^{Decreased Responsiveness to Chemical Itch in Old Mice}

Qiaofeng Zhao, Mitsutoshi Tominaga, Yayoi Kamata, Sumika Toyama, Kotaro Honda, Hang Ma, Eriko Komiya, and Kenji Takamori.

Abstract: Aging is associated with altered itch perception, potentially due to changes in neuronal function and pruriceptive signaling. The underlying mechanisms, however, remain unclear. We investigated age-related differences in itch sensitivity at behavioral, cellular, and molecular levels. Young and old mice were intradermally injected with various pruritogens, including small molecules (histamine, chloroquine, and serotonin). Additionally, immunofluorescence staining was performed to analyze the expression of TRPV1 and Cav3.2. Old mice exhibited reduced scratching behavior following injections, and their neuronal responses to histamine and chloroquine were diminished. Although all treated groups showed increased mechanical alloknesis, the effect was less pronounced in old animals. The expression of TRPV1 and Cav3.2 was also reduced in dorsal root ganglia neurons of old mice. These findings suggest that aging impairs both functional responsiveness and molecular signaling in sensory neurons, contributing to reduced chemical itch sensitivity in aged individuals.

Keywords: aging; calcium imaging; Cav3.2; dorsal root ganglion; pruritus; TRPV1; itch mechanisms

Meningeal regulatory T cells inhibit nociception
In female mice

Élora Midavaine1, Beatriz C. Moraes1, Jorge Benitez1, Sian R. Rodriguez1, Joao M. Braz1, Nathan P. Kochhar1, Walter L. Eckalbar1, Lin Tian2, Ana I. Domingos3, John E. Pintar4,
Allan I. Basbaum1*†, Sakeen W. Kashem5,6

Pain prevalence is higher in women across multiple conditions, and chronic pain severity
is frequently altered during gender affirming hormonal therapy (1). Although
there is evidence that T cells contribute to sexually dimorphic pain processing, the exact
mechanisms remain unclear (2). Regulatory T cells (Treg cells) are a subset of CD4+ T cells
defined by the expression of the master transcriptional regulator FOXP3, which is encoded
by a gene found on the X chromosome. In addition to their critical function in restraining
inflammation, Treg cells are major contributors of tissue reparative and supportive functions
(3, 4). However, it is not known whether and how Treg cells directly alter neuronal activity to
modulate nociception, independently of their immunomodulatory functions (5, 6). In this
study, we examined the role of Treg cells in regulating pain sensing in mice.

^{Inhibitory immunoreceptors CD300a and CD300lf cooperate to regulate mast cell activation}

Gyemin noh

Hanbin Lee 1,2, Chigusa Nakahashi-Oda 1,3,�, Wenxin Lyu 1,2, Mamoru Tanaka1,4,
Akiyoshi Rai1,5, Yoichi Muramoto 1,5, Yaqiu Wang1,2, Seiya Mizuno6, Kazuko Shibuya 1,3, and
Akira Shibuya 1,3,7,�

Abstract
Mast cells (MCs) play a central role in allergic immune responses. MC activation is regulated by several inhibitory immunoreceptors. The CD300
family members CD300a and CD300lf recognize phospholipid ligands and inhibit the FcεRI-mediated activating signal in MCs. While CD300a
binds to phosphatidylserine (PS) to inhibit MCs activation, CD300lf function is less clear due to its ability to bind with ceramide and PS.
Moreover, it also remains blurring whether CD300a and CD300lf function independently, cooperatively, or by interfering with each other in regulating
MC activation. Using imaging and flow cytometric analyses of bone marrow-derived cultured MCs (BMMCs) from wild-type (WT),
Cd300a–/–, Cd300lf–/–, and Cd300a–/–Cd300lf–/– mice, we show that CD300lf and CD300a colocalized with PS externalized to the outer leaflet of
the plasma membrane with a polar formation upon activation, and CD300lf cooperates with CD300a to inhibit BMMCs activation. CD300lf also
colocalized with extracellular ceramide in addition to the internal PS on the cell surface, which results in stronger inhibition of MC activation than
CD300lf binding to PS alone. Similarly, although both Cd300a–/– and Cd300lf–/– mice showed decreased rectal temperatures compared with WT
mice in the model of passive systemic anaphylaxis, Cd300a–/–Cd300lf–/– mice showed lower rectal temperature than either Cd300a–/– or
Cd300lf–/– mice. Our results demonstrate the cooperativity of multiple inhibitory receptors expressed on MCs and their regulatory functions
upon binding to respective ligands.
Keywords: CD300a, CD300lf, ceramide, mast cells, phosphatidylserine

https://doi.org/10.1093/jimmun/vkae030

Processing of pain and itch information by modality-specific neurons within the anterior cingulate cortex in mice

Hyoung-Gon Ko 1,2 ,HyunsuJung 3,4,9, Seunghyo Han1,9, Dong Il Choi4,9,
Chiwoo Lee4,9, Ja Eun Choi4,JihaeOh4,ChuljungKwak3,DaeHeeHan3,
Jun-Nyeong Kim1,SanghyunYe 4,JiahLee4,JaehyunLee4,KyungminLee 5,
Jae-Hyung Lee 6,MinZhuo7,8 & Bong-Kiun Kaang3,

Pain and itch are aversive sensations with distinct qualities, processed in
overlapping pathways and brain regions, including the anterior cingulate
cortex (ACC), which is critical for their affective dimensions. However, the
cellular mechanisms underlying their processing in the ACC remain unclear.
Here, we identify modality-specific neuronal populations in layer II/III of the
ACC in mice involved in pain and itch processing. Using a synapse labeling
tool, we show that pain- and itch-related neurons selectively receive synaptic
inputs from mediodorsal thalamic neurons activated by pain and itch stimuli,
respectively. Chemogenetic inhibition of these neurons reduced pruriception
ornociception without affecting the opposite modality. Conversely, activation
of these neurons did not enhance stimulus-specific responses but commonly
increased freezing-like behavior. These findings reveal that the processing of
itch and pain information in the ACC involves activity-dependent and
modality-specific neuronal populations, and that functionally distinct ACC neuronal subsets process pain and itch

Neuronal substance P-driven MRGPRX2-dependent mast cell degranulation products differentially promote vascular permeability

 https://doi.org/10.3389/fimmu.2024.1477072

Cell. 2024 Oct 24:S0092-8674(24)01149-8.

 doi: 10.1016/j.cell.2024.10.001. Online ahead of print.

Structure-guided discovery of bile acid derivatives for treating liver diseases without causing itch

Jun Yang ¹, Tianjun Zhao ², Junping Fan ³, Huaibin Zou ⁴, Guangyi Lan ⁵, Fusheng Guo ¹, Yaocheng Shi ³, Han Ke ³, Huasheng Yu ⁶, Zongwei Yue ¹, Xin Wang ⁷, Yingjie Bai ⁷, Shuai Li ⁸, Yingjun Liu ⁸, Xiaoming Wang ⁸, Yu Chen ⁹, Yulong Li ¹⁰, Xiaoguang Lei ¹¹

• PMID: 39476841
• DOI: 10.1016/j.cell.2024.10.001

Abstract

Chronic itch is a debilitating symptom profoundly impacting the quality of life in patients with liver diseases like cholestasis. Activation of the human G-protein coupled receptor, MRGPRX4 (hX4), by bile acids (BAs) is implicated in promoting cholestasis itch. However, the detailed underlying mechanisms remain elusive. Here, we identified 3-sulfated BAs that are elevated in cholestatic patients with itch symptoms. We solved the cryo-EM structure of hX4-Gq in a complex with 3-phosphated deoxycholic acid (DCA-3P), a mimic of the endogenous 3-sulfated deoxycholic acid (DCA-3S). This structure revealed an unprecedented ligand-binding pocket in MRGPR family proteins, highlighting the crucial role of the 3-hydroxyl (3-OH) group on BAs in activating hX4. Guided by this structural information, we designed and developed compound 7 (C7), a BA derivative lacking the 3-OH. Notably, C7 effectively alleviates hepatic injury and fibrosis in liver disease models while significantly mitigating the itch side effects.

Keywords: 3-sulfonated bile acids; MRGPRX4; OCA; bile acids; cholestatic pruritus; cryo-EM structure; deoxycholic acid; farnesoid X receptor; liver diseases; non-alcoholic steatohepatitis.