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 Metric | CON (n=5) | HFD (n=5) | TLR2/4-/-(n=5) |
| Late stage weight (g) | 26 ± 3 | 39 ± 3 | 51 ± 3 |
| Late stage fasting blood glucose (mg/dL) | 150 ± 22 | 190 ± 22 | 172 ± 22 |
| HPL (sec) | Early: 3.6 ± 0.3 Late: 3.5 ± 0.4 | Early: 5.7 ± 0.3 Late: 5.5 ± 0.4 | Early: 4.4 ± 0.3 Late: 6.1 ± 0.4 |
| Sural NCV (m/s) | Early: 22.0 ± 0.7 Late: 23.9 ± 0.7 | Early: 18.5 ± 0.7 Late: 17.9 ± 0.7 | Early: 20.0 ± 0.7 Late: 17.2 ± 0.9 |
| Late stage Ly6C- circulating myeloid cells (104 cells/mL) | 7.8 ± 2.6 | 14.0 ± 2.7 | 4.8 ± 2.7 |
| Late stage circulating myeloid F4/80 expression (mean florescent intensity) | 978 ± 961 | 1383 ± 1019 | 9967 ± 1019 |
| Late stage CCL-12 sural nerve gene expression (relative quantity) | 1.16 ± 0.24 | 0.59 ± 0.28 | 0.32 ± 0.24 |
| Phenotypic Metric | CON (n=5) | HFD (n=5) | TLR2/4-/-(n=5) |
| Late stage weight (g) | 26 ± 3 | 39 ± 3 | 51 ± 3 |
| Late stage fasting blood glucose (mg/dL) | 150 ± 22 | 190 ± 22 | 172 ± 22 |
| HPL (sec) | Early: 3.6 ± 0.3 Late: 3.5 ± 0.4 | Early: 5.7 ± 0.3 Late: 5.5 ± 0.4 | Early: 4.4 ± 0.3 Late: 6.1 ± 0.4 |
| Sural NCV (m/s) | Early: 22.0 ± 0.7 Late: 23.9 ± 0.7 | Early: 18.5 ± 0.7 Late: 17.9 ± 0.7 | Early: 20.0 ± 0.7 Late: 17.2 ± 0.9 |
| Late stage Ly6C- circulating myeloid cells (104 cells/mL) | 7.8 ± 2.6 | 14.0 ± 2.7 | 4.8 ± 2.7 |
| Late stage circulating myeloid F4/80 expression (mean florescent intensity) | 978 ± 961 | 1383 ± 1019 | 9967 ± 1019 |
| Late stage CCL-12 sural nerve gene expression (relative quantity) | 1.16 ± 0.24 | 0.59 ± 0.28 | 0.32 ± 0.24 |
S. Elzinga: None. B. Murdock: None. J.M. Hayes: None. M.A. Tabbey: None. E.L. Feldman: None.
