RhoA Targeting Suppresses Cold-Induced Platelet Lesion and Allows Refrigerated Storage of Functional Human Platelets to Fourteen Days

Platelet transfusion is required for the support therapy of patients with hematological disorders and cancer. Current practice of donor-derived platelet storage at room temperature (RT) associates with an inherent risk of microbial contamination and a limit of 5-7 day shelf life. Refrigerated platelets are hemostatically superior than RT platelets but their survival in circulation is severely reduced. Storage in cold temperature induces loss of galactosylation/sialylation of platelet GPIb with exposure of b-N-acetyl glucosamine of N-linked glycans, which clusters on the platelet plasma membrane. Upon transfusion, these clusters are recognized by macrophages and hepatocytes resulting in lectin-mediated platelet clearance. We hypothesized that the long-term refrigerated storage lesion depends on the mislocalization of membrane-bound glycosyl- and syalyl-transferases in lipid rafts and endocytotic intermediates of cold-stored platelets. By using a combination of genetic and pharmacological approaches, we investigated whether the three major members of the Rho GTPase family, RHOA, RAC1 and/or CDC42, which are molecular switches regulating actomyosin dynamics and signaling in platelets. We found that cooling of platelets induces a sustained activation of RhoA and Rac1, but not Cdc42 in mouse and human platelets. Inducible genetic deletion of platelet RhoA in mice prevents clearance of cold-stored platelets upon transfusion in wild-type congenic animals (WT: 2±0.5 hrs x fraction of infusate; RhoA^Δ/Δ: 8± 0.7 hrs x fraction of infusate; p≤0.05). When human platelets were stored in either plasma or PAS-IIIM (PAS-E) for up to 14 days, the inclusion in the storage medium of a rationally designed RHOA inhibitor G04 can prevent the phagocytosis of 14-day refrigerated platelets by activated macrophages in vitro (RT-stored, vehicle-treated platelets: 20%±4; cold stored, vehicle-treated 70±5%; cold-treated, G04(10μM)- treated: 25±3%; p≤0.001) or in vivo clearance as assessed by the area under the curve of surviving human platelets (hrs x fraction of infusate) transfused into clodronate-treated, sub-lethally irradiated non-obese diabetic, γ_c^-/- (NSG) mice (RT-stored, vehicle-treated platelets: 16±1.0; cold-stored, vehicle-treated: 6±0.5; cold-stored, G04(10μM)-treated: 15±0.6; p≤0.001). This inhibition is reversible by either a wash or a 3-fold dilution that resulted in a reversion of the inhibitory effect on aggregation and in vivo correction of the bleeding time of mice pre-treated with aspirin (RT-stored, vehicle-treated: 45±4 sec.; cold-stored, vehicle-treated: 150±10 sec.; cold-stored, G04(10μM)-treated: 76±3.8 sec.; p≤0.001). Mechanistically, RHOA inhibition prevents the cold-induced cytoskeleton/shape change and spreading on fibrinogen through the prevention of the formation of lipid rafts enriched in glycosyl- and syalyl-transferase activities and the endocytosis of vacuoles enriched in GPIbα. Addition of the lipid raft disruptor b-cyclodextrin, but not of the RHOA downstream effector ROCK inhibitor Fasudil, phenocopies the effect of G04 on the prevention of cold-induced platelet damage. Thus, RHOA is the key mediator of the platelet storage lesion through a ROCK independent mechanism and its reversible inhibition allows the functional maintenance of cold-stored platelets in both survival and hemostatic properties. Our pre-clinical data support the concept that a platelet additive solution containing a low-affinity RHOA inhibitor is useful in preventing platelet storage lesion while fully maintaining their hemostatic function after 14 days of storage. A rationally designed cold storage regimen is highly feasible, which could resolve the platelet clearance problem and meet an urgent need in transfusion medicine for the support therapy of patients with thrombocytopenia or thrombocytopathy.