This preclinical study used an Escherichia coli infection in mice to model post‑UTI chronic pelvic pain (PUPP). Infection produced a persistent pelvic allodynia phenotype that the authors used to assess mechanisms sustaining long‑term pain after UTI.
Two complementary approaches targeting brain microglia reduced persistent pelvic pain. First, pharmacologic depletion of microglia using PLX5622 attenuated pelvic allodynia. Second, pharmacologic inhibition of microglial activity with minocycline similarly reduced the pain phenotype. These results indicate that microglia play a central role in the maintenance of chronic pelvic pain in this model.
The interventions that altered microglial number or activity reduced pain behaviors but did not affect all outcomes examined (see section on dissociation below). The authors interpret these data as evidence that microglial activity is necessary for sustained post‑UTI pelvic nociceptive sensitization.
Morphological analysis of microglia in the prefrontal cortex of PUPP mice revealed features consistent with activation. Specifically, microglia exhibited reduced branching complexity and a less ramified phenotype compared with controls, a pattern generally interpreted as a transition from a surveillant to an activated state.
These structural changes in prefrontal cortex microglia were correlated with the presence of persistent pelvic allodynia, supporting a central nervous system component to post‑UTI pain maintenance in this model.
To characterize the molecular state of brain myeloid cells, the authors performed transcriptomic profiling of CD11b+ cells isolated from the brain. The transcriptional profile in PUPP animals was described as a reactive microglial signature.
Key features of this signature included enrichment for chemokines, genes related to NFκB signaling, and immediate early response genes. Pathway analysis implicated processes involved in immune regulation and leukocyte recruitment. Together, the transcriptional data complement the morphological findings and support a shift toward a pro‑inflammatory, reactive microglial phenotype in PUPP.
The study investigated Toll‑like receptor 4 (TLR4) as a candidate mediator of microglial reactivity and pain maintenance. Both general (whole‑animal) and microglia‑specific deletion of TLR4 were reported to reduce pelvic allodynia in the post‑UTI model.
TLR4 deletion also reduced microglial morphological features associated with activation, suggesting that TLR4 signaling contributes to the structural and functional activation of microglia observed in PUPP. These genetic loss‑of‑function data support a causal role for microglial TLR4 in sustaining post‑UTI chronic pelvic pain in this mouse model.
Complementing genetic approaches, the authors tested pharmacologic TLR4 inhibition in vitro. TLR4 blockade suppressed lipopolysaccharide (LPS)‑induced NFκB activation in microglial cells, reduced secretion of proinflammatory cytokines, and lowered CD68 expression, a marker associated with microglial activation.
These in vitro findings align with the in vivo genetic results and support a mechanistic model in which TLR4 signaling in microglia promotes NFκB‑dependent inflammatory responses that contribute to persistent pelvic nociception after UTI.
Although microglial depletion and TLR4 loss reduced persistent pelvic allodynia, microglial depletion did not improve urinary dysfunction measures or anxiety‑ and depression‑like behaviors assessed in the study. This indicates that the mechanisms sustaining pelvic nociception can be at least partly dissociated from those producing lower urinary tract dysfunction or affective behavioral changes in this model.
The absence of effect on urinary and affective endpoints suggests that microglial TLR4–dependent pathways specifically contribute to pain maintenance rather than driving all post‑UTI sequelae.
The authors conclude that microglial TLR4 is a critical mediator of post‑UTI chronic pelvic pain in their mouse model. Convergent evidence from microglial depletion, pharmacologic inhibition, transcriptional profiling, genetic TLR4 deletion, and in vitro TLR4 blockade supports a model where infection triggers a reactive microglial program—enriched for chemokines and NFκB‑related genes—driven in part by TLR4 and contributing to persistent pelvic allodynia.
These data identify microglial activation and TLR4 signaling as potential mechanistic targets for interrupting maintenance of chronic pelvic pain after UTI. The report is a preprint and has not undergone peer review; details beyond those presented in the article were not reported in the source.