Tau, a microtubule-associated protein, plays a critical role in the pathophysiology of neurons. However, whether tau protein is expressed in smooth muscle cells is unknown. Thus, we tested the hypothesis that tau protein is expressed in the primary cultures of smooth muscle cells. Here, we report that tau protein is expressed and constitutively phosphorylated at threonine 181 in various smooth muscle cell types, including human pulmonary artery smooth muscle cells, bronchial airway smooth muscle cells, and cerebral artery smooth muscle cells. Immunofluorescence staining revealed that phosphorylated tau at threonine 181 is more organized in the cell than is total tau protein. A protein phosphatase inhibitor, calyculin A, induced the formation of higher molecular weight species of phosphorylated tau, as visualized by Western blotting, indicating the occurrence of tau aggregation. Immunofluorescence analysis also showed that calyculin A caused the aggregation of phosphorylated tau and disrupted the cytoskeletal organization. These results demonstrate the existence of tau protein in smooth muscle cells, and that smooth muscle tau is susceptible to protein phosphorylation and aggregation. Lung smooth muscle tau may therefore play an important role in pulmonary pathophysiology.

Ischemic stroke is a major cause of death among patients with systemic hypertension. The narrowing of the lumen of the brain vasculature contributes to the increased incidence of stroke. While hyalinosis represents the major pathological lesions contributing to vascular lumen narrowing and stroke, the pathogenic mechanism of brain vascular hyalinosis has not been well characterized. Thus, the present study examined the postmortem brain vasculature of human patients who died of ischemic stroke due to systemic hypertension. Hematoxylin and eosin staining and immunohistochemistry showed the occurrence of brain vascular hyalinosis with infiltrated plasma proteins along with the narrowing of the vasa vasorum and oxidative stress. Transmission electron microscopy revealed endothelial cell bulge protrusion into the vasa vasorum lumen and the occurrence of endocytosis in the vasa vasorum endothelium. The treatment of cultured microvascular endothelial cells with adrenaline also promoted the formation of the bulge as well as endocytic vesicles. The siRNA knockdown of sortin nexin-9 (a mediator of clathrin-mediated endocytosis) inhibited adrenaline-induced endothelial cell bulge formation. Adrenaline promoted protein-protein interactions between sortin nexin-9 and neural Wiskott–Aldrich syndrome protein (a regulator of actin polymerization). Spontaneously hypertensive stroke-prone rats also exhibited lesions indicative of brain vascular hyalinosis, the endothelial cell protrusion into the lumen of the vasa vasorum, and endocytosis in vasa vasorum endothelial cells. We propose that endocytosis-dependent endothelial cell bulge protrusion narrows the vasa vasorum, resulting in ischemic oxidative damage to cerebral vessels, the formation of hyalinosis, the occurrence of ischemic stroke, and death in systemic hypertension patients.

• The eIF4A inhibitor zotatifin with the BCL-2 inhibitor venetoclax is a promising combination therapy for AML.

Targeted therapies like Venetoclax have increased the options available to acute myeloid leukemia (AML) patients, but survival remains poor due to drug resistance and disease relapse. We found that the translation initiation factor EIF4A1, which unwinds complex mRNA structures in the 5' UTR of oncogenic transcripts, is highly expressed in AML stem- and progenitor-like cells. Inhibiting eIF4A with the small molecule Zotatifin reduces translation of transcripts related to the cell cycle and survival. This results in downregulation of AKT, STAT-5, and MCL-1 and underlies synergy of Zotatifin with Venetoclax. The drug combination promotes apoptosis across AML genotypes, while the effect on healthy blood cells is limited. Using in vivo relapsed and refractory AML patient-derived xenograft models, the combination significantly suppressed tumor burden and prolonged survival of xenografted mice. These results support eIF4A-mediated protein translation as a therapeutic target in AML.

Disclosures. Cutler:Ruth L. Kirschstein Postdoctoral Individual National Research Service Award: Research Funding; Astellas: Consultancy; Rigel: Consultancy; Ox