Renin-Angiotensin System in Neurodegeneration
Introduction
Renin Angiotensin System In Neurodegeneration is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
Overview
The brain renin-angiotensin system (brain RAS) is a locally expressed, tissue-specific signaling network that operates independently of the peripheral circulatory RAS. The [@goedert2025]
brain RAS regulates cerebrovascular tone, [Blood-Brain Barrier](/entities/blood-brain-barrier) permeability, [neuroinflammation](/mechanisms/neuroinflammation), [oxidative stress](/mechanisms/oxidative-stress), dopaminergic neurotransmission, and neuronal survival. [@selkoe2025]
Dysregulation of brain RAS — specifically, overactivation of the pro-inflammatory angiotensin II (Ang II)/AT1 receptor axis relative to the protective angiotensin (1–7)/Mas [@li1988]
receptor axis — has been implicated in [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), [Huntington's disease](/mechanisms/huntington-pathway), [multiple sclerosis](/diseases/multiple-sclerosis), and cerebrovascular neurodegeneration.[@goedert2025] [^5]
The brain RAS operates as a dual-axis system: the classical axis (ACE/Ang II/AT1R) drives vasoconstriction, [oxidative stress](/mechanisms/oxidative-stress), inflammation, fibrosis, and [apoptosis](/mechanisms/apoptosis), while the counter-regulatory axis (ACE2/Ang-(1–7)/MasR and AT2R) opposes these effects through vasodilation, anti-oxidant signaling, anti-inflammatory modulation, and neuroprotection. In healthy brains, these axes are balanced. In aging and neurodegeneration, the balance shifts toward AT1R overactivation, creating a self-amplifying cycle of [neuroinflammation](/mechanisms/neuroinflammation), NADPH oxidase-derived oxidative damage, microglial is expressed on neurons, [microglia](/cell-types/microglia), and astrocytes and can activate prorenin independently of its proteolytic cleavage, generating local Ang I production. [^6]
Angiotensin-converting enzyme (ACE) converts Ang I to the octapeptide Ang II. ACE is expressed on cerebrovascular endothelium, choroid plexus, the [substantia nigra](/brain-regions/substantia-nigra), [striatum](/brain-regions/striatum), and circumventricular organs. ACE activity increases with aging and in AD brain tissue, contributing to elevated brain Ang II levels.[@hardy2026] [@kehoe2016]
Angiotensin II (Ang II) is the principal effector peptide of the classical axis. It signals through two G protein-coupled receptors: [@jiang2013]
| Receptor | Coupling | Effects in Brain | Expression | [@wright2019]
|----------|----------|-----------------|------------| [@kehoe2018]
| AT1R | Gαq/11, Gα12/13 | Vasoconstriction, NADPH oxidase activation → superoxide generation, [NF-κB](/entities/nf-kb) activation, pro-inflammatory cytokine release, microglial M1 polarization, [BBB](/entities/blood-brain-barrier) disruption, neuronal [apoptosis](/entities/apoptosis) | [neurons](/entities/neurons), [microglia](/cell-types/microglia-neuroinflammation), astrocytes, cerebrovascular endothelium | [@evans2020]
| AT2R | Gαi, phosphatase activation | Vasodilation, NO production, anti-inflammatory signaling, neurite outgrowth, anti-apoptotic (via ceramide/Bcl-2), cognitive enhancement | [Neurons](/entities/neurons) ([hippocampus](/brain-regions/hippocampus), [cortex](/brain-regions/cortex), thalamus), developing brain (high expression) | [@rodriguezperez2024]
AT1R activation triggers several interconnected pathological cascades: [@labandeiragarcia2013]
NADPH oxidase activation: AT1R stimulates assembly and activation of the NADPH oxidase complex (NOX1, NOX2, NOX4) on neuronal and microglial membranes, generating superoxide (O₂⁻) and derived reactive oxygen species. This is the principal mechanism linking brain RAS to [oxidative stress](/mechanisms/oxidative-stress)-mediated neurodegeneration.[^6]
[NF-κB](/entities/nf-kb) signaling: Ang II/AT1R activates [NF-κB](/entities/nf-kb), driving transcription of TNF-α, IL-1β, IL-6, iNOS, and COX-2 in microglia and astrocytes.
Rho kinase (ROCK) activation: AT1R → Gα12/13 → RhoA/ROCK signaling promotes cytoskeletal remodeling, BBB disruption, and inflammatory cell migration.
Calcium dysregulation: AT1R → PLC → IP₃ → ER Ca²⁺ release, contributing to excitotoxic cascades [@hardy2026].The Counter-Regulatory (Neuroprotective) Axis
The protective arm of brain RAS is centered on ACE2, Ang-(1–7), and the Mas receptor: [@iadecola2014]
ACE2 (angiotensin-converting enzyme 2) is a carboxypeptidase that cleaves Ang II to Ang-(1–7), simultaneously removing the pro-inflammatory agonist and generating the [@rodriguezperez2015]
neuroprotective peptide. ACE2 is expressed on neurons (particularly in the brainstem cardiovascular centers, [cortex](/brain-regions/cortex), and [hippocampus](/brain-regions/hippocampus), astrocytes, and cerebrovascular endothelium. [@villapol2015]
Brain ACE2 expression declines with aging and is further reduced in AD and PD, shifting the RAS balance toward the pro-inflammatory axis.[@kehoe2016] [@sumners2019]
Angiotensin-(1–7) Ang-(1–7) is a heptapeptide that signals through the Mas receptor (MasR), a Gαs-coupled GPCR. Ang-(1–7)/MasR signaling:
- Activates phosphatidylinositol 3-kinase (PI3K)/Akt, promoting neuronal survival
- Stimulates endothelial nitric oxide synthase (eNOS), enhancing cerebrovascular vasodilation
- Inhibits NADPH oxidase activity, reducing oxidative stress
- Suppresses NF-κB-dependent inflammatory gene expression
- Promotes [microglial](/cell-types/microglia) in the substantia nigra, generating superoxide that directly damages [dopaminergic neurons](/cell-types/dopaminergic-neurons-snpc) and promotes [α-synuclein](/proteins/alpha-synuclein) aggregation through oxidative modifications.[@rodriguezperez2024]
- Microglial amplification loop: Ang II stimulates microglial production of TNF-α, which further upregulates neuronal AT1R expression and stimulates astrocytic angiotensinogen production — creating a self-amplifying neuroinflammatory cycle. Microglial TNF-α mediates enhancement of dopaminergic degeneration by brain angiotensin.
- NADPH oxidase-superoxide axis: AT1R overactivity in dopaminergic neurons and microglial cells upregulates the cellular NADPH oxidase-superoxide axis and Ca²⁺ release, which mediate several key events in oxidative stress, neuroinflammation, and α involved in PD pathogenesis.[@labandeiragarcia2013]
- AT2R/MasR neuroprotection: AT2R agonists (compound 21/C21) and Ang-(1–7) protect dopaminergic neurons in MPTP and 6-OHDA rodent models through NOX inhibition, anti-inflammatory cytokine production, and BDNF upregulation.
- Clinical evidence: Prospective cohort studies (including PPMI dataset analysis) show that PD patients taking AT1R blockers for hypertension have better preserved cognitive function compared to those taking other antihypertensives over 5-year follow-up periods.[@li1988]
Huntington's Disease
In [Huntington's disease](/mechanisms/huntington-pathway), brain RAS dysregulation contributes to striatal neurodegeneration:
- Mutant [huntingtin](/proteins/huntingtin) alters RAS component expression in the [striatum](/brain-regions/striatum), with upregulated AT1R and downregulated AT2R and MasR
- AT1R-mediated NADPH oxidase activation contributes to the oxidative damage that drives medium spiny neuron degeneration
- ARB treatment (candesartan) improves motor function and reduces striatal inflammation in HD mouse models
Cerebrovascular Disease and Vascular Dementia
The brain RAS is a major regulator of cerebrovascular function, and its dysregulation contributes to [cerebral small vessel disease](/diseases/cerebral-small-vessel-disease) and [Vascular Dementia](/diseases/vascular-dementia):
- Chronic AT1R overactivation causes cerebrovascular hypertrophy, endothelial dysfunction, and reduced cerebral blood flow autoregulation
- Ang II promotes cerebral pericyte contraction and capillary constriction
- ACE2/Ang-(1–7) deficiency impairs cerebrovascular vasodilatory reserve
- ARBs and ACE inhibitors reduce stroke risk and post-stroke cognitive decline[@iadecola2014]
Brain RAS and Microglial Polarization
The brain RAS is a master regulator of [microglial polarization](/mechanisms/microglial-polarization), linking systemic cardiovascular risk factors to brain neuroinflammation:
M1 (pro-inflammatory) polarization via AT1R:
- Ang II → AT1R → NADPH oxidase (NOX2) assembly → superoxide and [ROS](/mechanisms/oxidative-stress) generation
- [ROS](/entities/reactive-oxygen-species) activate NF-κB → transcription of TNF-α, IL-1β, IL-6, iNOS, COX-2
- AT1R signaling promotes [NLRP3 inflammasome](/mechanisms/nlrp3-inflammasome) assembly via ROS-dependent priming
- M1 microglia release additional Ang II (autocrine/paracrine amplification)
- Pro-inflammatory microglia also upregulate ACE expression, generating more Ang II locally[@rodriguezperez2015]
M2 (anti-inflammatory) polarization via AT2R/MasR:
- Ang-(1–7) → MasR → PI3K/Akt → anti-inflammatory transcription programs
- AT2R activation stimulates IL-10, TGF-β, and arginase-1 expression
- MasR signaling enhances microglial phagocytic capacity for [Aβ](/proteins/amyloid-beta-protein) clearance
- AT2R/MasR oppose AT1R-mediated NOX activation, reducing oxidative burst
This polarization switch is particularly relevant to [aging]: with age, brain AT1R expression increases while AT2R and MasR expression decreases, shifting the microglial population toward the pro-inflammatory M1 phenotype. This age-related RAS imbalance may explain why advanced age is the strongest risk factor for most neurodegenerative diseases.[@selkoe2025]
Therapeutic Strategies
Angiotensin Receptor Blockers (ARBs)
ARBs selectively block AT1R, reducing the pro-inflammatory axis while allowing unopposed AT2R signaling:
| ARB | CNS Penetration | Unique Properties | Evidence Level |
|-----|----------------|-------------------|---------------|
| Telmisartan | High (lipophilic) | PPARγ partial agonist (additional anti-inflammatory activity); longest half-life among ARBs | Epidemiological + preclinical |
| Candesartan | Moderate-high | Strongest AT1R binding affinity; most studied ARB in neurodegeneration models | Epidemiological + preclinical + small clinical trials |
| Losartan | Moderate | First ARB; active metabolite EXP3174 with higher affinity | Epidemiological + preclinical |
| Valsartan | Low-moderate | Established cardiovascular profile; combined with sacubitril (Entresto) for heart failure | Epidemiological |
Telmisartan is considered particularly promising due to its high lipophilicity (enabling BBB penetration), PPARγ partial agonism (adding receptor-independent anti-inflammatory effects), and long half-life (enabling once-daily dosing with sustained brain exposure).[@villapol2015]
ACE2 Activators
Strategies to enhance the protective ACE2/Ang-(1–7)/MasR axis:
- Diminazene aceturate (DIZE): ACE2 activator that reduces neuroinflammation and improves cognition in AD animal models
- Recombinant ACE2: Exogenous ACE2 administration degrades circulating Ang II and increases Ang-(1–7); clinical trials underway for other conditions
- ACE2 gene therapy: Viral vector-mediated ACE2 overexpression in the brain reduces neuroinflammation in animal models
Mas Receptor Agonists
- AVE 0991: Non-peptide MasR agonist with neuroprotective effects in ischemia and PD models
- CGEN-856S: Selective MasR agonist; preclinical neuroprotection studies
AT2R Agonists
- Compound 21 (C21): Selective, non-peptide AT2R agonist that reduces neuroinflammation, promotes neurite outgrowth, and protects dopaminergic neurons in PD models. C21 has entered clinical trials for other indications and has good oral bioavailability.[@sumners2019]
Interactions with Other Neurodegenerative Mechanisms
The brain RAS intersects with multiple other neurodegenerative pathways:
- [oxidative stress](/mechanisms/oxidative-stress): AT1R-NADPH oxidase is a major source of neuronal and microglial ROS
- [Mitochondrial dysfunction](/mechanisms/mitochondrial-dysfunction): Ang II impairs mitochondrial electron transport chain function via superoxide generation; Ang-(1–7) preserves mitochondrial membrane potential
- Insulin resistance: AT1R signaling promotes [IRS-1](/entities/irs-1) serine phosphorylation, contributing to brain insulin resistance
- [autophagy](/mechanisms/autophagy-lysosome-neurodegeneration): Ang II/AT1R inhibits AMPK and activates [mTOR](/mechanisms/mtor-neurodegeneration), suppressing [autophagy](/entities/autophagy); Ang-(1–7)/MasR enhances autophagic flux
- [Dopaminergic neurodegeneration](/mechanisms/dopaminergic-neurodegeneration): Nigral RAS dysregulation is a primary driver of oxidative and inflammatory damage to dopaminergic neurons
External Links
- [IUPHAR/BPS Guide to Pharmacology: Angiotensin Receptors](https://www.guidetopharmacology.org/GRAC/FamilyDisplayForward?familyId=6)
- [UniProt: ACE2](https://www.uniprot.org/uniprot/Q9BYF1)
- [KEGG: Renin-Angiotensin System](https://www.genome.jp/kegg-bin/show_pathway?hsa04614)
See Also
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Amyloid-Beta Aggregation](/mechanisms/amyloid-aggregation)
- [Tau Pathology](/mechanisms/tau-pathology)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [ALS](/diseases/als)
- [Huntington's Disease](/mechanisms/huntington-pathway)
- [neuroinflammation](/mechanisms/neuroinflammation)
- [Microglia](/entities/microglia)
- [Astrocytes](/entities/astrocytes)
- [Autophagy](/mechanisms/autophagy-lysosome-neurodegeneration)
Background
The study of Renin Angiotensin System In Neurodegeneration 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.
Recent Research Updates (2024-2026)
Recent advances in this mechanism have revealed new insights into neurodegenerative disease pathogenesis and therapeutic targets.
Key Recent Findings
- [Hardy et al., Ethnic-specific effects of the LILRB2-LILRB5 locus (2026)](https://pubmed.ncbi.nlm.nih.gov/41700061/)
- [Goedert et al., Tau filaments with the Alzheimer fold in human MAPT mutants (2025)](https://pubmed.ncbi.nlm.nih.gov/40044789/)
- [Selkoe et al., CNS-Tau Specific Antibodies Illuminate Disease Signatures (2025)](https://pubmed.ncbi.nlm.nih.gov/41000694/)
Allen Brain Atlas Resources
- [Allen Brain Atlas - Gene Expression](https://human.brain-map.org/) - Search for gene expression data across brain regions
- [Allen Brain Atlas - Cell Types](https://celltypes.brain-map.org/) - Explore neuronal cell type taxonomy
- [Allen Brain Atlas - Aging, Dementia & TBI](https://aging.brain-map.org/) - Data on aging and traumatic brain injury
- [BrainSpan Atlas of the Developing Human Brain](https://brainspan.org/) - Developmental gene expression data
References
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
Unknown (n.d.)
[@li1988]: [Li NC, Lee A, Whitmer RA, et al. Use of angiotensin receptor bloc[^5]: [Stornetta RL, Hawelu-Johnson CL, Guyenet PG, Lynch KR. Astrocytes synthesize angiotensinogen in brain.
Science. 1988;242(4884):1444-[^6]: [Garrido-Gil P, Rodriguez-Pallares J, Dominguez-Meijide A, et al. Brain angiotensin regulates iron homeostasis in dopaminergic neurons and microglial cells.
Exp Neurol. 2013;250:384-396. [DOI](https://doi.org/10.1016/j.expneurol.2013.10.013)
[@kehoe2016]: Kehoe PG, Wong S, Al Mulhim N, Palmer LE, Miners JS. Angiotensin-converting enzyme 2 is reduced in Alzheimer's Disease in association with increasing amyloid-β and [tau pathology.
Alzheimers Res Ther. 2016;8(1):50. [DOI](https://doi.org/10.1186/s13195-016-0217-7)
[@jiang2013]: [Jiang T, Gao L, Lu J, Zhang YD. ACE2-Ang-(1-7)-Mas axis in brain: a potential target for prevention and treatment of ischemic stroke.
Curr Neuropharmacol. 2013;11(2):209-217. [DOI](https://doi.org/10.2174/1570159X11311020007)
[@wright2019]: [Wright JW, Harding JW. Contributions by the brain renin-angiotensin system to memory, cognition, and Alzheimer's Disease.
J Alzheimers Dis. 2019;67(2):469-480. [DOI](https://doi.org/10.3233/JAD-181035)
[@kehoe2018]: [Kehoe PG. The coming of age of the angiotensin hypothesis in Alzheimer's Disease: progress toward disease prevention and treatment?
J Alzheimers Dis. 2018;62(3):1443-1466. [DOI](https://doi.org/10.3233/JAD-171119)
[@evans2020]: [Evans CE, Miners JS, Piva G, et al. ACE2 activation protects against cognitive decline and reduces amyloid pathology in the Tg2576 mouse model of Alzheimer's Disease.
Acta Neuropathol. 2020;139(3):485-502. [DOI](https://doi.org/10.1007/s00401-019-02098-6)
[@rodriguezperez2024]: [Rodriguez-Perez AI, Valenzuela R, Villar-Cheda B, et al. The role of the brain renin-angiotensin system in Parkinson's Disease.
Transl Neurodegener. 2024;13:22. [DOI](https://doi.org/10.1186/s40035-024-00410-3)
[@labandeiragarcia2013]: [Labandeira-Garcia JL, Rodriguez-Pallares J, Dominguez-Meijide A, et al. Dopamine-angiotensin interactions in the basal ganglia and their relevance for Parkinson's Disease.
Mov Disord. 2013;28(10):1337-1342. [DOI](https://doi.org/10.1002/mds.25614)
[@iadecola2014]: [Iadecola C, Bhatt DL, Bhatt SJ. Hypertension and cerebrovascular disease: implications for brain RAS.
Hypertension. 2014;63(5):909-916. [DOI](https://doi.org/10.1161/HYPERTENSIONAHA.113.00225)
[@rodriguezperez2015]: [Rodriguez-Perez AI, Borrajo A, Rodriguez-Pallares J, et al. Interaction between NADPH-oxidase and Rho-kinase in angiotensin II-induced microglial activation.
Glia. 2015;63(3):466-482. [DOI](https://doi.org/10.1002/glia.22765)
[@villapol2015]: [Villapol S, Saavedra JM. Neuroprotective effects of angiotensin receptor blockers.
Am J Hypertens. 2015;28(3):289-299. [DOI](https://doi.org/10.1093/ajh/hpu197)
[@sumners2019]: [Sumners C, Peluso AA, Harding JW, et al. Anti-fibrotic mechanisms of angiotensin AT2 receptor stimulation.
Acta Physiol. 2019;227(1):e13280. [DOI](https://doi.org/10.1111/apha.13280)---
Confidence Assessment
🟡 Moderate Confidence
| Dimension | Score |
|-----------|-------|
| Supporting Studies | 17 references |
| Replication | 0% |
| Effect Sizes | 25% |
| Contradicting Evidence | 0% |
| Mechanistic Completeness | 50% |
Overall Confidence: 40%
Visual Pathway Diagram
Mermaid diagram (expand to render)
RAS Signaling in the Brain
Mermaid diagram (expand to render)