Hypothesis

Pharmacologic inhibition of lactate dehydrogenase (LDH) preferentially LDH‑A will attenuate immunosenescence by simultaneously suppressing pathogenic Th17 differentiation and NLRP3 inflammasome lactylation in perivascular adipose tissue (PVAT), thereby improving vascular function in aged organisms.

Mechanistic Rationale

IL‑6 trans‑signaling drives Th17 cell differentiation through up‑regulation of glycolysis and lactate dehydrogenase activity【3】. The resulting lactate fuels two downstream effects: (1) it provides a biosynthetic and signaling metabolite that sustains the Th17 pathogenic phenotype, and (2) it serves as the substrate for protein lactylation, a post‑translational modification that fine‑tunes NLRP3 inflammasome activation【4】. When glycolysis is blocked, caspase‑1 activation is suppressed, confirming that lactate production is required for NLRP3 signaling【4】. We propose that LDH inhibition creates a metabolic bottleneck where pyruvate accumulates instead of being converted to lactate. Elevated pyruvate can (a) inhibit mitochondrial ROS production, thereby dampening NLRP3 activation independently of lactylation, and (b) act as a weak histone deacetylase inhibitor that promotes FOXP3 stability, favoring regulatory T‑cell (Treg) persistence over Th17 conversion. This dual action—reducing both the lactate‑dependent Th17 driver and the lactate‑dependent NLRP3 lactylation—offers a mechanistic advantage over selective IL‑6 trans‑signaling blockade, which only upstreamly limits glycolysis initiation.

Experimental Design

1. Animal models: Use 20‑month‑old C57BL/6 mice (aged) and age‑matched young controls.
2. Interventions:
   • LDH‑A specific inhibitor (e.g., FX11) administered via osmotic pump for 4 weeks.
   • Parallel groups receive anti‑IL‑6R antibody (MR16‑1) to block trans‑signaling.
   • Combination group receives both LDH‑A inhibitor and anti‑IL‑6R.
   • Control groups receive vehicle or isotype antibody.
3. Readouts:
   • Flow cytometry of PVAT stromal vascular fraction for Th17 (CD4+IL‑17A+) and Treg (CD4+FoxP3+) frequencies.
   • Western blot and mass spectrometry for NLRP3 lactylation (K‑lac) and caspase‑1 p20 cleavage.
   • Lactate and pyruvate concentrations in PVAT homogenates (enzymatic assays).
   • Vascular function assessed by ex vivo aortic ring tension measurements (endothelium‑dependent relaxation).
   • Serum IL‑6, soluble IL‑6R, and classic vs trans‑signaling activity (STAT3 phosphorylation in hepatocytes).
4. Statistical analysis: Two‑way ANOVA with post‑hoc Tukey test; n=8 per group for adequate power.

Expected Outcomes

• LDH‑A inhibition will reduce PVAT lactate levels and increase pyruvate, correlating with decreased Th17 frequencies and preserved Treg numbers.
• NLRP3 lactylation and caspase‑1 activation will be significantly lowered in LDH‑A‑treated aged mice, mirroring effects seen with glycolysis blockade【4】.
• Vascular dysfunction (impaired aortic relaxation) will be rescued, approaching young‑control levels.
• Anti‑IL‑6R alone will lower Th17 but only modestly affect NLRP3 lactylation; the combination will produce synergistic suppression of both pathways beyond either monotherapy.

Potential Pitfalls and Falsification

If LDH‑A inhibition fails to reduce NLRP3 lactylation or Th17 infiltration despite confirmed metabolic shift (lower lactate, higher pyruvate), the hypothesis that lactate is the indispensable metabolic node linking IL‑6 trans‑signaling to inflammasome activation in PVAT would be falsified. Conversely, observing improved vascular function without changes in Th17 or NLRP3 lactylation would suggest alternative LDH‑dependent mechanisms, prompting refinement of the mechanistic model.