Protein tyrosine phosphatase 1B deficiency improves glucose homeostasis in insulin-dependent diabetes mellitus treated with leptin

Leptin, a hormone secreted by adipocytes, exhibits therapeutic potential for the treatment of insulin-dependent diabetes mellitus (IDDM). Protein tyrosine phosphatase 1B (PTP1B) is a key enzyme that negatively regulates leptin receptor signaling. Here, the role of PTP1B in the treatment of IDDM was investigated using PTP1B deficient (KO) mice and a PTP1B inhibitor. IDDM wild-type (WT) mice induced by streptozotocin showed marked hyperglycemia compared to non-IDDM WT mice. KO mice displayed significantly improved glucose metabolism equivalent to non-IDDM WT mice, whereas peripheral or central administration of leptin partially improved glucose metabolism in IDDM WT mice. Peripheral combination therapy of leptin and a PTP1B inhibitor in IDDM WT mice improved glucose metabolism to the same level as non-IDDM WT mice. Leptin was shown to act on the arcuate nucleus in the hypothalamus to suppress gluconeogenesis in liver and enhance glucose uptake in both brown adipose tissue and soleus muscle via the sympathetic nervous system. These effects were enhanced by PTP1B deficiency. Thus, treatment of IDDM with leptin, PTP1B deficiency or a PTP1B inhibitor was shown to enhance leptin activity in the hypothalamus to improve glucose metabolism. These findings suggest a potential alternative therapy for IDDM.