Transplantation of wild-type white adipose tissue normalizes metabolic, immune and inflammatory alterations in leptin-deficient ob/ob mice

Abstract

Leptin-deficient ob/ob mice exhibit several metabolic and immune abnormalities, including thymus atrophy and markedly reduced inflammatory responses. We evaluated whether transplantation of wild-type (WT) white adipose tissue (WAT) into ob/ob mice could mimic the effect of recombinant leptin administration in normalizing metabolic, immune and inflammatory abnormalities. Female ob/ob mice received a subcutaneous transplantation of WAT obtained from WT littermates. A separate group of ob/ob mice was sham-operated. Despite raising leptin levels to only 15% of those observed in WT mice, WAT transplantation normalized metabolic abnormalities (glycemia, ALT, liver weight) in ob/ob mice and prevented further body weight gain. The transplanted group demonstrated normalization of thymus and spleen cellularity, thymocyte subpopulations and rates of thymocyte apoptosis. In the model of dextran sulfate sodium-induced colitis, WAT transplantation restored inflammation to levels equivalent to those of WT mice. Colonic production of IL-6 and MIP-2 was markedly reduced in the non-transplanted ob/ob group compared to transplanted ob/ob and WT mice. Our data indicate that WAT transplantation is an effective way to normalize metabolic as well as immune and inflammatory parameters in ob/ob mice. The threshold of leptin sufficient to normalize metabolic, immune and inflammatory function is significantly lower than levels present in lean WT mice. Finally, leptin derived exclusively from WAT is sufficient to normalize metabolic, immune and inflammatory parameters in ob/ob mice.

Figure 1. Effect of WAT transplantation on body weight

Body weight was measured in ob/ob mice transplanted with WAT (closed squares), sham-operated ob/ob mice (open squares) and WT mice (closed circles) starting on the day of WAT transplant and continuing until day 47. Data are mean +/− SEM of 10 mice per group. BW of ob/ob sham was significantly different from that ob/ob transplant starting on day 17 and continuing until day 47.

Figure 2. Effect of WAT transplantation on liver weight, ALT and glucose levels

Liver and serum were obtained from ob/ob mice transplanted with WAT (hatched columns), sham-operated ob/ob mice (open columns) and WT mice (closed columns) on day 47. Panel A: liver weight as percent of BW; Panel B: Serum ALT levels; Panel C: blood glucose levels. Data are mean +/− SEM of 10 mice per group. *** p<0.001 versus ob/ob transplant and WT.

Figure 3. Effect of WAT transplantation on thymocyte subpopulations

Thymocytes were isolated from the thymus of ob/ob mice transplanted with WAT (hatched columns), sham-operated ob/ob mice (open columns) and WT mice (closed columns) and analyzed by flow cytometry as described in the Methods section. Data are mean +/− SEM of 5 mice per group. *** p<0.001 versus ob/ob transplant and WT.

Figure 4. DSS-induced intestinal inflammation: effect of WAT transplantation

ob/ob mice transplanted with WAT (closed squares), sham-operated ob/ob mice (open circles) and WT mice (closed circles) received DSS for 5 days following the schedule described in the Methods section. Clinical score was evaluated daily. Data are mean +/− SEM of 5 mice per group. ** p<0.01, *** p<0.001 versus ob/ob transplant and WT.

Figure 5. Effect of WAT transplantation on colonic production of IL-6 and MIP-2

On day 8 of administration of either regular drinking water (open columns) or DSS (closed colums), colon cultures were performed and levels of IL-6 (panel A) and MIP-2 (panel B) evaluated in the supernatants. Data are mean +/− SEM of 5 mice per group. ** p<0.01, *** p<0.001 versus ob/ob transplant and WT treated with DSS.