Unfolded Protein Response as a Compensatory Mechanism and Potential Therapeutic Target in PLN R14del Cardiomyopathy

BACKGROUND

Phospholamban (PLN) is a critical regulator of calcium cycling and contractility in the heart. The loss of arginine at position 14 in PLN (R14del) is associated with dilated cardiomyopathy with a high prevalence of ventricular arrhythmias. How the R14 deletion causes dilated cardiomyopathy is poorly understood, and there are no disease-specific therapies.

METHODS

We used single-cell RNA sequencing to uncover PLN R14del disease mechanisms in human induced pluripotent stem cells (hiPSC-CMs). We used both 2-dimensional and 3-dimensional functional contractility assays to evaluate the impact of modulating disease-relevant pathways in PLN R14del hiPSC-CMs.

RESULTS

Modeling of the PLN R14del cardiomyopathy with isogenic pairs of hiPSC-CMs recapitulated the contractile deficit associated with the disease in vitro. Single-cell RNA sequencing revealed the induction of the unfolded protein response (UPR) pathway in PLN R14del compared with isogenic control hiPSC-CMs. The activation of UPR was also evident in the hearts from PLN R14del patients. Silencing of each of the 3 main UPR signaling branches (IRE1, ATF6, or PERK) by siRNA exacerbated the contractile dysfunction of PLN R14del hiPSC-CMs. We explored the therapeutic potential of activating the UPR with a small molecule activator, BiP (binding immunoglobulin protein) inducer X. PLN R14del hiPSC-CMs treated with BiP protein inducer X showed a dose-dependent amelioration of the contractility deficit in both 2-dimensional cultures and 3-dimensional engineered heart tissues without affecting calcium homeostasis.

CONCLUSIONS

Together, these findings suggest that the UPR exerts a protective effect in the setting of PLN R14del cardiomyopathy and that modulation of the UPR might be exploited therapeutically.

A positive and reversible relationship between adrenergic nerves and alpha-1A adrenoceptors in rat arteries

We evaluated the relationship between the presence of adrenergic nerves and the presence of alpha-1 adrenoceptors (alpha-1 AR) in the arterial tree of the rat. The thoracic aorta and the carotid, mammary, renal and femoral arteries were isolated from 20-week-old male WKY rats, along with the superior mesenteric artery and small (first order) and resistance-sized (third order) side branches of this vessel. Norepinephrine content ([NE]) and specific binding of 300 pM [3H]prazosin were determined. To estimate the total density of alpha-1 AR ([alpha-1 AR]) as well as the density of alpha-1A AR ([alpha-1A AR]), binding experiments were performed with and without pretreatment of the preparations with the irreversible alpha-1B AR and alpha-1D AR antagonist chloroethylclonidine and in the absence and presence of the alpha-1A AR selective ligand (+)-niguldipine (30 nM). Also the presence of mRNA for alpha-1A AR was evaluated by use of reverse transcriptase-polymerase chain reaction (RT-PCR). In intact rats, arterial [NE] ranged between 0.1 and 15 ng/microgram DNA, arterial [alpha-1 AR] ranged between 12.4 and 46.8 fmol/mg protein and [alpha-1A AR] ranged between 0.05 and 27.9 fmol/mg protein. There was no significant correlation between [alpha-1 AR] and [NE]. However, with respect to the [alpha-1A AR] a significant correlation between [NE] and [alpha-1A AR] was observed. RT-PCR analysis confirmed the expression of alpha-1A AR in the densely innervated mesenteric resistance-sized arteries. Two weeks after chemical sympathectomy of the rats with 6-hydroxydopamine (i) arterial [NE] was markedly reduced, and (ii) a distinct reduction in the [alpha-1A AR] as percentage of the total [alpha-1 AR] density in mesenteric artery side branches was noted. These findings indicate that there is a positive and reversible relationship between the presence of adrenergic nerves and that of alpha-1A AR in rat arteries.