Marta Inmaculada Sanz-Cuadrado

Obesity is a global health problem linked to the development of metabolic syndrome (MetS) and comorbidities such as metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH). These diseases are characterised by systemic inflammation, lipid accumulation and tissue damage, which contribute to liver fibrosis and dysfunction. Pleiotrophin (PTN), a cytokine known for its role in tissue regeneration and energy metabolism, has emerged as a potential regulator of liver homeostasis. Herein, we demonstrate that Ptn deletion protects against body weight gain, metainflammation and high-fat diet (HFD)-induced MASLD and MASH development. Furthermore, our work uncovers the molecular mechanisms by which PTN may promote lipid synthesis and hepatic extracellular matrix remodelling. Results highlight PTN as a critical modulator of liver metabolism and systemic inflammation in the context of obesity, identifying it as a promising therapeutic target for the treatment of MASLD, MASH and related metabolic disorders, and point to a sexual dimorphism in adaptive metabolic strategies, with females demonstrating a greater degree of protection against the liver-damaging effects of diet-induced obesity. HIGHLIGHTS: Females are more protected against the liver-damaging effects of the high-fat diet (HFD), suggesting a sexual dimorphism in adaptive metabolic strategies. PTN regulates lipid metabolism by promoting lipogenesis and lipid accumulation in liver cells through the activation of AKT and the inhibition of AMPKα; the absence of PTN reverses this process. Deletion of Ptn protects against high-fat diet (HFD)-induced weight gain, systemic inflammation, hepatic lipid accumulation, and the development of steatosis and liver fibrosis. PTN is a key modulator of metabolic, inflammatory and remodelling processes in the liver, and it is proposed as a promising therapeutic target for MASLD, MASH and other metabolic comorbidities. Graphical PTN liver signalling pathway.: acetyl-CoA carboxylase (ACC); 5’ adenosine monophosphate-activated protein kinase (AMPK); protein kinase B (AKT); aquaporin 9 (AQP9); diacylglycerides (DAG); diacylglycerol O-acyltransferase 2 (DGAT2); free fatty acids (FFA); hepatic stellate cell (HSC); insulin receptor (IR); pleiotrophin (PTN); triacylglycerides (TAG).

Pleiotrophin (PTN) is crucial for embryonic development and pancreas organogenesis as it regulates metainflammation, metabolic homeostasis, thermogenesis, and glucose tolerance. Pleiotrophin deletion is associated with a lipodystrophic phenotype in which adipose tissue plasticity is altered in late life. This study explored the impact of pleiotrophin deletion on pancreatic morphology and function in later life. We analyzed glucose tolerance and circulating parameters on female wild-type (Ptn^+/+) and knock-out (Ptn^−/−) mice. At 9 and 15 months, we conducted morphometric analyses of pancreatic islets and evaluated the levels of insulin, glucagon, somatostatin, glucose transporter 2 (GLUT2), vesicle-associated membrane protein 2 (VAMP2), and synaptosome-associated protein 25 (SNAP25) via immunofluorescence. The effect of PTN on glucose-stimulated insulin secretion (GSIS) was evaluated in INS1E cells and isolated islets. Ptn^−/− mice showed hyperinsulinemia, impaired glucose tolerance, and increased homeostatic model assessment for insulin resistance (HOMA-IR) with age. While Ptn^+/+ islets enlarge with age, in Ptn^−/− mice, the median size decreased, and insulin content increased. Vesicle transport and exocytosis proteins were significantly increased in 9-month-old Ptn^−/− islets. Islets from Ptn^−/− mice showed impaired GSIS and decreased cell membrane localization of GLUT2 whereas, PTN increased GSIS in INS1E cells. Ptn deletion accelerated age-related changes in the endocrine pancreas, affecting islet number and size, and altering VAMP2 and SNAP25 levels and GLUT2 localization leading to impaired GSIS and insulin accumulation in islets.

In the first trimester of pregnancy the human placenta grows rapidly, making it sensitive to changes in the intrauterine environment. To test whether exposure to an environment in utero often associated with obesity modifies placental proteome and function, we performed untargeted proteomics (LC-MS/MS) in placentas from 19 women (gestational age 35–48 days, i.e. 5+0–6+6 weeks). Maternal clinical traits (body mass index, leptin, glucose, C-peptide and insulin sensitivity) and gestational age were recorded. DNA replication and cell cycle pathways were enriched in the proteome of placentas of women with low maternal insulin sensitivity. Driving these pathways were the minichromosome maintenance (MCM) proteins MCM2, MCM3, MCM4, MCM5, MCM6 and MCM7 (MCM-complex). These proteins are part of the pre-replicative complex and participate in DNA damage repair. Indeed, MCM6 and γH2AX (DNA-damage marker) protein levels correlated in first trimester placental tissue (r = 0.514, P<0.01). MCM6 and γH2AX co-localized to nuclei of villous cytotrophoblast cells, the proliferative cell type of the placenta, suggesting increased DNA damage in this cell type. To mimic key features of the intrauterine obesogenic environment, a first trimester trophoblast cell line, i.e., ACH-3P, was exposed to high insulin (10 nM) or low oxygen tension (2.5% O2). There was a significant correlation between MCM6 and γH2AX protein levels, but these were independent of insulin or oxygen exposure. These findings show that chronic exposure in utero to reduced maternal insulin sensitivity during early pregnancy induces changes in the early first trimester placental proteome. Pathways related to DNA replication, cell cycle and DNA damage repair appear especially sensitive to such an in utero environment.