Investigation of LRP1-mediated Choroid Plexus transcytosis of leptin to the CSF and modulation of the satiety-inducing effects of leptin on multiple downstream brain areas.

• Applicant: Dr. Marta Porniece-Kumar
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Molecular and Cellular Neurology and Neuropathology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 511088898

Special neural networks in the brain coordinate adaptive changes in food intake, energy expenditure as well as motivation for food reward by integrating peripheral signals, such as leptin. One route of entry to reach LepR in these regions is through the epithelial blood-cerebrospinal fluid barrier of the choroid plexus (ChP). The large surface area of the ChP (10-50% of that of the BBB) suggests high-capacity molecular transcytosis via the ChP. Low-density lipoprotein receptor-related protein 1 (LRP1) is an endocytic receptor highly expressed in the ChP, and LRP1 polymorphisms are associated with obesity in humans. It has been suggested that at the blood-cerebrospinal fluid barrier (BCSFB) LRP1 is a key regulator of leptin transcytosis because ChP-specific knockout of LRP1 in mice impairs systemic glucose homeostasis as the mice exhibit a prediabetic phenotype of hyperleptinemia and systemic insulin resistance. Furthermore, intracerebroventricular (i.c.v.), but not intraperitoneal (i.p.) injections of leptin suppress food intake in these animals. In the first part of the study, I plan to establish two-photon imaging methods to characterize leptin transcytosis across BCSFB in vivo while administering fluorescently labeled leptin to awake mice using steady-state intravascular infusion in fasted and fed wild-type mice to assess feeding state-dependent regulation of leptin transport in CSF. Secondly, by recording the transcytosis of fluorescent leptin in mice either overexpressing or lacking LRP1 at the ChP I will assess the bidirectional effects (reduction and augmentation) on leptin transcytosis and on glucose homeostasis. Leptin modulates the activity of reward pathways and regulates food intake by decreasing the hedonic value of the food. One principal site of leptin action hypothesized to be sensitive to ChP transcytosis of leptin is at the dopaminergic neurons of the ventral tegmental area (VTA). Distinct leptin actions converge to increase inhibitory tone onto the VTA dopaminergic neurons, thereby regulating of motivational salience of food-predicting cues.In the second part of the study, I plan to dissect the effect LRP1 in leptin transcytosis across the ChP on downstream signaling of leptin at VTA dopaminergic neurons. I hypothesize that the reduction of leptin transport by decreasing the expression of LRP1 in the ChP is predicted to reduce access of the leptin to the VTA, and increase VTA dopaminergic activity, whereas overexpressing LRP1 in the ChP would have the opposite effect. Hence, I will record calcium transients from VTA dopaminergic neurons together with the dynamics of red fluorescence in both VTA vasculature and in perineuronal parenchyma via two-photon imaging in head-fixed mice to characterize the effect of reduced and saturated leptin transport in the ChP on dopaminergic neuron activity in VTA.

• DFG Programme: WBP Fellowship
• International Connection: USA
• Host: Professorin Dr. Maria K. Lehtinen, Ph.D.