Cardiomyocyte-specific Tbk1 deletion aggravated chronic doxorubicin cardiotoxicity via inhibition of mitophagy.

Doxorubicin (Dox) use is limited by Dox-induced cardiotoxicity. TANK-blinding kinase 1 (TBK1) is an important kinase involved in the regulation of mitophagy, but the role of TBK1 in cardiomyocytes in chronic Dox-induced cardiomyopathy remains unclear. Cardiomyocyte-specific Tbk1 knockout (Tbk1CKO) mice received Dox (6 mg/kg, injected intraperitoneally) once a week for 4 times, and cardiac assessment was performed 4 weeks after the final Dox injection. Adenoviruses encoding Tbk1 or containing shRNA targeting Tbk1, or a TBK1 phosphorylation inhibitor were used for overexpression or knockdown of Tbk1, or inhibit phosphorylation of TBK1 in isolated primary cardiomyocytes. Our results revealed that moderate Dox challenge decreased TBK1 phosphorylation (with no effect on TBK1 protein levels), resulting in compromised myocardial function, obvious mortality and overt interstitial fibrosis, and the effects were accentuated by Tbk1 deletion. Dox provoked mitochondrial membrane potential collapse and oxidative stress, the effects of which were exacerbated and mitigated by Tbk1 knockdown, specific inhibition of phosphorylation and overexpression, respectively. However, Tbk1 （Ser172A） overexpression did not alleviate these effects. Further scrutiny revealed that TBK1 exerted protective effects on mitochondria via SQSTM1/P62-mediated mitophagy. Tbk1 overexpression mediated cardioprotective effects on Dox-induced cardiotoxicity were cancelled off by Sqstm1/P62 knockdown. Moreover, TBK1-mitophagy-mitochondria cascade was confirmed in heart tissues from dilated cardiomyopathy patients. Taken together, our findings denoted a pivotal role of TBK1 in Dox-induced mitochondrial injury and cardiotoxicity possibly through its phosphorylation and SQSTM1/P62-mediated mitophagy.

TREM2 Insufficiency Protects against Pulmonary Fibrosis by Inhibiting M2 Macrophage Polarization.

Rationale Idiopathic pulmonary fibrosis (IPF) is a lung disease with high mortality, limited treatment options and an unknown aetiology. M2 macrophages play a critical role in the pathological process of IPF. Triggering receptor expressed on myeloid cells-2 (TREM2) participates in the regulation of macrophages, although its role in IPF remains elusive. METHODS: This study examined the role of TREM2 in macrophage regulation using a well-established bleomycin (BLM)-induced pulmonary fibrosis (PF) mouse model. TREM2 insufficiency was induced by intratracheal treatment with TREM2-specific siRNA. The effects of TREM2 on IPF were evaluated using histological staining and molecular biological methods. RESULTS: TREM2 expression levels were significantly elevated in the lungs of IPF patients and mice with BLM-induced pulmonary fibrosis mice. Bioinformatics analysis revealed that IPF patients with higher TREM2 expression had a shorter survival time, and that TREM2 expression was closely associated with fibroblasts and M2 macrophages. Gene Ontology (GO) enrichment analysis showed that found TREM2-related differentially expressed genes (DEGs) were associated with inflammatory responses, extracellular matrix (ECM) and collagen formation. Single-cell RNA sequencing analysis revealed that TREM2 was predominantly expressed in macrophages. TREM2 insufficiency inhibited BLM-induced pulmonary fibrosis and M2 macrophage polarization. Mechanistic studies showed that TREM2 insufficiency suppressed the activation of STAT6 and the expression of fibrotic factors such as Fibronectin (Fib), Collagen I (Col I) and α- smooth muscle actin (α-SMA). CONCLUSION: Our study showed that TREM2 insufficiency might alleviate pulmonary fibrosis possibly through macrophage polarization regulation via STAT6 activation, providing a promising macrophage-related approach for the clinical therapy of pulmonary fibrosis.