RNA Tag METTL3 Drives Lung Scarring by Destabilizing a Key Fat-Droplet Protein

Idiopathic pulmonary fibrosis, a relentless scarring disease of the lung with a median survival of roughly three years, has long resisted the efforts of researchers seeking a complete explanation of its origins. A new study published in the Journal of Cellular and Molecular Medicine now adds a striking piece to the puzzle, showing that a master regulator of RNA chemistry called METTL3 promotes both fat accumulation and fibrotic scarring in the lung by chemically tagging the messenger RNA of a lipid-droplet protein known as PLIN2, thereby marking that transcript for destruction. The work, led by researchers affiliated with Chongqing Medical University, suggests that the METTL3-PLIN2 axis could become a fresh therapeutic target in a disease where current antifibrotic drugs slow but do not halt progression.

The chemical modification at the heart of the study is N6-methyladenosine, abbreviated m6A, the most abundant internal modification found in messenger RNA. In this process, a methyl group is attached to the nitrogen at position six of adenosine bases, a change that can alter how efficiently a transcript is translated, where it localizes, and, crucially, how long it survives before being degraded by the cell’s RNA-decay machinery. METTL3 is the catalytic core of the methyltransferase complex that writes these marks. Because m6A methylation has already been implicated in cancer, cardiovascular disease, and a range of fibrotic disorders, and because previous work showed that silencing METTL3 blocks the conversion of fibroblasts into scar-forming myofibroblasts, the team reasoned that the enzyme might also govern the lipid disturbances that increasingly appear central to pulmonary fibrosis.

That lipid connection is not incidental. Lipids serve not only as structural components of cellular membranes but also as signalling molecules that modulate fibroblast activation and extracellular matrix production, and dysregulated lipid metabolism has emerged as a critical factor in the pathogenesis of idiopathic pulmonary fibrosis. The protein PLIN2, a member of the perilipin family, coats the surface of intracellular lipid droplets and acts as a gatekeeper, controlling the entry of lipases and their cofactors into the stored lipids and thereby regulating lipolysis. PLIN2 has been linked to myocardial infarction, obesity, fatty liver disease, and lipogenic differentiation in lung fibrosis, but its relationship with METTL3 had never been explored.

To establish the disease context, the researchers used the well-characterized bleomycin model, in which the chemotherapy drug bleomycin is delivered directly into the airways of mice to provoke fibrotic injury that resembles the human condition. Histological examination with haematoxylin and eosin and Masson’s trichrome staining confirmed that bleomycin destroyed normal lung architecture and drove collagen deposition. Molecular assays showed elevated levels of the fibrosis markers collagen I and alpha-smooth muscle actin, while Nile Red fluorescence staining of lung sections revealed a marked increase in lipid deposition. Critically, METTL3 expression was significantly upregulated in the fibrotic lungs. The same pattern appeared in vitro: WI-38 human embryonic lung fibroblasts treated with transforming growth factor beta 1, a standard mimic of the fibrotic environment, also raised their METTL3 levels.

The team then asked what happens when METTL3 is removed. Using short hairpin RNA to knock down the enzyme in TGF-beta1-treated WI-38 cells, they observed a broad calming of the fibrotic program. Expression of lipogenesis markers including fatty acid synthase, acetyl-CoA carboxylase 1, SREBP1, and PPARalpha, all of which had been elevated by TGF-beta1, fell back toward baseline. Collagen I and alpha-smooth muscle actin declined at both the messenger RNA and protein levels, a result confirmed by immunofluorescence imaging of alpha-smooth muscle actin. Oil Red O staining showed that the abundance of lipid droplets induced by TGF-beta1 was partly abolished when METTL3 was silenced, demonstrating that the enzyme’s influence extends from scar formation to fat handling within the same cells.

The mechanistic core of the paper lies in what METTL3 does to PLIN2. When the researchers silenced METTL3, PLIN2 expression rose. Methylated RNA immunoprecipitation showed that the m6A levels on PLIN2 transcripts dropped in parallel, and RNA immunoprecipitation confirmed a direct physical interaction between METTL3 and the PLIN2 RNA. Using the SRAMP prediction database, the team identified five candidate methylation sites, selected the three with the highest confidence, and tested them individually with a dual-luciferase reporter assay in which the wild-type or site-mutated PLIN2 sequence was inserted downstream of a luciferase gene. Silencing METTL3 increased reporter activity only for the construct containing site 2, pinpointing that single adenosine as the functionally relevant methylation site. Actinomycin D chase experiments, which block new RNA synthesis and allow existing transcripts to decay, showed that METTL3 knockdown significantly prolonged PLIN2 messenger RNA half-life, confirming that the enzyme normally destabilizes the transcript through m6A-dependent decay.

To prove that PLIN2 is not merely a bystander but the functional downstream effector, the researchers performed an epistasis experiment. When they knocked down PLIN2 in cells in which METTL3 had already been silenced, the protective effects of METTL3 loss were reversed. The suppression of lipogenesis markers was abrogated, collagen I and alpha-smooth muscle actin climbed back up, and the reduction in lipid droplets was counteracted. In other words, removing PLIN2 restored the fibrotic and lipid-accumulating phenotype even in the absence of METTL3, placing PLIN2 squarely downstream of the methyltransferase in the pathway that connects RNA methylation to scar formation.

The in vivo experiments reinforced the story. Twenty mice per group were randomly assigned to control, bleomycin, bleomycin plus a control short hairpin RNA, or bleomycin plus shMETTL3 delivered intratracheally by adenovirus. Over 28 days, bleomycin reduced survival, while METTL3 knockdown improved it. Histology showed that silencing METTL3 impeded the destruction of lung structure and the deposition of collagen fibres. Nile Red staining demonstrated that the lipid accumulation driven by bleomycin was counteracted by METTL3 knockdown, and the elevated collagen I and alpha-smooth muscle actin levels in fibrotic lungs fell after METTL3 interference. Immunohistochemistry revealed that PLIN2, which was downregulated in the bleomycin model, was restored by METTL3 silencing, mirroring the cellular findings and tying improved survival and tissue architecture to the restored lipid-droplet protein.

The findings fit into a growing body of work implicating m6A machinery in fibrotic disease across organs. METTL3 knockdown has been reported to inhibit fibroblast proliferation and migration in cardiac fibrosis, to ameliorate kidney fibrosis by reducing fibrotic marker expression, and to promote macrophage pyroptosis that aggravates liver fibrosis. In the lung specifically, METTL3-mediated methylation has been shown to drive fibroblast differentiation into myofibroblasts through the miR-21/PTEN pathway, and m6A-modified circular RNAs have been linked to ferroptosis in pulmonary fibrosis. The new study extends this landscape by identifying PLIN2 as a novel methylation substrate and by connecting RNA epigenetics directly to lipid metabolism, a dimension of pulmonary fibrosis biology that involves lipofibroblast activation, lung remodelling, and pathways such as lysophosphatidic acid signalling.

The authors are careful to note the limitations of their work. WI-38 embryonic fibroblasts, while genetically stable and widely used to study the fibroblast-to-myofibroblast transition, cannot fully recapitulate the pathology of primary lung fibroblasts from patients with idiopathic pulmonary fibrosis, and embryonic cells may differ from adult disease fibroblasts in epigenetic and lipid metabolic profiles, so validation in MRC-5 cells or primary patient fibroblasts will be needed. The team validated a single methylation site by reporter assay but did not perform transcriptome-wide m6A mapping such as MeRIP-seq or miCLIP to exclude additional sites, and the role of PLIN2 in vivo requires further preclinical testing. Even so, the central conclusion stands: METTL3 promotes lipid deposition and fibrosis by destabilizing PLIN2 messenger RNA in an m6A-dependent manner, and interventions that raise PLIN2 expression, whether directly or by silencing METTL3, offer a conceptually new route to treating a disease that urgently needs one.

Subject of Research: The role of METTL3-mediated m6A modification of PLIN2 in lipid metabolism and pulmonary fibrosis

Article Title: METTL3 Promotes Lipid Deposition and Pulmonary Fibrosis by Destabilizing PLIN2 in a m6A‐Dependent Manner

Article References: Liu, Q., Xu, R., & Du, X. (2026). METTL3 Promotes Lipid Deposition and Pulmonary Fibrosis by Destabilizing PLIN2 in a m6A‐Dependent Manner. Journal of Cellular and Molecular Medicine, 30(17), Article e71239. https://doi.org/10.1111/jcmm.71239

Image Credits: AI Generated

DOI: 10.1111/jcmm.71239

Keywords: idiopathic pulmonary fibrosis, METTL3, m6A methylation, PLIN2, lipid metabolism, RNA modification, pulmonary fibrosis, fibroblasts, myofibroblast, bleomycin model, epitranscriptomics, TGF-beta1