Antigen-driven T cell-macrophage interactions mediate the interface between innate and adaptive immunity in histidyl-tRNA synthetase-induced myositis

Introduction

Previous work in humans has demonstrated that both innate and adaptive immune signaling pathways contribute to the pathogenesis of idiopathic inflammatory myopathy (IIM), a systemic autoimmune disease targeting muscle as well as extra-muscular organs. To better define interactive signaling networks in IIM, we characterized the cellular phenotype and transcriptomic profiles of muscle-infiltrating cells in our established murine model of histidyl-tRNA synthetase (HRS)-induced myositis.

Methods

Myositis was induced in wild type (WT) and various congenic/mutant strains of C57BL/6 mice through intramuscular immunization with recombinant HRS. Histopathological, immunohistochemical, flow cytometric, and transcriptomic assessments were used to characterize the functional relationship between muscle-infiltrating cell populations in these strains lacking different components of innate and/or adaptive immune signaling.

Results

RAG1 KO mice developed markedly reduced muscle inflammation relative to WT mice, demonstrating a key requirement for T cells in driving HRS-induced myositis. While the reduction of mononuclear cell infiltrates in CD4-Cre.MyD88fl/fl conditional knockout mice and OT-II TCR transgenic mice highlighted roles for both innate and TCR-mediated/adaptive immune signaling in T cells, diminished inflammation in Lyz2-Cre.MyD88fl/fl conditional knockout mice underscored the importance of macrophage/myeloid cell populations in supporting T cell infiltration. Single cell RNA sequencing-based clustering of muscle-infiltrating subpopulations and associated pathway analyses showed that perturbations of T cell signaling/function alter the distribution and phenotype of macrophages, fibroblasts, and other non-lymphoid cell populations contributing to HRS-induced myositis.

Discussion

Overall, HRS-induced myositis reflects the complex interplay between multiple cell types that collectively drive a TH1-predominant, pro-inflammatory tissue phenotype requiring antigen-mediated activation of both MyD88- and TCR-dependent T cell signaling pathways.

Mutation of a Ubiquitin Carboxy Terminal Hydrolase L1 Lipid Binding Site Alleviates Cell Death, Axonal Injury, and Behavioral Deficits After Traumatic Brain Injury in Mice

Ubiquitin carboxy terminal hydrolase L1 (UCHL1) is a protein highly expressed in neurons that may play important roles in the ubiquitin proteasome pathway (UPP) in neurons, axonal integrity, and motor function after traumatic brain injury (TBI). Binding of reactive lipid species to cysteine 152 of UCHL1 results in unfolding, aggregation, and inactivation of the enzyme. To test the role of this mechanism in TBI, mice bearing a cysteine to alanine mutation at site 152 (C152A mice) that renders UCHL1 resistant to inactivation by reactive lipids were subjected to the controlled cortical impact model (CCI) of TBI and compared to wild type (WT) controls. Alterations in protein ubiquitination and activation of autophagy pathway markers in traumatized brain were detected by immunoblotting. Cell death and axonal injury were determined by histological assessment and anti-amyloid precursor protein (APP) immunohistochemistry. Behavioral outcomes were determined using the beam balance and Morris water maze tests. C152A mice had reduced accumulation of ubiquitinated proteins, decreased activation of the autophagy markers Beclin-1 and LC3B, a decreased number of abnormal axons, decreased CA1 cell death, and improved motor and cognitive function compared to WT controls after CCI; no significant change in spared tissue volume was observed. These results suggest that binding of lipid substrates to cysteine 152 of UCHL1 is important in the pathogenesis of injury and recovery after TBI and may be a novel target for future therapeutic approaches.

Abolishing UCHL1's hydrolase activity exacerbates TBI-induced axonal injury and neuronal death in mice

Ubiquitin (Ub) C-terminal hydrolase L1 (UCHL1) is a multifunctional protein that is expressed in neurons throughout brain at high levels. UCHL1 deletion is associated with axonal degeneration, progressive sensory motor ataxia, and premature death in mice. UCHL1 has been hypothesized to play a role in the pathogenesis of neurodegenerative diseases and recovery after neuronal injury. UCHL1 hydrolyzes Ub from polyubiquitinated (poly-Ub) proteins, but also may ligate Ub to select neuronal proteins, and interact with cytoskeletal proteins. These and other mechanisms have been hypothesized to underlie UCHL1's role in neurodegeneration and response to brain injury. A UCHL1 knockin mouse containing a C90A mutation (C90A) devoid of hydrolase activity was constructed. The C90A mouse did not develop the sensory and motor deficits, degeneration of the gracile nucleus and tract, or premature death as seen in UCHL1 deficient mice. C90A and wild type (WT) mice were subjected to the controlled cortical impact (CCI) model of traumatic brain injury (TBI), and cell death, axonal injury and behavioral outcome were assessed. C90A mice exhibited decreased spared tissue volume, greater loss of CA1 hippocampal neurons and greater axonal injury as detected using anti-amyloid precursor protein (APP) antibody and anti- non-phosphorylated neurofilament H (SMI-32) antibody immunohistochemistry after CCI compared to WT controls. Poly-Ub proteins and Beclin-1 were elevated after CCI in C90A mice compared to WT controls. Vestibular motor deficits assessed using the beam balance test resolved by day 5 after CCI in WT mice but not in C90A mice. These results suggest that the hydrolase activity of UCHL1 does not account for the progressive neurodegeneration and premature death seen in mice that do not express full length UCHL1. The hydrolase activity of UCHL1 contributes to the function of the ubiquitin proteasome pathway (UPP), ameliorates activation of autophagy, and improves motor recovery after CCI. Thus, UCHL1 hydrolase activity plays an important role in acute injury response after TBI.

Development of novel NEMO-binding domain mimetics for inhibiting IKK/NF-κB activation

Nuclear factor κB (NF-κB) is a transcription factor important for regulating innate and adaptive immunity, cellular proliferation, apoptosis, and senescence. Dysregulation of NF-κB and its upstream regulator IκB kinase (IKK) contributes to the pathogenesis of multiple inflammatory and degenerative diseases as well as cancer. An 11-amino acid peptide containing the NF-κB essential modulator (NEMO)-binding domain (NBD) derived from the C-terminus of β subunit of IKK, functions as a highly selective inhibitor of the IKK complex by disrupting the association of IKKβ and the IKKγ subunit NEMO. A structure-based pharmacophore model was developed to identify NBD mimetics by in silico screening. Two optimized lead NBD mimetics, SR12343 and SR12460, inhibited tumor necrosis factor α (TNF-α)- and lipopolysaccharide (LPS)-induced NF-κB activation by blocking the interaction between IKKβ and NEMO and suppressed LPS-induced acute pulmonary inflammation in mice. Chronic treatment of a mouse model of Duchenne muscular dystrophy (DMD) with SR12343 and SR12460 attenuated inflammatory infiltration, necrosis and muscle degeneration, demonstrating that these small-molecule NBD mimetics are potential therapeutics for inflammatory and degenerative diseases.

D-Amino Acid Substitution of Peptide-Mediated NF-κB Suppression in mdx Mice Preserves Therapeutic Benefit in Skeletal Muscle, but Causes Kidney Toxicity

In Duchenne muscular dystrophy (DMD) patients and the mdx mouse model of DMD, chronic activation of the classical nuclear factor-κB (NF-κB) pathway contributes to the pathogenesis that causes degeneration of muscle fibers, inflammation and fibrosis. Prior studies demonstrate that inhibition of inhibitor of κB kinase (IKK)-mediated NF-κB activation using L-isomer NF-κB essential modulator (NEMO)-binding domain (NBD) peptide-based approaches reduce muscle pathology in the mdx mouse. For our studies, the NBD peptide is synthesized as a fusion peptide with an eight-lysine (8K) protein transduction domain to facilitate intracellular delivery. We hypothesized that the d-isoform peptide could have a greater effect than the naturally occurring L-isoform peptide due to the longer persistence of the D-isoform peptide in vivo. In this study, we compared systemic treatment with low (1 mg/kg) and high (10 mg/kg) doses of L- and D-isomer 8K-wild-type-NBD peptide in mdx mice. Treatment with both L- or D-isoform 8K-wild-type-NBD peptide resulted in decreased activation of NF-κB and improved histology in skeletal muscle of the mdx mouse. However, we observed kidney toxicity (characterized by proteinuria), increased serum creatinine, activation of NF-κB and pathological changes in kidney cortex that were most severe with treatment with the D-isoform of 8K-wild-type-NBD peptide. The observed toxicity was also seen in normal mice.

NF-κB inhibition delays DNA damage-induced senescence and aging in mice

The accumulation of cellular damage, including DNA damage, is thought to contribute to aging-related degenerative changes, but how damage drives aging is unknown. XFE progeroid syndrome is a disease of accelerated aging caused by a defect in DNA repair. NF-κB, a transcription factor activated by cellular damage and stress, has increased activity with aging and aging-related chronic diseases. To determine whether NF-κB drives aging in response to the accumulation of spontaneous, endogenous DNA damage, we measured the activation of NF-κB in WT and progeroid model mice. As both WT and progeroid mice aged, NF-κB was activated stochastically in a variety of cell types. Genetic depletion of one allele of the p65 subunit of NF-κB or treatment with a pharmacological inhibitor of the NF-κB-activating kinase, IKK, delayed the age-related symptoms and pathologies of progeroid mice. Additionally, inhibition of NF-κB reduced oxidative DNA damage and stress and delayed cellular senescence. These results indicate that the mechanism by which DNA damage drives aging is due in part to NF-κB activation. IKK/NF-κB inhibitors are sufficient to attenuate this damage and could provide clinical benefit for degenerative changes associated with accelerated aging disorders and normal aging.

Effect of nuclear factor κB inhibition on serotype 9 adeno-associated viral (AAV9) minidystrophin gene transfer to the mdx mouse

Gene therapy studies for Duchenne muscular dystrophy (DMD) have focused on viral vector-mediated gene transfer to provide therapeutic protein expression or treatment with drugs to limit dystrophic changes in muscle. The pathological activation of the nuclear factor (NF)-κB signaling pathway has emerged as an important cause of dystrophic muscle changes in muscular dystrophy. Furthermore, activation of NF-κB may inhibit gene transfer by promoting inflammation in response to the transgene or vector. Therefore, we hypothesized that inhibition of pathological NF-κB activation in muscle would complement the therapeutic benefits of dystrophin gene transfer in the mdx mouse model of DMD. Systemic gene transfer using serotype 9 adeno-associated viral (AAV9) vectors is promising for treatment of preclinical models of DMD because of vector tropism to cardiac and skeletal muscle. In quadriceps of C57BL/10ScSn-Dmd(mdx)/J (mdx) mice, the addition of octalysine (8K)-NF-κB essential modulator (NEMO)-binding domain (8K-NBD) peptide treatment to AAV9 minidystrophin gene delivery resulted in increased levels of recombinant dystrophin expression suggesting that 8K-NBD treatment promoted an environment in muscle tissue conducive to higher levels of expression. Indices of necrosis and regeneration were diminished with AAV9 gene delivery alone and to a greater degree with the addition of 8K-NBD treatment. In diaphragm muscle, high-level transgene expression was achieved with AAV9 minidystoophin gene delivery alone; therefore, improvements in histological and physiological indices were comparable in the two treatment groups. The data support benefit from 8K-NBD treatment to complement gene transfer therapy for DMD in muscle tissue that receives incomplete levels of transduction by gene transfer, which may be highly significant for clinical applications of muscle gene delivery.

Systemic delivery of NEMO binding domain/IKKγ inhibitory peptide to young mdx mice improves dystrophic skeletal muscle histopathology

The activation of nuclear factor κB (NF-κB) contributes to muscle degeneration that results from dystrophin deficiency in human Duchenne muscular dystrophy (DMD) and in the mdx mouse. In dystrophic muscle, NF-κB participates in inflammation and failure of muscle regeneration. Peptides containing the NF-κB Essential Modulator (NEMO) binding domain (NBD) disrupt the IκB kinase complex, thus blocking NF-κB activation. The NBD peptide, which is linked to a protein transduction domain to achieve in vivo peptide delivery to muscle tissue, was systemically delivered to mdx mice for 4 or 7 weeks to study NF-κB activation, histological changes in hind limb and diaphragm muscle and ex vivo function of diaphragm muscle. Decreased NF-κB activation, decreased necrosis and increased regeneration were observed in hind limb and diaphragm muscle in mdx mice treated systemically with NBD peptide, as compared to control mdx mice. NBD peptide treatment resulted in improved generation of specific force and greater resistance to lengthening activations in diaphragm muscle ex vivo. Together these data support the potential of NBD peptides for the treatment of DMD by modulating dystrophic pathways in muscle that are downstream of dystrophin deficiency.

Improvement of the mdx mouse dystrophic phenotype by systemic in utero AAV8 delivery of a minidystrophin gene

Duchenne muscular dystrophy (DMD) is a devastating primary muscle disease with pathological changes in skeletal muscle that are ongoing at the time of birth. Progressive deterioration in striated muscle function in affected individuals ultimately results in early death due to cardio-pulmonary failure. As affected individuals can be identified before birth by prenatal genetic testing for DMD, gene replacement treatment can be started in utero. This approach offers the possibility of preventing pathological changes in muscle that begin early in life. To test in utero gene transfer in the mdx mouse model of DMD, a minidystrophin gene driven by the human cytomegalovirus promoter was delivered systemically by an intraperitoneal injection to the fetus at embryonic day 16. Treated mdx mice studied at 9 weeks after birth showed widespread expression of recombinant dystrophin in skeletal muscle, restoration of the dystrophin-associated glycoprotein complex in dystrophin-expressing muscle fibers, improved muscle pathology, and functional benefit to the transduced diaphragm compared with untreated littermate controls. These results support the potential of the AAV8 vector to efficiently cross the blood vessel barrier to achieve systemic gene transfer to skeletal muscle in utero in a mouse model of muscular dystrophy, to significantly improve the dystrophic phenotype and to ameliorate the processes that lead to exhaustion of the skeletal muscle regenerative capacity.

Full-length dystrophin gene transfer to the mdx mouse in utero

In utero gene therapy for genetic diseases, such as muscular dystrophies, offers potential advantages over postnatal treatment including vector delivery at the earliest point in the disease and treatment prior to full maturation of the immune system. This study examines in utero gene delivery of full-length murine dystrophin to the murine mdx model for Duchenne muscular dystrophy using a high-capacity adenoviral vector. We examined dystrophin expression, spread of vector, morphology and specific force production of the tibialis anterior muscle 9 weeks after intramuscular in utero injection. Recombinant dystrophin was expressed in the hindlimb muscles, with the majority of animals having expression in two muscles of the injected hindlimb. The dystrophin-glycoprotein complex was restored in those muscle fibers expressing recombinant dystrophin. Analysis of the percentage of dystrophin-expressing muscle fibers with centrally placed nuclei revealed effective protection from cycles of degeneration and regeneration normally seen in muscle fibers lacking dystrophin. However, due to low levels of muscle gene transfer, further advances in the efficiency of adenoviral vector-mediated gene delivery would be required for clinical applications of in utero gene therapy for primary myopathies such as Duchenne muscular dystrophy.

Patterns of gene expression from in utero delivery of adenoviral-associated vector serotype 1

Adenoviral-associated viral vectors (AAV) have shown significant promise for efficient gene delivery to multiple tissues. Studies of different serotypes of AAV revealed different expression patterns provided by gene delivery in postnatal mice. Previous in utero gene delivery studies of AAV serotype 2 (AAV2) demonstrated efficient gene expression in certain fetal tissues depending on route of administration. We studied the pattern of gene expression from AAV serotype 1 (AAV1) using intramuscular, intraperitoneal, and intravascular routes of administration in embryonic day 16 C57BL/6 mice. Limb skeletal muscle transduction was only achieved with AAV1 by intramuscular administration. The levels of gene expression were 20-fold higher than a comparable administration of AAV2. Diaphragm muscle transduction by AAV1 was achieved at the highest level by intraperitoneal administration, and to a lesser degree by intravascular administration. All delivery routes resulted in transgene expression in the lung. Our results indicate that AAV1 can offer higher transgene expression in fetal skeletal muscle than AAV2 with intramuscular administration. The transgene expression pattern in different tissues, which depends on vector serotype and route of administration, will need to be considered in planning therapeutic studies for specific disorders.

Comparison of high-capacity and first-generation adenoviral vector gene delivery to murine muscle in utero

In utero gene delivery could offer the advantage of treatment at an early stage for genetic disorders such as Duchenne muscular dystrophy (DMD) in which the inevitable process of muscle degeneration is already initiated at birth. Furthermore, treatment of fetal muscle with adenoviral (Ad) vectors is attractive because of a high density of Ad receptors, easy vector accessibility due to immaturity of the basal lamina and the possibility of treating stem cells. Previously, we demonstrated the efficient transduction of fetal muscle by high-capacity Ad (HC-Ad) vectors. In this study, we compared HC-Ad and first-generation Ad (FG-Ad) vectors for longevity of lacZ transgene expression, toxicity and induction of immunity after direct vector-mediated in utero gene delivery to fetal C57BL/6 mice muscle 16 days after conception (E-16). The total amount of beta-galactosidase (betagal) expressed from the HC-Ad vector remained stable for the 5 months of the study, although the concentration of betagal decreased due to muscle growth. Higher survival rates that reflect lower levels of toxicity were observed in those mice transduced with an HC-Ad vector as compared to an FG-Ad vector. The toxicity induced by FG-Ad vector gene delivery was dependent on mouse strain and vector dose. Animals treated with either HC-Ad and FG-Ad vectors developed non-neutralizing antibodies against Ad capsid and antibodies against betagal, but these antibodies did not cause loss of vector genomes from transduced muscle. In a mouse model of DMD, dystrophin gene transfer to muscle in utero using an HC-Ad vector restored the dystrophin-associated glycoproteins. Our results demonstrate that long-term transgene expression can be achieved by HC-Ad vector-mediated gene delivery to fetal muscle, although strategies of vector integration may need to be considered to accommodate muscle growth.

Biocompatibility of adenoviral vectors in poly(vinyl chloride) tubing catheters with presence or absence of plasticizer di-2-ethylhexyl phthalate

Adenoviral (Ad) vectors feature attractive characteristics for gene therapy of a wide variety of diseases. In many cases, the Ad vector must be administered using catheters and other plastic medical devices. Although poly(vinyl chloride) is one of the most frequently used catheter materials, it is relatively rigid and requires the addition of a plasticizer such as di-2-ethylhexyl phthalate (DEHP) to increase its flexibility. In this study, we demonstrated that exposure to a DEHP-containing catheter decreased the infectivity of Ad vectors but not the total particle number of the vector. Loss of Ad vector infectivity was directly related to the time of exposure to the DEHP-containing catheter, but it was not due to simple leaching of the chemical from the plastic. The loss of Ad vector infectivity could be prevented by preflushing the tube with albumin. Careful consideration of the compatibility between gene therapy vectors and medical delivery devices will be critical to the success of human gene therapy applications.

Fetal muscle gene transfer is not enhanced by an RGD capsid modification to high-capacity adenoviral vectors

High levels of alpha(v) integrin expression by fetal muscle suggested that vector re-targeting to integrins could enhance adenoviral vector-mediated transduction, thereby increasing safety and efficacy of muscle gene transfer in utero. High-capacity adenoviral (HC-Ad) vectors modified by an Arg-Gly-Asp (RGD) peptide motif in the HI loop of the adenoviral fiber (RGD-HC-Ad) have demonstrated efficient gene transfer through binding to alpha(v) integrins. To test integrin targeting of HC-Ad vectors for fetal muscle gene transfer, we compared unmodified and RGD-modified HC-Ad vectors. In vivo, unmodified HC-Ad vector transduced fetal mouse muscle with four-fold higher efficiency compared to RGD-HC-Ad vector. Confirming that the difference was due to muscle cell autonomous factors and not mechanical barriers, transduction of primary myogenic cells isolated from murine fetal muscle in vitro demonstrated a three-fold better transduction by HC-Ad vector than by RGD-HC-Ad vector. We hypothesized that the high expression level of coxsackievirus and adenovirus receptor (CAR), demonstrated in fetal muscle cells both in vitro and in vivo, was the crucial variable influencing the relative transduction efficiencies of HC-Ad and RGD-HC-Ad vectors. To explore this further, we studied transduction by HC-Ad and RGD-HC-Ad vectors in paired cell lines that expressed alpha(v) integrins and differed only by the presence or absence of CAR expression. The results increase our understanding of factors that will be important for retargeting HC-Ad vectors to enhance gene transfer to fetal muscle.