Galectin-3, histone deacetylases, and Hedgehog signaling:Possible convergent targets in schistosomiasis-induced liver fibrosis

Schistosomiasis affects approximately 240 million people in the world. Schistosoma mansoni eggs in the liver induce periportal fibrosis and hepatic failure driven by monocyte recruitment and macrophage activation, resulting in robust Th2 response. Here, we suggested a possible involvement of Galectin-3 (Gal-3), histone deacetylases (HDACs), and Hedgehog (Hh) signaling with macrophage activation during Th1/Th2 immune responses, fibrogranuloma reaction, and tissue repair during schistosomiasis. Gal-3 is highly expressed by liver macrophages (Kupffer cells) around Schistosoma eggs. HDACs and Hh regulate macrophage polarization and hepatic stellate cell activation during schistosomiasis-associated fibrogenesis. Previously, we demonstrated an abnormal extracellular matrix distribution in the liver that correlated with atypical monocyte-macrophage differentiation in S. mansoni-infected, Gal-3-deficient (Lgals3-/-) mice. New findings explored in this review focus on the chronic phase, when wild-type (Lgals3+/+) and Lgals3-/- mice were analyzed 90 days after cercariae infection. In Lgals3-/- infected mice, there was significant inflammatory infiltration with myeloid cells associated with egg destruction (hematoxylin and eosin staining), phagocytes (specifically Kupffer cells), numerically reduced and diffuse matrix extracellular deposition in fibrotic areas (Gomori trichrome staining), and severe disorganization of collagen fibers surrounding the S. mansoni eggs (reticulin staining). Granuloma-derived stromal cells (GR cells) of Lgals3-/- infected mice expressed lower levels of alpha smooth muscle actin (α-SMA) and eotaxin and higher levels of IL-4 than Lgals3+/+ mice (real-time PCR). The relevant participation of macrophages in these events led us to suggest distinct mechanisms of activation that culminate in defective fibrosis in the liver of Lgals3-/- infected mice. These aspects were discussed in this review, as well as the possible interference between Gal-3, HDACs, and Hh signaling during progressive liver fibrosis in S. mansoni-infected mice. Further studies focused on macrophage roles could elucidate these questions and clear the potential utility of these molecules as antifibrotic targets

Inflammatory infiltrate is amplified in the absence of Gal-3 in <i>S</i>. <i>mansoni</i>-infected mice.

<p>Hematoxylin & eosin staining show granulomas of Lgals-3+/+ mice (A) and Lgals-3-/- mice (B), where abundant myeloid cells were detected around the eggs. Myeloid cells were preferentially localized around the eggs in Lgals-3+/+ mice (C,E). In contrast, myeloid cells were abundant around the eggs and inside the hepatic parenchyma in Lgals-3-/- mice (D,F), suggesting a local amplification instead of central mobilization. Hematoxylin & eosin staining. Real-time RT-PCR to IL-5 (G) and Eotaxin (H) expressed by GR-HSCs from Lgals-3+/+ and Lgals-3-/- mice reinforce the hypothesis of local myeloid amplification. The relative value was obtained in relation to HPRT expression. Each bar represents the mean ±SEM, <i>n</i> = 5. These graphs are representative of three experiments. *P≤0.05 compared with Lgals3+/+ mice. Magnification: A-B: 100x; C-F: 1,000x. <i>n</i> = 5 mice per group.</p

Schematic illustration of different stages of schistosomiasis and opening questions in the field.

<p>(A) Schematic illustrating liver histological architecture upon schistosomiasis infection in Lgals3+/+ and Lgals3-/- mice. Schistosomules accumulate in the hepatic portal system. Monocytes are recruited by eggs and worms antigens, becoming the central players during the first steps of the establishment of the disease. Macrophages trigger bone marrow mobilization and myofibroblast activation that, in turn, bring hepatocytes into the inflammatory process. By contrast, in Schistosoma-infected Lgals3-/- mice, macrophages are not properly activated, suggesting disturbances in monocyte recruitment, Sonic hedgehog (Shh) secretion, HDAC activity, and extracellular matrix deposition by myofibroblast cells. (B) Suggestion of possible mechanisms to be investigated in the near future.</p

Local Kupffer cells show a decreased phagocytic activity in <i>S</i>. <i>mansoni</i>-infected Lgals3-/- mice.

<p>Classical pigmented Kupffer cells were not observed around granulomas from Lgals3-/- mice (B,D) in contrast to a high phagocytic activity found in Lgals3+/+ mice (A,C). A-B: Hematoxylin & eosin staining. C-D: Gomori trichrome staining. Magnification: 400x. <i>n</i> = 5 mice per group.</p

Gal-3 is necessary for fibrotic concentric granulomas in <i>S</i>. <i>mansoni</i> infected mice and myofibroblast activation.

<p>Hematoxylin & eosin and Gomori trichrome staining show classical concentric fibrotic granulomas of Lgals3+/+ (A,C dashed line) and more diffuse and dispersed collagen fibers around the <i>S</i>. <i>mansoni</i> eggs of Lgals3-/- mice (B,D dashed line). Real-time reverse transcription PCR (RT-PCR) to alpha smooth muscle actin (E) and IL-4 (F) expressed by granuloma-hepatic stellate cells (GR-HSCs) from Lgals3+/+ and Lgals3-/- mice shows the imbalance between extracellular matrix production and proinflammatory cytokines. The relative value was obtained in relation to the Hypoxanthine Guanine Phosphoribosyl Transferase (HPRT) expression. Each bar represents the mean ±SEM, <i>n</i> = 5. These graphs are representative of three experiments. *P≤0.05 compared with Lgals3+/+ mice. Magnification: 400x. <i>n</i> = 5 mice per group.</p