APOD - Apolipoprotein D | Elisa - Clia - Antibody - Protein

Background:

Apolipoprotein D (APOD) is a protein encoded by the APOD gene located on chromosome 3 in humans. It belongs to the lipocalin family of proteins, which are characterized by a conserved tertiary structure known as the lipocalin fold. APOD is widely expressed in various tissues throughout the body, including the brain, liver, kidney, and adipose tissue. While APOD was initially named for its association with lipoproteins, its primary function is not directly related to lipid metabolism. Instead, APOD is involved in various physiological processes, including lipid transport, antioxidation, neuroprotection, and modulation of inflammation.APOD is known to bind to a variety of lipophilic molecules, including cholesterol, fatty acids, and steroid hormones. It may participate in the transport of these molecules within the bloodstream or across cell membranes. Additionally, APOD exhibits antioxidant properties, scavenging free radicals and protecting cells from oxidative damage.In the central nervous system, APOD is highly expressed in specific brain regions, where it plays a role in neuronal survival, synaptic plasticity, and response to injury. It has been implicated in neurodegenerative diseases such as Alzheimer's disease, where it may modulate amyloid beta toxicity and promote neuronal resilience. The expression of the APOD gene can be regulated by various factors, including hormones, growth factors, and cellular stressors. For example, its expression can be induced by steroid hormones and oxidative stress, suggesting a role in adaptive responses to physiological challenges.

Protein Structure:

• Primary Structure: APOD consists of 189 amino acids.
• Secondary Structure: It has a characteristic lipocalin fold, with beta-barrel structures forming a ligand-binding pocket.
• Tertiary Structure: The beta-barrel creates a hydrophobic core that can bind various small hydrophobic molecules.
• Quaternary Structure: APOD can exist as a monomer or associate with other lipoproteins, particularly HDL.

Classification and Subtypes:

APOD belongs to the lipocalin family, characterized by their ability to bind and transport small hydrophobic molecules. Unlike other apolipoproteins, which are typically involved in lipid binding and transport, lipocalins like APOD have broader ligand specificity.

Function and Biological Significance:

• Lipid Transport: APOD is involved in the transport and metabolism of lipids, particularly cholesterol and phospholipids.
• Antioxidant Role: It has antioxidant properties, protecting cells from oxidative stress by binding and neutralizing reactive molecules.
• Neuroprotection: APOD is highly expressed in the central nervous system and is thought to play a protective role in neurodegenerative diseases and brain injury.
• Inflammation Modulation: APOD modulates inflammatory responses, with altered levels observed in various inflammatory diseases.

Interactions:

• Lipoprotein Interactions: APOD is primarily associated with HDL but can also interact with low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL).
• Receptor Interactions: It interacts with specific cell surface receptors to facilitate lipid uptake and metabolism.
• Ligand Binding: APOD binds various small hydrophobic molecules, including cholesterol, progesterone, and arachidonic acid.

Clinical Issues:

• Neurodegenerative Diseases: Elevated levels of APOD have been observed in Alzheimer's disease and other neurodegenerative conditions, suggesting a protective or compensatory role.
• Cardiovascular Disease: Changes in APOD levels are associated with cardiovascular diseases, potentially influencing HDL function and cholesterol metabolism.
• Cancer: Altered APOD expression has been reported in several cancers, though its precise role in tumorigenesis is not fully understood.
• Inflammatory Diseases: Elevated APOD levels are seen in chronic inflammatory conditions, including rheumatoid arthritis and inflammatory bowel disease.

Summary:

Apolipoprotein D (APOD) is a multifunctional glycoprotein involved in lipid transport, antioxidant defense, and modulation of inflammatory responses. As a member of the lipocalin family, it binds a variety of small hydrophobic molecules and is associated with HDL in the bloodstream. APOD's roles extend beyond lipid metabolism, with significant implications in neuroprotection, cardiovascular health, and inflammatory diseases. Alterations in APOD expression are linked to numerous pathological conditions, highlighting its importance as a potential biomarker and therapeutic target in various diseases. Further research is essential to fully understand APOD's diverse functions and its impact on human health.