ROBO1 x SLIT2

The Slit2 guidance ligand and its Roundabout (Robo) family of receptors regulate axonal guidance and vascular patterning during cardiac morphogenesis, yet the role of Slit2-Robo signaling in the adult heart remains unclear. Here, we identified epicardium-derived Slit2 as highly enriched in neonatal cardiac fibroblasts (cFBs) but markedly reduced in adult hearts. Following myocardial infarction (MI), Slit2 transiently increases in the infarct border zone seven days post-MI but declines significantly after one month. In vitro, Slit2 overexpression in cFBs selectively upregulated angiogenic genes during myofibroblast differentiation without affecting extracellular matrix (ECM) gene expression. In vivo, AAV9-mediated cardiac-specific overexpression of Slit2 (AAV9-cTNT-Slit2) improved cardiac function, increased endothelial cell (EC) proliferation and vascular density, but did not alter fibrotic deposition following MI. Conditioned media from Slit2-overexpressing cFBs promoted EC proliferation, activation, and tube forming abilities, consistent with the increased expression of pro-angiogenic Robo1 and other vascular growth factors in the myocardium of AAV9-Slit2-treated hearts. Additionally, Slit2 overexpression attenuated cardiomyocyte hypertrophy after MI and suppressed fetal gene expression in vitro. Mechanistically, Slit2 appears to mediate its cardioprotective effects through enhanced interactions with Robo1 in cFBs and ECs. These findings support Slit2-Robo signaling as a promising therapeutic target for improving blood vessel formation and maintaining cardiac muscle integrity following ischemic injury.

Visual sensation relies on retinal circuitry to receive environmental inputs and convey relevant information for behavioral outputs. Many species depend on gaze stabilization behaviors, such as the optokinetic reflex (OKR), to perceive and correct for global motion. OKR calculation begins in the retina, where ON direction-selective ganglion cells (oDSGCs) respond to slow visual motion and deliver information to the accessory optic system (AOS) to inform oculomotor outputs. Here, we find that the guidance receptor roundabout-1 (Robo1) and its ligand Slit2 are selectively expressed in mammalian retinal AOS components and refine oDSGC circuitry to constrain OKR gain for appropriate image stabilization responses. Robo1 or Slit2 loss-of-function (LOF) mutants exhibit an increase in OKR gain, reducing directional asymmetry by elevating naturally weaker OKR responses. These behavioral enhancements largely arise from alterations in the retina, and loss of Slit2 in starburst amacrine cells (SACs) enhances oDSGC firing properties, with increased spike responses, excitatory synaptic puncta, and downstream AOS activation. These findings reveal that the Slit2/Robo1 signaling tunes oDSGC circuitry to maintain regulated image stabilization behavior.