Epidemiological studies indicate that age has strong impact on the natural course
of NAFLD but the underlying mechanisms of this phenomenon are elusive.
The aim of this study was to assess whether there are age dependent differences in
lipid metabolism and NASH development in primary hepatocytes and a murine model, respectively.
Methods and Results: Upon Stimulation with free fatty acids hepatocytes isolated from 4 week old mice
revealed significantly higher lipid accumulation than hepatocytes isolated from 14
week old mice. Furthermore, we started feeding a NASH-inducing Western type diet (high
fat, fructose and cholesterol) to male C57BL/6 mice at the age of 4 or 14 weeks. After
12 weeks HFD-feeding mice of both age classes revealed a significant increase of body
weight, hepatic triglyceride and free-fatty-acid levels compared to control mice fed
with standard chow. Furthermore, hydroxynonenal staining and increased Ncf-1 and Nox2
expression were indicative for oxidative stress. However, all these changes were significantly
higher in the old mice. Similarly, serum transaminase levels, hepatic pro-inflammatory
(TNF, IL-1, MCP-1) and pro-fibrogenic (TGF-beta, TIMP-1, Collagen I) gene expression,
activation of hepatic stellate cells (evidenced by alpha-sma expression), and histological
fibrosis were significantly higher in the older mice. Affimetrix gene expression microarray
analysis identified approximately 400 genes which were differenzially expressed in
the livers of old mice compared to young mice after HFD-feeding. These genes could
be clustered in different pathways which mainly affect fat digestion and absorption
and peroxisomal activity. Several genes encoding for factors known to be increased
during liver injury were more induced in old compared to young mice in response to
HFD-feeding. In contrast and notably, the transcriptional factor ZBTB-16 was strongly
up-regulated in the livers of young mice after HFD-feeding, while it was even slightly
reduced in old mice after HFD-feeding. We confirmed this result in a second murine
NASH model (Matsuzawa et al. Hepatology 2007) but in contrast, hepatic ZBTB-16 expression
was significantly increased in non-NASH related models of hepatocellular damage (bile
duct ligation and chronic CCl4 application). Similarly, hepatic ZBTB-16 expression
was significantly increased patients with chronic viral hepatitis or alcohol abuse
but not in NASH patients.
Conclusions: There is significant age-dependent variation in mice in the susceptibility to NASH
development and progression, which seems to be caused at least in part by differences
in the lipid metabolisms in hepatocytes. The identification of the underlying molecular
mechanisms of these differences may have prognostic as well as therapeutic implications
for the progression of NAFLD. As one potential factor we identified the transcription
factor ZBTB-16, the role of which in NAFLD-progression is currently under investigation.
