Background: The extracellular matrix is associated with the pathophysiology of diabetic complications; however, the role of chondroitin sulfate (CS) remains unclear. To clarify the effects of CS on diabetic neuropathy (DN), we assessed the effect of genetically reducing CS in mice through disruption of a gene encoding the rate-limiting CS-synthesizing enzyme, i.e., CS N-acetylgalactosaminyltransferase-1 (T1).
Methods: T1 knockout (T1KO) mice were generated from the C57BL/6N strain and C57BL/6N were prepared as wild type (WT). Diabetes was induced through streptozotocin injection in 6-week-old male mice. All data were obtained 3 weeks after streptozotocin injection.
Results: In the heat radiant test, while thermal nociception in nondiabetic WT and T1KO mice were normal and significantly disrupted in diabetic WT mice, that in diabetic T1KO mice was preserved. The number of plantar peripheral nerve fibers was also significantly decreased in diabetic WT mice; however, that in diabetic T1KO mice were relatively normal. Furthermore, immunohistochemistry revealed loss of calcitonin gene-related peptide-positive neurons in the dorsal root ganglia (DRG) in diabetic WT mice, which contains a cluster of sensory neuron bodies. In contrast, those neurons were protected in diabetic T1KO mice. Hence, nociception and thermoception are preserved in diabetic T1KO mice. To investigate the mechanisms underlying these events, we analyzed gene expression in DRG through real-time polymerase chain reaction and confirmed the suppression of caspase-3 and caspase-9 in diabetic T1KO mice, compared to those in diabetic WT mice. However, levels of Bcl2, TNF-α, MMP9, and reactive oxygen species-related enzymes (HO-1, NOX) did not differ significantly between WT and T1KO diabetic mice.
Conclusions: Reduced CS production is suggested to have potentially beneficial effects on preventing DN by suppressing apoptotic signaling and could be a cutting-edge target of clinical application.
H. Ishiguro: Research Support; Self; MSD K.K., Sanofi K.K., Eli Lilly and Company. T. Ushiki: None. A. Kawasaki: None. K. Cho: None. M. Masuko: None. K. Sango: None. M. Igarashi: None. H. Sone: Research Support; Self; Novo Nordisk Inc., Eli Lilly and Company, MSD K.K., Chugai Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd., Takeda Development Center Asia, Pte. Ltd., Daiichi Sankyo Company, Limited, Ono Pharmaceutical Co., Ltd., Kyowa Hakko Kirin Co., Ltd., Sanofi, Kowa Pharmaceuticals America, Inc., Eisai Inc..