| Neprilysin (NEP / CD10 / MME) | |
|---|---|
| Gene | MME |
| UniProt | P08473 |
| PDB Structures | 1DMT, 6GID, 5JMY |
| Molecular Weight | ~97 kDa (glycosylated) |
| Localization | Type II transmembrane protein; cell surface, extracellular (soluble form) |
| Protein Family | M13 zinc metalloprotease family |
| Diseases | Alzheimer's Disease, Cerebral Amyloid Angiopathy, Lewy Body Dementia |
Neprilysin (Nep Cd10 Mme) is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
[Neprilysin[/proteins/neprilysin (NEP), also known as membrane metallo-endopeptidase (MME), neutral endopeptidase 24.11, enkephalinase, common acute lymphoblastic leukemia antigen (CALLA), and cluster of differentiation 10 (CD10), is a 97 kDa type II zinc-dependent metalloprotease encoded by the MME gene on chromosome 3q25.2. [Neprilysin is the primary [amyloid-beta[/entities/amyloid-beta ([Aβ)-degrading enzyme in the brain and is considered a key regulator of cerebral [Aβ[/entities/amyloid-beta homeostasis ([Iwata et al., 2001]https://doi.org/10.1126/science.1065972)).
NEP activity accounts for approximately 50% of total [Aβ[/entities/amyloid-beta clearance in the brain, as demonstrated by studies in which NEP deficiency leads to an approximately twofold increase in endogenous Aβ levels in vivo (Bhatt & Bhargava, 2025). The age-dependent decline in neprilysin expression and activity in vulnerable brain regions — particularly the [hippocampus[/brain-regions/hippocampus and [cerebral cortex[/brain-regions/cortex — is strongly implicated in the pathogenesis of sporadic [Alzheimer's disease[/diseases/alzheimers (AD) (Yasojima et al., 2001). This makes neprilysin one of the most intensively studied therapeutic targets for amyloid-lowering strategies in AD.
[Neprilysin[/proteins/neprilysin is a type II integral membrane protein consisting of 750 amino acids with three distinct domains (Oefner et al., 2000):
The crystal structure of the neprilysin ectodomain reveals two multiply connected folding subdomains that embrace a large central cavity containing the active site (Oefner et al., 2000). Key structural features include:
A soluble form of neprilysin (sNEP) is generated by proteolytic cleavage of the ectodomain from the cell surface, releasing it into the extracellular space and body fluids. Plasma sNEP levels decrease with aging and correlate inversely with AD severity.
[Neprilysin[/proteins/neprilysin is the rate-limiting enzyme for Aβ catabolism in the brain. It cleaves [Amyloid-Beta[/proteins/Amyloid-Beta peptides (both Aβ40 and Aβ42) at multiple sites within their sequences, generating smaller, non-toxic fragments that are readily cleared (Iwata et al., 2001). Critically:
As a broad-specificity endopeptidase, neprilysin cleaves numerous bioactive peptides at the amino side of hydrophobic residues:
| Substrate | Biological Significance |
|---|---|
| Enkephalins (Met/Leu-enkephalin) | Pain modulation — NEP terminates opioid peptide signaling |
| Substance P | Inflammation, nociception |
| Natriuretic peptides (ANP, BNP, CNP) | Cardiovascular homeostasis — basis for sacubitril therapy |
| Bradykinin | Vasodilation, inflammation |
| Neurotensin | Neuromodulation |
| Oxytocin | Social behavior, reproduction |
| Glucagon | Glucose metabolism |
| Endothelin-1 | Vasoconstriction |
| Somatostatin | Neuroendocrine regulation |
[Neprilysin[/entities/neprilysin is widely expressed in the CNS, with highest levels in the [striatum[/brain-regions/striatum, [substantia nigra[/brain-regions/substantia-nigra, [hippocampus[/brain-regions/hippocampus, and cholinergic [neurons[/entities/neurons of the [basal forebrain[/cell-types/cholinergic-basal-forebrain (Yasojima et al., 2001). In the [hippocampus[/brain-regions/hippocampus, NEP is enriched at the outer molecular layer of the dentate gyrus and stratum lacunosum-moleculare of CA1 — regions that receive input from the [entorhinal cortex[/brain-regions/entorhinal-cortex, which is among the earliest affected in AD.
The link between neprilysin and [Alzheimer's disease[/diseases/alzheimers centers on the [amyloid cascade hypothesis]: if Aβ production by [BACE1[/proteins/bace1-protein and [γ-secretase[/proteins/gamma-secretase exceeds Aβ clearance, peptide accumulates and drives downstream tau] pathology], [neuroinflammation[/mechanisms/neuroinflammation, and [neuronal death].
Age-related NEP decline: NEP mRNA and protein levels decline by ~50% in the [hippocampus[/brain-regions/hippocampus and temporal [cortex[/brain-regions/cortex of aged humans and AD patients compared to young controls (Yasojima et al., 2001). This decline is region-specific, matching the topographic distribution of Aβ plaque deposition.
Genetic evidence: NEP-deficient mice crossed with [APP[/genes/app transgenic models develop accelerated amyloid pathology. A 2025 study demonstrated that NEP deficiency in App^NL-F knock-in mice accelerates Aβ plaque formation more prominently than [IDE[/genes/ide deficiency in both sexes, confirming NEP as the dominant Aβ-degrading enzyme in vivo (Bhatt & Bhargava, 2025).
Inverse correlation with plaques: In postmortem AD brains, regions with the lowest NEP activity ([hippocampus[/brain-regions/hippocampus, temporal [cortex) have the highest amyloid plaque burden, while regions with high NEP activity (cerebellum, caudate) are relatively spared (Yasojima et al., 2001).
Decreased NEP expression in cerebrovascular smooth muscle cells and perivascular [astrocytes[/cell-types/astrocytes contributes to Aβ deposition in blood vessel walls in [cerebral amyloid angiopathy[/diseases/cerebral-amyloid-angiopathy (CAA). NEP activity is reduced in leptomeningeal vessels of CAA patients, and the extent of reduction correlates with CAA severity (Carpentier et al., 2006).
Sacubitril, a pharmacological NEP inhibitor used in the heart failure drug sacubitril/valsartan (Entresto®), has raised important questions about its potential impact on brain Aβ levels. By inhibiting NEP-mediated degradation of beneficial natriuretic peptides, sacubitril provides cardiovascular benefit — but it may also impair Aβ clearance. Recent studies show that long-term sacubitril/valsartan treatment increases plasma Aβ42 and Aβ40 levels, potentially confounding [plasma Aβ biomarker] testing (Ali et al., 2024). Whether chronic NEP inhibition increases AD risk remains an active area of investigation.
NEP also degrades [alpha-synuclein[/proteins/alpha-synuclein fragments in vitro, and reduced NEP activity has been reported in the [substantia nigra[/brain-regions/substantia-nigra of [Parkinson's disease[/diseases/parkinsons patients. The role of NEP in [Lewy body dementia[/diseases/lewy-body-dementia and [synucleinopathies[/mechanisms/synucleinopathies is less well-characterized than in AD but represents an emerging area of research.
Several approaches aim to increase brain NEP levels to enhance Aβ clearance:
| Approach | Description | Status |
|---|---|---|
| Gene therapy | AAV-mediated delivery of NEP to hippocampus/cortex | Preclinical — reduces plaques in [APP[/genes/app mice |
| [BBB[/entities/blood-brain-barrier-penetrating NEP | Engineered sNEP-scFc-scFv8D3 bispecific construct achieves 20× brain uptake vs soluble NEP | Preclinical (Meier et al., 2022) |
| Somatostatin analogs | Somatostatin upregulates NEP transcription; analogs being tested | Preclinical |
| Exercise | Physical activity increases hippocampal NEP expression in rodent models | Epidemiological + preclinical |
| Valproic acid | [HDAC[/entities/hdac-enzymes inhibitor that upregulates NEP expression | Preclinical |
Viral vector-mediated NEP overexpression has shown promise in preclinical AD models:
Because NEP is a large transmembrane protein that does not efficiently cross the [blood-brain barrier[/entities/blood-brain-barrier, engineered constructs have been developed:
NEP expression is regulated by several transcription factors and signaling pathways:
NEP promoter hypermethylation has been observed in AD brains, contributing to transcriptional silencing. [HDAC[/entities/hdac-enzymes inhibitors and DNA demethylating agents can restore NEP expression in cell and animal models, suggesting [epigenetic mechanisms] as therapeutic targets.
The study of Neprilysin (Nep Cd10 Mme) has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.