CGG repeat expansion in LRP12 in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the degeneration of motor neurons. Although repeat expansion in C9orf72 is its most common cause, the pathogenesis of ALS isn't fully clear. In this study, we show that repeat expansion in LRP12, a causative variant of oculopharyngodistal myopathy type 1 (OPDM1), is a cause of ALS. We identify CGG repeat expansion in LRP12 in five families and two simplex individuals. These ALS individuals (LRP12-ALS) have 61-100 repeats, which contrasts with most OPDM individuals with repeat expansion in LRP12 (LRP12-OPDM), who have 100-200 repeats. Phosphorylated TDP-43 is present in the cytoplasm of iPS cell-derived motor neurons (iPSMNs) in LRP12-ALS, a finding that reproduces the pathological hallmark of ALS. RNA foci are more prominent in muscle and iPSMNs in LRP12-ALS than in LRP12-OPDM. Muscleblind-like 1 aggregates are observed only in OPDM muscle. In conclusion, CGG repeat expansions in LRP12 cause ALS and OPDM, depending on the length of the repeat. Our findings provide insight into the repeat length-dependent switching of phenotypes.

LRP12 is an endogenous transmembrane inactivator of α4 integrins

Dynamic regulation of integrin activation and inactivation is critical for precisely controlled cell adhesion and migration in physiological and pathological processes. The molecular basis for integrin activation has been intensively studied; however, the understanding of integrin inactivation is still limited. Here, we identify LRP12 as an endogenous transmembrane inhibitor for α4 integrin activation. The LRP12 cytoplasmic domain directly binds to the integrin α4 cytoplasmic tail and inhibits talin binding to the β subunit, thus keeping integrin inactive. In migrating cells, LRP12-α4 interaction induces nascent adhesion (NA) turnover at the leading-edge protrusion. Knockdown of LRP12 leads to increased NAs and enhanced cell migration. Consistently, LRP12-deficient T cells show an enhanced homing capability in mice and lead to aggravated chronic colitis in a T cell-transfer colitis model. Altogether, LRP12 is a transmembrane inactivator for integrins that inhibits α4 integrin activation and controls cell migration by maintaining balanced NA dynamics.

Intranuclear inclusions in muscle biopsy can differentiate oculopharyngodistal myopathy and oculopharyngeal muscular dystrophy

Oculopharyngodistal myopathy (OPDM) and oculopharyngeal muscular dystrophy (OPMD) are similar and even believed to be indistinguishable in terms of their myopathological features. To address the diagnostic gap, we evaluated the muscle biopsy samples for p62 expression by immunohistochemistry and compared the occurrence and the frequency of intranuclear inclusions among the individuals with OPDM (harboring CGG repeat expansion in LRP12 (n = 19), GIPC1 (n = 6), or NOTCH2NLC (n = 7)), OPMD (n = 15), and other rimmed vacuolar myopathies. We found that myonuclei with p62-positive intra-nuclear inclusions (myo-INIs) were significantly more frequent in OPMD (11.9 ± 1.1%, range 5.9-18.6%) than in OPDM and other rimmed vacuolar myopathies (RVMs) (0.9-1.5% on average, range 0.0-2.8%, p < 0.0001). In contrast, INIs in non-muscle cells such as blood vessels, peripheral nerve bundles, and muscle spindles (non-muscle-INIs) were present in OPDM, but absent in OPMD. These results indicate that OPMD can be differentiated from OPDM and other RVMs by the frequent presence of myo-INIs; and in OPDM, the presence of non-muscle-INIs in muscle pathology should be a diagnostic hallmark.

Expanded clinical spectrum of oculopharyngodistal myopathy type 1

INTRODUCTION/AIMS

Heterozygous CGG repeat expansions in low-density lipoprotein receptor-related protein 12 (LRP12) have recently been identified as a cause of oculopharyngodistal myopathy (OPDM), and the disease is designated as OPDM type 1 (OPDM1). In contrast to broadening of our knowledge on the genetic background of OPDM, what we know of the clinical phenotype of genetically confirmed OPDM1 remains limited.

METHODS

This investigation was a single-center case series study of OPDM consisting of ten patients from seven families. Repeat-primed polymerase chain reaction and Southern blot analyses were performed to confirm the CGG repeat expansions in LRP12. Clinical findings were retrospectively reviewed.

RESULTS

Seven patients from five families were identified as having CGG repeat expansions in LRP12. We found a high prevalence of axial muscle involvement, such as neck muscle weakness (6/7) and fatty infiltration in the rectus abdominis muscle, as revealed by computed tomography (5/5). We identified patients with very subtle oculopharyngeal symptoms, mimicking isolated distal myopathy. Muscle specimens were collected from the biceps brachii and tibialis anterior muscles of three patients. Myopathic changes were more severe with more atrophic fibers forming clusters in the tibialis anterior than the biceps brachii muscles of these three patients. No rimmed vacuoles were observed in the biceps brachii muscles in two of the three patients.

DISCUSSION

This study shows the expanded clinical spectrum of OPDM1, highlighting the importance of axial muscle evaluation in OPDM1. Considering patients with very subtle oculopharyngeal symptoms, genetic analysis of LRP12 should be considered in patients with isolated distal myopathy.

Synovial mesenchymal stem cell-derived extracellular vesicles alleviate chondrocyte damage during osteoarthritis through microRNA-130b-3p-mediated inhibition of the LRP12/AKT/β-catenin axis

BACKGROUND

Synovial mesenchymal stem cells (SMSCs) have been discussed as promising tools for protecting chondrocytes from loss and inhibiting osteoarthritis (OA). This work infocuses on the function of SMSC-derived extracellular vesicles (EVs) in chondrocytes during OA and the molecular mechanism.

METHODS

EVs were extracted from SMSCs and identified. Chondrocytes were treated with interleukin (IL)-1β to induce an OA-like condition in vitro and then treated with EVs. The proliferation, apoptosis, migration, extracellular matrix (ECM) degradation and inflammation in chondrocytes were examined. Key microRNAs (miRNAs) carried by EVs were screened using a microarray analysis, and the downstream molecules involved were explored using bioinformatic analysis. Rescue experiments were performed to validate the involvements of these molecules in EV-mediated events.

RESULTS

EVs restored proliferation and migration while reduced apoptosis, ECM degradation and the secretion of pro-inflammatory cytokines in chondrocytes induced by IL-1β. miR-130b-3p was significantly elevated in chondrocytes after EVs treatment. Knockdown of miR-130b-3p blocked the protective roles of EVs against IL-1β-induced damage to chondrocytes. miR-130b-3p was found to target LDL receptor related protein 12 (LRP12) mRNA in chondrocytes. Overexpression of LRP12 counteracted the effects of EVs as well and activated the AKT/β-catenin signaling pathway.

CONCLUSION

This study provided evidence that EVs alleviate chondrocyte damage during OA through miR-130b-3p-mediated inhibition of the LRP12/AKT/β-catenin axis. This study may offer novel thoughts into the protection of chondrocytes and the management of OA.