Apmap, or adipocyte plasma membrane-associated protein, is a single transmembrane arylesterase and glycosyl type II transmembrane protein. It is mainly distributed in the plasma membrane and endoplasmic reticulum of adipocytes and plays a crucial role in adipogenesis [2,3]. Apmap has been implicated in lipid transport, and is associated with pathways such as the Wnt/β-catenin pathway [3]. It also has potential importance in various biological processes like cancer cell phagocytosis, meat quality determination, and viral infection [1,2,5]. Genetic models, especially knockout models, are valuable for studying its functions.

In Apmap-knockout mice, the absence of the full-length APMAP protein, which is the only isoform expressed in humans, leads to an improved metabolic phenotype upon diet-induced obesity. This includes enhanced insulin sensitivity, preserved glucose tolerance, increased respiratory exchange ratio, decreased inflammatory marker gene expression, and reduced adipocyte size. APMAP was found to interact with extracellular collagen cross-linking matrix proteins lysyl oxidase-like 1 and 3, and their expression was decreased in Apmap-knockout mice, indicating decreased fibrotic potential in epididymal white adipose tissue [6]. In cancer research, loss of Apmap in cancer cells synergizes with tumour antigen-targeting monoclonal antibodies and/or CD47-blocking monoclonal antibodies to drive increased phagocytosis across various cancer cell types, and also inhibits tumour growth in mice [1]. In cervical cancer, high expression of Apmap is associated with poor prognosis, and knockdown of Apmap in vitro significantly inhibits the migration ability of cervical cancer cells by suppressing the activation of the Wnt/β-catenin pathway [3].

In conclusion, Apmap is a multi-functional protein involved in adipogenesis, lipid and lipoprotein homeostasis, and has implications in diseases such as obesity-related metabolic disorders and cancers [2,4,6]. Studies using Apmap knockout mouse models have revealed its role in modulating metabolic phenotypes and cancer cell susceptibility to phagocytosis, providing insights into potential therapeutic targets for these disease areas.