Fibroblast Markers: New Insights and Molecular Signatures

Fibroblasts are essential connective tissue cells involved in wound healing, extracellular matrix production, and disease progression. Advances in molecular biology have refined our understanding of fibroblast diversity by identifying specific markers that distinguish subpopulations with distinct functions. These insights are key to developing targeted therapies for fibrosis and cancer.

Research shows fibroblast marker expression varies by tissue type and pathological state. Understanding these molecular signatures provides a foundation for studying fibroblast heterogeneity and its implications in health and disease.

Common Surface Markers

Fibroblasts display diverse surface markers that distinguish them from other cell types and define their roles across tissues. One widely studied marker is platelet-derived growth factor receptor alpha (PDGFRα), a transmembrane protein involved in fibroblast proliferation and extracellular matrix remodeling. PDGFRα+ fibroblasts regulate collagen deposition and growth factor signaling, making this marker valuable for characterizing fibroblast activity in different organs.

Fibroblast activation protein (FAP), a serine protease, is absent in quiescent fibroblasts but highly expressed during tissue remodeling, such as wound healing and fibrosis. Its enzymatic activity degrades extracellular matrix components, facilitating tissue restructuring. Because of its selective expression in activated fibroblasts, FAP has been explored as a therapeutic target, with monoclonal antibodies and small-molecule inhibitors under investigation for modulating fibroblast-driven pathologies.

Thy-1 (CD90) is another key surface marker involved in cell adhesion, migration, and signaling. Its expression varies across fibroblast subtypes and tissues. In dermal fibroblasts, CD90 is linked to enhanced migration and extracellular matrix production, while in lung fibroblasts, it alters responses to fibrotic stimuli. This variability highlights the complexity of fibroblast populations and the need for context-specific analysis when using CD90 as a marker.

Integrins such as α-SMA (alpha-smooth muscle actin) and integrin β1 (CD29) further define fibroblast subpopulations. α-SMA is particularly relevant in myofibroblasts, which contribute to wound contraction and extracellular matrix deposition. Persistent α-SMA activation can lead to pathological fibrosis. Integrin β1 facilitates fibroblast adhesion and mechanotransduction, allowing them to sense and respond to environmental changes. These integrins provide additional specificity in distinguishing fibroblast subsets.

Intracellular Markers

Intracellular markers offer deeper insights into fibroblast identity and activation states. Vimentin, an intermediate filament protein, is a hallmark of mesenchymal cells, including fibroblasts. It maintains cellular integrity and supports mechanotransduction, enabling fibroblasts to adapt to environmental cues. Elevated vimentin expression is common in activated fibroblasts during tissue remodeling and fibrosis.

Alpha-smooth muscle actin (α-SMA) is predominantly associated with myofibroblasts, a fibroblast subset involved in wound contraction and extracellular matrix deposition. While quiescent fibroblasts exhibit low α-SMA expression, its upregulation signals a transition to a contractile phenotype, often in response to transforming growth factor-beta (TGF-β) signaling. Persistent α-SMA expression contributes to fibrosis, making it a reliable marker for assessing fibroblast activation.

Heat shock protein 47 (HSP47) is a collagen-specific chaperone that assists in collagen folding and secretion. Its expression is tightly regulated during fibrosis, with increased levels correlating with excessive collagen production. HSP47 has been explored as a therapeutic target, with small-molecule inhibitors under investigation to prevent aberrant extracellular matrix accumulation.

Fibroblasts also exhibit metabolic markers that reflect their activation state. Lactate dehydrogenase A (LDHA), a key enzyme in glycolysis, is upregulated in activated fibroblasts, particularly in hypoxic conditions. This metabolic shift supports fibroblast proliferation and extracellular matrix remodeling. Similarly, glutaminase-1 (GLS1), an enzyme involved in glutamine metabolism, sustains nucleotide and amino acid biosynthesis during rapid cellular expansion. These metabolic markers provide additional dimensions for characterizing fibroblast heterogeneity.

Markers Linked to Fibrosis

Fibrosis is marked by excessive extracellular matrix accumulation, leading to tissue stiffening and organ dysfunction. Fibroblast activation in fibrosis is associated with distinct molecular signatures. Periostin, a matricellular protein, facilitates collagen cross-linking and enhances fibroblast adhesion. Elevated periostin expression is documented in fibrotic lung, liver, and kidney tissues, where it contributes to persistent matrix deposition. High periostin levels correlate with disease severity in idiopathic pulmonary fibrosis (IPF) and liver cirrhosis, making it a potential biomarker for disease progression.

Connective tissue growth factor (CTGF), a downstream effector of TGF-β signaling, promotes fibroblast proliferation and extracellular matrix synthesis. CTGF inhibition has been shown to attenuate fibrosis in preclinical models. Pamrevlumab, a monoclonal antibody against CTGF, has shown promise in clinical trials for IPF and pancreatic fibrosis, highlighting the therapeutic potential of targeting fibroblast-associated markers.

Fibroblast-specific protein 1 (FSP1), also known as S100A4, is another fibrosis-linked marker, particularly in epithelial-to-mesenchymal transition (EMT)-derived fibroblasts. Unlike resident fibroblasts, EMT-derived fibroblasts emerge from epithelial cells that acquire mesenchymal characteristics. FSP1 expression is associated with fibroblast motility and invasiveness, facilitating their migration into fibrotic lesions. Elevated FSP1 levels are observed in renal and cardiac fibrosis, where they correlate with increased tissue scarring and poor functional outcomes.

Markers in Tumor Microenvironments

Cancer-associated fibroblasts (CAFs) in tumor microenvironments exhibit distinct molecular signatures that contribute to tumor progression, metastasis, and therapy resistance. Fibroblast activation protein (FAP) is highly upregulated in CAFs across multiple cancer types, including pancreatic, colorectal, and breast carcinomas. FAP remodels the extracellular matrix, creating a permissive environment for tumor invasion. Its selective expression in tumor-associated fibroblasts has made it a target for therapies, including FAP-specific chimeric antigen receptor (CAR) T-cell treatments and radiolabeled inhibitors for tumor imaging.

Podoplanin (PDPN) has emerged as a marker of CAFs with pro-metastatic properties. PDPN expression correlates with enhanced tumor cell migration and invasion through interactions with platelet-derived factors that facilitate metastatic dissemination. In squamous cell carcinomas, PDPN-positive fibroblasts are linked to poor prognosis, suggesting their potential as biomarkers for aggressive tumor behavior. PDPN’s role in lymphangiogenesis further underscores its contribution to cancer progression, making it a potential therapeutic target.

Single-Cell Profiling of Marker Heterogeneity

Single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics have transformed the understanding of fibroblast diversity by identifying distinct subpopulations with unique molecular signatures. Traditional bulk RNA sequencing masked fibroblast heterogeneity, whereas single-cell approaches now reveal subsets with pro-fibrotic, immunomodulatory, or tumor-supportive functions.

Single-cell studies show fibroblast subpopulations dynamically shift states based on environmental cues. In fibrotic diseases, scRNA-seq has identified clusters with high COL1A1 and ACTA2 expression, indicative of myofibroblastic activity, while others exhibit inflammatory or senescent profiles. Similarly, cancer-associated fibroblasts include subsets with either tumor-promoting or tumor-suppressive functions, challenging the notion that all CAFs uniformly support tumor progression. Spatial transcriptomics further refines this understanding by mapping fibroblast subtypes within tissue architecture, demonstrating their context-dependent roles. These insights pave the way for more precise therapeutic interventions targeting specific fibroblast subsets.

Tissue-Specific Variations of Fibroblast Markers

Fibroblast marker expression varies across tissues, reflecting their diverse roles in organ function and injury response. While core markers like vimentin and PDGFRα are broadly expressed, tissue-specific markers distinguish fibroblasts in different anatomical locations.

In the skin, dermal fibroblasts express DPP4 and CD26, which regulate extracellular matrix turnover and contribute to wound healing. Regional heterogeneity within dermal fibroblasts influences their regenerative capacities.

Lung fibroblasts express high levels of WNT2 and matrix-remodeling proteins such as MMP7, which are critical for maintaining alveolar structure and responding to pulmonary injury. This molecular signature differentiates them from fibroblasts in other organs and underscores their role in lung homeostasis and fibrosis.

Cardiac fibroblasts show enriched expression of periostin and TCF21, reflecting their involvement in myocardial repair and scar formation following cardiac injury. These tissue-specific markers not only aid in fibroblast identification but also provide insights into organ-specific pathologies, guiding the development of targeted therapies for pulmonary fibrosis, cardiac remodeling, and skin disorders.