Dashdulam Davaanyam

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by the accumulation of amyloid-beta (Aβ) plaques and neurofibrillary tangles. Beyond these hallmark pathological features, the complex pathogenesis of AD involves cellular dysfunctions associated with chronic oxidative stress and neuroinflammation. Central to these inflammatory pathways is the extracellular release of the nuclear protein high-mobility group box 1 (HMGB1) from neurons and microglia. Extracellular HMGB1 disrupts homeostatic and reparative microglial functions, impairing the phagocytic clearance of amyloid-beta and driving neuroinflammation to accelerate AD pathogenesis. Consequently, targeting HMGB1 offers a promising therapeutic strategy for AD. This review examines recent progress and key insights regarding HMGB1-associated neuroinflammatory pathology in AD. We evaluate its regulation across transcriptional upregulation, cellular redistribution, age-related alterations, and Aβ-associated pathology. We further detail the pleiotropic effects of extracellular HMGB1, including neuroinflammation, defective Aβ phagocytic clearance, and genomic instability. Finally, we discuss the potential clinical utility of targeting HMGB1 to mitigate AD progression and provide HMGB1-related perspectives for future studies.

Rationale: There is no effective pharmacotherapy for obesity hypoventilation syndrome (OHS). Intranasal leptin augments the hypercapnic ventilatory response (HCVR), attenuates upper airway obstruction, and increases ventilation during sleep in diet-induced obese (DIO) mice. Respiratory effects of leptin can be attenuated by serotonergic antagonists. Objectives: To establish if serotonergic innervation of the hypoglossal motoneurons (XII MN) mediates effects of leptin on OHS. Methods: We examined effects of intranasal leptin on the HCVR, sleep architecture, arousal latency, flow limited (obstructed) and non-flow limited breathing, genioglossus muscle (GG) activity and metabolic rate across sleep/wake states in the presence and absence of serotonergic neurons innervating XII MN in DIO Sert-flp mice expressing FlpO recombinase in the serotonergic neurons. These mice were transfected into the XII MN with retrograde adeno-associated virus carrying either FlpO -dependent caspase or control yellow fluorescent protein (YFP). Measurements and Main Results: Control YFP virus was densely localized to the serotonergic neurons of the medullary raphe (MR), but not the dorsal raphe (DR), and these neurons were ablated by caspase. Leptin enhanced the HCVR, increased arousal latency in males, but not in females, and these effects were abolished by caspase. Neither leptin nor caspase affected sleep architecture or metabolic rate. Leptin increased GG activity awake and during NREM sleep, attenuated pharyngeal obstruction and increased minute ventilation in NREM and REM sleep. All effects of leptin were abolished by the FlpO -dependent caspase. Conclusions: Leptin treats OHS by stimulating MR serotonergic neurons, which project to XII MN and stimulate pharyngeal muscles during sleep.

Study Objectives: Sex differences in sleep disorders have been reported. Sleep disordered-breathing (SDB) is more prevalent in men, whereas women are more prone to insomnia. Mouse models have been extensively used in sleep research, but sex differences are not routinely taken into account. We performed a comprehensive examination of sleep architecture, breathing during sleep, and chemosensitivity in male and female C57BL/6 J mice. Methods: Mice instrumented with EEG/EMG electrodes underwent full-polysomnography inside a whole-body plethysmography chamber. Ventilatory responses to hypoxia (10% O2, 3% CO2) and to two regimens of hypercapnia (8% CO2 balanced in 20.9% O2 vs 8% CO2 balanced in 65% O2) were measured. Female mice underwent bilateral ovariectomy (OVX) and repeated the assessments. Results: Female mice showed more frequent arousals from sleep, increased apnea frequency and increased respiratory variability compared to males. Hypoxic chemoreflex did not differ between sexes, but CO2 chemosensitivity was significantly augmented in females. The carotid body inactivation by hyperoxia attenuated CO2 chemoreflex responses in females, but not in males. OVX reduced CO2 chemosensitivity, but did not affect respiratory variability, while the apnea index increased. Conclusions: In C57BL/6 J mice, we found significant sex differences in sleep. Females manifested a more severe SDB phenotype characterized by more frequent arousals and heightened CO2 responsiveness compared to males. Our findings also suggested that more robust peripheral CO2 chemoreflexes may account for sleep disruptions in female mice. Our findings further implicate ovarian hormones in respiratory control.

Diet‐induced obesity (DIO) is associated with increased circulating level of the hormone leptin. We have previously shown that leptin augments hypoxic ventilatory response in mice, and the response is abolished by carotid body (CB) denervation, and that leptin induces hypertension in DIO acting on transient receptor potential melastatin 7 (Trpm7) channels in CB. However CB chemosensory responses in DIO have not been sufficiently elucidated. The aim of this study was to examine the effects of DIO and leptin on carotid sinus nerve (CSN) activity and the role of Trpm7 at normoxic and hypoxic conditions. We measured afferent CSN activity using a novel ex vivo perfused CB preparation in four groups of mice on the C57BL/6J background: lean wild type, DIO wildtype, Trpm7^flox‐DIO transfected with adenoviral vectors harbouring Cre‐recombinase and green fluorescent protein (Ad‐Cre‐GFP) or control GFP (Ad‐GFP). Leptin augmented CSN responses to normoxic (PO₂ = 100 Torr) and hypoxic (PO₂ = 60 Torr) conditions. Compared to lean male mice, in DIO mice (a) CSN response to hypoxia was 50% greater, (b) leptin had a greater impact on CSN activity at normoxic and hypoxic conditions. Leptin‐induced CSN activities were attenuated by Trpm7 antagonist FTY720 and by Trpm7 knockdown in CB. There was no significant difference between CB chemosensitivity response to leptin in male and female mice. We conclude that CB chemosensitivity is increased in DIO compared to lean mice, and CB Trpm7 channel could be a therapeutic target for obesity‐related hypertension. image Key points: We have developed a novel ex vivo perfused murine carotid body (CB) preparation to evaluate carotid sinus nerve (CSN) activity using physiologically relevant levels of PO₂ at normoxic and hypoxic conditions. Diet‐induced obesity (DIO) increases baseline (normoxic) CSN activity, independent of leptin. DIO augments CB hypoxic chemoreflex gain via leptin. The effect of leptin on CB hypoxic chemoreflex is completely abolished by a Trpm7 blocker FTY720 and prevented by Trpm7 knockdown in CB. FTY720 does not have any effect on CSN activity in the absence of leptin. Taken together our new findings provide direct evidence that obesity increases CB chemoreflex via the leptin‐Trpm7 pathway.

RATIONALE: The carotid body (CB), a small organ located in the neck, which plays a significant role in sensing hypoxia and regulating the sympathetic nervous system, Overactivation of CB can contribute to increased sympathetic activity often observed in obesity, leading to potential complications like hypertension and metabolic dysfunction. We have shown high levels of expression of Trpm7 mRNA in the CB of diet induced obese (DIO) mice, which can potentially lead to augmented CB chemoreflex. We have also shown that Trpm7 expression in CB is regulated by leptin and that TRPM7 blockade treats hypertension in DIO. In the present study we have examined and quantified the Trpm7 channel expression in the CBs at the protein level in lean and DIO mice, using the immunofluorescence intensity signal in IMARIS. Methods: Carotid artery bifurcations with the CBs were isolated from lean and DIO mice and standard procedures were followed to prepare the CB sections (15 micron) for immunofluorescence. In this study, following primary antibodies were used; (a) to label CB type I cells - chicken anti-tyrosine hydroxylase (TH), (b) to label TRPM7 channels/receptors - rabbit anti-TRPM7, and (c) to label CB type II cells - rat anti-glial fibrillary acidic protein (GFAP). Fluorescent images were captured with a Zeiss Spinning disk confocal microscope and all images were taken using the same scanning parameters. All images were taken at 40x oil-immersion objective and 4.56 μm interval with 20-slice z-stack. Images were saved in the “czi” format, and processed in ZEN blue software and TRPM7 intensity was analyzed in Imaris 10.2 software. We quantified the fluorescence intensity of TRPM7 expression using a surface object which was created in the 3D view to define the region of interest (ROI) and normalized the TRPM7 intensity with total type I cell TH and type II cell GFAP intensities in the CB. CBs from C57BL/6J lean (n=2) and DIO (n=3) male mice were used and minimum of three images were analyzed per mouse. Result: Immunofluorescence data confirmed the presence of TRPM7 channel protein expressions in the CBs of both lean and DIO mice. Quantitative analysis of fluorescence intensity indicated noticeable and significant increase of TRPM7 channel expression in the CBs of DIO compared to lean mice. Conclusion: Overall, the study supported our previous observation of the Trpm7 channel mRNA expression. TRPM7 signaling in the CB could be a target for the treatment of obesity induced hypertension. Grant support: NIH R01 HL133100 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Obesity is associated with increased circulating level of the hormone leptin. Previously we have shown in mice that, leptin induces hypertension acting on transient receptor potential melastatin 7 (Trpm7) channels in the carotid body (CB), a multi-modal peripheral chemoreceptor that controls breathing and drives sympathetic tone. Further, leptin augments hypoxic ventilatory response in mice, and the response is abolished by CB denervation. This suggests a potential increase in CB chemosensitivity. However, no comparative study of CB chemosensory responses has been conducted in lean and obese mice to support this notion. To address this, we measured afferent carotid sinus nerve (CSN) activity, using a novel ex vivo perfused mouse (male/female) CB preparation from four groups of mice with C57BL/6J background : (i) lean (male b.w. 35 ± 0.5 gm and female b.w.24±1.8 gm), (ii) obese (DIO) (male b.w. 53 ± 1.5gm), (iii) Trpm7 ^flox -DIO + Ad-Cre-GFP (male b.w. 42± 1.2gm and (iv) Trpm7 ^flox -DIO + Ad-GFP (male b.w. 41± 1.4 gm). We found that in obese male mice, compared to lean male mice; (a) CB CSN baseline activity and response to hypoxia (PO ₂ =60 Torr) were 50% greater, (b) in presence of leptin (50nM), CB CSN responses to normoxia (PO ₂ =100Torr) and hypoxia were 50% and 150% greater respectively. Leptin-induced increase in CB CSN responses were reduced by Trpm7 antagonist FTY720 (3µM) in both lean and obese animals. There was no significant difference between CB chemosensitivity response to leptin in lean male and female mice.Trpm7 knockdown in CB did not affect hypoxic chemoreflex, but abolished responses to leptin and FTY720. Immuno-quantification of Trpm7 receptors indicated overall upregulation of CB Trpm7 receptor in obese compared to lean mice. We conclude that, increased sensitization of CB in obese mice leads to increase in CB chemosensitivity compared to lean mice and functional inhibition of CB Trpm7 receptors could be a therapeutic target for obesity related hypertension. Grant support: NIH R01 HL1331000. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

RATIONALE: Obesity is a major cause hypertension. We have previously shown that in diet induced obese (DIO) mice leptin induces hypertension acting in the carotid bodies (CB) via the leptin-leptin receptor LEPR ^b – transient receptor potential melastatin 7 (TRPM7) pathway. DIO mice have high levels of Lepr ^b and Trpm7 gene expression in CB, and pharmacological inhibition and gene knockdown of LEPR ^b and TRPM7 in CB treat DIO-induced hypertension. Furthermore, we have demonstrated that leptin increases Trpm7 expression in the carotid body type I glomus cells via epigenetic mechanisms demethylating the Trpm7 promoter. Leptin binding to LEPR ^b activates gene transcription via STAT3 phosphorylation. We hypothesize that leptin demethylates the Trpm7 promoter at the pSTAT3 site and that methylation of this region using specific methylated oligonucleotides in vivo will decrease CB Trpm7 gene expression and BP in DIO mice. Methods: We performed in silico analysis of the Trpm7 promoter to identify putative pSTAT3 binding site(s) and used PC-12 cell culture, which are phenotypically similar to the CB type I cells, to determine if leptin regulates the Trpm7 promoter methylation at the pSTAT3 site. Next, we compared Trpm7 promoter methylation in C57BL/6J DIO male mice (n=4) and lean male mice (n=5). Finally, we generated methylated oligonucleotides complimentary to the STAT3 binding site of the Trpm7 promoter and examined the effect of these oligonucleotides on BP. DIO male mice (n = 10) were implanted with telemetry in the left femoral artery for continuous BP monitoring. BP measurements were performed at baseline and, 3-4 days after oligonucleotides application to the CB area. Results: I n silico analysis of the Trpm7 promoter showed that it contains putative binding sites for the transcription STAT3 and revealed CG dinucleotides (CpGs) where DNA methylation occurs. Leptin demethylated the STAT3 binding site of the Trpm7 promoter in PC-12 cells. DIO mice showed high levels of CB Trpm7 gene expression and low levels of promoter methylation at the STAT3 binding site compared to lean mice. DIO increased mean arterial pressure by 11.4 mm Hg during the day ( p<0.0 001 ) and by 7.1 mm Hg at night ( p <0.001 ) compared to the lean mice. CB administration of the methylated oligonucleotide specific for the STAT3 binding site of the Trpm7 promoter attenuated obesity-induced hypertension ( p<0.01 ) during the day, when animals were predominantly asleep, decreasing mean arterial pressure by 4.2 mmHg. Conclusion: Our study has shown that epigenetic blockage of the Trpm7 promoter in the CB attenuated obesity-induced hypertension. NIH R01 HL1331000, HL128970 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Obesity and comorbid sleep apnea are key predisposing factors to hypertension. Obesity increases circulating leptin levels and hyperleptinemia may contribute to hypertension but mechanisms are not clear. Here, we have shown that knockdown of the leptin receptor LepR^b in the carotid body decreased blood pressure and treated hypertension in diet-induced obese mice. Thus, we identified a novel mechanism of obesity hypertension and a novel drug target, LepR^b in the carotid body.