S100A1 Mouse

What is S100A1 and where is it primarily expressed in mice?

S100A1 is a calcium-binding protein belonging to the S100 family, which comprises at least 21 members sharing high sequence homology but distinct expression patterns . In mice, S100A1 is prominently expressed in the heart where it regulates calcium cycling, and in the central nervous system, specifically in the hippocampus, cerebral cortex, and amygdala . It is also expressed in endothelial cells throughout the vasculature, where it plays a crucial role in regulating nitric oxide production .

What are the primary phenotypic characteristics of S100A1 knockout mice?

S100A1 knockout mice exhibit several distinct phenotypic characteristics:

• They develop normally with brains presenting normal morphology despite S100A1 expression in wild-type hippocampus, cerebral cortex, and amygdala

• They display elevated mean arterial pressure (99±4 mmHg versus 77±3 mmHg in wild-type), constituting a hypertensive phenotype

• Male S100A1 knockout mice demonstrate significantly higher mean arterial pressure than females (122±5 versus 93±3 mmHg)

• They show reduced anxiety-like responses and enhanced exploratory activities in behavioral tests, predominantly in males

• They exhibit normal spatial learning and memory capabilities in water maze tests

How does S100A1 deficiency affect cardiovascular function in mice?

S100A1 deficiency results in significant cardiovascular alterations:

• Systemic hypertension that is more pronounced in males

• Pulmonary hypertension characterized by increased right ventricular (RV) weight/body weight ratio and elevated RV pressure

• Increased wall thickness of muscularized pulmonary arteries and reduced microvascular perfusion

• Significantly higher mortality following myocardial infarction (21% survival in knockout mice versus 69% in wild-type)

• Death typically occurs through progressive hemodynamic collapse rather than cardiac arrhythmias

The hemodynamic parameters comparing wild-type and S100A1 knockout mice are summarized in the following table:

What gender-specific differences are observed in S100A1 knockout mice?

Significant gender dimorphism exists in S100A1 knockout mice:

• Male knockout mice exhibit substantially higher mean arterial pressure compared to females (122±5 vs. 93±3 mmHg)

• Males demonstrate dramatically reduced survival after myocardial infarction compared to females (4% vs. 27%)

• Even in sham-operated conditions, male knockout mice showed mortality while no deaths occurred in female knockout mice or wild-type mice

• The exploratory behavior phenotype is more pronounced in males

These findings suggest that S100A1 interacts with gender-specific physiological mechanisms, possibly involving hormonal factors.

How can researchers assess vascular function in S100A1 knockout mice?

Methodologically sound approaches to assess vascular function include:

• Isolated vessel preparations from aortas and mesenteric arteries to measure acetylcholine-evoked vasodilatation

• Isolated lung preparations to evaluate basal nitric oxide production and dose-responsiveness to vasodilators

• Measurement of angiotensin II-induced pulmonary vascular resistance changes

• Direct measurement of nitric oxide production in isolated endothelial cells

• Analysis of phosphorylation status of eNOS, Akt, and ERK1/2 in pulmonary endothelial cells

What behavioral tests are most appropriate for studying S100A1 knockout mice?

Based on the identified phenotypes, the following behavioral tests are recommended:

• Water maze tests for spatial learning and memory assessment, as S100A1 is expressed in hippocampus but its absence does not affect spatial memory

• Avoidance-approach tests to assess anxiety-like responses and exploratory activities, where significant phenotypes have been observed

• Gender-stratified behavioral analysis, given the more pronounced behavioral changes in male knockout mice

Does S100A1 deficiency alter neuronal or glial cell morphology in mice?

Despite S100A1 expression in the hippocampus, cerebral cortex, and amygdala of wild-type mice, S100A1 knockout mice do not exhibit alterations in brain cytoarchitecture . Astrocytes and neurons of knockout mice do not differ from those of wild-type mice regarding shape, distribution, and density . S100A1 partially co-localizes with the astrocyte marker glial fibrillary acidic protein (GFAP) in the stratum radiatum of the hippocampus in wild-type mice .

What is the relationship between S100A1 and nitric oxide signaling in vascular function?

S100A1 binds directly to endothelial nitric oxide synthase (eNOS) and is critical for optimal nitric oxide production . In S100A1 knockout mice:

• Basal nitric oxide production is reduced in isolated lung preparations and endothelial cells

• Acetylcholine-evoked vasodilatation is significantly impaired in both aortas and mesenteric arteries

• S100A1-induced phosphorylation of eNOS, Akt, and ERK1/2 is attenuated in pulmonary endothelial cells

• Pre-treatment of knockout lungs with S100A1 can attenuate angiotensin II-induced increases in pulmonary arterial pressure, suggesting reversibility of the phenotype

How does S100A1 deficiency impact endothelial cell survival?

S100A1 plays a significant role in endothelial cell survival:

• Basal and TNF-α-induced endothelial cell apoptosis is greater in S100A1 knockout mice compared to wild-type

• Cell survival is enhanced by S100A1 treatment, indicating a direct protective effect

• The endothelial dysfunction in S100A1 knockout mice appears to result partly from disruption of normal S100A1 capacity to promote endothelial cell survival

What therapeutic approaches are being developed based on S100A1 research?

S100A1ct, a synthetic peptide derived from the C-terminal α-helix (residues 75-94) of S100A1 with an N-terminal solubilization tag, has demonstrated promising therapeutic potential:

• It functions as a cell-penetrating peptide with positive inotropic and antiarrhythmic properties

• It enhances cardiomyocyte calcium cycling in a dose-dependent manner

• It prevents β-adrenergic receptor-triggered calcium imbalances by targeting SERCA2a and RyR2 activity

• When modified with a cardiomyocyte targeting peptide tag (cor-S100A1ct), it shows enhanced biological and therapeutic potency

• It has demonstrated improved contractile performance and survival in pre-clinical heart failure models with reduced ejection fraction

How can researchers investigate calcium handling in S100A1-deficient cardiomyocytes?

Methodological approaches to study calcium handling include:

• Isolation of primary cardiomyocytes from S100A1 knockout and wild-type mice

• Calcium imaging using fluorescent indicators to measure calcium transients

• Patch-clamp techniques to assess calcium channel function

• Biochemical analysis of calcium-handling proteins (SERCA2a, RyR2, phospholamban)

• Assessment of sarcoplasmic reticulum calcium content and calcium leak

• Evaluation of response to β-adrenergic stimulation

• Testing of S100A1ct peptide effects on calcium cycling parameters in isolated cardiomyocytes

What are the most critical considerations when designing experiments with S100A1 knockout mice?

When designing experiments with S100A1 knockout mice, researchers should consider:

• Gender stratification, given the significant gender-dependent differences in phenotype

• Age-matching, as cardiovascular phenotypes may progress with age

• Appropriate controls (wild-type littermates) for genetic background consistency

• Baseline blood pressure assessment prior to any cardiovascular interventions

• Assessment of endothelial function in both pulmonary and systemic circulations

• Recognition of increased mortality risk in experimental myocardial infarction models, particularly in males

• Consideration of compensatory mechanisms involving other S100 family members due to possible functional redundancy