Defects in MAP1S‐mediated autophagy cause reduction in mouse lifespans especially when fibronectin is overexpressed

Abstract

SummaryAutophagy is a cellular process that executes the turnover of dysfunctional organelles and misfolded or abnormally aggregated proteins. Microtubule‐associated protein MAP1S interacts with autophagy marker LC3 and positively regulates autophagy flux. LC3 binds with fibronectin mRNA and facilitates its translation. The synthesized fibronectin protein is exported to cell surface to initiate the assembly of fibronectin extracellular matrix. Fibronectin is degraded in lysosomes after it is engulfed into cytosol via endocytosis. Here, we show that defects in MAP1S‐mediated autophagy trigger oxidative stress, sinusoidal dilation, and lifespan reduction. Overexpression of LC3 in wild‐type mice increases the levels of fibronectin and γ‐H2 AX, a marker of DNA double‐strand breakage. LC3‐induced fibronectin is efficiently degraded in lysosomes to maintain a balance of fibronectin levels in wild‐type mice so that the mice live a normal term of lifespan. In the LC3 transgenic mice with MAP1S deleted, LC3 enhances the synthesis of fibronectin but the MAP1S depletion causes an impairment of the lysosomal degradation of fibronectin. The accumulation of fibronectin protein promotes liver fibrosis, induces an accumulation of cell population at the G0/G1 stage, and further intensifies oxidative stress and sinusoidal dilatation. The LC3‐induced overexpression of fibronectin imposes stresses on MAP1S‐deficient mice and dramatically reduces their lifespans. Therefore, MAP1S‐mediated autophagy plays an important role in maintaining mouse lifespan especially in the presence of extra amount of fibronectin.

Selective Reversible Inhibition of Autophagy in Hypoxic Breast Cancer Cells Promotes Pulmonary Metastasis

“…Supporting this, transcriptome and functional proteomic analysis indicated both integrin and several downstream pathway constituents were enriched in HRE-dnULK1 tumors and cell lines. These findings are in agreement with recent studies reporting autophagy to be a regulator of fibrogenesis and fibronectin-mediated migration(26,39–41). Furthermore, autophagy has been shown to modulate cell migration through β1-integrin membrane recycling, in which the loss of autophagy prevents integrin sequestration within autophagosomes and subsequent degradation in lysosomes (26).…”

Spermidine Prolongs Lifespan and Prevents Liver Fibrosis and Hepatocellular Carcinoma by Activating MAP1S-Mediated Autophagy

“…All animals received humane care according to the criteria outlined in the “Guide for the Care and Use of Laboratory Animals” prepared by the National Academy of Sciences and published by the National Institutes of Health (NIH publication 86-23 revised 1985). Wild-type (MAP1S +/+ ) and MAP1S knockout mice (MAP1S −/− ) were bred and genotyped as described in detail in our previous publications (16,27). …”

“…Cox proportional-hazard analysis with univariate or multivariate method was used to explore the effect of variables on overall survivals. Liver tissues collected from 18-month old mice were either frozen or fixed for either immunoblot analysis or staining with dihydroethidine hydrochloride to measure oxidative stress or with Hematoxylin and Eosin (H&E) to analyze sinusoidal dilatation as we previously reported (16). The intensities of protein bands were quantified using ImageJ software and normalized by the levels of loading control β-Actin.…”

“…Liver tissue sections were stained with H&E and lesion area of liver were quantified using ImageJ software. Liver fibrosis was visualized by Sirius Red staining and quantified by the contents of hydroxyproline, and levels of α-SMA were analyzed either by immunoblot or immunostaining as we previously reported (16). …”

“…As a sequence homologue of the microtubule-associated protein MAP1A and MAP1B, MAP1S similarly interacts with mammalian autophagy marker LC3 (12–14), and bridges autophagy components with microtubules and mitochondria to affect the biogenesis and degradation of autophagosomes and suppress genome instability and diethylnitrosamine (DEN)-induced HCC (14,15). Autophagy defects caused by MAP1S depletion promote oxidative stress, liver sinusoidal dilatation and fibronectin-induced liver fibrosis and reduce mouse lifespans (16). Higher levels of MAP1S in tumor tissues predict longer survivals for human patients suffering from either prostate adenocarcinomas (17) or clear cell renal cell carcinomas (18).…”