Deletion of Nhlh2 results in a defective torpor response and reduced Beta adrenergic receptor expression in adipose tissue.
BACKGROUND
Mice with a targeted deletion of the basic helix-loop-helix transcription factor, Nescient Helix-Loop-Helix 2 (Nhlh2), display adult-onset obesity with significant increases in their fat depots, abnormal responses to cold exposure, and reduced spontaneous physical activity levels. These phenotypes, accompanied by the hypothalamic expression of Nhlh2, make the Nhlh2 knockout (N2KO) mouse a useful model to study the role of central nervous system (CNS) control on peripheral tissue such as adipose tissue.


METHODS
Differences in body temperature and serum analysis of leptin were performed in fasted and ad lib fed wild-type (WT) and N2KO mice. Histological analysis of white (WAT) and brown adipose tissue (BAT) was performed. Gene and protein level expression of inflammatory and metabolic markers were compared between the two genotypes.


RESULTS
We report significant differences in serum leptin levels and body temperature in N2KO mice compared with WT mice exposed to a 24-hour fast, suggestive of a defect in both white (WAT) and brown adipose tissue (BAT) function. As compared to WT mice, N2KO mice showed increased serum IL-6 protein and WAT IL-6 mRNA levels. This was accompanied by slight elevations of mRNA for several macrophage markers, including expression of macrophage specific protein F4/80 in adipose, suggestive of macrophage infiltration of WAT in the mutant animals. The mRNAs for beta3-adrenergic receptors (beta3-AR), beta2-AR and uncoupling proteins were significantly reduced in WAT and BAT from N2KO mice compared with WT mice.


CONCLUSIONS
These studies implicate Nhlh2 in the central control of WAT and BAT function, with lack of Nhlh2 leading to adipose inflammation and altered gene expression, impaired leptin response to fasting, all suggestive of a deficient torpor response in mutant animals.
Wankhade
Umesh D
UD
Department of Human Nutrition, Foods and Exercise, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States of America.
Vella
Kristen R
KR
Fox
Dana L
DL
Good
Deborah J
DJ
D052437:Adipocytes, Brown / Q000166:cytology / Q000378:metabolism; D052438:Adipocytes, White / Q000166:cytology / Q000378:metabolism; D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000172:deficiency* / Q000235:genetics*; D015415:Biomarkers / Q000378:metabolism; D001831:Body Temperature; D004734:Energy Metabolism; D005215:Fasting; D017353:Gene Deletion; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D055786:Gene Knockout Techniques; D007249:Inflammation / Q000235:genetics; D020738:Leptin / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D008297:Male; D051379:Mice; D011943:Receptors, Adrenergic, beta / Q000235:genetics / Q000378:metabolism*
D000943:Antigens, Differentiation; D051792:Basic Helix-Loop-Helix Proteins; D015415:Biomarkers; D020738:Leptin; D011943:Receptors, Adrenergic, beta; C484104:Nhlh2 protein, mouse; C036763:monocyte-macrophage differentiation antigen
Am J Physiol. 1999 Jun;276(6):R1569-78
10362733
Mol Pharmacol. 1993 Aug;44(2):264-70
8102781
Endocrinology. 1996 Sep;137(9):4054-7
8756584
Nature. 1978 Aug 31;274(5674):900-2
683329
Am J Physiol. 1998 Nov;275(5):R1399-411
9791054
Am J Physiol. 1997 Feb;272(2 Pt 2):R656-61
9124491
J Pharmacol Exp Ther. 1966 Dec;154(3):493-8
5928249
J Clin Endocrinol Metab. 1998 May;83(5):1407-13
9589630
Am J Physiol Endocrinol Metab. 2007 Aug;293(2):E444-52
17473055
Nat Genet. 1997 Apr;15(4):397-401
9090387
N Engl J Med. 2009 Apr 9;360(15):1509-17
19357406
J Clin Invest. 1996 Jun 15;97(12):2898-904
8675704
Am J Physiol. 1967 Jan;212(1):207-12
6016006
Diabetes. 2009 Jul;58(7):1526-31
19401428
Physiol Behav. 2007 Jul 24;91(4):343-51
17521684
Science. 1989 Sep 8;245(4922):1118-21
2570461
Endocrinology. 2007 Nov;148(11):5339-47
17702843
Science. 2002 Aug 2;297(5582):843-5
12161655
Am J Physiol. 1998 Nov;275(5):R1488-93
9791065
PLoS One. 2008;3(12):e4038
19107190
Am J Physiol. 1995 Mar;268(3 Pt 2):R744-51
7900918
Endokrynol Pol. 2010 Mar-Apr;61(2):160-8
20464701
Nat Med. 1998 Oct;4(10):1152-6
9771748
Am J Physiol Regul Integr Comp Physiol. 2008 Aug;295(2):R417-28
18550869
J Auton Nerv Syst. 1996 Sep 12;60(3):206-8
8912272
FEBS Lett. 1995 Oct 9;373(2):131-4
7589451
Mol Endocrinol. 2004 Sep;18(9):2123-31
15243132
Mol Endocrinol. 2008 Jun;22(6):1438-48
18356286
J Neurosci. 2006 Jan 4;26(1):241-5
16399693
Mech Ageing Dev. 2003 May;124(5):663-78
12735906
Am J Physiol. 1998 Jul;275(1):R291-9
9688991
J Biol Chem. 1995 Dec 8;270(49):29483-92
7493988
Acta Physiol Scand. 2003 Mar;177(3):351-7
12609006
Endocrinology. 2004 Apr;145(4):1503-13
14701669
J Neuroendocrinol. 2007 Jul;19(7):499-510
17532796
Nature. 1994 Dec 1;372(6505):425-32
7984236
EMBO J. 1991 Dec;10(12):3721-7
1718744
Am J Physiol. 1991 Jan;260(1 Pt 2):R47-51
1992827
Endocrinology. 2007 Apr;148(4):1550-60
17194736
PLoS One. 2009;4(5):e5516
19436734
Cell. 2004 Jan 23;116(2):337-50
14744442
Mol Pharmacol. 1991 Dec;40(6):895-9
1684635
Biochem Biophys Res Commun. 1996 Jun 25;223(3):660-5
8687452
J Biol Chem. 1991 Dec 15;266(35):24053-8
1721063
Physiol Behav. 2002 Nov;77(2-3):387-402
12419415
FEBS Lett. 1995 Jul 24;368(3):488-90
7635205
Obesity (Silver Spring). 2010 Apr;18(4):682-9
19851310
J Clin Invest. 2007 Nov;117(11):3475-88
17885689
Exerc Sport Sci Rev. 2008 Oct;36(4):187-92
18815487