Cell Stress and Cardiac Injury in Sepsis

Evidence

Two recent studies approach sepsis-related injury at different biological scales. One traces an immune-cell stress pathway through human transcriptomic data, cultured cells, and mouse models. The other examines cardiac rhythm, heart rate, troponin, and one-year mortality in critically ill adults. Together they do not prove one continuous mechanism, but they test a shared question: which signals reflect the damaging host response beyond the infection itself?

The mechanistic study focused on death-associated protein kinase 2 (DAPK2), an enzyme whose role in sepsis had been uncertain. Analyses of public human blood datasets found higher DAPK2 expression in sepsis, concentrated in monocyte and macrophage clusters. In primary mouse macrophages and human THP-1 macrophage-like cells, the investigators linked DAPK2 upregulation to TLR4–MyD88–NF-κB signaling after inflammatory stimulation.

The team then used mice lacking DAPK2 specifically in macrophages. In both cecal ligation-and-puncture polymicrobial sepsis and lipopolysaccharide-induced endotoxemia, those mice had better survival, lower circulating inflammatory cytokines, less macrophage death, and less lung and liver injury than control mice. Bacterial burdens and spread into blood did not differ significantly by genotype in the polymicrobial model. That distinction matters: the experimental benefit was associated with a changed host response, not demonstrated improvement in bacterial clearance.

Biochemical experiments placed HSPA5, a protein that restrains the endoplasmic-reticulum stress sensor IRE1α, downstream of DAPK2. DAPK2 bound HSPA5 and phosphorylated it at serine 588, accelerating its ubiquitin-mediated proteasomal degradation. Reduced HSPA5 allowed greater IRE1α activation. In DAPK2-deficient mice, inhibiting HSPA5 erased much of the survival and inflammation advantage, while co-inhibiting IRE1α countered that effect. These interventions establish a pathway within the tested cell and mouse systems; they do not establish a human therapy.

The clinical study was a secondary analysis of a retrospective cohort from one Swedish hospital. It included 586 adults admitted to critical care between 2012 and 2021 with sepsis requiring vasopressor support and a high-sensitivity cardiac troponin T measurement within 48 hours. Of these patients, 177 had pre-existing atrial fibrillation (AF), 112 developed new-onset AF, and 297 had no AF. Elevated troponin, defined as at least 15 ng/L, appeared in 546 patients, or 93%.

AF status explained only 1.2% of variation in troponin concentrations, while the highest recorded heart rate explained virtually none. In unadjusted analyses, one-year mortality was higher with pre-existing AF (hazard ratio 2.4, 95% confidence interval 1.8–3.2) and new-onset AF (1.8, 1.3–2.5) than without AF. In the multivariable model, new-onset AF remained associated with mortality (1.5, 1.1–2.2), as did higher log-transformed troponin (1.3, 1.1–1.4). Highest heart rate per 10-beat-per-minute increase was not associated with mortality (1.0, 0.95–1.1). These are prognostic associations, not evidence that AF or troponin caused death.

Analysis — Stress burden beyond heart rate

The cross-study pattern is that sepsis injury may be better represented by specific stress-response signals than by a simple measure of physiological speed. In the mouse experiments, DAPK2 amplified macrophage endoplasmic-reticulum stress, inflammation, and cell death without measurably changing bacterial burden. In the human cohort, troponin and AF carried prognostic information that highest recorded heart rate did not, arguing against a purely rate-driven explanation for myocardial injury. It is an analysis—not an established link—to view these findings as evidence that immune-cell stress and cardiac vulnerability are parallel readouts of a broader dysregulated host response. The clinical study did not measure DAPK2, HSPA5, or IRE1α, and the mechanistic study did not test AF or troponin outcomes. A useful emerging research direction would pair immune-pathway measurements with repeated rhythm, troponin, and cardiac-function assessments in the same prospective sepsis cohort. Such work could test whether molecular stress states precede, accompany, or merely correlate with cardiac injury; the present studies cannot answer that question.

Limitations

The DAPK2 study is predominantly preclinical. Human evidence came from reanalysis of public transcriptomic datasets, not an intervention or prospective patient cohort. Mouse cecal ligation and puncture and endotoxemia reproduce selected features of sepsis but cannot capture its full clinical diversity. The study did not identify the E3 ubiquitin ligase responsible for HSPA5 degradation, rule out every additional phosphorylation site, define the interaction structurally, or test a selective DAPK2 inhibitor. Its macrophage-specific genetic model also leaves effects in other cell types unresolved.

The cardiac study was retrospective, observational, and single-center. Troponin testing was clinician-directed, which may have selected patients with suspected cardiac involvement. AF duration and burden were unavailable; highest heart rate within 72 hours may miss sustained tachycardia; and echocardiography was available for only 305 patients. Adjustment cannot eliminate residual confounding from illness severity or underlying cardiovascular disease. Finally, these studies are complementary rather than replications: one supplies a candidate immune mechanism in experimental systems, while the other supplies human prognostic associations. Neither establishes that the DAPK2 pathway causes cardiac injury, and neither supports treatment or follow-up instructions.