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Presence of thyrotropin receptor in infant adipocytes
1Department of Pediatrics, Huddinge University Hospital, Karolinska Institute, Sweden.
Insights
Thyroid-stimulating hormone (TSH) promotes fat breakdown in infants, acting directly on fat cells. This study confirms TSH receptor presence in adipose tissue, highlighting TSH
Area of Science:
- Endocrinology
- Metabolic Adaptation
- Adipose Tissue Biology
Background:
- Infants exhibit significantly elevated Thyroid-Stimulating Hormone (TSH) levels post-birth, crucial for metabolic adaptation.
- Previous studies indicated bovine TSH (bTSH) induces lipolysis in infant adipocytes, with a blunted response to catecholamines.
Purpose of the Study:
- To investigate the lipolytic effect of human recombinant TSH (hTSH) on isolated human infant adipocytes.
- To determine the presence and expression of the TSH receptor (TSHR) in human adipose tissue.
Main Methods:
- Incubation of isolated infant adipocytes with hTSH and isoprenaline.
- Blocking lipolytic effects using TSH receptor (TSHR) antibodies.
- Detection of TSHR RNA via reverse transcriptase-PCR and Northern blot hybridization in infant and adult adipose tissue.
Main Results:
- hTSH induced a significant lipolytic response in infant adipocytes, comparable to isoprenaline.
- The lipolytic effect of hTSH was fully inhibited by TSHR antibodies.
- TSHR RNA was detected in infant and adult adipocytes and adipose tissue, with higher expression in infant tissue.
Conclusions:
- TSH directly stimulates lipolysis in human infant adipocytes via the TSH receptor.
- The presence and higher expression of TSHR in infant adipose tissue suggest a key role in neonatal metabolic adaptation.
- TSH actively participates in the metabolic adjustments required after birth.
Abstract:
In healthy infants, the levels of TSH are known to peak at 50-100 times adult values during the first days of life. In studies of isolated human infant adipocytes, we have earlier shown that bovine TSH (bTSH) has a strong lipolytic effect, accompanied by a blunted response of adipocytes to catecholamines. In this study, we used human recombinant TSH (hTSH), and incubation of adipocytes with hTSH induced a lipolytic response similar to that obtained with the beta-adrenergic receptor agonist isoprenaline in adipocytes isolated from three infants. The lipolytic effect of hTSH was completely blocked by inhibitory TSH receptor (TSHR) antibodies. The TSHR mediates the effects of TSH in the thyroid, and it has been detected in some extrathyroid tissues, but not in isolated human adipocytes or childhood adipose tissue. In this study, we found TSHR RNA in infant and adult adipose tissues and isolated adipocytes with reverse transcriptase-PCR. The sequence of the amplified PCR product agreed with the published sequence. Northern blot hybridization on RNA prepared from infant adipose tissue showed a transcript of the expected size, and the expression of TSHR seemed higher in infant than in adult adipose tissue. In conclusion, this study indicates that TSH plays an active role in the metabolic adaptation after birth.