MR-409 promotes neurogenesis and improves neurological function after cerebral ischemia through attenuation of...

Neurological recovery during the chronic phase of ischemic stroke (IS) remains a major clinical challenge. Our previous studies showed that the growth hormone-releasing hormone analogue (GHRH-A) MR-409 promotes neurogenesis and improves neurological outcomes. However, the underlying mechanisms remain unclear. Here, a transient middle cerebral artery occlusion (tMCAO) mouse model was used to investigate whether early modulation of microglial activation mediates these effects. MR-409 (2.5, 5, or 10 μg, s.c.) was administered immediately after tMCAO and daily for 3, 7, 14, or 28 days depending on the experimental design. The GHRH receptor antagonist MIA-602 and the microglial inhibitor minocycline (MINO) were used to assess mechanism involvement. We found that MR-409 (10 μg, s.c.) significantly reduced infarct volume and brain edema and improved function and cerebral blood flow at 3 days. It suppressed hippocampal microglial activation and promoted M2 polarization at 3-7 days, decreasing TNF-α, IL-1β, and IL-6 while increasing CD206, Arg-1, and YM1/2, which were reversed by MIA-602. MR-409 enhanced hippocampal neurogenesis, increasing Nestin⁺, Tbr2⁺, and DCX⁺ cells at 7-14 days and newborn neuron survival at 28 days. These effects were enhanced by MINO but abolished by MIA-602. Functionally, MR-409 or MINO improved motor performance at 7 days, whereas only MR-409 improved both motor and cognitive function at 28 days. These findings indicate that MR-409 promotes long-term neurological recovery by attenuating acute microglial activation, improving the post-ischemic microenvironment, and enhancing hippocampal neurogenesis, highlighting its therapeutic potential for IS.