Metabolic dysfunction-associated steatotic liver disease represents an escalating health challenge across India. Previous investigations relied largely on cross-sectional analyses, failing to capture dynamic physiological shifts. Consequently, clinicians often miss the progressive biological alterations governing steatosis and hepatic injury. A landmark study now illuminates the temporal regulation of activin follistatin in MASLD across thirty weeks of high-fat feeding. By examining distinct longitudinal intervals, researchers revealed how hepatokines fluctuate between tissue and circulation. Therefore, evaluating these dynamic profiles provides essential insights into hepatic pathophysiology and disease staging.

Understanding Activin Follistatin in MASLD Across Disease Progression

High-fat dietary intake induces weight gain, hepatomegaly, and triglyceride accumulation in hepatic parenchyma. However, the endocrine response of the liver is far from linear. In early stages at eight weeks, the liver attempts metabolic adaptation against caloric overload. By twenty weeks, chronic lipid excess triggers overt hepatocellular stress and metabolic dysregulation. Finally, sustained dietary injury at thirty weeks drives persistent tissue damage. Throughout this continuum, researchers monitored the activin-follistatin axis to map stage-dependent fluctuations. Activin A belongs to the transforming growth factor-beta superfamily, promoting inflammatory cascades and tissue remodeling. Conversely, follistatin acts as an endogenous binding protein neutralizing activin bioavailability. Furthermore, follistatin-like 3 provides extracellular buffering. When lipid accumulation intensifies, the equilibrium between these antagonistic molecules shifts significantly. As a result, hepatocytes experience altered autocrine and paracrine cues. Understanding these staged responses helps clinicians recognize that single-point assessments fail to reflect true disease trajectory.

Temporal Discordance Between Hepatic Transcriptome and Protein Secretion

A central finding of this investigation is the discordance between hepatic transcripts and circulating protein levels. Specifically, hepatic Inhba messenger RNA expression was elevated at eight and thirty weeks of high-fat feeding. In sharp contrast, plasma and hepatic activin A protein concentrations peaked exclusively at twenty weeks. This divergence demonstrates robust post-transcriptional and translational regulation during disease progression. Similarly, hepatic follistatin displayed an unexpected compartmental dissociation. Hepatic Fst gene transcription increased during early steatosis, yet hepatic follistatin protein decreased markedly at twenty and thirty weeks. Meanwhile, circulating follistatin and follistatin-like 3 concentrations remained unchanged throughout the study. Therefore, systemic follistatin failed to mirror intrahepatic depletion. These discrepancies prove that messenger RNA quantification alone cannot reliably predict functional protein concentrations. Moreover, hepatic storage and systemic secretion operate under distinct regulatory controls during metabolic stress. Clinical researchers must therefore avoid assuming serum levels match intrahepatic protein concentrations.

Shift in Receptor Profiles and Canonical SMAD2/3 Pathway Activation

The biological impact of altered hepatokines depends directly on downstream receptor dynamics. In this study, activin receptors ACVR2B and ACVR1 exhibited distinct protein kinetics over time. ACVR2B protein showed sustained elevation across twenty and thirty weeks of dietary challenge. Conversely, ACVR1 protein displayed a transient peak at twenty weeks before normalizing. Consequently, this kinetic receptor profile favored canonical activin signaling over alternative pathways. In addition, the systemic activin A-to-follistatin ratio increased significantly at twenty weeks. Similarly, the activin A-to-follistatin-like 3 ratio rose at this critical intermediate timepoint. Because follistatin buffering declined intrahepatically, free activin A engaged receptors without hindrance. Accordingly, immunoblotting revealed marked elevation in the phospho-to-total SMAD2/3 ratio at twenty and thirty weeks. Phosphorylated SMAD2/3 translocates to the nucleus, driving fibrogenic gene transcription in hepatic stellate cells. Thus, prolonged high-fat feeding promotes canonical activin signaling, establishing an intrahepatic environment primed for progressive fibrosis.

Circulating GDF15 Kinetics and Longitudinal Metabolic Stress

Growth differentiation factor 15 represents another vital stress-responsive hepatokine induced during metabolic derangement. Throughout thirty weeks of high-fat feeding, hepatic Gdf15 messenger RNA exhibited sustained transcriptional induction. In parallel, circulating plasma GDF15 protein levels rose significantly at both eight and twenty weeks. Furthermore, statistical analysis demonstrated a strong positive correlation between circulating GDF15 and plasma activin A. This correlation reflects a shared physiological response to cumulative nutritional and organellar stress. Under physiological conditions, GDF15 acts centrally through hindbrain receptors to modulate appetite and energy expenditure. However, in persistent dietary excess, elevated GDF15 signals ongoing cellular injury rather than successful metabolic compensation. Because GDF15 tracks with hepatic lipid accumulation, it serves as a sensitive indicator of organ stress. Moreover, its synchronous elevation with activin A suggests coordinated activation of downstream pathways. Therefore, measuring circulating GDF15 alongside activin components offers valuable insight into evolving hepatocellular strain before histological architectural distortion occurs.

Translational Insights and Diagnostic Implications for Indian Clinicians

These experimental findings carry substantial clinical relevance for physicians managing metabolic disorders across India. The South Asian phenotype exhibits heightened susceptibility to visceral adiposity, severe insulin resistance, and steatohepatitis at lower body mass index thresholds. Consequently, Indian clinicians routinely encounter patients whose fatty liver disease progresses silently despite modest lifestyle abnormalities. Understanding the temporal kinetics of activin, follistatin, and GDF15 helps clinicians interpret disease stages accurately. For instance, a transient peak in circulating activin A at intermediate stages may herald active SMAD2/3-driven fibrogenesis. Conversely, stable serum follistatin levels do not exclude significant intrahepatic follistatin depletion. Furthermore, circulating GDF15 serves as a dependable indicator of cumulative mitochondrial and metabolic strain in diabetic cohorts. As non-invasive biomarker panels evolve, integrating these dynamic hepatokines will improve clinical risk stratification. Clinicians can thereby identify patients at risk of rapid fibrotic progression earlier. Ultimately, deciphering longitudinal hepatokine kinetics empowers medical practitioners to implement targeted interventions before irreversible cirrhosis develops.

Why do hepatic mRNA levels differ from circulating protein levels in MASLD?

Hepatic messenger RNA transcription does not guarantee immediate protein translation or systemic release during metabolic stress. The study demonstrates that cellular translation, intracellular degradation, and compartmental protein secretion undergo independent regulation over time. Consequently, hepatic Inhba and Fst gene transcription can rise while intrahepatic protein pools decline or circulate transiently. Clinicians must therefore understand that gene expression does not always correlate linearly with functional circulating hepatokine concentrations in progressive liver pathology.

What role does the activin-to-follistatin ratio play in hepatic fibrosis?

Activin A promotes tissue remodeling and hepatic stellate cell activation through canonical SMAD2/3 phosphorylation. Follistatin and follistatin-like 3 normally bind and neutralize activin A, maintaining hepatic tissue homeostasis. However, during chronic high-fat feeding, intrahepatic follistatin protein decreases while activin A peaks at intermediate stages. This imbalanced ratio unleashes free activin A to stimulate receptor complexes and drive SMAD2/3 signaling. Consequently, this signaling cascade promotes profibrotic gene transcription and accelerates progressive hepatic fibrosis.

How does GDF15 correlate with activin A during metabolic liver injury?

Growth differentiation factor 15 and activin A are both stress-responsive hepatokines induced by nutrient excess and cellular strain. In high-fat diet models, circulating GDF15 levels rise steadily and correlate positively with plasma activin A. While GDF15 attempts to modulate systemic metabolism via hindbrain receptors, activin A drives local inflammation and remodeling. Therefore, simultaneous elevations in both biomarkers indicate heightened hepatocellular stress and identify metabolic liver disease stages exhibiting accelerated risk for fibrotic parenchymal transformation.

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References

Kim MJ et al. Temporal regulation of activin, follistatin, and growth differentiation factor 15 in the liver and circulation during high-fat diet-induced fatty liver disease. Korean J Physiol Pharmacol. 2026 Oct 07. doi: 10.4196/kjpp.26.031. PMID: 42838888.

Yndestad A, et al. Roles of transforming growth factor-β signaling in liver disease. Cytokine Growth Factor Rev. 2013;24(3):285-295.

Mullican SE, et al. GFRAL is the receptor for GDF15 and the ligand promotes weight loss in mice and nonhuman primates. Nat Med. 2017;23(10):1150-1157.