Loss of Hypothalamic Somatostatin (SST) Contributes to Bone Marrow (BM) Dysfunction and Diabetic Retinopathy (DR) in Type 2 Diabetic Rats

Abstract

Purpose: Since loss of retinal SST and circulating SST occurs in DR, we asked if loss of hypothalamic SST production would impact the innervation and function of the BM and influence DR in T2D rat model. Methods: Brain sections of BBZ/Wor rats with 4 months of diabetes and age-matched nondiabetic lean BBZ rats were immuno-stained for SST, Iba-1 and Neu-N. To examine the neuronal connection between the BM and pre-sympathetic brainstem and hypothalamic areas, both control and diabetic rats were injected in a blinded manner with GFP-transgenic pseudorabies virus (PRV-152) into their femurs. Four days later rats were euthanized and brain sections prepared for colocalization of GFP with SST. DR was assessed by enumeration of acellular capillaries in trypsin-digested retinas. Results: Injection of PRV into femur showed the presence of active virus in neurons of the paraventricular nucleus of the hypothalamus (PVN), rostral ventrolateral medulla and nucleus tractus solitarius of the brain of control rats. Colocalization studies showed that periventricular hypothalamic SST neurons were also GFP+ and directly innervated the BM. Quantitation showed that diabetic rats had significantly fewer GFP+ neurons in the PVN (n=6, *P<0.05), supporting neuronal loss. SST staining of brain sections showed significant reduction in the number of SST+ cells in diabetic rats (58±5) compared with nondiabetic rats (88±6) (n=6, *P<0.05). The density of Iba-1+ microglia increased, while the NeuN+ neurons decreased in the hypothalamus supporting an increase of regional inflammation and neuronal loss. Diabetic rats showed an increase in acellular capillaries compared to controls (15± 4 vs. 4±1mm2) (p<0.001). Conclusions: These studies support the notion that periventricular hypothalamic SST neurons directly innervate BM and that preservation of this small, but important population is relevant to prevention of diabetes induced-BM dysfunction and development of DR. Disclosure A. Longhini: None. J. Thinschmidt: None. M. Boulton: None. M.A. King: None. M.B. Grant: None.