How Cell Metabolism Controls Appetite at the Source—Providing New Approaches to Diabetes and Obesity Treatment

Author | Asprosin is a protein hormone produced in mammalian white adipose tissue
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An article published in Cell in 2016 revealed the discovery journey of Asprosin [1]: Neonatal Progeroid Syndrome (NPS) is a rare genetic disorder characterized by extreme wasting and skin The appearance of aging due to the loss of the underlying fat layer
.

When medical geneticist Dr.
Atul R.
Chopra and his team were studying NPS individuals, they found that their FBN1 (fibrillin 1, fibrillin) gene was mutated, and pFBN1 (profibrillin, prefibrillin) was truncated during the coding process.
A segment was removed, resulting in the deletion of the C-terminus of pFBN1, and the deleted segment was named Asprosin (encoded by the two exons of the C-terminus of FBN1)
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Studies have shown that in the liver, Asprosin activates the rapid release of glucose through a cyclic adenosine monophosphate (cAMP)-dependent pathway
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Due to the lack of Asprosin in NPS patients, the release of glucose into the blood by the liver cannot be completed, so the body shows lower levels of blood sugar and insulin [1]; in the brain, Asprosin can cross the blood-brain barrier and stimulate the hypothalamus.
The hunger center Control appetite and weight
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There are two types of neurons in appetite control: AgRP neurons that stimulate appetite, and POMC neurons that suppress appetite
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Asprosin acts on both types of neurons: it activates the appetite-stimulating AgRP neurons and disables the appetite-suppressing POMC neurons [2]
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The discovery and research of asprosin has opened a whole new door for the treatment of diabetes and obesity, but also raised another question of concern: what is the receptor of asprosin? In 2019, a study reported the liver asprosin receptor OR4M1 (Olfr734 is a mouse homologous gene) [3]
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After knocking out Olfr734 in mice, the mice showed obvious liver function defects, consistent with the related phenotype caused by Asprosin deletion, while the mice's appetite and body weight were not significantly affected, suggesting that there may be other Receptors regulate the function of Asprosin in the nervous system
.

Recently, the team of Atul R.
Chopra from the Harrington Institute for Discovery in the United States published an article titled Protein tyrosine phosphatase receptor d serves as the orexigenic asprosin receptor in the journal Cell Metabolism, identifying the receptor that regulates the orexigenic activity of Asprosin— - protein tyrosine phosphatase receptor d (Ptprd)
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Loss of Ptprd resulted in loss of appetite, wasting in mice, and no response to both endogenous and exogenous asprosin
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Interestingly, the soluble ligand-binding domain of Ptprd (Ptprd-LBD) can treat obese mice by sequestering asprosin in plasma to suppress appetite and blood sugar
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To identify the orexigenic receptors for Asprosin, the authors carried out immunoprecipitation experiments by co-incubating recombinant Asprosin with mouse brain tissue lysates, followed by protein profiling to detect Asprosin-interacting proteins
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Among the 58 interacting proteins identified in three independent experiments, the authors found only one membrane-bound receptor, Ptprd
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Ptprd is a single-pass transmembrane receptor encoded by the Ptprd gene, which belongs to the leukocyte common antigen-related protein (LAR)/typer-IIa receptor protein tyrosine phosphatase [4], and is highly expressed in AgRP neurons [5]
.

Ptprd gene variants are associated with a variety of neurological diseases, such as addiction, Alzheimer's disease (AD), obsessive-compulsive disorder, etc.
, but the precise function of Ptprd in the nervous system remains unknown
.

Therefore, the authors explored the correlation between Ptprd and Asprosin orexin signaling pathway
.

First, it was confirmed by three different methods that Ptprd is indeed highly expressed in AgRP neurons, and then it was found by immunoprecipitation experiments that Asprosin mainly binds to the extracellular domain of PTPRD, and the affinity of the two is usually expressed in hormone-receptor interactions.
within the range
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The authors found that Ptprd-null (Ptprd-/-) mice were abnormally lean, with reduced appetite, significantly reduced subcutaneous and intra-abdominal fat masses, and significantly reduced energy expenditure and food intake, phenotypes that correlate with Asprosin dysfunction-induced diet Very similar to weight loss
.

What is the phenotype of a single Ptprd allele knockout? The authors tracked the body weight of Ptprd+/+ and Ptprd+/- (single Ptprd allele knockout) mice on a normal chow (NC) diet, and 10-week-old Ptprd+/- females weighed slightly less than wild-type, and the body weight of The slight reduction was accompanied by a significant reduction in food intake, with no significant change in energy expenditure
.

However, after feeding the mice a high-fat diet (HFD) for 10 weeks, the Ptprd+/- group ate nearly 40% less food and weighed nearly 4 g less than the WT female mice in the Ptprd+/- group, indicating that a single Ptprd Deletion of the allele protects female mice from HFD-induced obesity
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Interestingly, the metabolic consequences of single Ptprd allelic deletion were sex-related, with no significant differences in body weight, food intake, or energy expenditure between Ptprd+/- and Ptprd+/+ male mice in either NC or HFD
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The authors also constructed mice that specifically knocked out Ptprd in AgRP neurons
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Under NC, there were no significant differences in body weight, food intake or energy expenditure between AgRP-Cre+;Ptprdf/f and Ptprdf/f controls
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This is inconsistent with decreased body weight, appetite, and energy expenditure upon systemic Ptprd loss, suggesting that AgRP neuron-specific loss of Ptprd in NCs may be compensated by intact Asproin-Ptprd signaling in other cell types
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However, AgRP neuron-specific knockout of Ptprd protected female mice from diet-induced obesity under HFD
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The authors then examined the effect of Ptprd deletion on Asprosin-mediated activation of AgRP neurons
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Following knockout of Ptprd in AgRP neurons unilaterally in the adult mouse brain, AgRP neurons no longer responded to Asprosin, suggesting that Ptprd is absolutely necessary for asprosin-mediated activation of AgRP neurons
.

Further, the authors injected adenovirus carrying human FBN1 (containing a natural signal peptide) or human cleaved asprosin (containing an IL2 signal peptide to promote secretion) into the tail vein of WT and Ptprd-/- mice, and then detected Asprosin-GOF (gain -of-function) induced metabolic phenotype
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Following injection of Ad5-FBN1 or Ad5-Asprosin, WT mice exhibited overeating, higher blood glucose, and lower glucose tolerance, consistent with previous results, while Ptprd-/- mice exhibited no appetite suppression Any effect, its changes in blood glucose and glucose tolerance were essentially the same as in WT mice, suggesting that Ptprd is necessary for the orexigenic activity of Asprosin
.

Stat3 Phosphorylation and transcriptional activity can be used as detection indicators of Asprosin-mediated Ptprd signaling pathway
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The authors found that p-Stat3 levels were significantly reduced in the hypothalamus of Ad5-FBN1-injected mice after treatment of WT mice with Asprosin; conversely, p-Stat3 was significantly increased in the hypothalamus of Ptprd-/- mice
.

Knockdown of PTPRD in HEK293T cells by siRNA significantly increased p-Stat3 levels and Stat3 transcriptional activity
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Transfection of human cleaved asprosin into cells to enhance Asprosin levels in the medium resulted in a dose-dependent decrease in Stat3 transcriptional activity, and additional reintroduction of anti-Asprosin mAbs significantly enhanced Stat3 activity, indicating that extracellular Asprosin neutralization can Completely blocks Asprosin signaling
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More importantly, after Ptprd knockdown, cells did not respond to Asprosin-mediated inhibition of p-Stat3 levels and Stat3 transcriptional activity
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The authors have previously demonstrated the use of asprosin-neutralizing monoclonal antibodies as a treatment for metabolic syndrome in mice [7]
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Similar to the anti-asprosin mAb approach, the authors introduced the soluble ligand-binding domain of Ptprd (PTPRD-LBD) into the circulation of DIO mice, a mouse model of HFD-induced obesity, and subsequently tested whether Asprosin could be captured for sequestration, metabolic synthesis whether symptoms can be improved
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When recombinant Asprosin was incubated with PTPRD-LBD, the level of free Asprosin was significantly reduced by ELISA, indicating that Asprosin could be captured and sequestered by PTPRD-LBD
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The authors found that DIO mice with elevated plasma PTPRD-LBD had significantly lower levels of free asprosin in plasma, suggesting that plasma Asprosin could be successfully captured by PTPRD-LBD
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Daily food intake, body weight, blood glucose levels, and glucose tolerance were significantly reduced in DIO mice after introduction of PTPRD-LBD into plasma
.

These results are almost identical to the effects of Asprosin mAb in DIO mice
.

Furthermore, the authors also found that recombinant PTPRD-LBD was able to completely block Asproin-mediated activation of AgRP neurons in ex vivo hypothalamic slice electrophysiology
.

Overall, the researchers identified the orexin receptor for Asprosin, Ptprd
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In hypothalamic AgRP neurons, Asprosin acts as a high-affinity Ptprd ligand, regulating the activity of this circuit in a cell-autonomous manner
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Knockout of Ptprd resulted in a strong appetite loss, wasting, and an inability to respond to the orexogenic effects of Asprosin
.

Specific knockout of Ptprd in AgRP neurons elicits resistance to diet-induced obesity
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Introduction of a soluble Ptprd ligand-binding domain (Ptprd-LBD) into the mouse circulation suppresses appetite and blood glucose levels by trapping asprosin in plasma
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The research provides a new approach to the treatment of diabetes and obesity
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Original link: https://doi.
org/10.
1016/j.
cmet.
2022.
02.
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