Liver fibrosis is associated with changes in collagen fibril diameter and a shift in collagen type expression

Abstract

We hypothesize that, in liver fibrosis, control mechanisms regulating collagen fibril diameter are lost, leading to thickened fibers that compromise tissue integrity. To examine this, a mouse model (C57BL/6) of hepatic fibrosis, induced by carbon tetrachloride (CCl4) injection (i.p.0.3 ml/kg CCl4 or corn oil control) 2X/wk for 9 wks was used. This treatment induced centrilobular hepatic necrosis, inflammation and fibrosis. Electron microscopy of liver sections showed no differences in fibril diameters between control and CCl4-treated mice until wk 7. At 9 wks, the mean diameter in CCl4-treated mice was increased 15% (mean = 33 nm compared to 31 nm control). Diameter distribution was dramatically different. In control mice, 38% (70/184) of the fibril diameters were greater than 32 nm, while in CCl4 livers, 57% (105/184 ) were greater. We next evaluated expression of potential fibril diameter regulators, i.e., collagens V and XIV, using relative RT-PCR. Collagen I, III, V and XIV mRNA expression levels were unchanged until wk 7. Type I collagen mRNA increased 18-fold by 8 wks and was still 10 X control levels at 9 wks. Type III and V collagen mRNAs were about 6 X control levels at 8 and at 9 wks. In contrast, type XIV collagen mRNA in treated mice rose to only 4 X control levels at 8 wks and was merely 2 X controls at 9 wks. These data confirm that fibrillar collagen I and III mRNA amounts increase greatly by 8 and 9 wks of chronic CCl4 treatment. Of the diameter regulators, collagen V keeps pace, but collagen XIV does not. This suggests that type XIV collagen is likely responsible in part for normal liver fibril diameter regulation. Its not being concomitantly increased as type I collagen increases suggests that fibrosis may be a consequence of dysregulation of collagen fibril diameter.