Fig. 7.

Biogenesis of chylomicrons. TG is synthesized de novo via gpat, agpat, pap, and dgat, or remodeled via mogat and dgat. MTTP chaperones ApoB in the ER where it forms a complex with a dense lipid particle, of which the major component is PC. We hypothesize that without dietary PC the dense lipid particle level is low, and the ApoB-lipid particle complex is not formed. This will destabilize ApoB and it will be degraded, a process in which edem1 and hsp70 are central. ApoAI-V merges with the ApoB-lipid complex mediating expansion of the particle with TG [47], and the particle is transported to the Golgi facilitated by the coatomer complex COPII of which Sar1b is a part [36]. Fatty acids are absorbed by peripheral tissue in the body and a large part of the FAs originating from TG is ß-oxidized in the mitochondria. However, if dietary PC is low the dense lipid particles will not be formed and a large excess of TG will accumulate in the ER. These will be incorporated into CLDs (stippled arrows).