A PARP inhibitor, rucaparib, improves cardiac dysfunction in ADP-ribose-acceptor hydrolase 3 ( Arh3 ) deficiency

Aims

Patients with ADP-ribose-acceptor hydrolase 3 ( ARH3 ) deficiency exhibit stress-induced childhood-onset neurodegeneration with ataxia and seizures (CONDSIAS). ARH3 degrades protein-linked poly(ADP- ribose) (PAR) synthesized by poly(ADP-ribose)polymerase (PARP)-1 during oxidative stress, leading to cleavage of the ADP-ribose linked to protein. ARH3 deficiency leads to excess accumulation of PAR, resulting in PAR-dependent cell death or parthanatos. Approximately one-third of patients with homozygous mutant ARH3 die from cardiac arrest, which has been described as neurogenic, suggesting that ARH3 may play an important role in maintaining myocardial function. To address this question, cardiac function was monitored in Arh3 -knockout (KO) and - heterozygous (HT) mice.

Methods and results

Arh3 -KO male mice displayed cardiac hypertrophy by histopathology and decreased cardiac contractility assessed by MRI. In addition, both genders of Arh3 -KO and -HT mice showed decreased cardiac contractility by dobutamine stress test assessed by echocardiography. A direct role of ARH3 on myocardial function was seen with a Langendorff-perfused isolated heart model . Arh3 -KO male mouse hearts showed decreased post-ischemic rate pressure products, increased size of ischemia-reperfusion (IR) infarcts, and elevated PAR levels. Consistently, in vivo IR injury showed enhanced infarct size in Arh3 -KO mice in both genders. In addition, Arh3 -HT male mice showed increased size of in vivo IR infarcts. Treatment with an FDA-approved PARP inhibitor, rucaparib, improved cardiac contractility during dobutamine-induced stress and exhibited reduced size of in vivo IR infarcts. To understand better the role of ARH3, CRISPR-Cas9 was used to generate different Arh3 genotypes of myoblasts and myotubes. Incubation with H2O2 decreased viability of Arh3 -KO and -HT myoblasts and myotubes, resulting in PAR-dependent cell death that was reduced by PARP inhibitors or by transfection with the Arh3 gene.

Conclusion

ARH3 regulates PAR homeostasis in myocardium to preserve function and protect against oxidative stress; PARP inhibitors reduce the myocardial dysfunction seen with Arh3 mutations.

ADP-ribose-acceptor hydrolase 2 ( Arh2 ) deficiency results in cardiac dysfunction, tumorigenesis, inflammation, and decreased survival

ADP-ribosylation is a reversible reaction with ADP-ribosyltransferases catalyzing the forward reaction and ADP-ribose-acceptor hydrolases (ARHs) hydrolyzing the ADP-ribose acceptor bond. ARH2 is a member of the 39-kDa ARH family (ARH1-3), which is expressed in heart and skeletal muscle. ARH2 failed to exhibit any in vitro enzymatic activity. To determine its possible in vivo activities, Arh2 -knockout (KO) and - heterozygous (Het) mice were generated using CRISPR-Cas9. Arh2 -KO mice exhibited decreased cardiac contractility by MRI, echocardiography and dobutamine stress with cardiomegaly and abnormal motor function. Arh2 -Het mice showed results similar to those seen in Arh2 -KO mice except for cardiomegaly. Arh2 -KO and -Het mice and mouse embryonic fibroblasts (MEFs) developed spontaneous tumors and subcutaneous tumors in nude mice. We identified 13 mutations in Arh2 -Het MEFs and heterozygous tumors, corresponding to human ARH2 mutations in cancers obtained from COSMIC. Of interest, the L116R mutation in Arh2 gene plays a critical role in aggressive tumorigenesis in nude mice, corresponding to human ARH2 mutations in stomach adenocarcinoma. Both genders of Arh2 -KO and -Het mice showed increased unexpectedly deaths and decreased survival rate during a 24-month observation, caused by tumor, inflammation, non-inflammation (e.g., cardiomegaly, dental dysplasia), and congenital diseases. Thus, Arh2 plays a pivotal role in cardiac function, tumorigenesis, inflammation, and overall survival.

Macrodomain Mac1 of SARS-CoV-2 Nonstructural Protein 3 Hydrolyzes Diverse ADP-ribosylated Substrates

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for a global pandemic that resulted in more than 6-million deaths worldwide. The virus encodes several non-structural proteins (Nsps) that contain elements capable of disrupting cellular processes. Among these Nsp proteins, Nsp3 contains macrodomains, e.g., Mac1, Mac2, Mac3, with potential effects on host cells. Mac1 has been shown to increase SARS-CoV-2 virulence and disrupt ADP-ribosylation pathways in mammalian cells. ADP-ribosylation results from the transfer of the ADP-ribose moiety of NAD ⁺ to various acceptors, e.g., proteins, DNA, RNA, contributing on a cell's biological processes. ADP-ribosylation is the mechanism of action of bacterial toxins, e.g., Pseudomonas toxins, diphtheria toxin that disrupt protein biosynthetic and signaling pathways. On the other hand, some viral macrodomains cleavage ADP-ribose-acceptor bond, generating free ADP-ribose. By this reaction, the macrodomain-containing proteins interfere ADP-ribose homeostasis in host cells. Here, we examined potential hydrolytic activities of SARS-CoV-2 Mac1, 2, and 3 on substrates containing ADP-ribose. Mac1 cleaved α-NAD ⁺ , but not β-NAD ⁺ , consistent with stereospecificity at the C-1" bond. In contrast to ARH1 and ARH3, Mac1 did not require Mg ²⁺ for optimal activity. Mac1 also hydrolyzed O -acetyl-ADP-ribose and ADP-ribose-1"-phosphat, but not Mac2 and Mac3. However, Mac1 did not cleave α-ADP-ribose-(arginine) and ADP-ribose-(serine)-histone H3 peptide, suggesting that Mac1 hydrolyzes ADP-ribose attached to O- and N-linked functional groups, with specificity at the catalytic site in the ADP-ribose moiety. We conclude that SARS-CoV-2 Mac1 may exert anti-viral activity by reversing host-mediated ADP-ribosylation. New insights on Nsp3 activities may shed light on potential SARS-CoV-2 therapeutic targets.

IMPORTANCE

SARS-CoV-2, the virus responsible for COVID-19, encodes 3 macrodomain-containing proteins, e.g., Mac1, Mac2, Mac3, within non-structural proteins 3 (Nsp3). Mac1 was shown previously to hydrolyze ADP-ribose-phosphate. Inactivation of Mac1 reduced viral proliferation. Here we report that Mac1, but not Mac2 and Mac3, has multiple activities, i.e., Mac1 hydrolyzed. α-NAD ⁺ and O -acetyl-ADP-ribose. However, Mac1 did not hydrolyze β-NAD ⁺ , ADP-ribose-serine on a histone 3 peptide (aa1-21), and ADP-ribose-arginine, exhibiting substrate selectivity. These data suggest that Mac1 may have multi-function as a α-NAD ⁺ consumer for viral replication and a disruptor of host-mediated ADP-ribosylation pathways. Understanding Mac1's mechanisms of action is important to provide possible therapeutic targets for COVID-19.

Mono-ADP-ribosyltransferase 1 ( Artc1 )-deficiency decreases tumorigenesis, increases inflammation, decreases cardiac contractility, and reduces survival

Arginine-specific mono-ADP-ribosylation is a reversible post-translational modification; arginine-specific, cholera toxin-like mono-ADP-ribosyltransferases (ARTCs) transfer ADP-ribose from NAD ⁺ to arginine, followed by cleavage of ADP-ribose-(arginine)protein bond by ADP-ribosylarginine hydrolase 1 (ARH1), generating unmodified (arginine)protein. ARTC1 has been shown to enhance tumorigenicity as does Arh1 deficiency. In this study, Artc1 -KO and Artc1/Arh1 -double-KO mice showed decreased spontaneous tumorigenesis and increased age-dependent, multi-organ inflammation with upregulation of pro-inflammatory cytokine TNF- α . In a xenograft model using tumorigenic Arh1 -KO mouse embryonic fibroblasts (MEFs), tumorigenicity was decreased in Artc1 -KO and heterozygous recipient mice, with tumor infiltration by CD8 ⁺ T cells and macrophages, leading to necroptosis, suggesting that ARTC1 promotes the tumor microenvironment. Furthermore, Artc1/Arh1 -double-KO MEFs showed decreased tumorigenesis in nude mice, showing that tumor cells as well as tumor microenvironment require ARTC1. By echocardiography and MRI, Artc1 -KO and heterozygous mice showed male-specific, reduced myocardial contractility. Furthermore, Artc1 -KO male hearts exhibited enhanced susceptibility to myocardial ischemia-reperfusion-induced injury with increased receptor-interacting protein kinase 3 (RIP3) protein levels compared to WT mice, suggesting that ARTC1 suppresses necroptosis. Overall survival rate of Artc1 -KO was less than their Artc1 -WT counterparts, primarily due to enhanced immune response and inflammation. Thus, anti-ARTC1 agents may reduce tumorigenesis but may increase multi-organ inflammation and decrease cardiac contractility.

PARP1 inhibition alleviates injury in ARH3-deficient mice and human cells

Poly(ADP-ribosyl)ation refers to the covalent attachment of ADP-ribose to protein, generating branched, long chains of ADP-ribose moieties, known as poly(ADP-ribose) (PAR). Poly(ADP-ribose) polymerase 1 (PARP1) is the main polymerase and acceptor of PAR in response to DNA damage. Excessive intracellular PAR accumulation due to PARP1 activation leads cell death in a pathway known as parthanatos. PAR degradation is mainly controlled by poly(ADP-ribose) glycohydrolase (PARG) and ADP-ribose-acceptor hydrolase 3 (ARH3). Our previous results demonstrated that ARH3 confers protection against hydrogen peroxide (H2O2) exposure, by lowering cytosolic and nuclear PAR levels and preventing apoptosis-inducing factor (AIF) nuclear translocation. We identified a family with an ARH3 gene mutation that resulted in a truncated, inactive protein. The 8-year-old proband exhibited a progressive neurodegeneration phenotype. In addition, parthanatos was observed in neurons of the patient's deceased sibling, and an older sibling exhibited a mild behavioral phenotype. Consistent with the previous findings, the patient's fibroblasts and ARH3-deficient mice were more sensitive, respectively, to H2O2 stress and cerebral ischemia/reperfusion-induced PAR accumulation and cell death. Further, PARP1 inhibition alleviated cell death and injury resulting from oxidative stress and ischemia/reperfusion. PARP1 inhibitors may attenuate the progression of neurodegeneration in affected patients with ARH3 deficiency.

Role of a TRIM72 ADP-ribosylation cycle in myocardial injury and membrane repair

Mono-ADP-ribosylation of an (arginine) protein catalyzed by ADP-ribosyltransferase 1 (ART1) - i.e., transfer of ADP-ribose from NAD to arginine - is reversed by ADP-ribosylarginine hydrolase 1 (ARH1) cleavage of the ADP-ribose-arginine bond. ARH1-deficient mice developed cardiomyopathy with myocardial fibrosis, decreased myocardial function under dobutamine stress, and increased susceptibility to ischemia/reperfusion injury. The membrane repair protein TRIM72 was identified as a substrate for ART1 and ARH1; ADP-ribosylated TRIM72 levels were greater in ARH1-deficient mice following ischemia/reperfusion injury. To understand better the role of TRIM72 and ADP-ribosylation, we used C2C12 myocytes. ARH1 knockdown in C2C12 myocytes increased ADP-ribosylation of TRIM72 and delayed wound healing in a scratch assay. Mutant TRIM72 (R207K, R260K) that is not ADP-ribosylated interfered with assembly of TRIM72 repair complexes at a site of laser-induced injury. The regulatory enzymes ART1 and ARH1 and their substrate TRIM72 were found in multiple complexes, which were coimmunoprecipitated from mouse heart lysates. In addition, the mono-ADP-ribosylation inhibitors vitamin K1 and novobiocin inhibited oligomerization of TRIM72, the mechanism by which TRIM72 is recruited to the site of injury. We propose that a mono-ADP-ribosylation cycle involving recruitment of TRIM72 and other regulatory factors to sites of membrane damage is critical for membrane repair and wound healing following myocardial injury.

Cell adhesion to anosmin via α5β1, α4β1, and α9β1 integrins

Anosmin is an extracellular matrix protein, and genetic defects in anosmin result in human Kallmann syndrome. It functions in neural crest formation, cell adhesion, and neuronal migration. Anosmin consists of multiple domains, and it has been reported to bind heparan sulfate, FGF receptor, and UPA. In this study, we establish cell adhesion/spreading assays for anosmin and use them for antibody inhibition analyses to search for an integrin adhesion receptor. We find that α5β1, α4β1, and α9β1 integrins are needed for effective adhesive receptor function in cell adhesion and cell spreading on anosmin; adhesion is inhibited by both RGD and α4β1 CS1-based peptides. This identification of anosmin-integrin adhesion receptors should facilitate studies of anosmin function in cell and developmental biology.

Cloning and characterization of chicken α5 integrin: endogenous and experimental expression in early chicken embryos

Key roles for fibronectin and its integrin receptors have been postulated in the multiple cell-matrix interactions essential for chick embryo morphogenesis. However, mechanistic studies of these processes have been hampered by the current absence of sequence data and chicken cDNA clones for the major fibronectin receptor subunit, integrin α5 (ITGA5). We report here the sequence, endogenous expression pattern, and transfection of full-length chicken integrin α5. During early chicken embryonic development, α5 is highly expressed in cranial neural folds and migrating neural crest cells, suggesting potential roles in neural crest formation and migration. In fact, over-expression of this integrin in early neural tube selectively induces BMP5, a growth factor recently implicated in neural crest formation. Availability of these α5 integrin tools should facilitate studies of its functions in early embryonic development.

Extracellular matrix protein anosmin promotes neural crest formation and regulates FGF, BMP, and WNT activities

Neural crest cells are a transient stem cell-like population appearing during vertebrate embryonic development. Generation of the cranial neural crest is known to require a balanced combination of FGF and BMP levels. However, it is poorly understood how the functions of such growth factors are controlled in the extracellular space. Anosmin is an extracellular matrix protein implicated in FGF signaling and mutated in Kallmann syndrome. Here, we demonstrate that anosmin is synthesized locally in the cranial neural crest of chicken embryos and is essential for cranial neural crest formation. Anosmin upregulates FGF8 and BMP5 gene expression; it also enhances FGF8 activity while inhibiting BMP5 and WNT3a signaling. Taken together, our data establish that the matrix protein anosmin is required for cranial neural crest formation, with functional modulation of FGF, BMP, and WNT.