Exploring the delicate equilibrium between neprilysin and angiotensin-converting enzyme families in physiological regulation and disease pathology
Imagine your body contains thousands of molecular scissors that constantly snip proteins to keep you healthy. These scissors are proteases—specialized enzymes that cut proteins and peptides into smaller fragments. They control virtually all biological processes, from blood pressure regulation to brain function. When all protease scissors work in harmony, we experience health. But when their delicate balance tips—when some cut too much or too little—disease often follows .
The human genome encodes more than 500 proteases, representing about 2% of all human genes.
Among the most fascinating of these molecular scissors are two protease families: neprilysin (NEP) and angiotensin-converting enzyme (ACE). These proteases regulate crucial bodily functions, and their imbalance contributes to conditions ranging from heart disease to diabetes and Alzheimer's disease 5 . Recent research has revealed an unexpected complexity: these proteases don't work in isolation but form interconnected networks that require precise balancing. This article explores how NEP and ACE maintain our health, what happens when their balance is disrupted, and how scientists are developing new treatments targeting these essential enzymes.
The ACE protease functions as a critical regulator of blood pressure and cardiovascular function through its role in the renin-angiotensin system (RAS). Think of RAS as a sophisticated blood pressure control system with two opposing arms that keep each other in check 2 .
The classical ACE pathway acts as the accelerator in this system. ACE converts angiotensin I into angiotensin II, a potent blood vessel constrictor that increases blood pressure. This occurs through the ACE/angiotensin II/AT1 receptor axis, which exerts vasoconstrictive and pro-inflammatory effects 2 7 .
The counter-regulatory pathway serves as the brake. This arm centers around ACE2, a cousin of ACE discovered in 2000, which converts angiotensin II into angiotensin-(1-7). This peptide binds to the Mas receptor, producing effects that oppose angiotensin II: vasodilation (blood vessel widening) and anti-inflammatory actions. This is known as the ACE2/angiotensin-(1-7)/Mas receptor axis 2 7 .
Neprilysin belongs to a larger family of metalloproteinases with diverse biological roles. While ACE specializes in blood pressure regulation, NEP displays broader versatility, processing multiple peptide hormones involved in various physiological processes 5 .
NEP serves as a master regulator for numerous signaling peptides. It degrades enkephalins (natural pain-relieving compounds), amyloid-beta (the Alzheimer's-associated brain protein), and various cardiovascular peptides 5 7 . This wide-ranging activity positions NEP as a crucial modulator across multiple body systems.
The relationship between NEP and ACE extends beyond parallel functions to direct interactions. NEP can generate angiotensin-(1-7)—the beneficial peptide in the RAS system—from angiotensin I, sometimes more efficiently than ACE2 itself 1 . This demonstrates how these protease families form an interconnected network rather than operating independently.
| Feature | Angiotensin-Converting Enzyme (ACE) | Neprilysin (NEP) |
|---|---|---|
| Primary Biological Role | Blood pressure regulation via renin-angiotensin system | Processing of various peptide hormones |
| Key Substrates | Angiotensin I, bradykinin, enkephalins | Enkephalins, amyloid-beta, cardiovascular peptides |
| Key Products | Angiotensin II (vasoconstrictor) | Angiotensin-(1-7) (via angiotensin I processing) |
| Cellular Sites | Endothelial cells, epithelial cells | Various tissues including pancreatic islets, brain |
| Therapeutic Targeting | ACE inhibitors (captopril, lisinopril) | NEP inhibitors in heart failure drugs |
Balanced State: Health
In 2017, diabetes research uncovered a surprising connection between blood pressure regulation and blood sugar control. Scientists had known that the pancreatic islets (which produce insulin) contain a local renin-angiotensin system. They also knew that enhancing the ACE2/angiotensin-(1-7)/Mas receptor axis improved glucose-stimulated insulin secretion in diabetic models. The assumption had been that ACE2 was the primary enzyme responsible for producing beneficial angiotensin-(1-7) in pancreatic islets 1 .
However, a groundbreaking study revealed a different story: neprilysin, not ACE2, played the dominant role in processing angiotensin peptides in mouse pancreatic islets. The research showed that although angiotensin-(1-7) improved insulin secretion, this effect required its breakdown by neprilysin into smaller peptides—the intact angiotensin-(1-7) itself wasn't the active mediator 1 .
Pancreatic islets obtained from normal and NEP-deficient mice
Islets exposed to angiotensin peptides and their breakdown products
Specialized assays measured insulin release with glucose stimulation
siRNA and receptor blockers identified active signaling pathways
| Experimental Condition | Effect on Insulin Secretion | Scientific Implications |
|---|---|---|
| Angiotensin-(1-7) in wild-type islets | Enhanced insulin secretion | Confirmed previously observed beneficial effect |
| Angiotensin-(1-7) in NEP-deficient islets | No enhancement | Demonstrated neprilysin essential for this effect |
| Neprilysin-derived fragments in wild-type islets | Enhanced insulin secretion | Showed breakdown products are active |
| Neprilysin-derived fragments in NEP-deficient islets | No enhancement | Confirmed neprilysin requirement |
| Angiotensin-(1-2) in both islet types | Enhanced insulin secretion | Revealed a neprilysin-independent pathway |
| Mas receptor blockade | No effect on angiotensin-(1-2) action | Showed alternative signaling pathway |
This research carried crucial implications for diabetes therapy, suggesting that combining angiotensin-(1-7) compounds with neprilysin inhibitors (used in some heart failure medications) might unexpectedly worsen blood sugar control. It highlighted the importance of understanding the complex interactions within protease networks when designing treatments 1 .
Studying proteases like NEP and ACE requires specialized research tools that allow scientists to measure their activities, inhibit them selectively, and understand their biological functions. Here are some key reagents and methods used in this field:
| Tool Category | Specific Examples | Research Applications |
|---|---|---|
| ACE Substrates | Hippuryl-His-Leu (HHL), FAPGG, Mca-RPPGFSAFK(Dnp)-OH | Measuring ACE activity in laboratory assays |
| Inhibitors | Captopril, lisinopril (ACE inhibitors); thiorphan (NEP inhibitor); DX600 (ACE2 inhibitor) | Determining protease functions by blocking their activity |
| Receptor Blockers | A779 (Mas receptor antagonist); naloxone (opioid receptor antagonist) | Identifying which receptors mediate peptide actions |
| Genetic Tools | NEP-/- mice (genetically modified to lack neprilysin); siRNA for gene silencing | Studying protease functions in whole organisms |
| Activity Assays | Fluorescence-based assays, mass spectrometry, high-throughput screening | Detecting and quantifying protease activities |
| Molecular Modeling | 3D-QSAR, molecular docking, comparative molecular field analysis | Designing new inhibitors and understanding enzyme mechanisms |
These research tools have enabled remarkable discoveries about protease functions. For instance, fluorescence-based assays allow scientists to measure protease activity by monitoring the release of light-emitting molecules when a protease cuts a specific substrate 7 . Meanwhile, molecular docking helps researchers visualize how potential drug molecules might fit into the active sites of proteases like ACE, guiding the design of more effective and selective inhibitors 4 9 .
Advanced proteomic technologies now allow scientists to examine hundreds or thousands of proteins simultaneously. For example, proximity extension assays and aptamer-based proteomic platforms can measure countless proteins in tiny blood samples, revealing how protease networks change in various diseases 6 8 .
Understanding the delicate balance between NEP and ACE has already led to innovative treatments. Recent cardiovascular drugs combine neprilysin inhibition with standard therapies, allowing beneficial peptides to persist longer in the body. However, the complex interactions revealed by research—like the insulin secretion findings—highlight why we need to understand these systems thoroughly to avoid unexpected side effects 1 .
The therapeutic potential of targeting these proteases extends beyond cardiovascular disease. Research has revealed that ACE also degrades enkephalins, natural pain-relieving peptides in the brain. This discovery suggests that specific ACE inhibitors might enhance our body's natural pain relief mechanisms without the addiction risks of traditional opioids 7 .
Future protease treatments will likely become increasingly precise. Scientists are working to develop domain-specific ACE inhibitors that target only certain functions of the enzyme. For instance, an inhibitor that blocks ACE's pain-related actions without affecting blood pressure regulation could offer significant advantages 7 .
Similarly, research on ACE inhibitory peptides from food sources might lead to natural treatments with fewer side effects than synthetic drugs. Computational methods are helping design novel peptide structures that potently and selectively inhibit ACE 4 9 .
The growing understanding of protease networks reminds us that biological systems rarely operate through simple linear pathways. Instead, they function as complex, interconnected networks where altering one component can have unexpected ripple effects. As research continues, targeting the delicate balance between NEP, ACE, and related proteases will likely yield innovative treatments for many common diseases while illustrating the beautiful complexity of human biology.
The world of proteases reveals a fundamental truth of biology: balance is everything. The interplay between NEP and ACE families demonstrates how our bodies maintain health through precisely coordinated molecular processes. When this balance is disrupted, disease often follows. As research continues to unravel the complexities of these protease networks, we gain not only new treatment options but also a deeper appreciation for the sophisticated regulatory systems that keep us healthy. The molecular scissors that cut our proteins are far more than simple degraders—they are master regulators of life itself, and understanding their delicate balance opens new possibilities for medicine and health.