Kim Ravnskjaer

The vagus nerve connects the brain and pancreas and enhances postprandial endocrine secretion from the pancreas through cholinergic signaling, such as increasing insulin release immediately after food intake in the cephalic-phase insulin response (CPIR). Here, we investigated how obesity affects vagal regulation of pancreatic endocrine function using designer receptors exclusively activated by designer drugs (DREADDs) to manipulate vagal activity. As expected, the plasma concentration of insulin was increased by vagal activation in mice expressing the excitatory DREADD hM3Dq (M3 mice) and decreased by vagal inactivation in mice expressing inhibitory DREADD hM4Di (M4 mice). However, vagal activation in M3 mice with diet-induced obesity did not elicit an early increase in insulin and instead produced a delayed insulin decrease. Mathematical modeling showed that plasma insulin dynamics in these mice were best explained by a model incorporating both the insulin-increasing and insulin-decreasing effects of the vagus nerve. Furthermore, the insulin-decreasing effect was mediated by nitric oxide (NO)–dependent, noncholinergic signaling and was enhanced in obesity. In obese M3 mice, vagal deficiency of neuronal NO synthase (nNOS) abolished the insulin-decreasing effect and restored insulin release after vagal activation. Vagal nNOS deficiency also enhanced insulin release after voluntary feeding, consistent with the CPIR. These findings suggest that vagal NO action inhibits postprandial insulin release, particularly in obesity.

Eukaryotic genome replication is surveyed by the S-phase checkpoint, which coordinates sequential origin activation to prevent the exhaustion of poorly defined, rate-limiting replisome components ^1–3 . Here we show that excessive origin firing saturates chromatin-bound proliferating cell nuclear antigen (PCNA)—a sliding clamp for DNA polymerase processivity and Okazaki fragment processing ⁴ —thereby restricting further PCNA loading and lagging-strand synthesis when checkpoint control is lost. PCNA-associated factor 15 (PAF15) emerges as a dosage-sensitive regulator of this process ^5–9 . During unperturbed S phase, the entire soluble PAF15 pool binds to chromatin, leaving no reserve to stabilize PCNA under conditions of excessive origin activation. PAF15 binds to PCNA specifically on the lagging strand through a high-affinity PIP motif and occupies the DNA-encircling channel, protecting the clamp and associated enzymes from premature unloading by the ATAD5–RFC complex. Conversely, overexpression of PAF15 or forced redistribution to the leading strand disrupts replisome progression and induces cell death. These detrimental effects are mitigated by Timeless–Claspin, which blocks PAF15–PCNA binding on the leading strand. E2F4-mediated repression fine-tunes PAF15 expression to ensure optimal dosage and strand specificity. These findings reveal a previously unrecognized replisome constraint: when PAF15–PCNA assemblies are exhausted, the S-phase checkpoint globally restricts origin activation, linking a strand-specific rate-limiting mechanism to global replication dynamics.

Metabolic dysfunction–associated steatotic liver disease (MASLD) diagnosis and management have evolved rapidly alongside the increasing prevalence of obesity and related complications. Hepatology has expanded its focus beyond late-stage cirrhosis and portal hypertension to earlier, complex MASLD cases in younger patients, necessitating closer collaboration with endocrinology. The renaming of nonalcoholic fatty liver disease (NAFLD) to MASLD reflects its pathophysiology, reduces stigma, and has prompted new research directions. Noninvasive tests such as liver stiffness measurement now play a crucial role in diagnosis, reducing reliance on invasive liver biopsies. However, advanced omics technologies, despite their potential to enhance diagnostic precision and patient stratification, remain underutilized in routine clinical practice. Behavioral factors, including posttraumatic stress disorder (PTSD) and lifestyle choices, influence disease outcomes and must be integrated into patient management strategies. Primary care settings are critical for early screening to prevent progression to advanced disease, yet sizable challenges remain in implementing effective screening protocols. This Review explores these evolving aspects of MASLD diagnosis and management, emphasizing the need for improved diagnostic tools, multidisciplinary collaboration, and holistic care approaches to address existing gaps and ensure comprehensive patient care across all healthcare levels.

Background Metabolic dysfunction-associated steatotic liver disease (MASLD) affects roughly 1 in 3 adults and is a leading cause of liver transplants and liver related mortality. A deeper understanding of disease pathogenesis is essential to assist in developing blood-based biomarkers. Methods Here, we use data-independent acquisition mass spectrometry to assess disease-state associated protein profiles in human liver, blood plasma, and white adipose tissue (WAT). Results In liver, we find that MASLD is associated with an increased abundance of proteins involved in immune response and extracellular matrix (ECM) and a decrease in proteins involved in metabolism. Cell type deconvolution of the proteome indicates liver endothelial and hepatic stellate cells are the main source of ECM rearrangements, and hepatocytes are the major contributor to the changes in liver metabolism. In the blood, profiles of several MASLD-associated proteins correlate with expression in WAT rather than liver and so could serve as suitable liver disease predictors in a multi-protein panel marker. Moreover, our proteomics-based logistic regression models perform better than existing methods for predicting MASLD and liver fibrosis from human blood samples. Conclusions Our comprehensive proteomic analysis deepens the understanding of liver function and MASLD pathology by elucidating key cellular mechanisms and multi-organ interactions, and demonstrates the robustness of a proteomics-based biomarker panel to enhance diagnosis of MASLD and significant fibrosis.

Metabolic dysfunction-associated steatotic liver disease (MASLD) affects roughly 1 in 3 adults and is a leading cause of liver transplants and liver related mortality. A deeper understanding of disease pathogenesis is essential to assist in developing blood-based biomarkers. Here, we use data-independent acquisition mass spectrometry to assess disease-state associated protein profiles in human liver, blood plasma, and white adipose tissue (WAT). In liver, we find that MASLD is associated with an increased abundance of proteins involved in immune response and extracellular matrix (ECM) and a decrease in proteins involved in metabolism. Cell type deconvolution of the proteome indicate liver endothelial and hepatic stellate cells as main source of the ECM rearrangements, and hepatocytes as the major contributor to the changes in liver metabolism. In the blood, profiles of several MASLD-associated proteins that correlate with their expression in WAT rather than liver yet could serve as suitable liver disease predictors in a multi-protein panel marker. Moreover, our proteomics-based logistic regression models consistently outperform existing methods for predicting MASLD and liver fibrosis from human blood samples.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a growing healthcare problem with limited therapeutic options. Progress in this field depends on the availability of reliable preclinical models. Human precision-cut liver slices (PCLSs) have been employed to replicate the initiation of MASLD, but a comprehensive investigation into MASLD progression is still missing. This study aimed to extend the current incubation time of human PCLSs to examine different stages in MASLD. Healthy human PCLSs were cultured for up to 96 h in a medium enriched with high sugar, high insulin, and high fatty acids to induce MASLD. PCLSs displayed hepatic steatosis, characterized by accumulated intracellular fat. The development of hepatic steatosis appeared to involve a time-dependent impact on lipid metabolism, with an initial increase in fatty acid uptake and storage, and a subsequent down-regulation of lipid oxidation and secretion. PCLSs also demonstrated liver inflammation, including increased pro-inflammatory gene expression and cytokine production. Additionally, liver fibrosis was also observed through the elevated production of pro-collagen 1a1 and tissue inhibitor of metalloproteinase-1 (TIMP1). RNA sequencing showed that the tumor necrosis factor alpha (TNFα) signaling pathway and transforming growth factor beta (TGFβ) signaling pathway were consistently activated, potentially contributing to the development of inflammation and fibrosis. In conclusion, the prolonged incubation of human PCLSs can establish a robust ex vivo model for MASLD, facilitating the identification and evaluation of potential therapeutic interventions.