SEX-DEPENDENT MICROGLIAL ACTIVATION DURING SHORT-TERM HIGH-FAT DIET: THE ROLE OF JNK3

The hypothalamus is an integrative center that senses peripheral energy cues and coordinates neuroendocrine and behavioural responses to maintain metabolic homeostasis. High-fat diet (HFD) feeding disrupts this regulatory network, triggering hypothalamic inflammation, which is one of the earliest events preceding systemic metabolic dysfunction. However, the onset and progression of this inflammatory response, as well as its sex-dependent characteristics, remain poorly defined. Among candidate pathways, the c-Jun N-terminal kinase (JNK) family has been implicated in neuroinflammation, being JNK3 a brain-restricted isoform. Here, we investigated the temporal relationship between JNK activation and microglial polarization in male and female mice upon HFD initiation. Microglial activation and hypothalamic insulin resistance were analysed during early diet initiation. We found that males rapidly developed hypothalamic microinflammation after only three days of HFD, marked by a shift toward a proinflammatory microglial phenotype. In contrast, females exhibited an attenuated early inflammatory response, characterized by a progressive and sustained polarization toward an M2-like, anti-inflammatory microglial state as HFD continued. This sexually dimorphic microglial response closely paralleled JNK activation dynamics, suggesting a role for JNK signaling in shaping distinct immune programs. To test this, we used JNK3 knockout mice and found that loss of JNK3 abolished the female-specific M2 polarization, redirecting microglia toward a male-like proinflammatory phenotype. These findings identify JNK3 as a critical regulator of the protective, anti-inflammatory microglial responses in females during HFD challenge, and reveal a sex-specific neuroimmune mechanism that may influence long-term metabolic outcomes.