 k/ul were assigned to the thrombocytopenic group. In addition, two groups with similar demographics and normal platelet counts were randomly selected based on discharge outcome: alive vs. deceased (n= 88 per group). PF4 IgG Elisa and heparin neutralization were carried out in accordance with the manufacturer's instructions. A positive HIT result required an optical density (OD) greater than 0.4 and heparin neutralization greater than 50%. Statistical analysis was done in R studio (V.1.4.1717) to analyze demographics (age, gender, ethnicity), initial laboratory data, anticoagulation on admission, and thrombosis. Results Only 86 of the 3,672 (2.3%) patients admitted had thrombocytopenia. Only 1 of the 86 patients tested positive for HIT (1.1% ). 4 cases of the non-survivors (4.5%) tested positive for HIT compared to none of the survivors in the two groups with normal platelet counts. One of these 4 cases had a history of thrombosis (DVT). Interestingly, the PF4 Elisa ODs in non-survivors were significantly higher than in survivors (0.09 vs. 0.06, p-value< 0.001). Although the platelet count did not differ significantly between the two groups, the mean platelet volume (MPV) on admission and its maximum peak during hospitalization were significantly higher in non-survivors than in survivors. Conclusions We only found HIT positive cases among non-survivors, implying that HIT is associated with COVID severity. The incidence of HIT in severe COVID-19 patients appears to be higher than the pre-COVID-19 historical rates of HIT in hospitalized patients (<1%). Although thrombocytopenia is relatively uncommon in COVID-19 patients, the MPV was significantly higher in non-survivors, suggesting that platelet activation and destruction may explain the higher rate of HIT in COVID-19.
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