Liver regeneration is impaired in lipodystrophic fatty liver dystrophy mice

Abstract

We previously reported that mice subjected to partial hepatectomy exhibit rapid development of hypoglycemia followed by transient accumulation of fat in the early regenerating liver. We also showed that disrupting these metabolic alterations results in impaired liver regeneration. The studies reported here were undertaken to further characterize and investigate the functional importance of changes in systemic adipose metabolism during normal liver regeneration. The results showed that a systemic catabolic response is induced in each of two distinct, commonly used experimental models of liver regeneration (partial hepatectomy and carbon tetrachloride treatment), and that this response occurs in proportion to the degree of induced hepatic insufficiency. Together, these observations suggest that catabolism of systemic adipose stores may be essential for normal liver regeneration. To test this possibility, we investigated the hepatic regenerative response in fatty liver dystrophy (fld) mice, which exhibit partial lipodystrophy and have diminished peripheral adipose stores. The results showed that the development of hypoglycemia and hepatic accumulation of fat was attenuated and liver regeneration was impaired following partial hepatectomy in these animals. The fld mice also exhibited increased hepatic p21 expression and diminished plasma levels of the adipose-derived hormones adiponectin and leptin, which have each been implicated as regulators of liver regeneration.

Conclusion: These data suggest that the hypoglycemia that develops after partial hepatectomy induces systemic lipolysis followed by accumulation of fat derived from peripheral stores in the early regenerating liver, and that these events may be essential for initiation of normal liver regeneration.

Figure 1. Systemic Catabolism after Partial Hepatectomy

(A) Total, (B) lean, and (C) fat mass (percentage of corresponding initial mass) after partial hepatectomy or sham surgery (*p<0.005, **p<0.05 vs. sham).

Figure 2. Systemic Catabolism after CCl₄

(A) Total, (B) lean, and (C) fat mass after CCl₄ or vehicle (Veh; *p<0.005, **p<0.05 vs. vehicle). Immunohistochemical analysis of hepatocellular BrdU incorporation 48 hours after (D) vehicle and (E) CCl₄ (100 micron bar shown). (F) Summary of hepatocellular proliferation 24–72 hours after CCl₄ or vehicle (^#p<0.001 vs. vehicle).

Figure 3. Metabolic Changes after One-Third versus Two-Thirds Partial Hepatectomy

(A) Total, lean, and fat mass (*p=0.03, **p=0.02 vs. two-thirds partial hepatectomy); (B) blood glucose (*p=0.03 vs. two-thirds partial hepatectomy, p=0.5 vs. sham; **p=0.002 vs. sham); (C) hepatic triglyceride content (*p=0.04 vs. two-thirds partial hepatectomy, p=0.3 vs. sham; **p<0.001 vs. sham) 24 hours after sham, one-third, or two-thirds partial hepatectomy.

Figure 4. Liver Regeneration in fld Mice

Immunohistochemical analysis of hepatocellular BrdU incorporation 36 hours after partial hepatectomy (A, B) and H&E staining of liver 48 hours after partial hepatectomy (D, E) in control (fld/+) and fatty liver dystrophy (fld/fld) Lpin1-null mice (100 micron bar shown; arrowheads identify mitoses). (C) Summary of hepatocellular proliferation 0–72 hours after partial hepatectomy in control and fld mice (*p=0.003); hepatocellular proliferation in strain-matched wildtype (+/+) mice 36 hours after partial hepatectomy is also illustrated. (F) Summary of mitotic frequency 48–72 hours after partial hepatectomy in liver from control and fld mice.

Figure 5. Hepatic Cyclin D1, p21, and p27 Expression after Partial Hepatectomy in fldMice

Expression of Cyclin D1 mRNA (A, *p=0.02 vs. fld) and protein (B: representative immunoblot; C: summary of densitometric analysis of replicates; *p=0.04 vs. fld). Expression of p21 and p27 protein (D: representative immunoblots; E–F: summary of densitometric analysis of replicates; *p≤0.04 vs. fld).

Figure 6. Hepatic and Systemic Metabolic Changes after Partial Hepatectomy in fld Mice

(A) Hepatic triglyceride content (*p<0.02 vs. fld; p = 0.08 vs. 12 hr control, 0.49 vs. 24 hr control; **p<0.002 vs. fld). (B) Blood glucose (*p=0.05, **p=0.002). (C) Plasma insulin (*p=0.008, **p<0.001).

Figure 7. Plasma Adiponectin and Leptin after Partial Hepatectomy in fld Mice

(A) Representative protein immunoblot and quantitative summary of (B) adiponectin and (C) leptin levels in plasma from control and fld mice after partial hepatectomy (B: *p<0.001 vs. corresponding control; **p=0.04 and ***p<0.001 vs. 0 hour control; C: *p=0.02 and **p=0.05 vs. 0 hour control, ***p<0.001 vs. 0 hour control and p=0.03 vs. fld).

Figure 8. STAT3 Activation and SOCS3 Expression after Partial Hepatectomy in fld Mice

(A) Representative protein immunoblot of hepatic phosphorylated (pSTAT3) and total STAT3, (B) quantitative summary of hepatic phosphorylated:total STAT3 (*p=0.04), and (C) hepatic mRNA expression of SOCS3 (*p≤0.02, **p=0.002 vs. fld) in control and fld mice after partial hepatectomy.