Background & objectives: Metabolic steatotic liver disease (MASLD), which affects more than 30% of the world's population, is associated with multisystemic comorbidities. We combined multidimensional OMICs approaches to explore the feasibility of using high-throughput targeted circulating proteomics to track systemic organ damage and to infer its underlying mechanisms at the molecular level. Desing: We tested a 92-plex panel of prioritised proteins with pathophysiological relevance to organ damage in serum samples of patients with in-depth phenotyping. We included proteomics data from 60,042 people in the discovery and validation stages. The identified protein was validated across diverse study designs and cross-proteomic platforms. Deconvolution strategies were used to investigate whether the affected liver is involved in expressing biomarkers of organ damage. To assess the cell type-specific transcriptional changes of the selected target we used liver organoid data. Results: The implicated proteins, including ADGRG1 (GPR56), are deregulated in patients with MASLD at-risk of progressive disease and significant fibrosis. ADGRG1 liver expression profile mirrors the circulation pattern. ADGRG1 levels were associated with increased risk of end-stage liver disease and a modest but clinically significant risk of death, chronic obstructive pulmonary disease, and ischaemic heart disease over 16 years of follow-up. Mechanistic insight shows that ADGRG1 shifts its transcriptional profile from low expression to upregulation in liver cells of the fibrotic niche in response to injury. Conclusions: Our study provides a framework of potential mechanisms associated with systemic organ injury that facilitates holistic management by stratifying patients with MASLD into subclasses at-risk of extrahepatic manifestations.

The authors have declared no competing interest.

Silvia Sookoian and Carlos J. Pirola are supported by grants PICT 2018-889, PICT 2019-0528, PICT 2018-00620 and PICT 2020-0799. Agencia Nacional de Promocion Cientifica y Tecnologica Argentina, FONCyT. Argentina.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Ethical approval. Biological specimens, including blood samples and liver biopsies, were collected from all subjects with written, informed consent under Institutional Review Board (Comite de Etica en Investigacion (CEI) intervenient Hospital A Zubizarreta Buenos Aires, Argentina) approved protocols with protocol numbers: 104/HGAZ/09, 89/100, 1204/2012, and updated and aproved DI-2019-376-GCABA-HGAZ, DI-2019-376-GCABA-HGAZ. Protocol entitled Biomarkers of systemic organ damage was registered with GCBA (Government of the City of Buenos Aires Argentina) protection data PRIISA BA (Plataforma de Registro Informatizado de Investigaciones en Salud de Buenos Aires-Buenos Aires Health Research Computerized Registry Platform): ethical approval was given under the reference number 8987. All data were de-identified prior to use in the study. All investigations were performed in accordance with the guidelines set forth in the 1975 Declaration of Helsinki, as revised in 1993.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

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I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

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I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

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The authors confirm that all relevant data generated in this study are included in the article and/or its supplementary information. Clinical data in this study can be found in Table 1 and Table S2. In accordance with the Ethics Committee of our institution and the Institutional Review Board of the GCBA regarding the protection of individual privacy, personal and sensitive data associated with phenotypic and proteomic data will only be available for controlled access and will be available from the corresponding author upon reasonable request. ADGRG1 protein-phenotype associations in the UKBB population stratified on ancestry can be found in Table S3. All RNA-seq data are publicly available from the Gene Expression Omnibus database (accession numbers (GSE135251, GSE162694) or Liver Cell Atlas (accession number GSE192742; Scripts Liver Atlas data: github.com/guilliottslab). Inference of cell-type involvement from single cell RNA-sequencing data are publicly available in GSE207889, and additional reanalysis of single cell expression can be found in Figure S7. Enriched gene ontology (GO) biological pathways associated with liver ADGRG1 expression in response to the inducing stimulus can be found in Tables S4-S6.