Liver-derived serum amyloid A (SAA) is present in plasma where it is mainly associated with HDL and from which it is cleared more rapidly than are the other major HDL-associated apolipoproteins. Although evidence suggests that lipid-free and HDL-associated forms of SAA have different activities, the pathways by which SAA associates and disassociates with HDL are poorly understood. In this study, we investigated SAA lipidation by hepatocytes and how this lipidation relates to the formation of nascent HDL particles. We also examined hepatocyte-mediated clearance of lipid-free and HDL-associated SAA. We prepared hepatocytes from mice injected with lipopolysaccharide or an SAA-expressing adenoviral vector. Alternatively, we incubated primary hepatocytes from SAA-deficient mice with purified SAA. We analyzed conditioned media to determine the lipidation status of endogenously produced and exogenously added SAA. Examining the migration of lipidated species, we found that SAA is lipidated and forms nascent particles that are distinct from apoA-I-containing particles and that apoA-I lipidation is unaltered when SAA is overexpressed or added to the cells, indicating that SAA is not incorporated into apoA-Icontaining HDL during HDL biogenesis. Like apoA-I formation, generation of SAA-containing particles was dependent on ABCA1, but not on scavenger receptor class B type I. Hepatocytes degraded significantly more SAA than apoA-I. Taken together, our results indicate that SAA's lipidation and metabolism by the liver is independent of apoA-I and that SAA is not incorporated into HDL during HDL biogenesis.
|Number of pages||10|
|Journal||Journal of Lipid Research|
|State||Published - 2020|
Bibliographical noteFunding Information:
This work was supported by National Institutes of Health Grant R01 HL134731 (to N.R.W. and F.C.d.B.) and U.S. Department of Veterans Affairs Grants CX000773 (to N.R.W.), and CX000975 (to L.R.T.). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The authors declare that they have no conflicts of interest with the contents of this article. Manuscript received 9 August 2019 and in revised form 6 January 2020. Published, JLR Papers in Press, January 9, 2020 DOI https://doi.org/10.1194/jlr.RA119000329
Copyright © 2020 Ji et al.
- Adenosine 5′-triphosphate
- Binding cassette transporter A1
- Inflammatory disease
- Lipid metabolism
- Liver metabolism
- Nascent high density lipoprotein
ASJC Scopus subject areas
- Cell Biology