Introduction

Sepsis is a systemic inflammatory response that is accompanied by multiple organ dysfunction, oxidative stress, and overmuch inflammatory cytokines [1] sepsis-induced cardiomyopathy (SIC) is one of the common and well-elucidated complications in sepsis and sepsis-induced shock, while Gram-negative bacterial endotoxin (Lipopolysaccharide, LPS) serves as a key sepsis mediator for septicemia-associated multiple organ dysfunction or mortality [2].

Encoded by the ICA1 gene, ICA69 has a limited cellular distribution and tissue distribution. Past study primarily highlighted the physiopathological function of ICA69 in organ-specific autoimmune illnesses including Type 1 diabetes (T1D) [3]. Thymic deletion of ICA69 expression, for instance, is adequate to give rise to inflammatory events in various organs [4]. Nevertheless, our research revealed that ICA69 was notably regulated upward in lipopolysaccharide-induced cardiac tissue. According to previous research findings, ICA69 enrichment occurs in the proximity of the Golgi complex and its N-terminal half involves a BAR domain, a component that could bend or bind membranes and has mutual effect with phosphatide [5]. And the BAR-domain family encompasses numerous constituents, the majority of which function in transport and endocytosis [6].

STING, composed of multiple assumed transmembrane regions, is primarily anchored as a homodimer in the ER membrane in resting conditions [7]. Recent work suggests that, after STING binds cGAMP, it transfers to the ER-Golgi intermedium compartment (ERGIC) and the Golgi via the process depending on the COPI (coat protein complex I), COPII complex and ARF GTPases [8, 9], which is essential for the phosphorylation of STING and subsequent IRF3 stimulation [10, 11]. As STING marks an imperative molecule that can modulate inflammation and defense response in SIC, and participates in septic heart damage via inducing cardiac muscle cell pyroptosis [12], these results hint that ICA69 may participate in STING-dependent innate immune response.

Ferroptosis is a ROS-related and iron-related cell death, which is crucial for organ damage and target treatment of tumors [13, 14]. Recent studies show that the ferroptosis induction via high-iron diet or Gpx4 consumption stimulates the STING-related DNA sensor pathway, which finally causes the infiltration of macrophagus and pancreatic tumorigenesis [Assessment of oxidative stress

our team carried out the specimen preparation as per the assay kit specification. The levels of malondialdehyde (MDA) [53], superoxide dismutase (SOD) [54], GSH/GSSG [55], total antioxidant capacity (T-AOC) [56] in serum and heart samples were measured via colorimetric determination by assay kits according to previous studies mentioned above. The results of MDA, SOD were expressed as a unit per mg protein (U/mg prot).

Iron in serum and cardiac tissue

The tissue weight was accurately weighed, while the homogenate was mechanically prepared in an ice bath at 2500 rpm for 10 min to produce a 10% supernatant. After the sample is prepared, the protein level can be detected by the BCA Protein Concentration Assay Kit to facilitate the subsequent calculation of Fe content in tissues or cells per unit protein weight. Afterwards, iron standard test sample and iron test base liquid were added in sequence. Eventually, we mix the well, while detecting the standard well at 562 nm with the enzyme plate analyzer, measuring the well absorbance, and finish the colorimetry within 1 h.

LDH and CK MB in cardiac tissue

The quantity of cardiac tissue creatine kinase isoenzyme (CK-MB) was determined by a biochemical analyzing machine automatically (ADVIA® 2400, Siemens Ltd., China). The enzyme activities of lactate dehydrogenase (LDH) in serum were identified by rapid and sensitive assay kits according to the instruction. Briefly, we produced the specimens for the standard curve by nicotinamide adenine dinucleotide mother liquor and LDH buffer. A 50 μL Reaction Mix with 48 μL LDH Assay Buffer in it and 2 μL LDH Substrate Mix was supplemented into the specimens or standard specimens for a whole hour at 37 °C free of light, producing a 450 nm absorbance.

Survival condition

The extra mice in all groups (n = 10) were raised to study the survival status. The mortality was daily documented at the identical time node, while the survival rate was computed within seven days posterior to LPS injection at 10 mg/kg or PBS.

Echocardiography

Echocardiography was implemented by a Vevo 3100 ultrasonic equipment with a 10-MHz linear array ultrasound transducer (Fujifilm, VisualSonics, USA) after mice were anesthetized by 1.5% isoflurane. As the medial echocardiographic readings were collected from 3–5 heart cycles, the heart function indexes, such as fractional shortening (FS), heart rate (bpm), ejection fraction (EF), etc., were documented.

Statistical analysis

The entire measured data here were depicted by average ± SEM or characteristic images of 1 representative from 3 separate assays. As GraphPad Prism 8.0.2 software for Windows was adopted for statistic observation, the comparison between the two groups was performed by Student’s t-test, and the diversities between the groups were compared by two-way ANOVA and corrected by Bonferroni, with survival condition assessed by Kaplan–Meier analysis. Human data were studied by Wilcoxon (Exact) rank-sum test, while association among the expression of ICA1 in PBMCs and Acute Physiology and Chronic Health Evaluation II value of septic cases was evaluated by the Pearson correlation analysis. A P < 0.05 was deemed as significant on statistics.