Analysis of MCFD2- and LMAN1-deficient mice demonstrates distinct functions in vivo

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• The LMAN1-MCFD2 complex facilitates endoplasmic reticulum (ER) to Golgi transport of coagulation factors V (FV) and VIII (FVIII).
• Genetic defects in LMAN1 or MCFD2 cause combined FV and FVIII deficiency, a bleeding disorder, in humans and previously in LMAN1-deficient mice.

Purpose of the Study:

• To investigate the in vivo function of MCFD2 and its interplay with LMAN1 in FV and FVIII transport.
• To explore the roles of LMAN1 and MCFD2 in the secretion of other proteins, such as alpha-1-antitrypsin (AAT).

Main Methods:

• Gene targeting to create MCFD2-deficient mice.
• Analysis of plasma levels of FV, FVIII, and AAT in wild-type, singly deficient (LMAN1 or MCFD2), and doubly deficient mice.
• Examination of AAT accumulation in the ER of hepatocytes.

Main Results:

• MCFD2-deficient mice exhibit reduced plasma FV and FVIII levels, more so than LMAN1-deficient mice.
• Double deficiency of LMAN1 and MCFD2 results in FV and FVIII levels similar to LMAN1-deficient mice, suggesting an alternative secretion pathway.
• MCFD2-null mice show normal survival, unlike LMAN1-null mice, but double deficiency leads to partial embryonic lethality.
• Decreased plasma AAT levels and ER accumulation were observed in all deficient mouse groups, indicating a role for LMAN1 and MCFD2 in AAT ER exit.

Conclusions:

• LMAN1 and MCFD2 have distinct, yet cooperative, roles in the ER-to-Golgi secretory pathway for FV and FVIII.
• An alternative pathway compensates for FV/FVIII secretion in the absence of both LMAN1 and MCFD2.
• LMAN1 and MCFD2 are essential for the efficient ER exit and secretion of AAT.