C/EBP Homologous Protein-induced Macrophage Apoptosis Protects Mice from Steatohepatitis

Abstract

Background:We hypothesized that C/EBP homologous protein mediates hepatocyte apoptosis in nonalcoholic steatohepatitis. Results: Paradoxically, Chop deletion protects from steatohepatitis by inducing apoptosis in activated macrophages. Conclusion: CHOP-dependent macrophage apoptosis in NASH highlights the cell type-specific complexity of the ER stress response. Significance: Therapeutic manipulation of mediators of ER stress response may have opposite effects in different cell populations; therefore, such studies should be interpreted cautiously.

Hepatocytes release ceramide-enriched pro-inflammatory extracellular vesicles in an IRE1α-dependent manner

“…PA induces ER stress and activates all three of the unfolded protein response sensors ( 16,35 ). We have extended these observations by demonstrating that PAmediated ER stress stimulates EV release from hepatocytes.…”

“…Furthermore, inhibition of macrophage activation, recruitment, or accumulation in the liver ameliorates steatohepatitis ( 16 ). Herein, we report that PA-induced ER stress leads to EV release.…”

“…Perturbations in ER function result in ER stress. ER stress is observed in NAFLD and PA-induced lipotoxicity ( 15,16 ). Indeed, PA can directly activate all three ER stress sensors: i ) inositol requiring enzyme 1 ␣ (IRE1 ␣ ); ii ) activating transcription factor 6 ␣ (ATF6 ␣ ); and iii ) protein kinase-like ER kinase (PERK).…”

“…For EV isolation, cells were cultured in growth medium supplemented with 5% EV-depleted FBS [prepared by overnight centrifugation at 100,000 g at 4°C according to standard protocols ( 20 )] and 1% BSA, with the addition of either PA or oleate (OA) as previously described by us ( 4 ), thapsigargin (Tg), or vehicle, respectively. Bone marrow-derived macrophages (BMDM s) were isolated from the long leg bones of C57Bl/6J mice, as previously described by us ( 16 ). Briefl y, dissected long bones were fl ushed with serum-free RPMI and cells were differentiated in 20% L929 cell conditioned medium containing RPMI and used on day 7 after differentiation.…”

“…Quantity and quality of RNA was measured spectrophotometrically using a NanoDrop ND1000 (Thermo Scientifi c), and RNA was reverse transcribed into cDNA by the iScript cDNA synthesis kit (Bio-Rad). Quantitative real-time PCR reactions were run on the LightCycler 480 (Roche), using the LightCycler 480 SYBR Green 1 Master Mix (Roche) and previously published primers ( 16 ).…”