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APCS

Official Full Name
amyloid P component, serum
Organism
Homo sapiens
GeneID
325
Background
The protein encoded by this gene is a glycoprotein, belonging to the pentraxin family of proteins, which has a characteristic pentameric organization. These family members have considerable sequence homology which is thought to be the result of gene duplication. The binding of the encoded protein to proteins in the pathological amyloid cross-beta fold suggests its possible role as a chaperone. This protein is also thought to control the degradation of chromatin. It has been demonstrated that this protein binds to apoptotic cells at an early stage, which raises the possibility that it is involved in dealing with apoptotic cells in vivo. [provided by RefSeq, Sep 2008]
Synonyms
SAP; PTX2; HEL-S-92n;
Bio Chemical Class
Pentraxin family
Protein Sequence
MNKPLLWISVLTSLLEAFAHTDLSGKVFVFPRESVTDHVNLITPLEKPLQNFTLCFRAYSDLSRAYSLFSYNTQGRDNELLVYKERVGEYSLYIGRHKVTSKVIEKFPAPVHICVSWESSSGIAEFWINGTPLVKKGLRQGYFVEAQPKIVLGQEQDSYGGKFDRSQSFVGEIGDLYMWDSVLPPENILSAYQGTPLPANILDWQALNYEIRGYVIIKPLVWV
Open
Disease
Amyloidosis, Idiopathic interstitial pneumonitis, Parkinsonism
Approved Drug
0
Clinical Trial Drug
4 +
Discontinued Drug
0

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Detailed Information

The APCS gene, which encodes the Serum Amyloid P Component (SAP), has become an important factor in a variety of immune-related processes and illnesses. This thorough analysis dives into the structure, function, and clinical importance of APCS and its protein product, SAP, emphasizing its many functions in health and sickness.

Molecular Characteristics and Structure

APCS, which is found on chromosome 1q23.2, is a member of the pentraxin protein family, which also contains CRP and PTX3. The gene encodes a 25 kDa glycoprotein that forms a unique pentameric structure similar to those observed in ancient creatures such as horseshoe crabs.

SAP's structure resembles that of legume lectins, with a flattened β-jellyroll shape. Each pentamer subunit has a short alpha-helix on one side and five double calcium binding sites on the other surface, which are essential for ligand binding. This structural arrangement enables SAP to interact with a broad spectrum of molecules, including DNA, chromatin, apoptotic debris, and a variety of pathogenic proteins.

Biological Functions and Mechanisms

SAP's multifarious biological functions come from its capacity to bind a variety of ligands in a calcium-dependent way. It plays a vital role in numerous critical processes.

1. Amyloid Interaction: SAP readily attaches to amyloid fibrils, accounting for up to 14% of the dry mass in amyloid deposits. This association stimulates fibrillogenesis and stabilizes fibrils, shielding them from proteolytic destruction.

2. Complement System Modulation: SAP interacts with numerous complement components, including C1q and ficolin family members, to regulate inflammatory processes.

3. Immune Cell Regulation: SAP interacts with Fc gamma receptors (FcγRs) to activate and polarize immune cells, notably monocytes and macrophages.

4. Debris Clearance: When cells die or tissues are damaged, SAP helps to eliminate cellular debris by adhering to exposed DNA and other intracellular components.

5. Lipid Metabolism: Its binding to lipoproteins implies that it has a role in lipoprotein metabolism, albeit this function is not fully understood.

Figure 1 summarizes the key functions of SAP in binding to ligands during cell death and modulating inflammatory responses through interactions with immune receptors.Figure 1. Functions of SAP. (Xi D, et al., 2015)

APCS in Disease Processes

SAP has shown strong anti-fibrotic capabilities in a variety of organ systems. SAP treatment decreased both fibrocyte counts and fibrosis symptoms in lung fibrosis animals. It reduces collagen deposition and profibrotic mediators while increasing anti-fibrotic macrophage phenotypes. Clinical studies using recombinant human SAP (rhPTX2) have shown encouraging outcomes in the treatment of idiopathic pulmonary fibrosis and myelofibrosis, as well as increasing lung function and bone marrow fibrosis.

Serum SAP levels link negatively with fibrosis advancement in chronic hepatitis and nonalcoholic fatty liver disease (NAFLD). SAP has been shown in experimental models to protect against carbon tetrachloride-induced liver damage, principally via inhibiting inflammatory responses and activating hepatic stellate cells.

Amyloidosis and neurodegenerative diseases

SAP's involvement in amyloidosis is complicated. While it is a significant component of amyloid deposits and helps to keep them stable, it has also become a therapeutic target. Clinical studies for systemic amyloidosis have shown promise with the introduction of CPHPC (miridesap), a medication that quickly clears circulating SAP, followed by anti-SAP antibodies (dezamizumab).

Elevated brain SAP levels are associated with dementia severity in neurodegenerative illnesses, including Alzheimer's disease (AD). SAP has been discovered in hippocampal tangles, plaques, and arteries in Alzheimer's patients, indicating that it enters the brain when the blood-brain barrier is weakened. Recent genetic research has connected APCS to Alzheimer's disease risk, Lewy body dementia, and plasma tau protein levels.

Cardiovascular Diseases

SAP's association with cardiovascular disorders is complicated. Higher SAP levels are linked to an increased risk of angina and combined cardiovascular events in older persons. SAP accumulates in atherosclerotic lesions and may stimulate cholesterol efflux via particular routes. However, its specific significance is still debated, with some research claiming that SAP deficiency reduces atherosclerosis progression in animal models.

SAP levels rise after an acute myocardial infarction and are associated with complement activation. Fascinatingly, in the setting of hypertensive cardiac disease, Serum Amyloid P (SAP) seems to be protective. It does this by reducing the formation of pro-fibrotic macrophages, therefore preventing cardiac remodeling—a mechanism usually linked with disease development. This fascinating ability emphasizes its possible relevance in control of cardiovascular health.

Disorders of Neuropsychiatry

Beyond its known function in neurodegenerative diseases, SAP has also been associated to many mental illnesses. People with major depressive disorder (MDD), for example, have been shown to have increased plasma SAP levels. These variations in SAP levels also correlate with the effectiveness of depressive medications. According to a recent research, SAP modulates serotonin transporter levels and their membrane localization—qualities that might directly affect the therapeutic effect of several antidepressants, including escitalopram. This link presents fresh directions for investigating focused therapies in mental health.

Diseases of Respiration and Infections

In respiratory illnesses and infections, SAP also is very important. Especially among younger patients, elevated SAP levels have been seen in severe instances of acute respiratory syndrome (SARS) and COVID-19. SAP found in the alveolar fluid of people with acute respiratory distress syndrome (ARS) points to possible active shaping of local immune responses inside the lungs.

Regarding microbiological diseases, SAP's natural defensive systems are also really remarkable. It can bind and neutralize a key structural component of gram-negative bacteria, lipopolysaccharide (LPS). SAP also improves complement-mediated phagocytosis, therefore helping to remove several bacterial infections like Streptococcus pneumoniae. These results emphasize its double function as both an active participant in immune defense and a sentinel.

These revelations of SAP's many roles in cardiovascular, neuropsychiatric, and respiratory domains together highlight its potential importance as a key biomarketer and therapeutic target for many different disorders.

References:

  1. Wang H, Nie Y, Sun Z, et al. Serum amyloid P component: Structure, biological activity, and application in diagnosis and treatment of immune-associated diseases. Mol Immunol. 2024;172:1-8.
  2. Xi D, Luo T, Xiong H, et al. SAP: structure, function, and its roles in immune-related diseases. Int J Cardiol. 2015;187:20-26.
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