Faithful duplication of the genome requires structure-specific endonucleases such as the RuvABC complex in Escherichia coli. These enzymes help to resolve problems at replication forks that have been disrupted by DNA damage in the template. Much less is known about the identities of these enzymes in mammalian cells. Mus81 is the catalytic component of a eukaryotic structure-specific endonuclease that preferentially cleaves branched DNA substrates reminiscent of replication and recombination intermediates. Here we explore the mechanisms by which Mus81 maintains chromosomal stability. We found that Mus81 is involved in the formation of double-strand DNA breaks in response to the inhibition of replication. Moreover, in the absence of chromosome processing by Mus81, recovery of stalled DNA replication forks is attenuated and chromosomal aberrations arise. We suggest that Mus81 suppresses chromosomal instability by converting potentially detrimental replication-associated DNA structures into intermediates that are more amenable to DNA repair.

Background Pulmonary artery involvement (PAI) in Takayasu arteritis (TAK) can lead to severe complications, but the relationship between the two has not been fully clarified. Methods We retrospectively investigated 166 consecutive patients with TAK who attended Kyoto University Hospital from 1997 to 2018. The demographic data, clinical symptoms and signs, comorbidities, treatments, and imaging findings were compared between patients with and without PAI. TAK was diagnosed based on the American College of Rheumatology Classification Criteria (1990) or the Japanese Clinical Diagnostic Criteria (2008). PAI was identified using enhanced computed tomography, magnetic resonance imaging, or lung scintigraphy. Results PAI was detected in 14.6% (n = 24) of total TAK patients. Dyspnea (25.0% vs. 8.6%; p = 0.043), pulmonary arterial hypertension (PAH) (16.7% vs. 0.0%; p < 0.001), ischemic heart disease (IHD) (29% vs. 9.3%; p = 0.018), respiratory infection (25.0% vs. 6.0%; p = 0.009), and nontuberculous mycobacteria (NTM) infection (20.8% vs. 0.8%; p < 0.001) were significantly more frequent, and renal artery stenosis (0% vs. 17%; p = 0.007) was significantly less frequent in TAK patients with PAI than in those without PAI. PAI and biologics were risk factors for NTM. Conclusions TAK patients with PAI more frequently have dyspnea, PAH, IHD, and respiratory infection, including NTM, than TAK patients without PAI.

Objective To investigate the association of autoantibodies with scleroderma renal crisis (SRC) among Japanese patients. Methods The clinical characteristics and mortality of 330 patients with systemic sclerosis (SSc) at Kyoto University Hospital were retrospectively analyzed, focusing on anti-topoisomerase I, anti-centromere, anti-RNA polymerase III (RNAPIII), and anti-U1-RNP. Logistic regression analyses were performed to examine the association of autoantibodies with the development and mortality of SRC. Results SRC was observed in 24 out of 330 SSc patients, including anti-topoisomerase I (n = 12/24, 50%), anti-RNAPIII (n = 7/24, 29%), anti-U1-RNP (n = 5/24, 21%), and anti-centromere (n = 3/24, 13%). Anti-U1-RNP (odds ratio [95% confidence interval], 3.63 [1.11–10.2]), anti-topoisomerase I (3.22 [1.37–7.57]), and anti-RNAPIII (3.29 [1.16–8.70]) were associated with the development of SRC. Furthermore, anti-topoisomerase I (6.00 [1.11–41.1]) was associated with the 1-year mortality of SRC. The 1-year survival rate after the onset of SRC among all patients and those positive for anti-topoisomerase I was 54% and 33%, respectively. In contrast, the survival rate in patients negative for anti-topoisomerase I was 75%, of which the survival rate of patients positive for anti-RNAPIII and anti-centromere was 83% and 100%, respectively. Conclusion Specific SSc-related autoantibodies were associated with the morbidity and mortality of SRC.

Anti-melanoma differentiation-associated gene 5 (MDA5) antibody, a dermatomyositis (DM)-specific antibody, is strongly associated with interstitial lung disease (ILD). Patients with idiopathic inflammatory myopathy (IIM) who are anti-MDA5 antibody positive [anti-MDA5 (+)] often experience chest symptoms during the active disease phase. These symptoms are primarily explained by respiratory failure; nevertheless, cardiac involvement can also be symptomatic. Thus, the aim of this study was to investigate cardiac involvement in anti-MDA5 (+) DM. A total of 63 patients with IIM who underwent electrocardiography (ECG) and ultrasound cardiography (UCG) during the active disease phase from 2016 to 2021 [anti-MDA5 (+) group, n = 21; anti-MDA5-negative (-) group, n = 42] were enrolled in the study, and their clinical charts were retrospectively reviewed. The ECG and UCG findings were compared between the anti-MDA5 (+) and anti-MDA5 (-) groups. All anti-MDA5 (+) patients had DM with ILD. The anti-MDA5 (+) group showed more frequent skin ulcerations and lower levels of leukocytes, muscle enzymes, and electrolytes (Na, K, Cl, and Ca) than the anti-MDA5 (-) group. According to the ECG findings obtained during the active disease phase, the T wave amplitudes were significantly lower for the anti-MDA5 (+) group than for the anti-MDA5 (-) group (I, II, and V4–6 lead; p &lt; 0.01; aVF and V3, p &lt; 0.05). However, the lower amplitudes were restored during the remission phase. Except for the E wave, A wave and Sep e’, the UCG results showed no significant differences between the groups. Four patients with anti-MDA5 (+) DM had many leads with lower T wave and cardiac abnormalities (heart failure, diastolic dysfunction, myocarditis) on and after admission. Though anti-MDA5 (+) patients clinically improved after immunosuppressive therapy, some of their ECG findings did not fully recover in remission phase. In conclusion, anti-MDA5 (+) DM appears to show cardiac involvement (electrical activity and function) during the active phase. Further studies are necessary to clarify the actual cardiac condition and mechanism of these findings in patients with anti-MDA5 (+) DM.

MDA5 is a cytoplasmic sensor of viral RNA, triggering type-I interferon (IFN-I) production. Constitutively active MDA5 has been linked to autoimmune diseases such as systemic lupus erythematosus, Singleton–Merten syndrome (SMS), and Aicardi-Goutières syndrome (AGS), a genetically determined inflammatory encephalopathy. However, AGS research is challenging due to the lack of animal models. We previously reported lupus-like nephritis and SMS-like bone abnormalities in adult mice with constitutively active MDA5 (Ifih1  G821S/+), and herein demonstrate that these mice also exhibit high lethality and spontaneous encephalitis with high IFN-I production during the early postnatal period. Increases in the number of microglia were observed in MDA5/MAVS signaling- and IFN-I-dependent manners. Furthermore, microglia showed an activated state with an increased phagocytic capability and reduced expression of neurotrophic factors. Although multiple autoantibodies including lupus-related ones were detected in the sera of the mice as well as AGS patients, Ifih1  G821S/+Rag2  -/- mice also exhibited upregulation of IFN-I, astrogliosis and microgliosis, indicating that autoantibodies or lymphocytes are not required for the development of the encephalitis. The IFN-I signature without lymphocytic infiltration observed in Ifih1  G821S/+ mice is a typical feature of AGS. Collectively, our results suggest that the Ifih1  G821S/+ mice are a model recapitulating AGS and that microglia are a potential target for AGS therapy.