Burn injury increases replication and apoptosis in murine brown adipose tissue

Abstract

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Objectives: Burn injury has been shown to stimulate the in vivo uptake of FDG by brown adipose tissue (BAT) in mice. Although we have recently demonstrated that this effect is associated with a marked increase in expression Uncoupling Protein-1 (UCP-1) mRNA, additional factors may modulate the process. Specifically, changes in FDG uptake may be affected by cellular replication and/or apoptosis in BAT. Proliferation can be evaluated using radiolabeled ¹²³I-FIAU; a uridine base that is incorporated into DNA. Apoptosis, or programed cell death, can be monitored using radiolabeled ^99mTc Annexin-V which binds to phosphotidyl serine residues that become exposed at the cell surface during apoptosis. In the present study, we examined the effect of burn injury on uptake of ¹²⁵I-FIAU and ^99mTc Annexin-V by BAT and white adipose tissue (WAT)in mice.

Methods: Male CD-1 mice weighing approximately 18 grams (Charles River Breeding Labs., Boston MA) were anesthetized with ether and the dorsum was shaven and subjected to thermal injury (20 % Total Body Surface Area, 90^oC, 9 seconds) followed by saline resuscitation (2 ml, IP). ¹²³I-FIAU was prepared by treating the precursor FAU (2’-fluoro-2’-deoxy-1β-D-arabinofuranosyluracil) with carrier-free Na¹²³I. ^99mTc Annexin-V was prepared by combining HYNIC-Annexin-V stannous tricine, (Thesus Imaging, North American Scientific) with ^99mTc sodium pertechnetate. Twenty four hours after burn injury, groups of 6 burned or sham control mice were injected with 30 μCi of ¹²⁵I-FIAU or 20 μCi of ^99mTc Annexin-V by tail vein. The ¹²⁵I-FIAU treated mice were sacrificed 24 hrs after injection and the ^99mTc Annexin-V treated mice were sacrificed 1 hour after injection by CO₂ asphyxiation and samples of BAT and WAT were collected. Radioactivity was measured with a well-type gamma counter. All results were expressed as % Injected Dose (mean ± sem).

Results: As indicaed in the table, thermal injury resulted in an approximately 2-fold increase in uptake of ¹²³I-FIAU in BAT of burned compared with control animals (p<0.01). A small and not statistically significant increase in uptake of ¹²³I-FIAU was detected in WAT of burned animals. A significant (p<0.05) increase in uptake of ^99mTc Annexin-V by BAT and WAT was observed in burned mice compared to controls. [table]

Conclusions: Burn injury produced a significant elevation in BAT uptake of both ¹²⁵I-FIAU and ^99mTc Annexin-V, suggesting that both cell replication and apoptosis are increased in this condition.

Uptake of ¹²³I-FIAU and ^99mTc Annexin by BAT and WAT at 24h After Burn Injury