Apolipoprotein M (ApoM) is a member of the lipocalin protein family. It is found associated with high density lipoproteins and to a lesser extent with low density lipoproteins and triglyceride-rich lipoproteins. It is positively related to leptin. It is mainly expressed in liver and kidney. ApoM is secreted through the plasma membrane but remains membrane-bound, where it is involved in lipid transport. It is important for the formation of prebeta-HDL and cholesterol efflux to HDL, and thereby inhibits formation of atherosclerotic lesions.