Systemic sclerosis, often called scleroderma, is a chronic, autoimmune and fibrotic disorder characterized by three interlocking processes: dysregulation of the immune system, abnormalities of the small blood vessels and progressive deposition of collagen and other extracellular matrix proteins that thicken and stiffen the skin and internal organs. Patients can suffer from digital ulcers, lung fibrosis, pulmonary hypertension and gastrointestinal complications, and despite decades of research, treatment options remain limited largely to immunosuppression and symptom management. One of the biochemical threads running through the disease is oxidative stress, an imbalance between the production of reactive oxygen species and the cellular defenses that neutralize them. Reactive oxygen species are highly damaging to DNA, and one of the most common lesions they produce is 8-oxo-7,8-dihydroguanine, a modified guanine base that, if left unrepaired, can mispair during DNA replication and trigger mutations or, critically in this context, provoke inappropriate immune signaling.

Cells are not defenseless against this kind of damage. The primary mechanism for removing oxidized DNA bases is base excision repair, or BER, a multi-step pathway that begins when a lesion-specific DNA glycosylase such as OGG1 recognizes and excises the damaged base, creating an abasic site. The enzyme AP endonuclease 1, known as APE1, then cleaves the DNA backbone at that site, and a cascade of downstream processing enzymes fills the gap with the correct nucleotide and seals the strand. APE1 is a particularly multifunctional protein; beyond its repair role, it also functions as a redox signaling factor that regulates the activity of several transcription factors, adding an additional layer of relevance in a disease driven by oxidative stress. A second repair pathway, nucleotide excision repair or NER, handles bulky, helix-distorting lesions such as those caused by ultraviolet light, using proteins including XPA and XPC to survey the genome. Prior work by other groups had already shown that patients with systemic sclerosis accumulate elevated levels of oxidative DNA damage in their blood cells, and that some of them carry polymorphisms in DNA repair genes, but no one had directly measured the transcriptional state of the repair machinery itself, nor asked whether that state could be changed by an intervention as simple as a vitamin supplement.

To address that gap, the Turkish research team recruited 52 female patients with systemic sclerosis and 31 age-matched healthy women as controls. All participants provided peripheral blood samples, from which the researchers extracted RNA and quantified the expression of four representative DNA repair genes by measuring their messenger RNA transcripts: the BER enzymes APE1 and OGG1, and the NER enzymes XPA and XPC. In parallel, they measured serum concentrations of 25-hydroxyvitamin D, the standard clinical marker of vitamin D status, and correlated these levels with validated disease activity scores that capture the severity and progression of each patient’s condition. The design included a prospective interventional arm: patients who were deficient in vitamin D received supplementation for six months, and their repair gene expression and serum vitamin D levels were reassessed at the end of the treatment period, allowing each patient to serve as her own biological baseline.

The baseline comparisons delivered a clear and selective signal. Expression of APE1 and OGG1, the two BER enzymes, was significantly lower in the systemic sclerosis patients than in the healthy controls, whereas the NER genes XPA and XPC showed no difference between the two groups. This selectivity is important. If DNA repair capacity were globally depressed in these patients, one might suspect a nonspecific effect of chronic illness, inflammation or medication. Instead, the pattern points specifically at the pathway responsible for oxidative base lesions, which is precisely the pathway one would expect to be stressed in a disease characterized by oxidative damage. It dovetails with earlier reports of high levels of oxidized DNA bases in the blood of scleroderma patients and with mechanistic studies showing that unrepaired oxidative DNA lesions can escape degradation by cytosolic nucleases and activate the cGAS-STING innate immune sensing pathway, a molecular circuit that detects misplaced DNA and drives type I interferon responses. Chronic activation of such DNA-sensing pathways is an increasingly recognized feature of autoimmune disease, which makes defective BER a plausible upstream contributor to the inflammatory fire that fuels systemic sclerosis.

The vitamin D story in this patient population was equally striking. Deficiency was highly prevalent among the patients, consistent with earlier clinical observations that low vitamin D is common in systemic sclerosis and has been linked to worse quality of life, more severe capillaroscopic abnormalities and greater disease severity. In the new study, serum vitamin D levels correlated inversely with disease activity scores, meaning that patients with the least vitamin D tended to have the most active disease. Correlation alone cannot establish direction, and the authors are careful not to overstate causality, but the pattern set the stage for the interventional question: if vitamin D status and repair gene expression move together, can restoring the vitamin lift the repair machinery?

The answer from the six-month supplementation arm was yes, at least at the transcriptional level. After the intervention, serum vitamin D concentrations rose significantly, and with them the expression of APE1 and OGG1 was up-regulated in the patients’ blood cells. Once again, the NER genes remained unaffected, mirroring the baseline selectivity and reinforcing the conclusion that the effect is specific to the BER pathway rather than a blanket change in DNA repair transcription. The researchers interpret this as a partial rescue of a micronutrient-dependent regulatory state: systemic sclerosis patients carry a transcriptional deficit in BER enzymes that is associated with vitamin D deficiency, and restoring vitamin D levels brings the expression of these enzymes partway back toward normal. Previous work by the same lead author had already shown that vitamin D supplementation reduces oxidative DNA damage in scleroderma patients with organ involvement, and studies in multiple sclerosis had reported that vitamin D can alter the expression of DNA repair genes, so the new findings extend and mechanistically deepen this emerging literature.

The mechanistic plausibility of the connection is strengthened by what is known about vitamin D biology. The active hormonal form of the vitamin, calcitriol, signals through the vitamin D receptor, a nuclear receptor that binds to specific DNA sequences and modulates the transcription of hundreds of target genes. Vitamin D signaling has documented effects on fibrosis, with experimental studies showing that it reduces collagen expression and induces an antifibrotic phenotype in mesenchymal cells, a property directly relevant to a fibrotic disease like systemic sclerosis. If BER gene promoters or the transcription factors governing them are among the receptor’s regulatory targets, the observed up-regulation of APE1 and OGG1 after supplementation becomes a coherent piece of biology rather than a statistical curiosity. It also reframes vitamin D not merely as an immunomodulator or an antifibrotic agent, but as a contributor to genomic maintenance, a role with implications well beyond this single disease.

The clinical implications, while preliminary, are appealing precisely because the intervention is so accessible. Vitamin D supplementation is inexpensive, widely available and generally safe at monitored doses, in sharp contrast to the immunosuppressive and antifibrotic drugs that form the current therapeutic backbone for systemic sclerosis. The authors propose that optimizing vitamin D status could serve as an adjunctive strategy, one that enhances DNA repair capacity, potentially reduces the burden of oxidative DNA lesions that provoke inflammatory and autoimmune signaling, and in doing so might help attenuate the inflammatory and fibrotic processes that drive the disease. They frame the vitamin D-BER axis as a potentially modifiable link between micronutrient status, genomic stability and disease activity, a formulation that immediately suggests follow-up studies: randomized controlled trials with clinical endpoints, measurements of actual BER enzyme activity and DNA lesion burden rather than transcript levels alone, and longer follow-up to see whether molecular changes translate into slower disease progression.

Several caveats deserve emphasis. The patient cohort was relatively modest, comprising 52 women, and systemic sclerosis shows important sex differences that make it difficult to generalize directly to male patients. Transcript abundance is an imperfect proxy for protein levels and enzymatic activity, and the six-month window, while sufficient to demonstrate a transcriptional response, is short relative to the decadal course of a chronic fibrotic disease. The inverse correlation between vitamin D and disease activity could reflect reverse causation, since more severely ill patients may be less mobile, less exposed to sunlight and more depleted of the vitamin. Nonetheless, the internal consistency of the findings, the pathway selectivity at both baseline and after intervention, and the agreement with prior independent evidence on oxidative damage, cGAS-STING signaling and vitamin D antifibrotic action give the results a credibility that invites replication.

What makes this study resonant beyond the scleroderma community is its broader message about the intersection of nutrition and genome biology. DNA repair has traditionally been studied through the lens of genetics, cancer and aging, with interventions framed in terms of pharmacology. The idea that a routine micronutrient, measured on a standard blood panel and corrected with a common supplement, can influence the transcriptional output of the cell’s mutational cleanup crew opens a genuinely different therapeutic angle for autoimmune and fibrotic diseases. For the millions of people worldwide living with systemic sclerosis, a condition for which effective options remain scarce, the prospect that correcting a vitamin deficiency might shore up one of the body’s most fundamental defenses against molecular damage is a small but genuinely hopeful step, and one that the field will now be pressed to test at scale.

Systemic sclerosis, which affects various organ systems, has long puzzled clinicians and researchers alike. Its heterogeneous nature often complicates clinical manifestations, leading to delayed treatment and possibly irreversible damage. Understanding the molecular underpinnings of this disease is crucial for developing effective management strategies. The findings presented in this new study not only shed light on the pathophysiology of dSSc but also emphasize the relevance of extracellular proteins in the disease landscape.

BAG3, or Bcl-2-associated athanogene 3, is a multi-functional protein involved in autophagy, apoptosis, and cellular stress responses. It plays an essential role in maintaining cellular homeostasis and protecting cells from stress-induced damage. Recent studies have shown that BAG3 is involved in numerous pathologies, ranging from cancer to neurodegenerative diseases. However, its specific function within the context of systemic sclerosis had remained largely elusive until now.

The elevated levels of extracellular BAG3 in early dSSc suggest that it may serve as a biomarker for disease progression or activity. In the study, researchers observed not only increased BAG3 levels in patients but also an association between these levels and disease severity. This correlation underscores the potential of BAG3 as a diagnostic tool, enabling clinicians to better gauge the extent and aggressiveness of the disease in affected individuals.

Furthermore, the study presents compelling evidence indicating that BAG3 may be involved in fibrotic processes characteristic of dSSc. Fibrosis, the excessive accumulation of extracellular matrix proteins, is a hallmark of systemic sclerosis. The role of BAG3 in promoting or regulating fibrotic pathways adds a complex layer of understanding to its function. Insights into these pathways could lead to innovative treatment strategies that target BAG3 directly or modulate its activity, offering new hope to patients struggling with this debilitating condition.

Research methodologies employed in this study were rigorous, utilizing both in vivo and in vitro models to elucidate the role of BAG3 in systemic sclerosis. The study’s authors implemented advanced techniques to measure BAG3 levels and assess its effects on cellular behavior under stress conditions. This comprehensive approach strengthens the reliability of the findings and provides a robust framework for future research.

In addition to its implications for diagnosis and treatment, the study also raises critical questions regarding the possible mechanisms underlying the elevation of BAG3 in dSSc. Is it a direct response to tissue damage, or does it signify a broader dysregulation in the immune system? The answers to these questions may provide a deeper understanding of the immunological landscape of systemic sclerosis, opening avenues for targeted therapies that address the root cause of disease rather than merely its symptoms.

The rising interest in extracellular vesicles and proteins such as BAG3 is indicative of a paradigm shift in biomedical research. Traditional approaches often focused on intracellular pathways, yet the emerging evidence highlights the importance of extracellular factors in disease progression. This study posits extracellular BAG3 as a pivotal player, reinforcing the notion that our understanding of disease mechanisms must extend beyond the confines of the cell.

The implications of this study extend beyond clinical practice; they suggest a potential for BAG3 to serve as a therapeutic target for drug development. If future research validates the role of BAG3 in fibrogenesis and immune regulation, pharmaceutical companies may prioritize this protein in their drug discovery pipelines. The next few years could see an influx of innovative treatments harnessing the properties of BAG3, ultimately improving outcomes for patients with systemic sclerosis and other fibrotic diseases.

As researchers continue to explore the multifaceted roles of BAG3, collaborative efforts across disciplines will be vital. Interactions among immunologists, rheumatologists, and molecular biologists will catalyze rapid developments in understanding the complex interactions at play in systemic sclerosis. These multidisciplinary teams will likely accelerate the translation of laboratory findings into clinical applications, paving the way for new therapeutic strategies that integrate insights from all facets of medical science.

Public engagement and awareness also play a crucial role in advancing research on systemic sclerosis. Ensuring that patients, caregivers, and the broader community understand the significance of discoveries like elevated extracellular BAG3 can foster support for research initiatives. Such awareness is essential for galvanizing funding and resources necessary for ongoing studies in this area. Educated patients can advocate for themselves and contribute to advancing the science behind systemic sclerosis, ultimately leading to better health outcomes.

In conclusion, the elevation of extracellular BAG3 in early diffuse systemic sclerosis presents a promising avenue for future research and clinical application. As the scientific community delves deeper into the implications of this finding, the potential for transformative impacts on diagnosis, prognosis, and treatment of systemic sclerosis becomes increasingly apparent. By harnessing the insights gained from BAG3 research, we may pave the way for novel therapeutic interventions and a brighter future for those affected by this challenging autoimmune disorder.

Subject of Research: Elevation of extracellular BAG3 in early diffuse systemic sclerosis.

Article Title: Extracellular BAG3 is elevated in early diffuse systemic sclerosis.

Article References:

Freedman, P., De Marco, M., Rosati, A. et al. Extracellular BAG3 is elevated in early diffuse systemic sclerosis.
Military Med Res 12, 37 (2025). https://doi.org/10.1186/s40779-025-00628-w

Image Credits: AI Generated

DOI: https://doi.org/10.1186/s40779-025-00628-w

Keywords: BAG3, diffuse systemic sclerosis, biomarkers, fibrosis, autoimmune diseases.