MCFD2, or multiple coagulation factor deficiency 2, is an EF-hand domain protein. It forms a calcium-dependent heteromeric complex with LMAN1 (also known as ERGIC-53), and this complex functions as a cargo receptor in the endoplasmic reticulum (ER)-to-Golgi transport pathway. This pathway is crucial for the efficient secretion of various glycoproteins, including coagulation factors V (FV) and VIII (FVIII), as well as α1-antitrypsin (AAT) [2,3,4,5]. Genetic mutations in MCFD2 can lead to combined deficiency of FV and FVIII, a rare bleeding disorder [1,2,3,4,5]. Mouse models have been instrumental in studying the function of MCFD2.

In MCFD2-deficient mice, plasma levels of FV and FVIII are reduced, with levels even lower than those in LMAN1-deficient mice [3]. However, in doubly deficient (MCFD2 and LMAN1) mice, FV and FVIII levels match the higher levels seen in LMAN1-deficient mice, suggesting an alternative pathway for FV/FVIII secretion in these mice [3]. All three groups of deficient mice (MCFD2-deficient, LMAN1-deficient, and doubly deficient) also show decreased plasma levels of AAT and comparable AAT accumulation in hepatocyte ER, indicating a role for MCFD2 in efficient ER exit of AAT [3]. RNAi targeting MCFD2 in mice leads to effective inhibition of MCFD2 expression, prolonged APTT, and decreased FVIII activity, suggesting its potential as an anticoagulant approach [1].

In conclusion, MCFD2 is essential for the ER-to-Golgi transport of key glycoproteins like FV, FVIII, and AAT. The study of MCFD2-deficient mouse models has provided valuable insights into the molecular mechanisms underlying combined FV and FVIII deficiency and the regulation of AAT secretion. These findings have implications for understanding bleeding disorders and developing new anticoagulant therapies.