Systemic sclerosis (SSc) is a multifactorial autoimmune connective tissue disease characterized by dermal fibrosis, chronic inflammation, and excessive extracellular matrix (ECM) deposition, with a pathophysiology that remains incompletely defined (Trojanowska, 2017; Varga et al., 2017). Among its severe complications, pulmonary arterial hypertension (PAH) occurs in 8–15 % of cases and significantly contributes to morbidity and mortality (Trojanowska, 2017). Additionally, pulmonary fibrosis, particularly in the context of idiopathic pulmonary fibrosis (IPF), represents a common and often fatal manifestation of SSc, for which no curative therapies are currently approved (Herzog et al., 2014).

Fibrotic progression in SSc is primarily mediated by increased collagen synthesis and deposition, orchestrated via sustained activation of the transforming growth factor-β (TGF-β)/Smad2/3 signaling axis (Trojanowska, 2017; Varga et al., 2017; Herzog et al., 2014). Moreover, dysregulated immune signaling involving type I and II interferons, interleukins IL-2, IL-6, and IL-23 is implicated in SSc pathogenesis and is largely transduced through the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway (Raja and Denton, 2015). Notably, hyperactivation of JAK2 has been identified in dermal fibroblasts of SSc patients, driven in part by elevated TGF-β expression (Dees et al., 2012). These findings underscore the potential of JAK/STAT signaling as a viable intracellular therapeutic target in fibrotic diseases such as SSc (Dees et al., 2012).

Clinical heterogeneity is a hallmark of SSc, with varying degrees of cutaneous and visceral involvement, contributing to challenges in disease classification and management (Varga et al., 2017; Adigun et al., 2020; Varga, 2008). To date, no disease-modifying pharmacological agent has gained regulatory approval for the treatment of SSc (Hunzelmann et al., 2008).

The JAK/STAT pathway is an evolutionarily conserved, pleiotropic signaling cascade essential for hematopoiesis, immune regulation, and cellular homeostasis (Rawlings, 2004). Aberrant activation of JAK/STAT signaling is associated with a broad spectrum of autoimmune and inflammatory disorders (You et al., 2020). Therapeutic targeting of this pathway has gained traction in recent years, particularly in the context of inflammatory arthritides and other immune-mediated diseases (Choy, 2019a).

Upadacitinib, a selective JAK1 inhibitor, has demonstrated clinical efficacy in moderate-to-severe rheumatoid arthritis and received approval by both the FDA (August 2019) and EMA (December 2019) following failure of conventional therapies (Duggan and Keam, 2019). Preclinical and clinical evidence suggests a potential role for JAK inhibition in SSc. For instance, Dees et al. demonstrated that TG101209, a selective JAK2 inhibitor, markedly reduced dermal fibrosis in both bleomycin-induced and TSK-1 murine models (Dees et al., 2012). Similarly, case-based evidence has shown that tofacitinib, a JAK1/3 inhibitor with partial JAK2 inhibition, rapidly ameliorated SSc-associated polyarthropathy (Komai et al., 2018). Tofacitinib has also demonstrated efficacy in other sclerosing disorders such as generalized deep morphea and eosinophilic fasciitis (Cao et al., 2019; Kim et al., 2018).

The emergence of both selective and pan-JAK inhibitors has introduced a novel therapeutic paradigm in the management of autoimmune and fibrotic diseases. Their dual anti-inflammatory and antifibrotic activities, particularly in dermal, musculoskeletal, and pulmonary compartments, represent a promising avenue for targeted intervention (You et al., 2020).

PD29 is a 29-amino acid synthetic peptide engineered to target pulmonary fibrosis. It has been shown to exert anti-angiogenic effects, inhibit matrix metalloproteinase (MMP) activity, and disrupt integrin-mediated adhesion and signaling in fibrotic tissues (Qingbo et al., 2019). Furthermore, PD29 has been implicated in modulating fibrotic signaling by partially regulating the expression of TGF-β1, Smad3, and Smad7 (Qingbo et al., 2019).

In this study, we investigated the antifibrotic and anti-inflammatory properties of Upadacitinib and PD29, both individually and in combination, in a bleomycin-induced murine model of SSc and in primary human lung fibroblasts derived from patients with IPF. Our analyses focused on the modulation of JAK/STAT and TGF-β signaling components at the transcriptional and translational levels, as well as the impact on collagen synthesis and ECM remodeling.