From molecular markers to architectural control: cytoskeletal checkpoints as the decisive state-access layer of the aging microglial targetome

The molecular complexity of microglial aging, extensively catalogued across transcriptomes, proteomes, and single-cell atlases, has not translated to mechanistic clarity about what to target or when. If anything, the growing list of altered molecules has made the prioritisation problem more difficult. We argue this reflects a systematic mismatch between the level at which dysfunction is measured and the level at which it is organised. In this perspective, the microglial cytoskeleton, the coordinated actin-microtubule machinery sustaining morphodynamic plasticity, mechanosensing, phagocytic capacity, and synaptic support, should not be viewed as a downstream readout of aging. Rather, it constitutes the control architecture whose failure, we propose, may initiate rather than merely accompany it. Accordingly, the most informative dementia targets are not age-associated molecules per se, but cytoskeletal checkpoints: regulatory nodes whose perturbation reorganises actin-microtubule coupling and, through this organization, propagates across signalling, metabolism, and circuit output. The microglial targetome should therefore be organised not as a catalogue of altered molecules but as a map of control leverage embedded within cytoskeletal architecture. Two proof-of-principle checkpoints establish this logic. Acute, microglia-specific loss of Profilin-1 (Pfn1), an actin-availability gatekeeper, is sufficient to collapse morphodynamic responsiveness and trigger an ERK/NF-κB-driven senescence-associated secretory phenotype, whose cytokine and MMP9 output selectively disrupts GABAergic synaptic function. By contrast, deletion of Arpc4 defines a mechanistically orthogonal axis: loss of branched actin nucleation impairs TGFβ receptor trafficking, prevents nuclear accumulation of SMAD2/3, and drives entry into a DAM-like state. This cascade appears to operate independently of ERK/NF-κB signaling, a prediction that remains to be tested directly, and establishes a distinct class of cytoskeletal checkpoint. Together, these two examples anchor a two-axis checkpoint taxonomy and underpin mCytoMAP, a sex-stratified, context-resolved decision framework ranking cytoskeletal targets according to reversibility, dissipation load, cell-state specificity, and circuit consequence. Within this framework, the central challenge becomes tractable: identifying which checkpoints can redirect the aging microglial state, and determining the biological contexts, including sex and disease stage, in which such interventions are most effective.