Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF) Restricts Inflammatory Progression through Limiting Macrophage Infiltration in DRG and Sciatic Nerve during Diabetic Peripheral Neuropathy

Diabetic peripheral neuropathy (DPN) is a prevalent complication affecting over half of individuals with diabetes. This study investigates the role of mesencephalic Astrocyte-derived neurotrophic factor (MANF) in DPN progression and its potential as a therapeutic target. Using a streptozotocin (STZ)-induced diabetic mouse model, we analyzed MANF expression in the dorsal root ganglia (DRG) and sciatic nerve and assessed the effects of recombinant human MANF (rhMANF) administration on DPN symptoms. Our findings show significant upregulation of MANF protein levels in the DRG of diabetic mice, along with an increased presence of MANF-expressing macrophages in both the DRG and sciatic nerve. Intravenous administration of rhMANF from Day 7 to Day 21 post-STZ injection yielded multiple beneficial outcomes. Notably, rhMANF treatment alleviated mechanical hypoalgesia, as measured by the paw mechanical withdrawal threshold (PMWT), and enhanced sciatic nerve conduction, improving motor nerve conduction velocity (MNCV). Additionally, it increased intradermal nerve density, indicated by more PGP9.5-positive nerve fibers in the plantar skin of treated diabetic mice. These improvements were associated with reduced macrophage infiltration in the DRG and sciatic nerve, marked by fewer CD68 and Iba-1 positive cells, and inhibition of inflammatory signaling pathways. Specifically, rhMANF treatment decreased NF-κB p65 phosphorylation and suppressed p38 MAPK phosphorylation, indicating reduced inflammation. In summary, our research underscores MANF's potential as a novel therapeutic target for DPN, particularly due to its anti-inflammatory properties. Further exploration of MANF could lead to the development of more effective treatments for this debilitating aspect of diabetes.