Hyperglycemia Synergises with Iron Deficiency and Leads to Microgliosis in the Developing Rat Hippocampus

Nicholas p. Dolan, University of Minnesota, Apple Valley, MN, United States; Kathleen Ennis-Czerniak, University of MN, United States; Brian Sandri, University of MN, United States; Raghu Rao, University of MN, United States

Background: Iron deficiency (ID) and hypoinsulinemic hyperglycemia (HG) are co-morbidities in preterm infants. Both ID and HG cause long-term hippocampus-mediated cognitive deficits. The combined effects of ID and HG on the developing hippocampus are not known.

Objectives: Examine the acute and long-term effects of ID with and without HG on the developing hippocampus.

Design/Methods: ID was induced in infant rats through feeding a low iron (3-6 ppm) diet to pregnant dams on gestational day 3 through postnatal day 7 (P7). Iron sufficient (IS) control dams were fed a standard diet throughout the experiment. Hypoinsulinemic HG was induced by injecting streptozotocin (STZ) on postnatal day two (P2). mRNA expression of iron transporters (Tfrc and Dmt1) and oxidative stress (Parp1) were determined using qPCR on P7. Microglia in the hippocampal subareas were determined using histochemistry on P65

Results: Mean Hct (%) on P7 was lower in ID groups (IS-CONT: 33.2 ± 0.94, IS-STZ: 35.3 ± 0.65, ID-CONT: 13.9 ± 0.48, ID-STZ:20.3 ± 0.83, p< 0.001; Fig 1A). Mean Hct (%) on P65 returned to normal for all groups (Fig 1B). Blood glucose (mg/dL) was elevated in both STZ groups (IS-CONT: 115.0 ± 3.3, IS-STZ: 226.8 ± 12.1, p< 0.001; ID-CONT: 95.0 ± 3.9 ID-STZ: 189.4 ± 15.7, p< 0.001). Transferrin receptor (Trfc) expression was upregulated 56% with ID compared to IS (p=0.002). The ID-STZ group was upregulated relative to every other group (p < 0.0001; Fig 2A). Divalent metal transporter-1 (Dmt1) expression was increased in the IS-STZ (38%), ID-CONT (62%) and ID-STZ (96%) compared to the IS control (p=0.01; Fig 2B). Poly [ADP-ribose] polymerase-1 (Parp1) expression was increased in the ID-STZ group only (p < 0.0001 Fig 2C). There was a greater number of microglia in the hippocampal CA1 region of ID-STZ brains compared to ID-CONT (Figure 3).

Conclusion: Increased Tfrc and Dmt1 expression are indicative of ID status in hippocampal tissue. Drastic upregulation in Tfrc and Dmt1 in the ID-STZ group suggests that HG has an aberrant, synergistic effect with ID. Parp1 upregulation suggests that HG leads to oxidative stress in the hippocampus of both IS and ID groups with higher oxidative stress in the ID group. Increased number of microglia in the CA1 region in the ID-STZ group could be due to worsened oxidative stress in that group. Increased microgliosis in CA1 may impair hippocampal development and function. (Satrom et al., 2018) .