Myeloid differentiation protein 2 (MD2), also known as lymphocyte antigen 96. It is involved in the binding of lipopolysaccharide to toll-like receptor (TLR4). Toll-like receptor 4 (TLR4) is associated with ischemic and hemorrhagic stroke. Meanwhile, TLR4 is an upstream molecule of inflammation, apoptosis and necroptosis. MD2 binds and activates TLR4, forming a complex. Therefore, blocking the interaction between MD2 and TLR4 can interrupt apoptosis and necrosis and provide neuroprotection. More interestingly, MD2 also directly acts on the mitosis-associated SRC (Sam68) to mediate cell death in neurons. We’ll introduce an MD2 inhibitor, TAT-CIRP, here. It is a transactivator (Tat) cold-inducible RNA-binding protein.

TAT-CIRP is neuroprotective and inhibits MD2 and TLR4-independent pathways.

In vitro, TAT-CIRP protects neurons from excitotoxic injury. Moreover, it (5 μM) attenuates apoptosis and necrosis induced by NMDA stimulation (50 μM; 1 hr) in neuronal cells through a TLR4-independent pathway.

In mouse models of ischemic and hemorrhagic stroke, TAT-CIRP (5-20 mg/kg) attenuates middle cerebral artery (MCA) occlusion (MCAO) and brain injury after ischemic stroke in mice. Tat, the cell membrane transduction domain of human immunodeficiency virus type 1, serves as a control peptide in this assay. TAT-CIRP (20 mg/kg; intravenous injection; single dose) also crosses the blood-brain barrier with a C_max value of 4762.6 μg/L and a half-life of approximately 90 minutes in a mouse model. High doses of TAT-CIRP (100 mg/kg; intravenously; once daily for 7 days) can not cause significant toxicity in mice.

Above all, TAT-CIRP effectively inhibits MD2 and exerts a strong neuroprotective effect against ischemic and hemorrhagic stroke. It also exhibits good pharmacokinetic characteristics and can cross the blood-brain barrier.

References:

[1] Fang Z, et al. Sci Transl Med. 2021 Jun 9;13(597):eabb6716.