Immortalized Rat Schwann Cells (IFRS1)

Insulin Promotes the Proliferation of IFRS1

Peripheral nerve function relies on Schwann cells which become dysfunctional during diabetic neuropathy. While insulin resistance and neuropathy connections are well-documented the specific effects of insulin on Schwann cells have not been thoroughly investigated. Saiki et al. used immortalized rat schwann cells (IFRS1) to examine how insulin directly impacts cell proliferation and myelin protein expression enhancement.

To determine if IFRS1 cells possess insulin receptors, they tested for insulin receptor beta (IR-beta) expression. Optical microscopy showed that IFRS1 cells were uniform (Fig. 1A). IR-beta presence was confirmed in IFRS1 through immunofluorescence staining (Fig. 1B) and identified as a 95 kDa band via Western blot (Fig. 1C). They assessed cell proliferation through MTT and CCK8 assays. The effect decreased to 1.6 ± 0.2-fold when exposed to LY294002 at a concentration of 3 μM (from 2.0 ± 0.2-fold). Phosphorylation of Akt and ERK was blocked by LY294002 at concentrations above 3 μM and PD98059 at concentrations above 30 nM. PD98059 showed no effect on the insulin-induced proliferation in the MTT assay results (Fig. 2A). Insulin increased IFRS1 proliferation by two-fold in CCK8 measurements (2.2 ± 0.3-fold; Fig. 2B) until LY294002 at 3 μM reduced it to 1.6 ± 0.2-fold which shows the PI3-K/Akt signaling pathway mediates insulin's effects. The compound PD98059 showed no impact on the insulin-induced proliferation rates measured with CCK8.

Fig. 1. Identification of insulin receptors (Saiki T, Nakamura N, et al., 2021).

Fig. 2. Insulin promotes the proliferation of IFRS1 (Saiki T, Nakamura N, et al., 2021).

Zonisamide Pretreatment Alleviates the OHP-Induced Toxicity against Immortalized Rat DRG Neurons, ND7/23, but Not against Immortalized Rat Schwann Cells, IFRS1

OHP functions as a platinum-based drug that induces peripheral neuropathy through attacks on dorsal root ganglion neurons. Zonisamide has exhibited neuroprotective activities toward adult rat DRG neurons in vitro and therefore, Takaku et al. aimed to assess its potential efficacy against OHP-induced neurotoxicity.

The researchers investigated oxaliplatin (OHP)-induced toxicity effects on immortalized rat DRG neurons (ND7/23) and Schwann cells (IFRS1) through the application of an MTS assay. A 6-hour pretreatment with zonisamide at 100 μM concentration improved ND7/23 cell viability significantly when these cells were exposed to OHP at 75 μM concentration for 24 hours, demonstrated in Figure 3a. The reduction in cell viability of IFRS1 cells was less severe than that of DRG neurons but zonisamide did not provide significant protection even when OHP exposure reached 48 hours (Fig. 3b and c). Zonisamide did not prevent OHP-caused death in immortalized mouse Schwann cells. The data shows zonisamide fails to protect Schwann cells while past research showed it does not improve IFRS1 cell proliferation or survival.

Fig. 3. Pretreatment with zonisamide alleviates the OHP-induced toxicity against ND7/23 cells, but not against IFRS1 cells (Takaku S and Sango K, 2022).