Serum amyloid A

Source: Wikipedia, the free encyclopedia.
Chr. 11 p15.1
Search for
StructuresSwiss-model
DomainsInterPro
Human Serum amyloid A2
Identifiers
Symbol
Chr. 11 p15.1-p14
Search for
StructuresSwiss-model
DomainsInterPro
Human Serum amyloid A3, pseudogene
Identifiers
SymbolSAA3P
Alt. symbolsSAA3
Chr. 11 p15.1-p14
Search for
StructuresSwiss-model
DomainsInterPro
Human Serum amyloid A4
Identifiers
SymbolSAA4
Alt. symbolsC-SAA
Chr. 11 p15.1-p14
Search for
StructuresSwiss-model
DomainsInterPro

Serum amyloid A (SAA) proteins are a family of apolipoproteins associated with high-density lipoprotein (HDL) in plasma. Different isoforms of SAA are expressed constitutively (constitutive SAAs) at different levels or in response to inflammatory stimuli (acute phase SAAs). These proteins are produced predominantly by the liver.[1]

Acute-phase serum amyloid A proteins

Acute-phase serum amyloid A proteins (A-SAAs) are secreted during the acute phase of

TNF-α. Both SAA1 and SAA2 are induced up to a 1000-fold in mice under acute inflammatory conditions following exposure to bacterial lipopolysaccharide (LPS).[2] Three A-SAA genes have also been identified in humans,[3] although the third gene, SAA3, is believed to represent a pseudogene that does not generate messenger RNA or protein.[4] Molecular weights of the human proteins are estimated at 11.7 kDa for SAA1[5] and 12.8 kDa for SAA4.[6]

Serum amyloid A (SAA) is also an acute phase marker that responds rapidly. Similar to CRP, levels of acute-phase SAA increase within hours after inflammatory stimulus, and the magnitude of increase may be greater than that of CRP. Relatively trivial inflammatory stimuli can lead to SAA responses. It has been suggested that SAA levels correlate better with disease activity in early inflammatory joint disease than do ESR and CRP. Although largely produced by hepatocytes, more recent studies show that SAA is produced by adipocytes as well, and its serum concentration is associated with body mass index.[7]

Constitutive serum amyloid A proteins

A fourth SAA (SAA4) was identified in humans and is expressed constitutively in the liver and, thus, is defined as a constitutive SAA (C-SAA).[8] A similar protein that is now also called SAA4 has since been identified in the mouse; it had originally been designated SAA5.[9][10]

References