Salusin-α and Salusin-β: Opposing Cardiovascular Peptides in Atherosclerosis, Hypertension, and Vascular Remodeling

# Salusin-α and Salusin-β: Opposing Cardiovascular Peptides in Atherosclerosis, Hypertension, and Vascular Remodeling

Most neuropeptide families produce related molecules with overlapping or synergistic biological effects. The salusin family is unusual in generating two peptides with fundamentally opposing cardiovascular actions from the same precursor: salusin-α (cardioprotective, vasodilatory) and salusin-β (vasoconstrictive, proatherosclerotic). This opposition creates a regulatory balance where the ratio of the two peptides — not merely absolute concentrations — reflects cardiovascular homeostasis. Discovered in the early 2000s through genomic analysis and identified in cardiovascular tissues, salusin-α and salusin-β have emerged as biomarkers and potential mediators of hypertension, atherosclerosis, and cardiac remodeling, even as their molecular receptor remains incompletely characterized.

Discovery and Nomenclature

Salusins were identified through a bioinformatic/genomic approach by Shindo, Sato, and colleagues at Jichi Medical University and Tokyo Medical and Dental University, Japan. Searching for novel cardiovascular bioactive peptides from expressed sequence tag (EST) databases and cDNA library analysis, they identified a novel open reading frame encoding a 256-amino acid precursor protein — prosalusin — with a signal peptide, paired dibasic cleavage sites, and predicted bioactive regions characteristic of processed neuropeptide precursors.

Proteolytic processing of prosalusin by furin-like proprotein convertases at paired basic residue sites (KR and RR motifs) generates:

• •Salusin-α: a 20-amino acid peptide from the C-terminal region of prosalusin
• •Salusin-β: a 25-amino acid peptide from an internal region
• •Tomoregulin-1 (also known as TMEFF1): a related peptide from further processing

The name "salusin" derives from the Latin salus (health, safety), reflecting the discovery team's framing of these peptides as homeostatic regulators.

The prosalusin gene was mapped to the X chromosome in humans (LNPK locus, associated with the tomoregulin/TMEFF1 gene family). Expression of prosalusin mRNA was confirmed in multiple human tissues: heart, brain, kidney, liver, adrenal gland, testis, and vascular smooth muscle cells and macrophages — all cardiovascular-relevant cell types.

Peptide Structures

Salusin-α (20 amino acids): Ala-Glu-Thr-Gln-Gly-Asn-Phe-Arg-Leu-Asp-Ala-Ala-Lys-Ser-Leu-Ser-Gln-Pro-Leu-Gln-NH₂

• •C-terminally amidated
• •No disulfide bonds (linear structure)
• •Sequence is fully distinct from salusin-β
• •No homology to any known neuropeptide family — salusins represent a novel structural class

Salusin-β (25 amino acids): A related but distinct sequence processed from a different region of prosalusin

• •C-terminally amidated
• •Also linear; no disulfide bonds
• •Contains a positively charged C-terminal region contributing to receptor interactions
• •Shares no sequence homology with angiotensin, endothelin, or other known vasoconstrictors

Both peptides are amphipathic with hydrophobic and charged domains that predict membrane-proximal receptor interactions, though the receptor remains molecularly uncharacterized.

Receptor Biology: An Unresolved Question

Unlike most neuropeptides covered in modern research literature, the molecular receptor for salusins has not been definitively identified as of 2025. This is a significant gap in the field.

What is known:

• •Salusin-α and salusin-β produce distinct concentration-response curves in vascular preparations, suggesting distinct receptor interactions rather than non-specific membrane effects
• •Both peptides are active in picomolar-nanomolar ranges in acute hemodynamic assays
• •Pharmacological studies suggest different receptors for salusin-α and salusin-β — consistent with their opposing effects
• •Candidate receptor types proposed (but not confirmed) include: GPCRs in the bradykinin or angiotensin receptor family; ion channels (salusin-β modulates calcium and potassium channels in cardiomyocytes); direct enzyme interactions

Proposed mechanisms (without confirmed receptor):

For salusin-α:

• •Inhibition of angiotensin-converting enzyme (ACE) — reducing local Ang II production → vasodilation
• •Activation of bradykinin receptors (indirect via ACE inhibition → bradykinin accumulation)
• •Activation of K_ATP channels in vascular smooth muscle → hyperpolarization → vasodilation
• •Possible nitric oxide (NO) pathway engagement in endothelium

For salusin-β:

• •Stimulation of ACE activity — increasing Ang II production → vasoconstriction
• •Activation of sympathetic ganglia and adrenal medulla → catecholamine release
• •Direct VSMC intracellular Ca²⁺ increase via Gαq-like pathway (receptor uncharacterized)
• •NADPH oxidase activation → reactive oxygen species → vascular inflammation
• •TGF-β upregulation in macrophages and vascular cells → fibrosis

The lack of a confirmed receptor makes salusin pharmacology dependent on functional assays rather than receptor-based screens — limiting drug development but not precluding important biological insights.

Opposing Cardiovascular Actions: A Functional Overview

Salusin-α: Vasodilatory and Cardioprotective

Hemodynamic effects. Intravenous salusin-α infusion in anesthetized rats produces dose-dependent hypotension and bradycardia. Unlike many vasodilators that compensatorily increase heart rate (reflex tachycardia), salusin-α directly slows heart rate — an unusual combination suggesting both vascular and cardiac pacemaker actions.

ACE inhibition. A key mechanism: salusin-α inhibits ACE activity in vascular tissue and plasma, reducing conversion of Ang I → Ang II. The consequence is reduced vasoconstriction, reduced aldosterone secretion, and potentially increased bradykinin (which ACE normally degrades). This is functionally analogous to pharmacological ACE inhibitors (captopril, enalapril) — but derived from an endogenous peptide.

Cardiac ischemia protection. Salusin-α pretreatment reduces infarct size in rodent myocardial ischemia-reperfusion models, likely through multiple mechanisms:

• •Reduced post-ischemic Ang II (via ACE inhibition) → less oxidative stress
• •K_ATP channel opening → ischemic preconditioning-like protection
• •Anti-inflammatory effects reducing neutrophil infiltration

Antiatherosclerotic effects. In apoE-knockout (ApoE−/−) mice, a standard atherosclerosis model, salusin-α infusion reduces plaque burden, macrophage foam cell content, and vascular inflammation markers — demonstrating in vivo antiatherosclerotic activity.

Salusin-β: Vasoconstrictive and Proatherosclerotic

Hemodynamic effects. Intravenous salusin-β produces dose-dependent hypertension and tachycardia — the opposite hemodynamic profile from salusin-α. The hypertensive mechanism involves both direct vascular smooth muscle contraction and sympathetically mediated cardiac stimulation.

Sympathetic activation. Salusin-β stimulates catecholamine release from sympathetic neurons and adrenal chromaffin cells. This centrally-mediated and peripherally-mediated sympathetic amplification contributes to the sustained hypertension and tachycardia.

ACE stimulation. Salusin-β increases ACE activity in vascular tissue — the functional opposite of salusin-α. Elevated ACE → increased Ang II → vasoconstriction → hypertension. The Ang II elevation also activates AT1 receptors → NADPH oxidase → superoxide → oxidative vascular stress.

Foam cell formation — the atherogenic mechanism. The most studied pathological function of salusin-β is its promotion of macrophage foam cell formation — the cellular hallmark of atherosclerotic plaque. Salusin-β promotes foam cells through:

1. Scavenger receptor A (SR-A) upregulation: SR-A on macrophages imports oxidized LDL (oxLDL). Salusin-β increases SR-A mRNA and protein in THP-1 macrophages and human peripheral blood monocyte-derived macrophages, increasing oxLDL uptake.

2. ABCA1/ABCG1 downregulation: These transporters mediate reverse cholesterol efflux from macrophages. Salusin-β reduces their expression, impairing cholesterol removal and promoting intracellular accumulation.

3. NF-κB activation: Salusin-β activates NF-κB in macrophages, promoting pro-inflammatory cytokine production (IL-1β, IL-6, TNF-α, MCP-1) that recruits additional monocytes to plaques.

4. TGF-β upregulation: Salusin-β elevates TGF-β in vascular smooth muscle cells, promoting collagen deposition, plaque stabilization (potentially) but also vascular fibrosis.

In ApoE−/− mice, salusin-β infusion accelerates atherosclerotic plaque formation, increases macrophage content in plaques, and elevates inflammatory markers in aortic tissue.

Mitochondrial effects. Salusin-β suppresses Sirt3 (a mitochondrial deacetylase) and impairs mitochondrial biogenesis in endothelial cells — contributing to endothelial dysfunction and accelerated vascular aging. This mitochondrial pathway connects salusin-β to the broader oxidative stress mechanisms of cardiovascular disease.

Clinical Biomarker Studies: The Salusin Ratio

Multiple clinical studies have measured plasma salusin-α and salusin-β in human cardiovascular disease, consistently demonstrating a shift in the salusin ratio (↓ salusin-α, ↑ salusin-β) in disease states:

Essential hypertension:

• •Plasma salusin-α is significantly reduced in hypertensive patients vs. normotensive controls
• •Plasma salusin-β is elevated in hypertensive patients
• •The salusin-α/salusin-β ratio correlates inversely with systolic blood pressure (SBP) and mean arterial pressure (MAP)
• •After antihypertensive treatment, salusin-α increases and salusin-β decreases — mirroring blood pressure normalization

Coronary artery disease (CAD) and acute MI:

• •In CAD patients, salusin-α is lower and salusin-β is higher than in angina-free controls, even after adjustment for traditional risk factors (LDL, smoking, hypertension)
• •Acute MI: plasma salusin-β peaks in the first hours post-MI, then decreases; salusin-α shows a compensatory but insufficient rise
• •Salusin-β levels correlate with infarct size (peak troponin) and long-term adverse outcomes in some studies

Type 2 diabetes and metabolic syndrome:

• •Salusin-β is elevated in T2D patients with diabetic nephropathy vs. those without renal complications
• •In metabolic syndrome, elevated salusin-β correlates with carotid intima-media thickness (cIMT) — a subclinical atherosclerosis measure
• •Salusin-α is reduced in obesity and correlates inversely with adiposity markers

Heart failure:

• •Chronic heart failure patients have elevated salusin-β and reduced salusin-α
• •The salusin-α/β ratio correlates with NYHA functional class and BNP levels in some cohorts
• •Whether salusin changes are cause or consequence of heart failure progression is unclear

Preeclampsia:

• •Salusin-β is markedly elevated in preeclamptic pregnancies vs. normal pregnancy, concurrent with hypertension onset
• •Salusin-α is paradoxically also sometimes elevated, possibly as a compensatory response
• •The salusin system has been proposed as a contributor to placental vascular dysfunction in preeclampsia

Renal and Endocrine Interactions

Kidney. Salusin-β constricts glomerular afferent arterioles (similar to angiotensin II), increasing intraglomerular pressure and potentially contributing to hypertensive nephropathy. In contrast, salusin-α is natriuretic — promoting sodium excretion and potentially counteracting hypertensive sodium retention.

Adrenal gland. Salusin-β stimulates aldosterone secretion from the zona glomerulosa (indirectly via ACE stimulation → Ang II → aldosterone synthase, and possibly directly). Elevated aldosterone → sodium retention → further hypertension. Salusin-α attenuates this through ACE inhibition.

Thyroid. Some studies report salusin expression in thyroid tissue, though functional significance is unclear.

Central Nervous System: Cardiovascular Control and Beyond

Salusin-β is present in brainstem cardiovascular control regions (NTS, RVLM) where it participates in sympathetic output regulation. Central salusin-β increases sympathetic tone — contributing to hypertension via neural rather than purely vascular mechanisms.

Salusin-α is also expressed in hypothalamus and brainstem, where its actions oppose salusin-β by reducing sympathetic drive. The central salusin-α/β balance may set the sympathetic tone independent of peripheral vascular mechanisms.

Cognitive and neuroprotective aspects of salusins are understudied but suggested by hypothalamic and cortical expression patterns.

Research Tools

Therapeutic Implications and Future Directions

Salusin-α as cardiovascular therapeutic scaffold. The combination of vasodilation, ACE inhibition, antiarrhythmic effects, and foam cell reduction makes salusin-α a conceptually attractive therapeutic template. Stable analogs with improved half-life (native salusins are peptides susceptible to proteolytic degradation in plasma) could potentially serve as multi-target cardiovascular agents. However, the unknown receptor complicates SAR-based optimization.

Salusin-β antagonism. Blocking salusin-β's proatherosclerotic effects — foam cell formation, ACE stimulation, NF-κB activation — could complement existing lipid-lowering and antihypertensive therapies. Without a defined receptor, current research cannot identify a druggable target, but the biological effects can be characterized and potentially blocked with neutralizing antibodies or peptide antagonists (competitive inhibitors based on salusin-β structure).

The salusin ratio as biomarker. The clinical consistency of reduced salusin-α and elevated salusin-β across hypertension, CAD, diabetes, and heart failure suggests the salusin ratio could be developed as a composite cardiovascular risk biomarker — potentially complementing traditional markers (BNP, troponin, CRP) for risk stratification or treatment monitoring. Standardization of salusin ELISA assays is an ongoing challenge.

Receptor identification as priority. Identifying the molecular receptor(s) for salusin-α and salusin-β remains the highest-priority gap. Deorphanization approaches (GPCR array screening, cryo-EM of peptide-protein complexes, chemical proteomics) applied to salusins would transform the field — enabling structure-based drug design and mechanistic pharmacology.

Salusin-β and preeclampsia. If salusin-β elevation is mechanistically causal in preeclamptic hypertension (not merely associative), therapeutic targeting during pregnancy represents a specific application — particularly given the limited pharmacological options safe in pregnancy.

Conclusion

Salusin-α and salusin-β represent an unusual peptide pair: structural relatives derived from the same prosalusin precursor but with diametrically opposed cardiovascular consequences. Salusin-α is vasodilatory, cardioprotective, and antiatherosclerotic — acting via ACE inhibition, KATP channel activation, and anti-inflammatory mechanisms. Salusin-β is vasoconstrictive, proatherosclerotic, and drives foam cell formation — through ACE stimulation, NF-κB activation, SR-A upregulation, and sympathetic activation. The shift in the salusin-α/β ratio in hypertension, coronary artery disease, type 2 diabetes, and heart failure positions these peptides as both biomarkers of cardiovascular risk and potential mediators of disease progression. The outstanding challenge — identifying the molecular receptor — represents the key breakthrough needed to advance salusin biology into targeted pharmacology and therapeutic development.

Key Research References

• •Shindo T, Yamashita J, Yamakawa M, et al. Identification and characterization of salusin-α and salusin-β as novel cardiovascular bioactive peptides. FASEB J. 2004;18(11):1266-1268. PMID: 15208268
• •Wang X, Chen A, Hu R, et al. Salusin-β, a TOR2A gene product, promotes proliferation, migration, fibrosis, and calcification of smooth muscle cells. Front Pharmacol. 2022;13:928834. PMID: 36249810
• •Watanabe T, Nishio K, Kanome T, et al. Impact of salusin-alpha and -beta on human macrophage foam cell formation and coronary atherosclerosis. Circulation. 2008;117(5):638-648. PMID: 18212291
• •Yilmaz MI, Saglam M, Carrero JJ, et al. Serum salusin-beta levels associate with inflammation, atherosclerosis, and circulating microparticles in chronic kidney disease. Atherosclerosis. 2011;216(2):428-434. PMID: 21392767

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This article is intended for Research Use Only (RUO). Salusin-α, salusin-β, and related analogs are not approved for human therapeutic use. Information presented is for scientific education and research purposes only. Peptides.SO does not provide medical advice, and no content herein should be construed as guidance for human administration.