The deficiency of a ubiquitously expressed cytoplasmic protein sequestosome1/p62 (SQSTM1), a multifunctional modulator of cell signaling, induces late onset obesity in mice. Rodriguez et al. (2006) first reported this phenotype by characterizing the sequestosome1 gene knockout (KO) mice and proposed an idea that enhanced adipogenesis is the major cause of obesity formation. However, we recently reevaluated the cause of obes...
The deficiency of a ubiquitously expressed cytoplasmic protein sequestosome1/p62 (SQSTM1), a multifunctional modulator of cell signaling, induces late onset obesity in mice. Rodriguez et al. (2006) first reported this phenotype by characterizing the sequestosome1 gene knockout (KO) mice and proposed an idea that enhanced adipogenesis is the major cause of obesity formation. However, we recently reevaluated the cause of obesity formation in the KO mice and proposed a new idea that the overeating due to reduced sensitivity of leptin signaling in the brain is the major reason for obesity formation (Harada et al., 2013). Recent comments by Mueller et al (J Neuroscience, letter Sep 27, 2013) on our paper provide an opportunity to discuss the function of SQSTM1 in the regulation of body weight and energy metabolism in animals.
The difference between the two ideas proposed by Rodriguez et al. (2006) and Harada et al. (2013) originated from their basic characterizations of obesity in the SQSTM1 deficient mice, particularly in food intake, pair- feeding experiments, and daily rhythm of oxygen consumption rate. It is noted that both groups observed increased food intake in the KO mice compared to wild type (WT) mice. Rodriguez et al. (2006) characterized food intake at the age between 5-8.5 months (20-34 weeks old) (Fig. 1 H, in Rodriguez et al.), showing mean values of about 43 (6.2) and 28 (4.0) g/week(day)/mouse (calculated from the figure) for KO and WT mice, respectively. This result shows KO mice eat chow roughly 50% more than WT mice. Harada et al. (2013) shows the food intake to be about 3.4 (24) and 3.0 (21) g/day(week)/mouse for KO and WT mice at 5-10 weeks old (Fig. 1 B), and the food intake by KO mice almost linearly increased with age; about 4.0 to 4.5 g/day/mouse from 20 to 34 weeks old. Restriction of food supply to 3.0 g/day/mouse eliminated the difference in body weight gain between KO and wild type mice during 5-15 weeks of age (Fig.1 D, in Harada et al). Rodriguez et al. (2006) also carried out a pair feeding experiment under different conditions and observed a higher body weight in KO mice than in WT mice at the end of the experiment (Supplemental Fig. 1 A and B). However, their conclusion was not warranted because they did not describe important experimental conditions such as amount of food supplied, age of mice, the time period, and the change of body weight in the two mice during the experiments. The measurement of oxygen consumption rate is also an important factor judging the change of energy metabolism in mice. Harada et al. (2013) showed a clear day rhythm of oxygen consumption expressed by VO2 (ml/g0.75) (Fig. 1 C), showing no difference between KO and WT mice (13-16 weeks old). However, the results shown by Rodriguez et al. (2006) did not show the day rhythm of oxygen consumption rate with the presence of large variations of the measurements making it difficult to draw any conclusions (Fig. 1 I, in Rodriguez et al). Thus, we conclude from our experimental results that the overeating is the main reason for the obesity formation in the SQSTM1 deficient mice.
The comment letter by Mueller et al. (2013) also pointed out the experiments using CNS-specific SQSTM1 KO mice, saying our results contradict with those shown in recent paper by Muller et al. (2013), which was published while our paper was under review process. They proposed a new idea for the obesity formation in the KO mice that SQSTM1 controls thermogenesis in brown adipocytes independent of its development or differentiation. In their paper they characterized that CNS-specific SQSTM1 KO mice showing no change in body weight gain compared to control SQSTM1 positive mice between 8-22 weeks old (Fig. 1 A, in Muller et al.). Harada et al. (2013) also conducted a similar experiment using body weight matched CNS-specific SQSTM1 KO and control SQSTM1 positive mice between 14 -40 weeks old (Fig. 2 E, in Harada et al.), showing only small differences in body weight gain between the two mice up to 25 weeks old, which is consistent with the result observed by Muller et al. (2013). However, the difference of body weight between the brain-specific KO and the control mice became significant only after 25 weeks old and marked at 30-40 weeks old. Notably, the body weight change after 22 weeks old is not included in the figure by Muller et al. (2013).
We don't deny the role of adipocytes in the obesity formation in SQSTM1 deficient mice, as Muller et al. (2013) show gradual but mild increase in body weight gain in adipocyte-specific SQSTM1 KO mice between 6-25 weeks old (Fig. 2 A, in Muller et al.). We would rather like to suggest a possible functional cooperation between adipose tissue and the brain in regulation of late-onset obesity through the functional loss of SQSTM1. Deficiency of SQSTM1 in adipocytes enhances its adipogenesis at the early stage initiating mild fat accumulation, which is consistent with the higher serum leptin levels as young as 3 weeks old (Fig. 4 A and B, in Harada et al). On the other hand the brain retains reduced sensitivity to leptin signaling, resulting in a steady increase in food intake and turning on the obesity program. Further precise studies are required to verify this idea and uncover the molecular function of SQSTM1 in body weight regulation and energy metabolism.
References
Harada H, et al. (2013), Deficiency of p62/sequestosome 1 causes hyperphagia due to leptin resistance in the brain. J Neurosci, 33(37):14767-14777.
Rodriguez A et al. (2006), Mature-onset obesity and insulinresistance in mice deficient in the signaling adapter p62. Cell Metab, 3:211-222.
Muller et al. (2013), p62 links beta-adrenergic input to mitochondria function and thermogenesis. J Clin Invest, 123:469-478.
None declared
Harada et al. report that p62 deficiency causes obesity as a result of hyperphagia and central leptin resistance, ignoring several findings arguing against a role of p62 in food intake. Obesity from p62 deficiency was first described by Rodriguez et al. (2006), who observed no difference in food intake between p62 knockout (ko) mice and wild-type (wt) littermates, indicating that hyperphagia cannot explain obesity in these...
Harada et al. report that p62 deficiency causes obesity as a result of hyperphagia and central leptin resistance, ignoring several findings arguing against a role of p62 in food intake. Obesity from p62 deficiency was first described by Rodriguez et al. (2006), who observed no difference in food intake between p62 knockout (ko) mice and wild-type (wt) littermates, indicating that hyperphagia cannot explain obesity in these mice. Harada et al. further report that CNS-specific p62 ko mice are equally obese as the global p62 ko mice. Here Harada et al. neither discuss nor cite a paper that used the identical Nestin-cre based approach to delete p62 in the CNS and that observed no metabolically relevant phenotype of these mice (Müller et al., 2012). The latter manuscript shows that adipocyte-specific p62 deletion leads to obesity despite no difference in food intake, arguing against a role of p62 in food intake. In line with Rodriguez et al. (2006), the adipocyte- specific p62 ko mice showed impaired energy metabolism due to decreased energy expenditure, an effect notably mediated in a cell autonomous manner and ignored by Harada et al. It is puzzling that the data shown by Harada et al. are contradictory to what has previously been shown for global and CNS- specific p62 ko mice. Notably, in Figure 2D, the p62 floxed Nestin-cre mice show a substantial p62 immunofluorescence in the CNS, suggesting only partial p62 deletion. Likewise, the PCR shown in Figure 2B shows a clear band in the p62 floxed Nestin-cre mice. Unfortunately, the manuscript lacks information about the self-made p62 antibody and no western blot was performed to confirm selective and specific p62 deletion. In summary, the study by Harada et al. warrants further clarification and a series of evidence ignored by Harada et al. indicates that obesity due to p62 deficiency is the result of impaired energy metabolism in the adipose tissue and is independent of food intake.
Harada H, Warabi E, Matsuki T, Yanagawa T, Okada K, Uwayama J, Ikeda A, Nakaso K, Kirii K, Noguchi N, Bukawa H, Siow RC, Mann GE, Shoda J, Ishii T, Sakurai T. Deficiency of p62/Sequestosome 1 Causes Hyperphagia Due to Leptin Resistance in the Brain. J Neurosci. 2013 Sep 11;33(37):14767-14777.
Rodriguez A, Duran A, Selloum M, Champy MF, Diez-Guerra FJ, Flores JM, Serrano M, Auwerx J, Diaz-Meco MT, Moscat J. Mature-onset obesity and insulin resistance in mice deficient in the signaling adapter p62. Cell Metab. 2006 Mar;3(3):211-22.
Müller TD, Lee SJ, Jastroch M, Kabra D, Stemmer K, Aichler M, Abplanalp B, Ananthakrishnan G, Bhardwaj N, Collins S, Divanovic S, Endele M, Finan B, Gao Y, Habegger KM, Hembree J, Heppner KM, Hofmann S, Holland J, Küchler D, Kutschke M, Krishna R, Lehti M, Oelkrug R, Ottaway N, Perez- Tilve D, Raver C, Walch AK, Schriever SC, Speakman J, Tseng YH, Diaz-Meco M, Pfluger PT, Moscat J, Tschöp MH. p62 links ß-adrenergic input to mitochondrial function and thermogenesis. J Clin Invest. 2013 Jan 2;123(1):469-78. doi: 10.1172/JCI64209. Epub 2012 Dec 21.
None declared