Prions in activated hepatic stellate cells: not a surprise after all

Hepatic stellate cells do not derive from the neural crest

BACKGROUND/AIMS

Hepatic stellate cells (HSC) have been hypothesised to derive from the neural crest, based on their expression of multiple neural/neuroendocrine features and their contacts with autonomic nerve endings.

METHODS

We studied the emergence of HSC in the liver during embryonic development in a transgenic mouse line expressing yellow fluorescent protein (YFP) in all neural crest cells and their derivatives. Cellular YFP expression in these mice was compared with desmin expression between embryonic day (E) 11.5 and adulthood.

RESULTS

YFP was abundantly expressed in neural crest cells delaminating from the neural tube and in all known neural crest-derived structures and cell populations. In particular, YFP expressing cells perfectly mimicked the spatial and temporal pattern of enteric nervous system development from neural crest cells migrating from the postotic region. Cells within the adrenal medulla were also YFP positive. Analysis of the liver showed that desmin-expressing, stellate-shaped, perisinusoidally located HSC were evident from E11.5 onwards. However, no detectable YFP expression was seen in the developing liver or in HSC, from E11.5 until adulthood.

CONCLUSIONS

These findings suggest HSC do not descend from the neural crest, and therefore may derive from the septum transversum mesenchyme, from endoderm or from the mesothelial liver capsule.

Neuroregulation of the neuroendocrine compartment of the liver

Liver progenitor cells as well as hepatic stellate cells have neuroendocrine features. Progenitor cells express chromogranin-A and neural cell adhesion molecule, parathyroid hormone-related peptide, S-100 protein, neurotrophins, and neurotrophin receptors, while hepatic stellate cells express synaptophysin, glial fibrillary acidic protein, neural cell adhesion molecule, nestin, neurotrophins, and their receptors. This phenotype suggests that these cell types form a neuroendocrine compartment of the liver, which could be under the control of the central nervous system. We recently showed that the parasympathetic nervous system promotes progenitor cell expansion after liver injury, since selective vagotomy reduces the number of progenitor cells after chemical injury in the rat. Similarly, after transplantation, which surgically denervates the liver, human livers that develop hepatitis have fewer progenitor cells than native, fully innervated livers with similar degrees of liver injury. There is also accumulating experimental evidence linking the autonomic system, in particular the sympathetic nervous system (SNS), with the pathogenesis of cirrhosis and its complications. Recently, it has been shown that hepatic stellate cells themselves respond to neurotransmitters. Moreover, inhibition of the SNS reduced fibrosis in carbon tetrachloride-induced liver injury. In view of the denervated state of transplanted livers, it is very important to unravel the neural control mechanisms of regeneration and fibrogenesis. Moreover, since there is a shortage of donor organs, a better understanding of the mechanisms of regeneration could have therapeutic possibilities, which could even obviate the need for orthotopic liver transplantation.

Alpha B-crystallin expression in human and rat hepatic stellate cells

BACKGROUND/AIMS

We searched for factors implicated in early hepatic stellate cell (HSC) activation in diseased liver, by means of suppression subtractive hybridization (SSH).

METHODS

SSH was performed between messenger RNA (mRNA) from normal rat HSC and mRNA from HSC, isolated from rats with acute D-galactosamine (Gal)-induced hepatitis.

RESULTS

One of the potentially upregulated factors which we found was alpha B-crystallin (ABCRYS), a small heat-shock protein and a chaperone known to protect the cell against protein degradation in conditions of cellular stress and known to associate with various types of intermediate filaments. Upregulation of ABCRYS mRNA in HSC, following Gal-intoxication (3.5-fold) as well as by culturing the HSC on plastic (20-30-fold), was confirmed by quantitative real-time reverse transcription polymerase chain reaction. The expression of ABCRYS protein in human and rat HSC was demonstrated by immunohistochemistry, in vitro and in vivo, in normal and diseased liver. Double-staining co-localized ABCRYS immunoreactivity with alpha-smooth muscle actin immunoreactivity in human liver and with desmin immunoreactivity in rat liver. In vivo upregulation of ABCRYS protein following Gal-intoxication was also shown, by comparison with desmin expression.

CONCLUSIONS

Human and rat HSC express ABCRYS mRNA and protein. Both are rapidly upregulated following HSC activation.