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Sex‐dependent Effects of High‐fat Diet and Stress on CNS Inflammation and Ceramides Production

The intake of a high‐fat diet (HFD) and exposition to stress are associated with development of a neuroinflammatory state in the central nervous system (CNS). Previously we found high levels of long‐chain (C18:0 and C20:0) ceramides in blood of rats fed an HFD that correlated with increased immobility in the forced swim test, suggesting that ceramides could contribute to the development of depressive‐like behavior. In the current study, we aimed to determine whether adding short‐term unpredictable stress (STUS) would exacerbate the effects of HFD on neuroinflammation and ceramide metabolism in the ventral hippocampus (VH) and the development of depressive‐like behavior. We hypothesized that exposure to HFD and STUS would cause a neuroinflammatory state and increased levels of long‐chained ceramides in the VH leading to depressive‐like behavior. To test this, male and female Sprague Dawley rats were administered either a low‐fat or high‐fat diet for eight weeks, while other groups of female and male rats were administered a low‐fat or high‐fat diet for 10 weeks with the inclusion of 4 days of random unpredictable stressors. After sacrifice, we assessed the expression of microglial (Iba‐1), neuroinflammatory state (NLRP3, HMGB1 and TNF‐α) and ceramide production markers (CerS5, CerS6, SMPD1 and SMPD3) in the VH. Female HFD rats showed increased expression of TNF‐α and HMGB‐1 independent of STUS, while male rats increased expression of Iba‐1, TNF‐α and NLRP3 after exposition to STUS, suggesting a sex‐dependent activation of inflammatory mediators. The assessment of enzymes that produce long‐chained ceramides revealed increased CerS5, CerS6 and SMPD1 mRNA only in the VH of female HFD rats exposed to STUS, suggesting sex differences in the production of long‐chained ceramides due to combined HFD and STUS. VH tissue and blood were collected to quantify ceramides by gas chromatography‐mass spectrometry (GC‐MS). Based on the expression of the enzymes involved in the production of ceramides, we expect that the GC‐MS assay will show increased C16 ceramides in female rats exposed to HFD and STUS. After diet completion, rats were subjected to sucrose grooming test and forced swim test to assess anhedonia and behavioral despair. Female HFD with STUS showed trending increases in grooming activity, reduced immobility and increased swimming time while male rats did not present any behavioral changes, suggesting less depressive‐like behavior in female rats. In conclusion, an HFD in combination with STUS causes sex‐dependent changes inflammatory state and long‐chained ceramides production without increasing depressive‐like behavior.