Neprilysin

Neprilysin. It is a membrane-bound zinc-dependent metalloprotease that plays a crucial role in the termination of signaling for a wide array of bioactive peptides. This enzyme is also known as common acute lymphoblastic leukemia antigen (CALLA) and cluster of differentiation 10 (CD10), reflecting its diverse roles in physiology and pathology. Its primary function is the catalytic degradation of numerous circulating neuropeptides and vasoactive peptides, thereby regulating their local concentrations and biological activity.

Structure and function

Neprilysin is a type II integral membrane protein with a short N-terminal cytoplasmic domain, a single transmembrane helix, and a large extracellular domain containing the active site. The catalytic domain features a characteristic HEXXH zinc-binding motif that is essential for its proteolytic activity. This enzyme exhibits a broad substrate specificity, efficiently cleaving peptides on the amino side of hydrophobic residues. Its structure is highly conserved across mammals, underscoring its fundamental biological importance. The enzyme's activity is optimal at a neutral pH and can be modulated by various endogenous inhibitors and post-translational modifications.

Biological role and expression

Within the central nervous system, neprilysin is a key regulator of amyloid-beta peptide metabolism and is critical for preventing the accumulation of amyloid plaques associated with Alzheimer's disease. In the cardiovascular system, it degrades natriuretic peptides like atrial natriuretic peptide and brain natriuretic peptide, as well as angiotensins and bradykinin, influencing blood pressure and fluid homeostasis. The enzyme is expressed on the surface of various cell types, including neurons, renal proximal tubule cells, vascular smooth muscle cells, and immune cells like lymphocytes. Its expression is regulated by factors such as steroid hormones, cytokines, and shear stress.

Clinical significance

Dysregulation of neprilysin activity is implicated in several major diseases. Reduced expression or activity in the brain is a significant risk factor for sporadic Alzheimer's disease, as it leads to impaired clearance of amyloid-beta. In the periphery, chronic inhibition of neprilysin can result in elevated levels of vasodilator peptides, producing a hypotensive effect. Conversely, its overexpression has been observed in certain malignancies, including acute lymphoblastic leukemia and prostate cancer, where it may influence tumor progression and cell proliferation. The enzyme is also a diagnostic marker for certain renal cell carcinoma subtypes and endometrial stromal sarcoma.

Inhibitors and therapeutic use

Pharmacological inhibition of neprilysin, combined with angiotensin receptor blockade, forms the basis of the angiotensin receptor-neprilysin inhibitor (ARNI) drug class. The prototype drug sacubitril/valsartan (Entresto) is a cornerstone in the treatment of heart failure with reduced ejection fraction, as it potentiates beneficial natriuretic peptides while blocking the renin-angiotensin-aldosterone system. Early neprilysin inhibitors like candoxatril and ecadotril were studied for hypertension but had limited clinical success. Current research is exploring neprilysin inhibitors for other conditions, including obesity and type 2 diabetes mellitus.

Research and discovery

Neprilysin was first identified in 1974 as a neutral endopeptidase from rabbit kidney brush border membranes. Its gene, MME, was later cloned and mapped to chromosome 3 in humans. Seminal work by researchers like Lloyd F. K. and Erdös E. G. characterized its role in degrading enkephalins and substance P. The landmark PARADIGM-HF trial, published in The New England Journal of Medicine in 2014, revolutionized heart failure therapy by demonstrating the superior efficacy of sacubitril/valsartan over enalapril. Ongoing investigations focus on its role in neurodegeneration, with studies exploring gene therapy and small-molecule activators to boost its activity in the brain as a potential strategy against Alzheimer's disease.

Category:Proteins Category:Enzymes Category:EC 3.4.24