Nitric oxide promotes caspase-independent hepatic stellate cell apoptosis through the generation of reactive oxygen species

Abstract

Hepatic stellate cells (HSCs) contribute to portal hypertension through multiple mechanisms that include collagen deposition, vasoconstriction, and regulation of sinusoidal structure. Under normal physiologic conditions, endothelial nitric oxide (NO) synthase-derived NO exerts paracrine effects on HSCs; however, in cirrhosis, NO generation is impaired in association with concomitant HSC activation and changes in sinusoidal structure, events that contribute significantly to the development of portal hypertension. These concepts, in combination with recent evidence that induction of HSC-selective apoptosis may represent a useful target for treatment of chronic liver disease, led us to examine if NO may further limit HSC function through apoptosis. Indeed, both NO donors and endothelial NO synthase overexpression promoted HSC apoptotic pathways. HSC death conferred by NO occurred through mitochondrial membrane depolarization and through a caspase-independent pathway. Furthermore, NO-induced apoptosis of HSC did not occur through the canonical pathways of soluble guanylate cyclase or protein nitration, but rather through the generation of superoxide and hydroxyl radical intermediates. Lastly, HSC isolated from rats after bile duct ligation were more susceptible to NO-induced apoptosis. These data indicate that NO promotes HSC apoptosis through a signaling mechanism that involves mitochondria, is mediated by reactive oxygen species, and occurs independent of caspase activation. Conclusion: We postulate that NO-dependent apoptosis of HSCs may maintain sinusoidal homeostasis, and may represent an additional beneficial effect of NO donors for therapy of portal hypertension.

Hepatic sinusoids in liver injury, inflammation, and fibrosis: new pathophysiological insights

“…NO production usually decreases, leading to an increasing intrahepatic pressure due to an inability to maintain intrasinusoidal autoregulation by vasodilatation [1,17]. In addition, decreased NO production activates a contractile phenotype of HSC, inducing extracellular matrix production and migratory capacity [18,19]. Finally, recent studies revealed the importance of angiogenesis in the process of fibrogenesis and their interdependency [12,20].…”

“…However, as described for SEC, HSC can undergo dramatic phenotype transformation in the context of liver injury: a decrease in NO production by SEC, which normally induces HSC quiescence, leads to HSC activation characterized by enhanced contractility, increased migratory capacity, deposition of extracellular matrix components such as fibronectin and collagen I or III, upregulation of smooth muscle alpha actin (a-SMA), and increased release of autocrine and paracrine factors. Besides this canonical NO pathway for quiescence and activation of HSC, [18,19] several other soluble factors from surrounding cells (such as hepatocytes, Kupffer-cells, and lymphocytes) play an important role in HSC activation [26]. Interestingly, studies of different extracellular matrices have revealed that matrix stiffness itself is a key determinant of HSC activation, although involved proteins and receptors have not been identified so far [27].…”

Retinol Binding Protein-Albumin Domain III Fusion Protein Deactivates Hepatic Stellate Cells

“…Primary rat HSCs were isolated as described previously (Langer et al, 2008). Briefly, livers were perfusion digested with collagenase and pronase.…”

Apoptosis of hepatic stellate cells mediated by specific protein nitration

“…The elevated Bax/Bcl-2 ratio so achieved would then induce the activation of caspases-9 and -3 leading to subsequent oligonucleosomal fragmentation, as we have also observed. Previous reports suggest that NO promotes caspase-independent HSC apoptosis probably mediated by nitrosylation of some cellular components [38]. The present results indicate that NO can also induce caspase-dependent apoptosis of HSC mediated by A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 16 protein nitration via the peroxynitrite produced by hepatic cells, and more importantly by infiltrating macrophages in inflammatory conditions [39,40].…”