Uveitis is a kind of inflammatory ocular disease that is the third leading cause of blindness worldwide, accounting for 5–10 % of global vision impairment, and up to 35 % of patients with uveitis may suffer severe vision loss [1,2]. An acknowledged animal model of uveitis is endotoxin-induced uveitis (EIU), which can be induced by lipopolysaccharide (LPS) injected into the footpad or vitreous body [3]. Microglia activation and the destruction of blood-retinal barrier (BRB) are the primary causes for pathological progression within uveitis [4]. Inflammatory signals activate retinal microglia, leading to BRB breakdown. Conversely, microglia depletion has been proved to impede inflammatory cytokines infiltration into the retina and protect BRB integrity. These findings suggest that targeting microglial activation could offer a novel therapeutic strategy for uveitis [5]. The current treatment of uveitis mainly relies on corticosteroids and immunosuppressive agents [6], nevertheless, long-term application can cause side effects such as elevated intraocular pressure, bone marrow suppression and liver function impairment. Thus, it is necessary to seek therapeutic drugs that can ensure the efficacy and reduce the toxic side effects.

The current evidence substantiates that microglial cell activation is involved in the progression of uveitis [7]. Microglia are resident immune cells in the retina. The activated microglia are divided into pro-inflammatory M1 type and anti-inflammatory M2 type. After LPS stimulation, M1 microglia transformed from a round and oval resting state into an amoeboid activated morphology, accompanied by increased secretion of the pro-inflammatory mediators TNF-α, iNOS and chemokines [8,9]. In contrast, M2 microglia highly express the anti-inflammatory markers CD206, IL-10 and Arg-1, these mediators collectively exert neuroprotective effects and sustain the M2 phenotype [10]. Under inflammatory stimulation, the M1/M2 balance in microglia is broken, activated microglia release a large number of inflammatory factors through transforming into M1 profile, which contribute to the breakdown of BRB and subsequent retinal damage [11]. Toll-like receptor 4 (TLR4), expressed on the microglial surface, plays a pivotal part in LPS-induced microglia activation. Upon LPS binding, TLR4 recruits medullary differentiation protein 88 (MyD88), activating downstream signaling nuclear factor-kappaB (NF-κB), and promoting the transcription of inflammatory mediators [12].

Panax notoginseng not only dispels blood stasis and stops bleeding, but also can reduce swelling and pain, is widely used in various inflammatory diseases in clinical practice, including tenosynovitis, cervicitis, periodontitis, esophagitis and so on [13] [14] [15] [16]. Ophthalmologists also often use Panax notoginseng to treat various ophthalmic diseases, such as glaucoma, retinal vein obstruction, and vitreous hemorrhage [17] [18] [19]. Importantly, Panax notoginseng can be used to treat uveitis. For example, Panax notoginseng compound was used for the treatment of uveitis, with a total effective rate of 70 %, while reducing inflammatory factors in serum, improving immune function, and increasing the level of CD8 in serum [20], the results of network pharmacology suggested that its pharmacological mechanism was related to NF-κB, TNF and other signaling pathways [21]. In addition, it has been reported that after 3 months of treatment for uveitis patients with Panax notoginseng compound combined with hormone, the visual acuity was significantly improved, the adverse hormone reactions were significantly reduced, and the effective rate reached 96 % [22]. In rabbit uveitis model, Panax notoginseng compound could alleviate choroidal and retinal edema, inhibit inflammatory cell infiltration, reduce CD3, CD4, CD8, CD20 positive cells, and decrease inflammatory factors in peripheral blood and aqueous humor [23]. Although Panax notoginseng is widely used in the treatment of uveitis, the current research focuses on the compounds, and the role of Panax notoginseng in the compound has not been elucidated. In this work, we investigated the protective effects of Panax notoginseng on EIU mice and BV2 cells. Subsequently, RNA sequencing analysis was applied to predict its underlying molecular mechanism followed further validation by western blot and QPCR. Moreover, the main active components of Panax notoginseng also verified the mechanism and revealed the substance basis for its therapeutic effects on retinal inflammation during EIU.