Two-pore channels (TPCs) acts as a hub for excitation-contraction coupling, metabolism and cardiac hypertrophy signalling

Ca2+ signaling is essential for cardiac contractility and excitability in heart function and remodeling. Intriguingly, little is known about the role of a new family of ion channels, the endo-lysosomal non-selective cation "two-pore channel" (TPCs) in heart function. Here we have used double TPC knock-out mice for the 1 and 2 isoforms of TPCs (Tpcn1/2-/-) and evaluated their cardiac function. Doppler-echocardiography unveils altered left ventricular (LV) systolic function associated with a LV relaxation impairment. In cardiomyocytes isolated from Tpcn1/2-/- mice, we observed a reduction in the contractile function with a decrease in the sarcoplasmic reticulum Ca2+ content and a reduced expression of various key proteins regulating Ca2+ stores, such as calsequestrin. We also found that two main regulators of the energy metabolism, AMP-activated protein kinase and mTOR, were down regulated. We found an increase in the expression of TPC1 and TPC2 in a model of transverse aortic constriction (TAC) mice and in chronically isoproterenol infused WT mice. In this last model, adaptive cardiac hypertrophy was reduced by Tpcn1/2 deletion. Here, we propose a central role for TPCs and lysosomes that could act as a hub integrating information from the excitation-contraction coupling mechanisms, cellular energy metabolism and hypertrophy signaling.

Matriptase processing of APLP1 ectodomain alters its homodimerization

The amyloid beta peptide (Aβ) is derived from the amyloid precursor protein (APP) by secretase processing. APP is also cleaved by numerous other proteases, such as the type II transmembrane serine protease matriptase, with consequences on the production of Aβ. Because the APP homolog protein amyloid-like protein 1 (APLP1) shares similarities with APP, we sought to determine if matriptase also plays a role in its processing. Here, we demonstrate that matriptase directly interacts with APLP1 and that APLP1 is cleaved in cellulo by matriptase in its E1 ectodomains at arginine 124. Replacing Arg124 with Ala abolished APLP1 processing by matriptase. Using a bioluminescence resonance energy transfer (BRET) assay we found that matriptase reduces APLP1 homodimeric interactions. This study identifies matriptase as the first protease cleaving APLP1 in its dimerization domain, potentially altering the multiple functions associated with dimer formation.

The type II transmembrane serine protease matriptase cleaves the amyloid precursor protein and reduces its processing to β-amyloid peptide

Recent studies have reported that many proteases, besides the canonical α-, β-, and γ-secretases, cleave the amyloid precursor protein (APP) and modulate β-amyloid (Aβ) peptide production. Moreover, specific APP isoforms contain Kunitz protease-inhibitory domains, which regulate the proteolytic activity of serine proteases. This prompted us to investigate the role of matriptase, a member of the type II transmembrane serine protease family, in APP processing. Using quantitative RT-PCR, we detected matriptase mRNA in several regions of the human brain with an enrichment in neurons. RNA sequencing data of human dorsolateral prefrontal cortex revealed relatively high levels of matriptase RNA in young individuals, whereas lower levels were detected in older individuals. We further demonstrate that matriptase and APP directly interact with each other and that matriptase cleaves APP at a specific arginine residue (Arg-102) both in vitro and in cells. Site-directed (Arg-to-Ala) mutagenesis of this cleavage site abolished matriptase-mediated APP processing. Moreover, we observed that a soluble, shed matriptase form cleaves endogenous APP in SH-SY5Y cells and that this cleavage significantly reduces APP processing to Aβ40. In summary, this study identifies matriptase as an APP-cleaving enzyme, an activity that could have important consequences for the abundance of Aβ and in Alzheimer's disease pathology.

Low doses of arginine butyrate derivatives improve dystrophic phenotype and restore membrane integrity in DMD models

A new approach to treating Duchenne muscular dystrophy was investigated by using the ester or amide covalent association of arginine [nitric oxide (NO) pathway] and butyrate [histone deacetylase (HDAC) inhibition] in mdx mice and patient myotubes. Two prodrugs were synthesized, and the beneficial effects on dystrophic phenotype were studied. Nerve excitability abnormalities detected in saline-treated mice were almost totally rescued in animals treated at low doses (50-100 mg/kg/d). Force and fatigue resistance were improved ≈60% and 3.5-fold, respectively, and the percentage of necrosis in heart sections was reduced ≈90% in the treated mice. A decrease of >50% in serum creatine kinase indicated an overall improvement in the muscles. Restoration of membrane integrity was studied directly by measuring the reduction (≈74%) of Evans blue incorporation in the limb muscles of the treated animals, the increase in utrophin level, and the normalization of lipid composition of the heart. In cultures of human myotubes (primary cells and cell line), both prodrugs and HDAC inhibitors increased by 2- to 4-fold the utrophin level, which was correctly localized at the membrane. β-Dystroglycan and embryonic myosin protein levels were also increased. Finally, a 50% reduction in the number of spontaneous Ca(2+) spikes was observed after treatment with NO synthase substrate and HDAC inhibitors. Overall, the beneficial effects were obtained with doses 10 (in vivo) and 5 (in vitro) times lower than those of the salt formulation. Altogether, these data constitute proof of principle of the beneficial effects of low doses of arginine butyrate derivatives on muscular dystrophy, enhancing the NO pathway and inhibiting HDAC.