Abstract
The mechanism by which the specific beta3-adrenoceptor agonist AJ-9677 relieves insulin resistance in vivo was investigated by studying its effects in the white and brown adipose tissues of the KK-Ay/Ta diabetic obese mouse model. AJ-9677 reduced the total weight of white adipose tissues by reducing the size of the adipocytes, an effect associated with the normalization of tumor necrosis factor-alpha (TNF-alpha) and leptin expression levels. The levels of uncoupling protein (UCP)-1 mRNA in brown adipose tissue were increased threefold. AJ-9677 caused a marked increase (20- to 80-fold) in the expression of UCP-1 in white adipose tissues. The levels of UCP-2 mRNA were increased in both the white and brown adipose tissues of diabetic obese mice, and AJ-9677 further upregulated UCP-2 mRNA levels in brown adipose tissue, but reduced its levels in white adipose tissue. UCP-3 mRNA levels were not essentially changed by AJ-9677. However, AJ-9677 significantly (two- to four-fold) upregulated the GLUT4 mRNA and protein levels in white and brown adipose tissues and the gastrocnemius. The generation of small adipocytes, presumably mediated by increased expression of UCP-1 in addition to increased lipolysis in response to AJ-9677, was associated with decreased TNF-alpha and free fatty acid production and may be the mechanism of amelioration of insulin resistance in KK-Ay/Ta diabetic obese mice.
Highlights
The mechanism by which the specific 3-adrenoceptor agonist AJ-9677 relieves insulin resistance in vivo was investigated by studying its effects in the white and brown adipose tissues of the KK-Ay/Ta diabetic obese mouse model
The effects of the 3-adrenoceptor on thermogenesis are believed to occur through activation and upregulation of uncoupling protein (UCP)-1, which is mainly expressed in brown adipose tissues
The expression levels of UCP-1, -2, and -3 mRNA in the gastrocnemius were very low compared with the adipose tissues, and they were not upregulated by AJ-9677 treatment (Fig. 5D)
Summary
White adipocytes were isolated from epididymal white adipose tissues of KK-Ay/Ta mice by collagenase type II (Sigma Chemical, St. Louis, MO) digestion according to the method described by Rodbell [25]. Measurements of TNF-␣ and leptin proteins secreted in isolated white adipose tissues (400–1,000 mg) were performed as described previously [26]. The method for determining the triglyceride and DNA contents in the epididymal and inguinal white adipose tissues was slightly modified from the method described by Okuno et al [23]. The internal standards (competitors) were prepared by PCR using template cDNA constructed with total RNA from epididymal white or interscapular brown adipose tissues and a specific set of oligonucleotides as primers (i.e., forward-short [S] and reverse) (Table 1).
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