Figure 1. Sdc1−/− mice are chronically cold- stressed.

A. Liver glycogen was measured for Sdc1−/− and wild type BALB/c mice under normal housing conditions (room temperature; RT; 21°C), after a 24-hour fast or after acute cold stress (90 mins at 4°C; n = 6). B. Serum triglycerides were measured for the same conditions. C. Mice of both genotypes were housed in metabolic cages at 23°C, fasted and their metabolic rates were measured (oxygen consumption, expressed as VO₂). In this example, Sdc1−/− mice entered torpor after 24 hours (indicated as a precipitous drop in O₂ consumption for two out of four Sdc1−/− mice in this experiment). None of the wild type (0/4) mice triggered torpor. D. In this example, measurements from 4 BALB/c (black lines) and 4 Sdc1−/− (red lines) mice were averaged (3/4 Sdc1−/− mice and 0/4 BALB/c mice entered torpor, indicated by the blue arrows). The housing temperature was shifted up to 31°C to illustrate their complete recovery (shown as VO₂/oxygen consumption and energy expenditure curves over 3 days). E. Brown adipose tissues were harvested from Sdc1−/− and BALB/c mice housed at 21°C. H&E-stained paraffin sections show that Sdc1−/− brown adipose shows depleted lipid stores (white cytoplasmic inclusions). F. To test for cold stress, lysates of brown adipose tissue (shown here from three independent mice) were assayed for activation of the checkpoint, pT¹⁸⁰Y¹⁸² p38α, either at room temperature or after acute cold stress (4°C). G. To confirm which isotypes of p38 were present and activated, the pattern of phospho-p38 was compared to Western blots probed with isotype-specific antibodies. H. Lysates were probed for UCP1, a marker of uncoupling in brown adipose tissue. Top panel, BAT from mice housed at various housing temperatures; bottom panel, assay of relative levels of UCP1 in Sdc1−/− mice housed at RT. I. To test whether the BAT of Sdc1−/− mice had initiated the full thermogenic program, levels of cold stress-induced mRNAs were measured by qPCR for tissues isolated from mice housed at RT and 4°C/cold (5 days) (PGC1α, n = 3) and for mice of different ages (6- and 13-week-old; Elovl3).