Microglial CRAC Channel Loss Enlarges Stroke Injury in Aged Mice
Ablating Stim1 and Stim2 in microglia did what the biology promised at one level: it reduced calcium signaling. It did not protect the brain after ischemic stroke. In aged mice, that genetic intervention was followed by larger infarcts, worse tissue injury, and a sex-specific pattern that cut against the expected anti-inflammatory benefit of dampening microglial CRAC channel activity.
The study focused on 15-month-old mice carrying microglial Stim1/Stim2 deletion through Cx3cr1-CreERT2. These endoplasmic reticulum calcium sensors normally gate calcium release-activated calcium channels, the pathway that helps drive calcium transients in immune cells. Because calcium signaling is often tied to inflammatory activation, the working assumption was straightforward: weaken the pathway, and the post-ischemic immune response should become less injurious. The data moved in the opposite direction.
Calcium Signals Fell, Yet Infarcts Grew
In vivo two-photon imaging confirmed that microglia lacking Stim1 and Stim2 produced calcium transients roughly one-third smaller during cortical spreading depolarizations. That finding verifies target engagement. The microglia were less able to generate the calcium responses that ordinarily follow tissue stress and ionic disturbance.
The stroke model used next was distal middle cerebral artery occlusion, tracked with multiparametric 9.4 T MRI. Six hours after occlusion, control and knockout mice looked broadly similar on the major early readouts: infarct size, edema, and diffusion did not separate. Lesion perfusion, however, trended lower in the knockout group. The divergence emerged later, after the first window of injury had already passed.
Between 6 and 48 hours, infarcts in control males did not expand. In male mice lacking microglial Stim1/Stim2, infarcts enlarged 2.7-fold over that same interval. By 48 hours, those knockout males carried infarcts 2.2-fold larger than controls. Female knockout mice did not show the same difference.
One sentence captures the biological surprise: dampening microglial calcium signaling worsened tissue loss after stroke.
Perfusion Support May Outweigh Inflammatory Dampening
The investigators did not stop at lesion volume. Lesions in the knockout animals also showed a lower apparent diffusion coefficient, a marker consistent with more severe tissue injury. That shift matters because diffusion restriction usually tracks with cellular energy failure, membrane damage, and the cascade that follows failure of ion homeostasis. The pattern suggests that the tissue surrounding the initial ischemic core was less able to recover when microglial CRAC signaling was removed.
Neither hemispheric swelling nor cerebral arterial anatomy explained the outcome difference. That detail closes off two obvious alternate explanations: the worsening was not simply a matter of more edema compressing tissue, and it was not driven by a grossly different vascular layout. What remained was the physiology of microglia itself and the timing of their response to ischemia.
The most plausible explanation offered by the data is also the most clinically relevant. Microglial CRAC signaling may help sustain perfusion in threatened tissue during the first days after ischemia, even if that same pathway can support pro-inflammatory activity. In this experiment, the perfusion-preserving role appears to have outweighed any benefit from reducing inflammation. That tradeoff is exactly why a pathway that looks harmful in one immune context can become protective in a living brain under ischemic stress.
Why a Shorter Calcium Response Can Still Be Harmful
Microglia are not passive bystanders after stroke. They sense ATP release, membrane breakdown, ionic shifts, and spreading depolarization, then coordinate local responses that can influence vascular tone, debris handling, cytokine release, and tissue repair. Calcium is central to that signaling network. Suppressing calcium influx through Stim1/Stim2-dependent channels likely blunts inflammatory programs, but it may also impair adaptive responses needed to preserve the penumbra.
This study lands in an uncomfortable but important place for translational neuroscience. In immune biology, lower calcium signaling often implies lower activation. In the ischemic brain, activation is not uniformly harmful. Some of the earliest post-stroke microglial functions may be stabilizing rather than destructive, especially when blood flow is precarious and tissue survival depends on tiny shifts in microvascular support.
The sex difference also deserves attention. Female knockout mice did not differ from controls in infarct size, while male knockout mice showed marked expansion. The article does not resolve why the response diverged by sex, but it does show that the injury phenotype was not uniform across the cohort. Any future therapeutic strategy aimed at microglial calcium channels would have to account for that heterogeneity rather than assume a single response across sexes.
Translational Caution for Microglial Ion-Channel Targeting
The result is a warning against reducing stroke immunobiology to a simple pro-inflammatory versus anti-inflammatory binary. A pathway that reduces inflammatory signaling can still worsen outcome if it also suppresses microglial functions that support perfusion or tissue resilience. In that setting, the first measurable benefit at the cellular level can become a net loss at the organ level.
Because this is a preprint, the findings should be read as hypothesis-generating rather than settled practice guidance. Even so, the experimental design is strong in the places that matter most: it confirms loss of calcium signaling, uses aged animals, follows injury over time, and measures infarct evolution rather than a single early snapshot. Those choices make the infarct expansion signal hard to dismiss.
For stroke biology, the message is direct. Microglial Stim1/Stim2-dependent calcium signaling is not just an inflammatory switch. In the first days after ischemia, it may be part of the machinery that keeps threatened tissue alive, and removing it can enlarge the final infarct instead of shrinking it.