Extended Data Fig. 8: Effect of lactate on EAE.

a, EAE development of mice after vehicle injection (n = 9), intraperitoneal (ip) (n = 10), nasal, or intravenous (iv) (n = 5 per group) L-LA or D-LA administration. b, IFNγ, IFNγIL-17 and IL-17 CD4 T cells in CNS isolated from mice from a 28 days after EAE induction (n = 3–4 per group). c–f, Heat map (c), GSEA (d) and IPA (e,f) analysis of RNA-seq of splenic DCs isolated from mice treated with vehicle, L-LA (e) and D-LA (f) 28 days after EAE induction. Statistical analysis was performed using two-way ANOVA for a and one-way ANOVA with Dunnett’s post-hoc test for selected multiple comparisons for b. Data shown as mean ± s.e.m.+++++

From: Lactate limits CNS autoimmunity by stabilizing HIF-1α in dendritic cells.

Autoimmune diseases, such as multiple sclerosis (MS), arise when the immune system mistakenly attacks the body's own tissues. Dendritic cells (DCs) play a crucial role in orchestrating immune responses, making them potential targets for therapeutic intervention. In this groundbreaking study published in Nature, Sanmarco et al. uncovered a novel regulatory mechanism within DCs that helped limit inflammation and autoimmune responses, paving the way for new therapeutic approaches.

The study began by investigating the role of HIF-1α, a transcription factor that is known to be activated by low oxygen levels, in DCs during central nervous system (CNS) inflammation. Using single-cell RNA sequencing, the researchers found that HIF-1α was expressed in both classical DC subsets (cDC1s and cDC2s) in the context of experimental autoimmune encephalomyelitis (EAE), a model of MS. Deletion of the HIF-1α gene in DCs using a conditional knockout mouse model worsened the severity of EAE, highlighting the importance of HIF-1α in controlling the immune response.

Further analysis revealed that DC activation triggered the production of lactate, a molecule that can stabilize HIF-1α. Lactate treatment of DCs reduced the expression of pro-inflammatory cytokines and suppressed the activation of effector T cells. Importantly, this anti-inflammatory effect was HIF-1α-dependent, suggesting a feedback loop where HIF-1α activation by lactate led to reduced DC pro-inflammatory responses.

The researchers then focused on understanding the metabolic changes associated with HIF-1α activation. They found that HIF-1α-deficient DCs exhibited altered mitochondrial function, with increased oxygen consumption and reduced expression of glucose transporters. Lactate treatment, however, reversed these changes and reduced oxygen consumption in wild-type DCs, suggesting a role for lactate in modulating mitochondrial metabolism.

They identified a key molecule, NDUFA4L2, that was upregulated by HIF-1α and played a critical role in limiting mitochondrial reactive oxygen species (mtROS) production. Overexpression of NDUFA4L2 in DCs abolished the mtROS-induced increase in pro-inflammatory gene expression and suppressed the production of pro-inflammatory cytokines. This demonstrated that NDUFA4L2 acted as a regulatory switch that limited mtROS-mediated inflammation in DCs.

mtROS and inflammation activate the unfolded protein response (UPR) and the transcription factor XBP1, which drives pro-inflammatory responses in DCs and macrophages. The researchers found that lactate treatment reduced the activation of XBP1 in DCs, while mtROS production induced by a specific mtROS activator abolished this effect. HIF-1α deficiency also led to increased XBP1 mRNA splicing, indicating a role for HIF-1α in limiting XBP1 activation.

They further explored the role of XBP1 in EAE using a conditional knockout mouse model. XBP1 deficiency improved the disease outcome, reduced the number of pro-inflammatory T cells, and suppressed the recall response to the myelin antigen MOG35-55. These findings suggested that NDUFA4L2-dependent suppression of mtROS production played a critical role in suppressing XBP1-dependent pro-inflammatory responses in DCs.

To translate their findings into a therapeutic approach, the researchers engineered a probiotic bacterium, Escherichia coli Nissle (EcN), to produce d-lactate (D-LA). They deleted the pta gene, which encodes an enzyme involved in acetate production, and introduced a plasmid containing the ldhA gene under a heat-inducible promoter. This allowed the production of D-LA at 37°C, the optimal temperature for probiotic viability.

When administered to mice with EAE, EcNLac (the engineered probiotic) increased the levels of D-LA in the plasma and gastrointestinal tract, and activated the HIF-1α-NDUFA4L2 signaling pathway in DCs. This led to a reduction in pro-inflammatory T cells and a significant improvement in disease symptoms. The probiotic did not affect the bacterial burden or the number of pathogen-specific T cells, indicating a specific targeting of the immune system.

This study revealed a novel immune metabolic pathway that involved the production of lactate by DCs, which stabilized HIF-1α and activated NDUFA4L2 to limit mtROS and XBP1-driven pro-inflammatory responses. This pathway provided a potential therapeutic target for autoimmune diseases, and the engineered probiotic offered a promising approach for long-term immune modulation.

Future studies could explore the broader implications of this pathway in other autoimmune diseases and investigate the role of other metabolites and signaling pathways in DC function. Additionally, the development of more sophisticated probiotic designs and the optimization of delivery methods could further enhance the therapeutic potential of this approach.

Overall, this study offers a valuable new understanding of DC biology and opens the door to innovative therapeutic strategies for autoimmune diseases, offering hope for patients suffering from these devastating conditions.

Reference:

1. Sanmarco LM, Rone JM, Polonio CM, Fernandez Lahore G, Giovannoni F, Ferrara K, Gutierrez-Vazquez C, Li N, Sokolovska A, Plasencia A, Faust Akl C, Nanda P, Heck ES, Li Z, Lee HG, Chao CC, Rejano-Gordillo CM, Fonseca-Castro PH, Illouz T, Linnerbauer M, Kenison JE, Barilla RM, Farrenkopf D, Stevens NA, Piester G, Chung EN, Dailey L, Kuchroo VK, Hava D, Wheeler MA, Clish C, Nowarski R, Balsa E, Lora JM, Quintana FJ. Lactate limits CNS autoimmunity by stabilizing HIF-1α in dendritic cells. Nature. 2023 Aug;620(7975):881-889.