TRAF2, an Innate Immune Sensor, Reciprocally Regulates Mitophagy and Inflammation to Maintain Cardiac Myocyte Homeostasis.

Mitochondria are essential for cardiac myocyte function, but damaged mitochondria trigger cardiac myocyte death. Although mitophagy, a lysosomal degradative pathway to remove damaged mitochondria, is robustly active in cardiac myocytes in the unstressed heart, its mechanisms and physiological role remain poorly defined. We discovered a critical role for TRAF2, an innate immunity effector protein with E3 ubiquitin ligase activity, in facilitating physiological cardiac myocyte mitophagy in the adult heart, to prevent inflammation and cell death, and maintain myocardial homeostasis.

TFEB activation in macrophages attenuates postmyocardial infarction ventricular dysfunction independently of ATG5-mediated autophagy.

Lysosomes are at the epicenter of cellular processes critical for inflammasome activation in macrophages. Inflammasome activation and IL-1ß secretion are implicated in myocardial infarction (MI) and resultant heart failure; however, little is known about how macrophage lysosomes regulate these processes. In mice subjected to cardiac ischemia/reperfusion (IR) injury and humans with ischemic cardiomyopathy, we observed evidence of lysosomal impairment in macrophages. Inducible macrophage-specific overexpression of transcription factor EB (TFEB), a master regulator of lysosome biogenesis (Mϕ-TFEB), attenuated postinfarction remodeling, decreased abundance of proinflammatory macrophages, and reduced levels of myocardial IL-1ß compared with controls. Surprisingly, neither inflammasome suppression nor Mϕ-TFEB-mediated attenuation of postinfarction myocardial dysfunction required intact ATG5-dependent macroautophagy (hereafter termed "autophagy"). RNA-seq of flow-sorted macrophages postinfarction revealed that Mϕ-TFEB upregulated key targets involved in lysosomal lipid metabolism. Specifically, inhibition of the TFEB target, lysosomal acid lipase, in vivo abrogated the beneficial effect of Mϕ-TFEB on postinfarction ventricular function. Thus, TFEB reprograms macrophage lysosomal lipid metabolism to attenuate remodeling after IR, suggesting an alternative paradigm whereby lysosome function affects inflammation.

Mechanism of microtubule plus-end tracking by the plant-specific SPR1 protein and its development as a versatile plus-end marker.

Microtubules are cytoskeletal polymers that perform diverse cellular functions. The plus ends of microtubules promote polymer assembly and disassembly and connect the microtubule tips to other cellular structures. The dynamics and functions of microtubule plus ends are governed by microtubule plus end-tracking proteins (+TIPs). Here we report that the Arabidopsis thaliana SPIRAL1 (SPR1) protein, which regulates directional cell expansion, is an autonomous +TIP. Using in vitro reconstitution experiments and total internal reflection fluorescence microscopy, we demonstrate that the conserved N-terminal region of SPR1 and its GGG motif are necessary for +TIP activity whereas the conserved C-terminal region and its PGGG motif are not. We further show that the N- and C-terminal regions, either separated or when fused in tandem (NC), are sufficient for +TIP activity and do not significantly perturb microtubule plus-end dynamics compared with full-length SPR1. We also found that exogenously expressed SPR1-GFP and NC-GFP label microtubule plus ends in plant and animal cells. These results establish SPR1 as a new type of intrinsic +TIP and reveal the utility of NC-GFP as a versatile microtubule plus-end marker.

Transcription Factor EB Activation Rescues Advanced αB-Crystallin Mutation-Induced Cardiomyopathy by Normalizing Desmin Localization.

Background Mutations in αB-crystallin result in proteotoxic cardiomyopathy with desmin mislocalization to protein aggregates. Intermittent fasting ( IF ) is a novel approach to activate transcription factor EB (TFEB), a master regulator of the autophagy-lysosomal pathway, in the myocardium. We tested whether TFEB activation can be harnessed to treat advanced proteotoxic cardiomyopathy. Methods and Results Mice overexpressing the R120G mutant of αB-crystallin in cardiomyocytes ( Myh6-Cry ABR 120G) were subjected to IF or ad-lib feeding, or transduced with adeno-associated virus- TFEB or adeno-associated virus-green fluorescent protein after development of advanced proteotoxic cardiomyopathy. Adeno-associated virus-short hairpin RNA-mediated knockdown of TFEB and HSPB 8 was performed simultaneously with IF . Myh6-Cry ABR 120G mice demonstrated impaired autophagic flux, reduced lysosome abundance, and mammalian target of rapamycin activation in the myocardium. IF resulted in mammalian target of rapamycin inhibition and nuclear translocation of TFEB with restored lysosome abundance and autophagic flux; and reduced aggregates with normalized desmin localization. IF also attenuated left ventricular dilation and myocardial hypertrophy, increased percentage fractional shortening, and increased survival. Adeno-associated virus- TFEB transduction was sufficient to rescue cardiomyopathic manifestations, and resulted in reduced aggregates and normalized desmin localization in Myh6-Cry ABR 120G mice. Cry ABR 120G-expressing hearts demonstrated increased interaction of desmin with αB-crystallin and reduced interaction with chaperone protein, HSPB 8, compared with wild type, which was reversed by both IF and TFEB transduction. TFEB stimulated autophagic flux to remove protein aggregates and transcriptionally upregulated HSPB 8, to restore normal desmin localization in Cry ABR 120G-expressing cardiomyocytes. Short hairpin RNA-mediated knockdown of TFEB and HSPB 8 abrogated IF effects, in vivo. Conclusions IF and TFEB activation are clinically relevant therapeutic strategies to rescue advanced R120G αB-crystallin mutant-induced cardiomyopathy by normalizing desmin localization via autophagy-dependent and autophagy-independent mechanisms.