GREM2 Human

What is GREM2 and what is its primary function in human physiology?

GREM2, previously named PRDC (Protein Related to DAN and Cerberus), is a secreted protein belonging to the differential screening-selected gene aberrative in the neuroblastoma (DAN) family. It functions primarily as an extracellular BMP antagonist, binding to certain bone morphogenetic proteins (BMPs) with high affinity and inhibiting their biological activities. GREM2 plays crucial roles in regulating osteogenesis and adipogenesis, with increasing evidence supporting its involvement in metabolic homeostasis . This secreted protein can be detected in human circulation using ELISA methodology, suggesting systemic effects beyond local tissue activity .

How is GREM2 related to the BMP signaling pathway?

GREM2 functions as a potent antagonist of BMP signaling by directly binding to BMP ligands, particularly BMP4 and BMP7, preventing them from interacting with their receptors. Research demonstrates that GREM2 attenuates the browning program of visceral preadipocytes partially by antagonizing the BMP4/7-SMAD1/5/8 signaling pathway . The antagonistic effect requires BMPR2 receptor participation, as genetic deletion of Bmpr2 in Pdgfrα+ preadipocytes abolished GREM2's inhibitory effects . Within the TGF-β/BMP signaling network, decreased activity is considered a contributing factor to fat accumulation and obesity development, with BMP4 mediating the browning of white adipose tissues to improve glucose and energy homeostasis, while BMP7 acts as a key regulator of classical brown adipose tissue development .

What are the main tissues where GREM2 is expressed in humans?

While human tissue-specific expression data is still being elucidated, animal model studies provide important insights. In mice, Grem2 is highly expressed in visceral fat and liver tissues . The significant positive correlation between circulating GREM2 levels and visceral fat volume in humans suggests that visceral adipose tissue may be a major source of this protein. Surgical removal of visceral fat in animal models has been shown to lower circulating Grem2 levels, further supporting this relationship . The expression pattern appears to be responsive to physiological stimuli, as Grem2 expression changes in response to external cues like cold exposure and fasting-refeeding cycles .

How is GREM2 associated with human central obesity?

Multiple independent cohort studies have established a significant association between circulating GREM2 levels and central obesity. Researchers have detected elevated GREM2 levels in severely obese subjects and validated this finding in a large-scale community population involving 10,327 subjects . Notably, serum GREM2 levels positively correlate with visceral fat volume as quantified by sophisticated 3D reconstruction methods . This association appears particularly pronounced in normal-weight subjects with central obesity, suggesting GREM2 might be especially relevant to the "metabolically unhealthy normal weight" phenotype . The relationship between GREM2 and visceral adiposity appears bidirectional, as experimentally increasing GREM2 levels reduces browning capacity of adipose tissue, while deletion enhances browning and reduces visceral fat content .

What methodologies are used to measure circulating GREM2 levels in clinical studies?

Current research primarily utilizes enzyme-linked immunosorbent assay (ELISA) methodology to quantify circulating GREM2 levels. Specifically, studies have employed a commercial Grem2 ELISA kit (dy2069, R&D) according to the manufacturer's protocol . For validation of the ELISA approach, both mouse and human recombinant GREM2 proteins (commercially available from R&D) have been used as standards . When conducting clinical investigations, researchers should consider using validated assays with appropriate controls, as standardization across studies remains important for comparative analyses.

How does GREM2 influence visceral fat accumulation?

GREM2 appears to promote visceral fat accumulation through multiple mechanisms. Most notably, it inhibits the browning program of visceral preadipocytes, which normally enhances energy expenditure . Experimental evidence shows that Grem2-overexpressed mice exhibited reduced browning ability of visceral fat, whereas Grem2 ablation enhanced browning capacity and reduced visceral fat content . At the molecular level, GREM2 achieves this by antagonizing BMP4/7-SMAD1/5/8 signaling, which normally promotes adipocyte browning . The inhibition occurs through BMPR2-dependent mechanisms, as genetic deletion of Bmpr2 in Pdgfrα+ preadipocytes abolished GREM2's antagonistic effects . This functional relationship suggests that targeting the GREM2-BMP axis could potentially modulate visceral adiposity.

What are the most effective animal models for studying GREM2 function?

Several complementary mouse models have proven valuable for investigating GREM2 biology:

These models can be subjected to metabolic challenges (cold exposure, fasting-refeeding cycles) and phenotypic analyses (metabolic cage assessment, glucose tolerance testing) . For comprehensive investigation, researchers should consider combining genetic models with environmental interventions and detailed tissue-specific analyses.

How can researchers effectively isolate and purify recombinant GREM2 protein for experimental studies?

A detailed purification protocol for recombinant mouse Grem2 has been established:

• Express Pet21b-mGrem2/BL21 (DE3) in LB medium with ampicillin (100 μM) for 3.5 hours

• Collect bacteria by centrifugation (6000 × g, 10 min, 4°C)

• Resuspend in lysate buffer and apply ultrasonic crushing

• Wash inclusion bodies with ultrasound treatment and dissolve in appropriate buffer

• Apply sequential chromatography:

  • Superdex 200 molecular sieve chromatography

  • SP cation exchange chromatography

  • Renaturation

  • Mono S cation exchange chromatography

  • Superdex 75 molecular sieve to remove polymers

• Concentrate purified mGREM2 to 1.6 mg/mL using 10-KD ultrafiltration concentration tube

• Store at -80°C for experimental use

Alternatively, commercially available mouse and human recombinant GREM2 proteins can be purchased from established suppliers like R&D for standardized experiments .

What are the key considerations when designing experiments to study GREM2-BMP interactions?

When investigating GREM2-BMP interactions, consider these methodological approaches:

• Co-immunoprecipitation studies using tagged proteins:

  • Expression constructs encoding Myc-tagged human BMP4 or BMP7

  • Flag-tagged mouse Grem2 cDNAs in pCMV-Entry expression vector

  • Transfection into HEK293T cells using Lipofectamine 2000

• Functional antagonism experiments:

  • Treatment of preadipocytes with recombinant GREM2 before or during differentiation

  • Co-treatment with recombinant BMP4 or BMP7 to assess competition

  • Analysis of downstream SMAD1/5/8 phosphorylation

• Genetic validation approaches:

  • Using receptor knockout models (e.g., Bmpr2 floxp/floxp; Pdgfrα-cre)

  • Comparing GREM2 effects in wild-type versus receptor-deficient cells

These experimental designs should include appropriate controls and concentration-response relationships to fully characterize the interactions.

How does GREM2 mechanistically antagonize BMP4/7-SMAD1/5/8 signaling in adipocytes?

GREM2 inhibits BMP4/7-SMAD1/5/8 signaling through direct extracellular antagonism of BMP ligands. As a secreted protein, GREM2 binds with high affinity to BMP4 and BMP7, preventing their interaction with cell surface receptors, particularly BMPR2 . This inhibition blocks the activation of the canonical BMP signaling cascade that would otherwise lead to SMAD1/5/8 phosphorylation and nuclear translocation . The requirement for BMPR2 in mediating GREM2's effects was demonstrated by genetic deletion experiments, where Bmpr2 knockout in Pdgfrα+ preadipocytes abolished GREM2's antagonistic effects . This mechanism is particularly relevant in visceral preadipocytes, where BMP signaling normally promotes the browning program that enhances energy expenditure and improves metabolic homeostasis .

What is the relationship between GREM2 and the browning program of adipose tissue?

GREM2 functions as a negative regulator of adipose tissue browning through several interconnected mechanisms:

• GREM2 antagonizes BMP4/7 signaling, which normally promotes browning of white adipocytes

• Grem2-overexpressing mice exhibit reduced browning ability of visceral fat

• Grem2 ablation enhances browning capacity of visceral fat and reduces visceral fat content

• The inhibitory effect occurs partially through the BMP4/7-BMPR2-SMAD1/5/8 signaling pathway

• Visceral fat of genetically obese (ob/ob) mice secretes more Grem2, potentially contributing to the reduced browning capacity characteristic of obesity

These findings establish GREM2 as a critical regulator of adipose tissue plasticity and energy expenditure, with implications for metabolic health and obesity intervention strategies.

How does GREM2 expression change in response to environmental stimuli?

GREM2 expression demonstrates dynamic responsiveness to various physiological challenges. In mouse models, Grem2 expression changes in response to external cues like cold exposure and fasting-refeeding cycles . Cold room stress (6°C for 10 days) has been used experimentally to assess how thermal challenges affect GREM2 levels and function . This adaptive regulation suggests GREM2 may participate in physiological responses to environmental stressors and energy balance fluctuations. Additionally, pathological conditions like obesity alter GREM2 expression patterns, with visceral fat of ob/ob mice secreting significantly more Grem2 compared to wild-type controls . Understanding these regulatory mechanisms could provide insights into GREM2's role in metabolic adaptation and identify potential intervention points.

How reliable is GREM2 as a biomarker for visceral adiposity assessment?

GREM2 shows promising characteristics as a biomarker for visceral adiposity:

• Serum GREM2 levels positively correlate with visceral fat volume quantified by 3D CT reconstruction methods

• Elevated GREM2 levels have been validated in multiple independent cohorts, including:

  • A severe obesity cohort (Genetics of Obesity in Chinese Youngs study)

  • A large community population (10,327 subjects from Shanghai)

  • A deep phenotyping study with detailed visceral fat measurement (MedSV study)

• GREM2 levels are notably higher in normal-weight subjects with central obesity, potentially identifying "metabolically unhealthy" phenotypes

While these findings suggest GREM2 could serve as a circulating biomarker for visceral adiposity, further studies comparing its diagnostic performance against established biomarkers and imaging techniques are needed to fully establish its clinical utility .

What cohort studies have investigated GREM2 in human populations?

Three independent cohorts have contributed valuable data on GREM2's clinical relevance:

These diverse cohorts provide complementary evidence supporting GREM2's association with human central obesity across different population contexts . The consistent findings across these varied cohorts strengthen the reliability of GREM2 as a biomarker for visceral adiposity.

What is the potential of targeting GREM2 for therapeutic intervention in obesity-related disorders?

The experimental evidence suggests several promising therapeutic approaches:

• Inhibiting GREM2 could potentially enhance browning of white adipose tissue, particularly visceral depots

• GREM2 blockade might reduce visceral fat accumulation, as demonstrated in knockout mouse models

• Targeting the GREM2-BMP4/7-BMPR2-SMAD1/5/8 signaling pathway could provide multiple intervention points

• As a secreted protein detectable in circulation, GREM2 represents an accessible target for biological therapeutics

Research explicitly highlights "the possibility of targeting GREM2 and its downstream pathways for clinical intervention of human visceral adiposity" . This potential therapeutic approach is particularly relevant given the strong association between visceral adiposity and metabolic disorders like type 2 diabetes and cardiovascular diseases . Further preclinical and translational studies are needed to validate GREM2 as a therapeutic target.