Project Summary
Chronic stress is a detrimental condition affecting brain physiology, cognition and mental health. Altered
cerebrovascular network has long been recognized as a potential modulator of neuronal function in response to
stress. However, key molecular substrates conveying signals from cerebrovascular input to functional pathways
in specific types of neurons are not fully understood. Our recent study with a chronic social defeat stress (CSDS)
paradigm indicates that a) hippocampal parvalbumin (PV)-expressing interneurons are a determinant of CSDS-
induced behavioral adaptations, b) hemoglobin (Hb) a- and ß-chain levels are drastically upregulated in
hippocampal PV neurons in stress-susceptible mice, and c) mitochondrial oxidative phosphorylation in PV
neurons is the most significant functional pathway associated with stress susceptibility. Because chronic stress
is known to cause cerebrovascular dysfunction and dysregulated blood flow in the brain, we hypothesize that PV
interneurons are a contiguous target of chronic stress, and Hb expressed in PV neurons is a critical node sensing
vascular input and regulating mitochondrial adaptation in PV neurons. The overarching goal of this study is to
establish a cell-type-specific deletion model of Hb and determine the role of Hb in chronic stress-induced PV
neuron adaptation and behavioral responses to chronic stress. First, we will use the CSDS model, and examine
the effect of an antihypertensive drug (captopril) on CSDS-induced microbleeds, BBB disruption, Hb induction
in PV neurons and behavioral outcomes to determine the relationship between vascular disruption and Hb
induction in PV neurons (Aim 1a). Hippocampal PV neuron-selective deletion of Hb ß-chain genes will be
achieved by injecting AAV-sgRNAs vector into the hippocampus of transgenic mice expressing Cas9 selectively
in PV neurons. The control and ß-chain-deleted mice will be subjected to CSDS, and behavioral responses to
CSDS will be measured (Aim 1b). After behavioral assays, the hippocampal tissues will be analyzed using a PV-
neuron-selective Translating Ribosome Affinity Purification (TRAP)/RNA-seq approach (Aim 2). Differentially
expressed genes (DEGs) will be analyzed by bioinformatic approaches to find altered functional pathways
including mitochondrial pathways (Aim 2). We aim to determine whether neuronal Hb is required for chronic
stress-induced behavioral changes (Aim 1b) and identify downstream genes and functional pathways influenced
by Hb deletion (Aim 2). Cell-type-specific deletion tools for neuronal Hb in conjunction with a cell-type-specific
TRAP/RNA-seq approach established in this study can be applicable to the future studies of Hb in other cell
types in different brain regions under various stress or disease models. The research paradigm established in
this study will facilitate an array of new studies paving the gap between stress-induced cerebrovascular deficit
and brain-cell-type-specific responses. Thus, the outcome of the proposed research could yield a broad impact
on the fields of mental health and brain disorders.
