BACKGROUND

L-type Ca1.2 channels play crucial roles in the regulation of blood pressure. Galectin-1 (Gal-1) has been reported to bind to the I-II loop of Ca1.2 channels to reduce their current density. However, the mechanistic understanding for the downregulation of Ca1.2 channels by Gal-1 and whether Gal-1 plays a direct role in blood pressure regulation remain unclear.

METHODS

In vitro experiments involving coimmunoprecipitation, Western blot, patch-clamp recordings, immunohistochemistry, and pressure myography were used to evaluate the molecular mechanisms by which Gal-1 downregulates Ca1.2 channel in transfected, human embryonic kidney 293 cells, smooth muscle cells, arteries from Lgasl1 mice, rat, and human patients. In vivo experiments involving the delivery of Tat-e9c peptide and AAV5-Gal-1 into rats were performed to investigate the effect of targeting Ca1.2-Gal-1 interaction on blood pressure monitored by tail-cuff or telemetry methods.

RESULTS

Our study reveals that Gal-1 is a key regulator for proteasomal degradation of Ca1.2 channels. Gal-1 competed allosterically with the Caβ subunit for binding to the I-II loop of the Ca1.2 channel. This competitive disruption of Caβ binding led to Ca1.2 degradation by exposing the channels to polyubiquitination. It is notable that we demonstrated that the inverse relationship of reduced Gal-1 and increased Ca1.2 protein levels in arteries was associated with hypertension in hypertensive rats and patients, and Gal-1 deficiency induces higher blood pressure in mice because of the upregulated Ca1.2 protein level in arteries. To directly regulate blood pressure by targeting the Ca1.2-Gal-1 interaction, we administered Tat-e9c, a peptide that competed for binding of Gal-1 by a miniosmotic pump, and this specific disruption of Ca1.2-Gal-1 coupling increased smooth muscle Ca1.2 currents, induced larger arterial contraction, and caused hypertension in rats. In contrasting experiments, overexpression of Gal-1 in smooth muscle by a single bolus of AAV5-Gal-1 significantly reduced blood pressure in spontaneously hypertensive rats.

CONCLUSIONS

We have defined molecularly that Gal-1 promotes Ca1.2 degradation by replacing Caβ and thereby exposing specific lysines for polyubiquitination and by masking I-II loop endoplasmic reticulum export signals. This mechanistic understanding provided the basis for targeting Ca1.2-Gal-1 interaction to demonstrate clearly the modulatory role that Gal-1 plays in regulating blood pressure, and offering a potential approach for therapeutic management of hypertension.