Toll-Like Receptors 2/4 and Diabetic Peripheral Neuropathy

Abstract

Peripheral neuropathy (PN) is a common, morbid complication of diabetes and prediabetes. Dysfunction of toll like receptors (TLR) 2 and 4 has been implicated in PN pathogenesis, and blocking TLR4 is proposed as a treatment for neuropathic pain. WT and TLR 2/4 global KO (TLR2/4-/-; n=5) mice were placed on a 60% high fat diet (HFD, n=5), with 5 WT controls provided a standard diet (CON, n=5). Mice underwent metabolic, neuropathic, and immunological phenotyping (Table 1) at early and late disease time points. TLR2/4-/- mice weighed more (P ≤ 0.023) but did not have increased fasting blood glucose levels. They had reduced hind paw withdrawal latencies (HPL) compared to HFD mice (P ≤ 0.01) and were similar to CON in early disease, but worsened in later disease. TLR2/4-/- mice consistently had lower sural nerve conduction velocities than CON and worsened as disease progressed (P ≤ 0.048). Immunophenotyping during late disease showed differences in the number of peripheral blood Ly6C- myeloid cells (P ≤ 0.05) and F4/80+ expression (P ≤ 0.0001). Inflammatory profiles of the sural nerve indicated a lower gene expression of the chemoattractant CCL-12 chemokine in TLR2/4-/- compared to CON mice. These results suggest that TLR2/4 KO may be initially protective against HFD induced neuropathy, but as PN progresses this effect is lost. Differences in circulating immune cells and CCL-12 gene expression may indicate an anti-inflammatory phenotype in TLR2/4-/- mice.Table 1. Metabolic, neuropathic and immunological phenotyping.Phenotypic MetricCON (n=5)HFD (n=5)TLR2/4-/-(n=5)Late stage weight (g)26 ± 339 ± 351 ± 3Late stage fasting blood glucose (mg/dL)150 ± 22190 ± 22172 ± 22HPL (sec)Early: 3.6 ± 0.3Late: 3.5 ± 0.4Early: 5.7 ± 0.3Late: 5.5 ± 0.4Early: 4.4 ± 0.3Late: 6.1 ± 0.4Sural NCV (m/s)Early: 22.0 ± 0.7Late: 23.9 ± 0.7Early: 18.5 ± 0.7Late: 17.9 ± 0.7Early: 20.0 ± 0.7Late: 17.2 ± 0.9Late stage Ly6C- circulating myeloid cells (104 cells/mL)7.8 ± 2.614.0 ± 2.74.8 ± 2.7Late stage circulating myeloid F4/80 expression (mean florescent intensity)978 ± 9611383 ± 10199967 ± 1019Late stage CCL-12 sural nerve gene expression (relative quantity)1.16 ± 0.240.59 ± 0.280.32 ± 0.24 Disclosure S. Elzinga: None. B. Murdock: None. J.M. Hayes: None. M.A. Tabbey: None. E.L. Feldman: None.