Ablation of SAMD1 in Mice Causes Failure of Angiogenesis, Embryonic Lethality

Pathological retention of LDL in the intima is involved in atherosclerosis, although the retention mechanisms are not well-understood. Previously, we reported Sterile Alpha Motif Domain Containing 1 (SAMD1), a protein secreted by intimal smooth muscle cells in atherosclerotic lesions, appears to bind LDL in extracellular matrix around intimal cells. Fab-fragment inhibitors of apparently irreversible SAMD1/LDL binding reduced LDL retention in carotid injury models, but did not have a significant effect on early spontaneous lesion development. Our histology of mouse atherosclerosis models revealed extensive SAMD1 expression, possibly related to cell phenotype modulation and antigen presentation. Although the normal function of SAMD1 is unknown, it may have multiple epigenetic roles. For this report, we generated SAMD1-/-, SAMD1-/+, and SAMD1-/+ apoE-/- mice to further explore SAMD1s role in atherosclerosis. SAMD1 was found in tissues throughout the SAMD1+/+ and SAMD1-/+ embryos. Homozygous loss of SAMD1 was embryonic lethal: at embryonic day 14, organs were partially developed and/or degraded; heads and brains were malformed; no blood vessels were observed; red blood cells were scattered and pooled, primarily near the embryo surface; and cell death was occurring. Development appeared normal in heterozygous SAMD1 embryos, but postnatal genotyping showed a reduced ability to thrive. Growth of atherosclerotic lesions in SAMD1-/+ apoE-/- after 35 weeks was not significantly less than in mice SAMD1+/+ apoE-/- mice.