<i>Sdc1−/−</i> mice are chronically cold- stressed.

<p><b>A</b>. Liver glycogen was measured for <i>Sdc1−/−</i> 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>B</b>. Serum triglycerides were measured for the same conditions. <b>C</b>. 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, <i>Sdc1−/−</i> mice entered torpor after 24 hours (indicated as a precipitous drop in O₂ consumption for two out of four <i>Sdc1−/−</i> mice in this experiment). None of the wild type (0/4) mice triggered torpor. <b>D</b>. In this example, measurements from 4 BALB/c (black lines) and 4 <i>Sdc1−/−</i> (red lines) mice were averaged (3/4 <i>Sdc1−/−</i> 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). <b>E</b>. Brown adipose tissues were harvested from <i>Sdc1−/−</i> and BALB/c mice housed at 21°C. H&E-stained paraffin sections show that <i>Sdc1−/−</i> brown adipose shows depleted lipid stores (white cytoplasmic inclusions). <b>F</b>. 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). <b>G</b>. 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. <b>H</b>. 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 <i>Sdc1−/−</i> mice housed at RT. <b>I</b>. To test whether the BAT of <i>Sdc1−/−</i> 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).