Daily Endocrinology Research Analysis
Three papers stood out today in endocrinology and metabolism: a mechanistic study identifies geranylgeranyl pyrophosphate–driven prenylation of Perilipin4 as a driver of metabolically unhealthy obesity and hepatic steatosis, a large real‑world comparative effectiveness analysis shows SGLT2 inhibitors outperform sulfonylureas and DPP-4 inhibitors as second-line therapy for type 2 diabetes, and a neuroscience study pinpoints hypothalamic Gpr45 signaling as a regulator of appetite and adiposity.
Summary
Three papers stood out today in endocrinology and metabolism: a mechanistic study identifies geranylgeranyl pyrophosphate–driven prenylation of Perilipin4 as a driver of metabolically unhealthy obesity and hepatic steatosis, a large real‑world comparative effectiveness analysis shows SGLT2 inhibitors outperform sulfonylureas and DPP-4 inhibitors as second-line therapy for type 2 diabetes, and a neuroscience study pinpoints hypothalamic Gpr45 signaling as a regulator of appetite and adiposity.
Research Themes
- Mechanistic drivers of metabolically unhealthy obesity and fatty liver
- Comparative effectiveness of second-line therapies in type 2 diabetes
- Hypothalamic GPCR targets for appetite and weight regulation
Selected Articles
1. Geranylgeranyl Pyrophosphate Promotes Hepatic Lipid Accumulation by Prenylation of Perilipin4.
In human and mouse livers, GGPP and its synthase GGPPS are elevated in metabolically unhealthy obesity. Hepatocyte-specific Ggpps deletion reduces hepatic lipid accumulation and improves insulin sensitivity by preventing GGPP-driven prenylation of Perilipin4, which otherwise promotes large lipid droplet formation. Pharmacologic GGPPS inhibition (DGBP) attenuated MUO phenotypes, nominating GGPP signaling as a druggable axis.
Impact: This study uncovers a previously unrecognized lipid droplet biogenesis mechanism that mechanistically links MUO to hepatic steatosis and insulin resistance and demonstrates pharmacologic tractability.
Clinical Implications: Although preclinical, targeting GGPPS/GGPP–Perilipin4 prenylation could yield therapies for MUO-associated fatty liver and insulin resistance and supports stratifying obese patients by metabolic health.
Key Findings
- GGPP and GGPPS are elevated in livers from MUO patients and mice compared with MHO counterparts.
- Hepatocyte-specific Ggpps knockout reduced hepatic lipid accumulation, decreased lipid droplet size, and improved insulin sensitivity.
- GGPP promotes Perilipin4 prenylation, enhancing large lipid droplet formation and exacerbating steatosis and insulin resistance.
- Pharmacologic GGPPS inhibition with DGBP attenuated MUO phenotypes in experimental models.
Methodological Strengths
- Integrated human and murine metabolomics with genetic (hepatocyte-specific knockout) and pharmacologic (GGPPS inhibition) interventions.
- Mechanistic dissection of lipid droplet biology via Perilipin4 prenylation provides causal linkage.
Limitations
- Predominantly preclinical evidence; human causal inferences are limited.
- Potential off-target effects and translational safety of GGPPS inhibition (DGBP) require further evaluation.
Future Directions: Validate GGPP–Perilipin4 prenylation in human cohorts with longitudinal outcomes, delineate safety/PK of GGPPS inhibitors, and assess efficacy in NASH/T2D clinical trials with biomarker endpoints.
BACKGROUND & AIMS: Metabolically unhealthy obesity (MUO) is characterized by hepatic steatosis and type 2 diabetes (T2D), distinct from metabolically healthy obesity (MHO). This study aimed to identify the key regulator responsible for MUO. METHODS: Metabolomics analysis was conducted to compare hepatic metabolite profiles between individuals with MUO and MHO and mice. Geranylgeranyl pyrophosphate (GGPP) levels and its synthetase geranylgeranyl diphosphate synthase (GGPPS) were quantified in human and murine liver tissues. Hepatocyte-specific Ggpps knockout mice (LKO) were generated to evaluate the effects of GGPP deficiency on MUO-associated phenotypes. Mechanistic studies focused on GGPP-dependent prenylation of the lipid droplet-associated protein Perilipin4 and its role in lipid droplet formation. The therapeutic potential of DGBP, a GGPPS inhibitor, was also tested in MUO models. RESULTS: GGPP and GGPPS protein expression were significantly elevated in the livers of patients with MUO and mice compared with counterparts with MHO. Hepatocyte-specific Ggpps knockout (LKO) mice exhibited reduced hepatic lipid accumulation, smaller lipid droplets, and improved insulin sensitivity, demonstrating GGPP's critical role in MUO pathogenesis. Mechanistically, GGPP promoted Perilipin4 prenylation, which enhanced large lipid droplet formation and exacerbated hepatic steatosis and insulin resistance. Pharmacologic inhibition of GGPPS with DGBP effectively attenuated MUO phenotypes, highlighting its therapeutic potential. CONCLUSIONS: Hepatic GGPP drives MUO progression by facilitating Perilipin4 prenylation, thereby promoting pathological lipid droplet expansion and insulin resistance. Targeting GGPP with inhibitors of GGPPS like DGBP represents a promising strategy for treating MUO. These findings provide novel insights into the metabolic heterogeneity of obesity and potential therapeutic interventions for MUO-related complications.
2. Comparative effectiveness of alternative second-line oral glucose-lowering therapies for type 2 diabetes: a precision medicine approach applied to routine data.
Using CPRD-linked routine care data (n=41,790) and combining target trial emulation with instrumental variable analysis, second-line SGLT2 inhibitors achieved greater HbA1c reduction than sulfonylureas or DPP-4 inhibitors when added after metformin. This provides real-world, methodologically rigorous support for choosing SGLT2i as preferred second-line therapy.
Impact: Large-scale causal inference applied to routine data directly informs drug choice at the point of care and aligns with precision medicine recommendations.
Clinical Implications: Clinicians should consider SGLT2 inhibitors as the preferred second-line oral agents after metformin for HbA1c lowering, alongside established cardio-renal benefits and patient characteristics.
Key Findings
- Analyzed 41,790 patients initiating second-line therapy after metformin in England (2015–2021) using CPRD linked data.
- Applied target trial emulation and instrumental variable analysis to mitigate confounding in comparative effectiveness.
- Second-line SGLT2 inhibitors produced greater HbA1c reduction than sulfonylureas or DPP-4 inhibitors.
Methodological Strengths
- Very large real-world cohort with primary–secondary care linkage (CPRD).
- Use of target trial emulation combined with instrumental variable analysis to reduce bias.
Limitations
- Observational design leaves residual confounding; numeric effect sizes are not detailed in the abstract.
- Outcomes focused on HbA1c; safety and patient-reported outcomes were not described in the abstract.
Future Directions: Quantify heterogeneity of treatment effects across patient subgroups, integrate safety/cost endpoints, and validate with pragmatic trials where feasible.
AIMS/HYPOTHESIS: National clinical guidelines recommend that second-line treatment for type 2 diabetes mellitus is chosen according to individuals' characteristics but there is limited evidence available to inform this choice. This paper's aim is to compare the effects on HbA METHODS: We accessed primary care-hospital linked data for 41,790 individuals from the Clinical Practice Research Datalink (CPRD) in England who initiated second-line treatment after metformin between 2015 and 2021. We combined target trial emulation with instrumental variable analysis to reduce the risk of confounding. The outcome was change in HbA RESULTS: The mean (95% CI) difference in HbA CONCLUSIONS/INTERPRETATION: Second-line treatment with SGLT2i is more effective than SU or DPP4i in reducing HbA
3. Uncovering the role of Gpr45 in obesity regulation.
Across multiple complementary mouse models, loss of Gpr45 increased body weight, food intake, and fat mass without affecting energy expenditure or core temperature. Deleting Gpr45 in Sim1+ or Vglut2+ (but not Vgat+) neurons, and specifically within PVH glutamatergic neurons, recapitulated obesity and hyperphagia, implicating PVH Gpr45 signaling as a key node for body weight regulation.
Impact: Identifies an orphan GPCR and a defined hypothalamic circuit element as a regulator of appetite and adiposity, opening a tractable GPCR target class for anti-obesity therapeutics.
Clinical Implications: While preclinical, agonists or positive modulators of Gpr45 acting in PVH glutamatergic neurons could represent a future anti-obesity strategy complementary to current incretin-based therapies.
Key Findings
- Global Gpr45 knockout mice show marked weight gain, hyperphagia, and increased fat mass without changes in energy expenditure or core temperature.
- Selective deletion in Sim1+ or Vglut2+ neurons, but not Vgat+ neurons, induces obesity and hyperphagia.
- PVH-targeted deletion of Gpr45 phenocopies metabolic changes, implicating PVH glutamatergic neurons as a major site of action.
Methodological Strengths
- Use of three complementary transgenic models (global KO, conditional floxed, CreERT2 knock-in) to triangulate function.
- Region- and cell-type–specific manipulations (PVH targeting; Vglut2/Sim1/Vgat cre-lines) strengthen causal circuit mapping.
Limitations
- Preclinical mouse data; human translational relevance and endogenous ligands for Gpr45 remain to be defined.
- Behavioral and metabolic phenotyping lacks pharmacologic rescue to demonstrate target tractability.
Future Directions: Identify endogenous/therapeutic ligands for Gpr45, map downstream signaling in PVH neurons, and evaluate translational relevance in primates and human genetics.
OBJECTIVES: G protein-coupled receptors (GPCRs) are the most druggable targets in biology due to their cell-type specificity, ligand binding, and cell surface accessibility. Underscoring this, agonists for GPCRs have recently revolutionized the treatment of diabetes and obesity. The rampant success of these compounds has invigorated interest in identifying additional GPCRs that modulate appetite and body weight homeostasis. One such potential therapeutic target is G-protein couped receptor 45 (Gpr45), an orphan GPCR expressed both centrally and peripherally. We aimed to explore the role of Gpr45 as well as neurons expressing Gpr45 in energy balance. METHODS: Three novel transgenic mouse models were engineered to investigate the functional contribution of Gpr45 to body weight and appetite regulation: 1) a global Gpr45 knockout, 2) a conditional floxed Gpr45 allele, and 3) a Gpr45-CreERT2 knock-in. Metabolic profiling was performed in global Gpr45 knockout animals including body weight, food intake, body mass, energy expenditure, and body temperature measurements. Animals harboring a conditional floxed Gpr45 allele were bred to mice expressing Cre-recombinase in excitatory neurons labeled via Vesicular glutamate transporter 2 (Vglut2), inhibitory cells expressing Vesicular GABA transporter (Vgat), or neurons marked by the transcription factor Single-minded 1 (Sim1) and monitored for body weight and food consumption. Additionally, floxed Gpr45 mice were bilaterally injected with AAV-Cre targeting the paraventricular nucleus of the hypothalamus (PVH) and body weight and food intake were evaluated. The Gpr45-CreERT2 knock-in model was used to express chronic and acute actuators to the PVH to assess the role of PVH RESULTS: Global Gpr45 disruption caused marked weight gain, increased food intake and fat mass, but no detectable alterations in core temperature or energy output. Selective deletion of Gpr45 from Sim1+ or excitatory Vglut2+ but not inhibitory Vgat+, neurons produced obesity and hyperphagia. Targeted deletion of Gpr45 from the PVH phenocopies these metabolic changes suggesting a major site of action of Gpr45 signaling is glutamatergic neurons residing in the PVH. Tetanus toxin light chain (TeNT) was used to permanently silence PVH CONCLUSIONS: Gpr45 is a putative therapeutic candidate that could be targeted to combat obesity and overeating.