Immunohistochemical localization of parvalbumin calcium-binding protein in the heart tissues of various species

What Is Parvalbumin for?

Parvalbumin (PA) is a small, acidic, mostly cytosolic Ca2+-binding protein of the EF-hand superfamily. Structural and physical properties of PA are well studied but recently two highly conserved structural motifs consisting of three amino acids each (clusters I and II), which contribute to the hydrophobic core of the EF-hand domains, have been revealed. Despite several decades of studies, physiological functions of PA are still poorly known. Since no target proteins have been revealed for PA so far, it is believed that PA acts as a slow calcium buffer. Numerous experiments on various muscle systems have shown that PA accelerates the relaxation of fast skeletal muscles. It has been found that oxidation of PA by reactive oxygen species (ROS) is conformation-dependent and one more physiological function of PA in fast muscles could be a protection of these cells from ROS. PA is thought to regulate calcium-dependent metabolic and electric processes within the population of gamma-aminobutyric acid (GABA) neurons. Genetic elimination of PA results in changes in GABAergic synaptic transmission. Mammalian oncomodulin (OM), the β isoform of PA, is expressed mostly in cochlear outer hair cells and in vestibular hair cells. OM knockout mice lose their hearing after 3–4 months. It was suggested that, in sensory cells, OM maintains auditory function, most likely affecting outer hair cells’ motility mechanisms.

Effects of estrogen via estrogen receptors on parvalbumin levels in cardiac myocytes of ovariectomized rats

The study investigated the effects of estrogen on parvalbumin (PV) levels in cardiac myocytes of ovariectomized rats, which is a model system for postmenopausal woman. Parvalbumin acts as a relaxing factor in cardiac myocytes. Adult female Wistar rats, 12 weeks old, were randomly divided into 5 groups of 10: sham-operated (SHAM), ovariectomized (OVX), and OVX receiving estrogen replacement of 10 μg/kg (Es10), 20 μg/kg (Es20) and 40 μg/kg (Es40). After 10 weeks, serum estrogen levels were measured and the α and β estrogen receptors in cardiac myocytes were investigated by immunohistochemistry. PV levels were examined by immunohistochemistry and Western blot analysis. Cardiac myocytes of all animals showed strong staining intensities for α immunoreactive (Es α-ir), but weak staining for β immunoreactive (Es β-ir) estrogen receptors. The Es α-ir was reduced in the cardiac myocytes of the OVX groups, but increased in the Es10, Es20 and Es40 groups. We therefore suggest that estrogen effects are mediated via Es α receptors rather than Es β receptors in female rat hearts. Estrogen and PV immunoreactive (PV-ir) levels and the intensity of the PV band observed in the OVX group were less than those of the SHAM group. In the Es10, Es20 and Es40 groups, the increased intensity of the PV-ir and PV bands correlated with the increased estrogen levels. The low PV levels in cardiac myocytes induced by low estrogen were restored by estrogen replacement therapy. Therefore a reduction of PV may lead to diastolic dysfunction in menopause.

Parvalbumin deficiency and GABAergic dysfunction in mice lacking PGC-1alpha

The transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC-1alpha) is a master regulator of metabolism in peripheral tissues, and it has been proposed that PGC-1alpha plays a similar role in the brain. Recent evidence suggests that PGC-1alpha is concentrated in GABAergic interneurons, so we investigated whether male and female PGC-1alpha -/- mice exhibit abnormalities in interneuron gene expression and/or function. We found a striking reduction in the expression of the Ca(2+)-binding protein parvalbumin (PV), but not other GABAergic markers, throughout the cerebrum in PGC-1alpha +/- and -/- mice. Furthermore, PGC-1alpha overexpression in cell culture was sufficient to robustly induce PV expression. Consistent with a reduction in PV rather than a loss of PV-expressing interneurons, spontaneous synaptic inhibition was not altered in PGC-1alpha -/- mice. However, evoked synaptic responses displayed less paired-pulse depression and dramatic facilitation in response to repetitive stimulation at the gamma frequency. PV transcript expression was also significantly reduced in retina and heart of PGC-1alpha -/- animals, suggesting that PGC-1alpha is required for proper expression of PV in multiple tissues. Together these findings indicate that PGC-1alpha is a novel regulator of interneuron gene expression and function and a potential therapeutic target for neurological disorders associated with interneuron dysfunction.

Effects of alcohol on the levels of parvalbumin in rat hearts

Chronic excessive alcohol administration has been reported to be associated with diastolic dysfunction. Parvalbumin (PV) is a calcium-binding protein present in cardiac myocytes and involved in mediating relaxation. Therefore, alteration of PV levels may affect relaxation in cardiac myocytes. This study investigated the effects of alcohol administration on the levels of PV in the rat heart. Male Wistar rats weighing 200-250 g were divided into 2 groups: control (C) and alcohol-treated groups. The control group was provided with distilled water and the alcohol groups were provided with either a low dose (LD, 2g/kg) or high dose of ethanol (HD, 5 g/kg) once daily for 21 days, 3 months or 6 months. The PV levels in the ventricles were investigated by immunohistochemistry and Western blot analysis. In the 21-day ethanol-treated groups, parvalbumin immunoreactivity (PV-ir) and protein levels were not different when compared to the C, LD and HD groups. In the 3-month ethanol-treated groups, PV-ir and PV protein levels were decreased in both the LD and HD groups compared to that of the control group. In the 6-month ethanol-treated groups, PV-ir and PV protein levels decreased significantly in both the LD and HD groups (P<0.05). This indicates that short-term ethanol treatment may not affect PV levels, whereas, long-term ethanol treatment clearly reduced PV levels. The decrease of PV was predominantly due to the direct toxic effects of alcohol rather than malabsorption caused by pathological changes in the duodenum and liver. The toxic effects of alcohol leading to a reduction of PV levels may lead to diastolic impairment.

Influence of aging and long-term swimming exercise on parvalbumin distribution in rat hearts

Parvalbumin (PV), which is a small (12kDa) cytoplasmic calcium-binding protein, has been implicated in mediating relaxation in cardiac myocytes. The influence of aging and exercise on the distribution of PV in rat heart was investigated. Male Wistar rats aged 3, 6, 12 and 18-months were divided into sedentary and exercise groups. The exercise group underwent exercise in the form of regular swimming for 6 months. The hearts were processed for immunohistochemistry and Western blotting. The intensity of PV immunoreactivity was strong in the 9 and 12-month hearts and decreased in the 18-month hearts. The smallest amount was detected in the 24-month rat hearts when compared to those of the 9, 12 and 18-month rat hearts. Significantly less PV was detected in the 18 and 24-month hearts compared to the 12-month rat hearts (P<0.05). The intensity of PV immunoreactivity was considerably stronger in hearts of the 9, 12 and 18-months exercised rats than in hearts of age-matched sedentary rats. However, in the hearts of 24-month rats, immunoreactivity was only slightly stronger in the exercised rats in comparison with those of sedentary rats. A significant increase of PV detection in hearts was found in the exercised rats in comparison with sedentary rats in the 9 (P<0.05) and 18-month samples (P<0.01). Our data indicate that PV is down-regulated in the rat heart during aging. In addition, our data indicate that long-term swimming exercise could induce an increase of PV expression.