Chronic iron overload causes activation of rat lipocytes in vivo

Abstract

Chronic iron overload can result in hepatic fibrosis and cirrhosis. Activated lipocytes, through increased production of collagen and extracellular matrix, play an important role in hepatic fibrogenesis in several types of experimental liver injury, but their contribution to hepatic injury after iron overload is unknown. This study examines the effect of iron overload on lipocyte activation, in vivo. Male Sprague-Dawley rats were fed a chow diet supplemented with 1% carbonyl iron for up to 20 mo. Controls were fed the chow diet alone. Lipocytes were prepared by sequential pronase and collagenase perfusion of the livers, followed by density-gradient centrifugation. Lipocyte activation was assessed by immunohistochemistry of liver sections and by Western blot analysis of alpha-smooth muscle actin expression in freshly isolated lipocytes. In addition, to measure the biosynthetic capability of these lipocytes, collagen and noncollagen protein production was determined after 3 days in culture, using [3H]proline incorporation. The hepatic iron concentration was increased by eightfold in the iron-loaded rats, and lipocytes from these animals expressed alpha-smooth muscle actin. Collagen production was increased by 2.5-fold, and noncollagen protein production was elevated by twofold in lipocytes isolated from iron-loaded rats. In the iron-loaded livers, autofluorescent material with the characteristics of lipofusion was present in periportal zones. Chronic iron overload expression results in the activation of lipocytes, as determined by increased expression of alpha-smooth muscle actin and by increased production of both collagen and noncollagen protein. This activation may contribute to iron-induced hepatic fibrogenesis.

Interferon gamma decreases hepatic stellate cell activation and extracellular matrix deposition in rat liver fibrosis

“…a-SMA, a marker of acti-scribed. 57 Nonspecific binding sites were blocked for 1 hour in phosphate-buffered saline containing 3% bovine serum alvated HSC, 6,[11][12][13][14][15] was detected on methanol-fixed, paraffinembedded sections, as previously described. 13 Briefly, liver bumin.…”

“…In addition to Western blot, which is based on tion, 9,46 and expression of a-SMA. 6,[11][12][13][14][15] Histological characterization of HSC has long been a specific immunoreaction, the colorimetric and morphometric methods for collagen detection use the selechampered by the lack of a specific marker expressed by these cells. Vitamin A or lipid content are unspecific tive binding of Sirius Red to collagen components.…”

“…6,[11][12][13][14][15]43 The earliest marker of HSC activation is probably the ferritin receptor expression, 36 followed by vation. The lack of major toxic effects demonstrated in vitro 37 and in vivo, in this and other 33 experimental immunoreactivity for a-SMA 6,11-15,43 and a decrease in vitamin A content.…”

Contribution of Hepatic Parenchymal and Nonparenchymal Cells to Hepatic Fibrogenesis in Biliary Atresia

“…A population of nonparenchymal cells known as hepatic stellate cells (HSCs) have been shown to be "activated" and therefore responsible for the increased production of type I collagen leading to hepatic fibrosis in pathological conditions of the adult human liver, [12][13][14] and in a number of experimental models of adult liver injury, [15][16][17][18][19][20] including cholestasis. [21][22][23][24] In liver injury, HSCs are transformed into myofibroblasts (activated HSCs), which produce increased levels of fibrillar collagen and express an intracellular microfilament protein, ␣-smooth muscle actin (SMA), which is traditionally used as a marker protein of the activated HSC phenotype (reviewed in Ref.…”

Evidence for altered hepatic matrix degradation in genetic haemochromatosis

“…Following liver injury, HSC become “activated”, develop a myofibroblast-like phenotype, and express markers such as α-smooth muscle actin (SMA) 9. In animal models of iron overload, HSC assume an activated phenotype,10 and are the major source of collagen type I 1011 In a recent study we showed the presence of activated HSC in haemochromatosis and showed that increasing HIC correlated with increasing HSC activation 12…”