Dietary interventions improve diabetic kidney disease, but not peripheral neuropathy, in a db/db mouse model of type 2 diabetes.

Patients with type 2 diabetes often develop the microvascular complications of diabetic kidney disease (DKD) and diabetic peripheral neuropathy (DPN), which decrease quality of life and increase mortality. Unfortunately, treatment options for DKD and DPN are limited. Lifestyle interventions, such as changes to diet, have been proposed as non-pharmacological treatment options for preventing or improving DKD and DPN. However, there are no reported studies simultaneously evaluating the therapeutic efficacy of varying dietary interventions in a type 2 diabetes mouse model of both DKD and DPN. Therefore, we compared the efficacy of a 12-week regimen of three dietary interventions, low carbohydrate, caloric restriction, and alternate day fasting, for preventing complications in a db/db type 2 diabetes mouse model by performing metabolic, DKD, and DPN phenotyping. All three dietary interventions promoted weight loss, ameliorated glycemic status, and improved DKD, but did not impact percent fat mass and DPN. Multiple regression analysis identified a negative correlation between fat mass and motor nerve conduction velocity. Collectively, our data indicate that these three dietary interventions improved weight and glycemic status and alleviated DKD but not DPN. Moreover, diets that decrease fat mass may be a promising non-pharmacological approach to improve DPN in type 2 diabetes given the negative correlation between fat mass and motor nerve conduction velocity.

Single-cell RNA-seq uncovers novel metabolic functions of Schwann cells beyond myelination.

Schwann cells (SCs) support peripheral nerves under homeostatic conditions, independent of myelination, and contribute to damage in prediabetic peripheral neuropathy (PN). Here, we used single-cell RNA sequencing to characterize the transcriptional profiles and intercellular communication of SCs in the nerve microenvironment using the high-fat diet-fed mouse, which mimics human prediabetes and neuropathy. We identified four major SC clusters, myelinating, nonmyelinating, immature, and repair in healthy and neuropathic nerves, in addition to a distinct cluster of nerve macrophages. Myelinating SCs acquired a unique transcriptional profile, beyond myelination, in response to metabolic stress. Mapping SC intercellular communication identified a shift in communication, centered on immune response and trophic support pathways, which primarily impacted nonmyelinating SCs. Validation analyses revealed that neuropathic SCs become pro-inflammatory and insulin resistant under prediabetic conditions. Overall, our study offers a unique resource for interrogating SC function, communication, and signaling in nerve pathophysiology to help inform SC-specific therapies.

Peripheral nerve involvement in hereditary spastic paraplegia characterized by quantitative magnetic resonance neurography.

BACKGROUND AND OBJECTIVES: Hereditary spastic paraplegias (HSPs) are heterogenous genetic disorders. While peripheral nerve involvement is frequent in spastic paraplegia 7 (SPG7), the evidence of peripheral nerve involvement in SPG4 is more controversial. We aimed to characterize lower extremity peripheral nerve involvement in SPG4 and SPG7 by quantitative magnetic resonance neurography (MRN). METHODS: Twenty-six HSP patients carrying either the SPG4 or SPG7 mutation and 26 age-/sex-matched healthy controls prospectively underwent high-resolution MRN with large coverage of the sciatic and tibial nerve. Dual-echo turbo-spin-echo sequences with spectral fat-saturation were utilized for T2-relaxometry and morphometric quantification, while two gradient-echo sequences with and without an off-resonance saturation rapid frequency pulse were applied for magnetization transfer contrast (MTC) imaging. HSP patients additionally underwent detailed neurologic and electroneurographic assessments. RESULTS: All microstructural (proton spin density [ρ], T2-relaxation time, magnetization transfer ratio) and morphometric (cross-sectional area) quantitative MRN markers were decreased in SPG4 and SPG7 indicating chronic axonopathy. ρ was superior in differentiating subgroups and identifying subclinical nerve damage in SPG4 and SPG7 without neurophysiologic signs of polyneuropathy. MRN markers correlated well with clinical scores and electroneurographic results. CONCLUSIONS: MRN characterizes peripheral nerve involvement in SPG4 and SPG7 as a neuropathy with predominant axonal loss. Evidence of peripheral nerve involvement in SPG4 and SPG7, even without electroneurographically manifest polyneuropathy, and the good correlation of MRN markers with clinical measures of disease progression, challenge the traditional view of the existence of HSPs with isolated pyramidal signs and suggest MRN markers as potential progression biomarkers in HSP.

Quantitative magnetic resonance neurographic characterization of peripheral nerve involvement in manifest and pre-ataxic spinocerebellar ataxia type 3.

BACKGROUND AND PURPOSE: Knowledge about the exact underlying pathophysiological changes involved in the genesis and progression of spinocerebellar ataxia type 3 (SCA3) is limited. Lower extremity peripheral nerve lesions in clinically, genetically and electrophysiologically classified ataxic and pre-ataxic SCA3 mutation carriers were characterized and quantified by magnetic resonance neurography (MRN). METHODS: Eighteen SCA3 mutation carriers and 20 age-/sex-matched healthy controls were prospectively enrolled. All SCA3 mutation carriers underwent detailed neurological and electrophysiological examinations. 3 T MRN covered the lumbosacral plexus and proximal thigh to the tibiotalar joint by using T2-weighted inversion recovery sequences, dual-echo relaxometry sequences with spectral fat saturation, and two gradient-echo sequences with and without an off-resonance saturation rapid frequency pulse. Detailed quantification of nerve lesions by morphometric and microstructural MRN markers, including T2 relaxometry and magnetization transfer contrast imaging, was conducted in all study participants. RESULTS: MRN detected peripheral nerve damage in ataxic and pre-ataxic SCA3. The quantitative markers proton spin density (ρ), T2 relaxation time, magnetization transfer ratio and cross-sectional area were decreased in SCA3, indicating chronic axonopathy. MTR and ρ identified early, subclinical nerve damage in pre-ataxic SCA3 and in SCA3 mutation carriers without polyneuropathy and were superior in differentiating between all subgroups. Additionally, microstructural markers correlated well with clinical symptom scores and electrophysiological results. CONCLUSIONS: Our data provide a comprehensive characterization of peripheral nerve damage in SCA3 and assist in understanding the mechanisms of the multisystemic disease evolution. Evidence of peripheral nerve involvement prior to the onset of clinically overt ataxia might have important implications for designing early intervention studies.

Characterization and quantification of alcohol-related polyneuropathy by magnetic resonance neurography.

BACKGROUND: We characterized and quantified peripheral nerve damage in alcohol-dependent patients (ADP) by magnetic resonance neurography (MRN) in correlation with clinical and electrophysiologic findings. METHODS: Thirty-one adult patients with a history of excessive alcohol consumption and age-/sex-matched healthy controls were prospectively examined. After detailed neurologic and electrophysiologic testing, the patient group was subdivided into ADP with alcohol-related polyneuropathy (ALN) and without ALN (Non-ALN). 3T MRN with anatomical coverage from the proximal thigh down to the tibiotalar joint was performed using dual-echo 2-dimensional relaxometry sequences with spectral fat saturation. Detailed quantification of nerve injury by morphometric (cross-sectional area [CSA]) and microstructural MRN markers (proton spin density [ρ], apparent T2-relaxation-time [T2app ]) was conducted in all study participants. RESULTS: MRN detected nerve damage in ADP with and without ALN. A proximal-to-distal gradient was identified for nerve T2-weighted (T2w)-signal and T2app in ADP, indicating a proximal predominance of nerve lesions. While all MRN markers differentiated significantly between ADP and controls, microstructural markers were able to additionally differentiate between subgroups: tibial nerve ρ at thigh level was increased in ALN (p < 0.0001) and in Non-ALN (p = 0.0052) versus controls, and T2app was higher in ALN versus controls (p < 0.0001) and also in ALN versus Non-ALN (p = 0.0214). T2w-signal and CSA were only higher in ALN versus controls. CONCLUSIONS: MRN detects and quantifies peripheral nerve damage in ADP in vivo even in the absence of clinically overt ALN. Microstructural markers (T2app , ρ) are most suitable for differentiating between ADP with and without manifest ALN, and may help to elucidate the underlying pathomechanism in ALN.

The Divergent Roles of Dietary Saturated and Monounsaturated Fatty Acids on Nerve Function in Murine Models of Obesity.

Neuropathy is the most common complication of prediabetes and diabetes and presents as distal-to-proximal loss of peripheral nerve function in the lower extremities. Neuropathy progression and disease severity in prediabetes and diabetes correlates with dyslipidemia in man and murine models of disease. Dyslipidemia is characterized by elevated levels of circulating saturated fatty acids (SFAs) that associate with the progression of neuropathy. Increased intake of monounsaturated fatty acid (MUFA)-rich diets confers metabolic health benefits; however, the impact of fatty acid saturation in neuropathy is unknown. This study examines the differential effect of SFAs and MUFAs on the development of neuropathy and the molecular mechanisms underlying the progression of the complication. Male mice Mus musculus fed a high-fat diet rich in SFAs developed robust peripheral neuropathy. This neuropathy was completely reversed by switching the mice from the SFA-rich high-fat diet to a MUFA-rich high-fat diet; nerve conduction velocities and intraepidermal nerve fiber density were restored. A MUFA oleate also prevented the impairment of mitochondrial transport and protected mitochondrial membrane potential in cultured sensory neurons treated with mixtures of oleate and the SFA palmitate. Moreover, oleate also preserved intracellular ATP levels, prevented apoptosis induced by palmitate treatment, and promoted lipid droplet formation in sensory neurons, suggesting that lipid droplets protect sensory neurons from lipotoxicity. Together, these results suggest that MUFAs reverse the progression of neuropathy by protecting mitochondrial function and transport through the formation of intracellular lipid droplets in sensory neurons.SIGNIFICANCE STATEMENT There is a global epidemic of prediabetes and diabetes, disorders that represent a continuum of metabolic disturbances in lipid and glucose metabolism. In the United States, 80 million individuals have prediabetes and 30 million have diabetes. Neuropathy is the most common complication of both disorders, carries a high morbidity, and, despite its prevalence, has no treatments. We report that dietary intervention with monounsaturated fatty acids reverses the progression of neuropathy and restores nerve function in high-fat diet-fed murine models of peripheral neuropathy. Furthermore, the addition of the monounsaturated fatty acid oleate to sensory neurons cultured under diabetic conditions shows that oleate prevents impairment of mitochondrial transport and mitochondrial dysfunction through a mechanism involving formation of axonal lipid droplets.

Peripheral nerve involvement in multiple sclerosis: Demonstration by magnetic resonance neurography.

OBJECTIVE: To detect and quantify peripheral nerve lesions in multiple sclerosis (MS) by magnetic resonance neurography (MRN). METHODS: Thirty-six patients diagnosed with MS based on the 2010 McDonald criteria (34 with the relapsing-remitting form, 2 with clinically isolated syndrome) with and without disease-modifying treatment were compared to 35 healthy age-/sex-matched volunteers. All patients underwent detailed neurological and electrophysiological examinations. Three Tesla MRN with large anatomical coverage of both legs and the lumbosacral plexus was performed by using 2-dimensional (2D) fat-saturated, T2-weighted (T2w) and dual echo turbo spin echo sequences as well as a 3D T2-weighted, fat-saturated SPACE sequence. Besides qualitative visual nerve assessment, a T2w signal quantification was performed by calculation of proton spin density and T2 relaxation time. Nerve diameter was measured as a morphometric criterion. RESULTS: T2w hyperintense nerve lesions were detectable in all MS patients, with a mean lesion number at thigh level of 151.5 ± 5.7 versus 19.1 ± 2.4 in controls (p < 0.0001). Nerve proton spin density was higher in MS (tibial/peroneal: 371.8 ± 7.7/368.9 ± 8.2) versus controls (tibial/peroneal: 266.0 ± 11.0/276.8 ± 9.7, p < 0.0001). In contrast, T2 relaxation time was significantly higher in controls (tibial/peroneal: 82.0 ± 2.1/78.3 ± 1.7) versus MS (tibial/peroneal: 64.3 ± 1.0/61.2 ± 0.9, p < 0.0001). Proximal tibial and peroneal nerve caliber was higher in MS (tibial: 52.4 ± 2.1mm2 , peroneal: 25.4 ± 1.3mm2 ) versus controls (tibial: 45.2 ± 1.4mm2 , p < 0.0015; peroneal: 21.3 ± 0.7mm2 , p = 0.0049). INTERPRETATION: Peripheral nerve lesions could be visualized and quantified in MS in vivo by high-resolution MRN. Lesions are defined by an increase of proton spin density and a decrease of T2 relaxation time, indicating changes in the microstructural organization of the extracellular matrix in peripheral nerve tissue in MS. By showing involvement of the peripheral nervous system in MS, this proof-of-concept study may offer new insights into the pathophysiology and treatment of MS. Ann Neurol 2017;82:676-685.

Dual CCR2/CCR5 antagonist treatment attenuates adipose inflammation, but not microvascular complications in ob/ob mice.

Diabetic peripheral neuropathy (DPN) and diabetic kidney disease (DKD) are common diabetic complications with limited treatment options. Experimental studies show that targeting inflammation using chemokine receptor (CCR) antagonists ameliorates DKD, presumably by reducing macrophage accumulation or activation. As inflammation is implicated in DPN development, we assessed whether CCR2 and CCR5 antagonism could also benefit DPN. Five-week-old ob/ob mice were fed a diet containing MK-0812, a dual CCR2-CCR5 receptor antagonist, for 8 weeks; DPN, DKD and metabolic phenotyping were then performed to determine the effect of CCR inhibition. Although MK-0812 reduced macrophage accumulation in adipose tissue, the treatment had largely no effect on metabolic parameters, nerve function or kidney disease in ob/ob mice. These results conflict with published data that demonstrate a benefit of CCR antagonists for DKD and hyperglycaemia. We conclude that CCR signaling blockade is ineffective in ob/ob mice and suspect that this is explained by the severe hyperglycaemia found in this model. It remains to be determined whether MK-0812 treatment, alone or in combination with improved glycaemic control, is useful in preventing diabetic complications in alternate animal models.

Mechanism for nitrogen isotope fractionation during ammonium assimilation by Escherichia coli K12.

Organisms that use ammonium as the sole nitrogen source discriminate between [(15)N] and [(14)N] ammonium. This selectivity leaves an isotopic signature in their biomass that depends on the external concentration of ammonium. To dissect how differences in discrimination arise molecularly, we examined a wild-type (WT) strain of Escherichia coli K12 and mutant strains with lesions affecting ammonium-assimilatory proteins. We used isotope ratio mass spectrometry (MS) to assess the nitrogen isotopic composition of cell material when the strains were grown in batch culture at either high or low external concentrations of NH3 (achieved by controlling total NH4Cl and pH of the medium). At high NH3 (≥ 0.89 µM), discrimination against the heavy isotope by the WT strain (-19.2‰) can be accounted for by the equilibrium isotope effect for dissociation of NH4(+) to NH3 + H(+). NH3 equilibrates across the cytoplasmic membrane, and glutamine synthetase does not manifest an isotope effect in vivo. At low NH3 (≤ 0.18 µM), discrimination reflects an isotope effect for the NH4(+) channel AmtB (-14.1‰). By making E. coli dependent on the low-affinity ammonium-assimilatory pathway, we determined that biosynthetic glutamate dehydrogenase has an inverse isotope effect in vivo (+8.8‰). Likewise, by making unmediated diffusion of NH3 across the cytoplasmic membrane rate-limiting for cell growth in a mutant strain lacking AmtB, we could deduce an in vivo isotope effect for transport of NH3 across the membrane (-10.9‰). The paper presents the raw data from which our conclusions were drawn and discusses the assumptions underlying them.

BTBR ob/ob mice as a novel diabetic neuropathy model: Neurological characterization and gene expression analyses.

Given the lack of treatments for diabetic neuropathy (DN), a common diabetic complication, accurate disease models are necessary. Characterization of the leptin-deficient BTBR ob/ob mouse, a type 2 diabetes model, demonstrated that the mice develop robust diabetes coincident with severe neuropathic features, including nerve conduction deficits and intraepidermal nerve fiber loss by 9 and 13 weeks of age, respectively, supporting its use as a DN model. To gain insight into DN mechanisms, we performed microarray analysis on sciatic nerve from BTBR ob/ob mice, identifying 1503 and 642 differentially expressed genes associated with diabetes at 5 and 13 weeks, respectively. Further analyses identified overrepresentation of inflammation and immune-related functions in BTBR ob/ob mice, which interestingly were more highly represented at 5 weeks, an observation that may suggest a contributory role in DN onset. To complement the gene expression analysis, we demonstrated that protein levels of select cytokines were significantly upregulated at 13 weeks in BTBR ob/ob mouse sciatic nerve. Furthermore, we compared our array data to that from an established DN model, the C57BKS db/db mouse, which reflected a common dysregulation of inflammatory and immune-related pathways. Together, our data demonstrate that BTBR ob/ob mice develop rapid and robust DN associated with dysregulated inflammation and immune-related processes.

Muscle-specific expression of LARGE restores neuromuscular transmission deficits in dystrophic LARGE(myd) mice.

Mutations in several glycosyltransferases underlie a group of muscular dystrophies known as glycosylation-deficient muscular dystrophy. A common feature of these diseases is loss of glycosylation and consequent dystroglycan function that is correlated with severe pathology in muscle, brain and other tissues. Although glycosylation of dystroglycan is essential for function in skeletal muscle, whether glycosylation-dependent function of dystroglycan is sufficient to explain all complex pathological features associated with these diseases is less clear. Dystroglycan glycosylation is defective in LARGE(myd) (myd) mice as a result of a mutation in like-acetylglucosaminyltransferase (LARGE), a glycosyltransferase known to cause muscle disease in humans. We generated animals with restored dystroglycan function exclusively in skeletal muscle by crossing myd animals to a recently created transgenic line that expresses LARGE selectively in differentiated muscle. Transgenic myd mice were indistinguishable from wild-type littermates and demonstrated an amelioration of muscle disease as evidenced by an absence of muscle pathology, restored contractile function and a reduction in serum creatine kinase activity. Moreover, although deficits in nerve conduction and neuromuscular transmission were observed in myd animals, these deficits were fully rescued by muscle-specific expression of LARGE, which resulted in restored structure of the neuromuscular junction (NMJ). These data demonstrate that, in addition to muscle degeneration and dystrophy, impaired neuromuscular transmission contributes to muscle weakness in dystrophic myd mice and that the noted defects are primarily due to the effects of LARGE and glycosylated dystroglycan in stabilizing the endplate of the NMJ.

Transcriptomic profiling of sciatic nerves and dorsal root ganglia reveals site-specific effects of prediabetic neuropathy.

Peripheral neuropathy (PN) is a severe and frequent complication of obesity, prediabetes, and type 2 diabetes characterized by progressive distal-to-proximal peripheral nerve degeneration. However, a comprehensive understanding of the mechanisms underlying PN, and whether these mechanisms change during PN progression, is currently lacking. Here, gene expression data were obtained from distal (sciatic nerve; SCN) and proximal (dorsal root ganglia; DRG) injury sites of a high-fat diet (HFD)-induced mouse model of obesity/prediabetes at early and late disease stages. Self-organizing map and differentially expressed gene analyses followed by pathway enrichment analysis identified genes and pathways altered across disease stage and injury site. Pathways related to immune response, inflammation, and glucose and lipid metabolism were consistently dysregulated with HFD-induced PN, irrespective of injury site. However, regulation of oxidative stress was unique to the SCN while dysregulated Hippo and Notch signaling were only observed in the DRG. The role of the immune system and inflammation in disease progression was supported by an increase in the percentage of immune cells in the SCN with PN progression. Finally, when comparing these data to transcriptomic signatures from human patients with PN, we observed conserved pathways related to metabolic dysregulation across species, highlighting the translational relevance of our mouse data. Our findings demonstrate that PN is associated with distinct site-specific molecular re-programming in the peripheral nervous system, identifying novel, clinically relevant therapeutic targets.

Lack of both bradykinin B1 and B2 receptors enhances nephropathy, neuropathy, and bone mineral loss in Akita diabetic mice.

An insertion polymorphism of the angiotensin-I converting enzyme gene (ACE) is common in humans and the higher expressing allele is associated with an increased risk of diabetic complications. The ACE polymorphism does not significantly affect blood pressure or angiotensin II levels, suggesting that the kallikrein-kinin system partly mediates the effects of the polymorphism. We have therefore explored the influence of lack of both bradykinin receptors (B1R and B2R) on diabetic nephropathy, neuropathy, and osteopathy in male mice heterozygous for the Akita diabetogenic mutation in the insulin 2 gene (Ins2). We find that all of the detrimental phenotypes observed in Akita diabetes are enhanced by lack of both B1R and B2R, including urinary albumin excretion, glomerulosclerosis, glomerular basement membrane thickening, mitochondrial DNA deletions, reduction of nerve conduction velocities and of heat sensation, and bone mineral loss. Absence of the bradykinin receptors also enhances the diabetes-associated increases in plasma thiobarbituric acid-reactive substances, mitochondrial DNA deletions, and renal expression of fibrogenic genes, including transforming growth factor beta1, connective tissue growth factor, and endothelin-1. Thus, lack of B1R and B2R exacerbates diabetic complications. The enhanced renal injury in diabetic mice caused by lack of B1R and B2R may be mediated by a combination of increases in oxidative stress, mitochondrial DNA damage and over expression of fibrogenic genes.

Modeling the innate inflammatory cGAS/STING pathway: sexually dimorphic effects on microglia and cognition in obesity and prediabetes.

Introduction: The prevalence of obesity, prediabetes, and diabetes continues to grow worldwide. These metabolic dysfunctions predispose individuals to neurodegenerative diseases and cognitive impairment, including dementias such as Alzheimer's disease and Alzheimer's disease related dementias (AD/ADRD). The innate inflammatory cGAS/STING pathway plays a pivotal role in metabolic dysfunction and is an emerging target of interest in multiple neurodegenerative diseases, including AD/ADRD. Therefore, our goal was to establish a murine model to specifically target the cGAS/STING pathway to study obesity- and prediabetes-induced cognitive impairment. Methods: We performed two pilot studies in cGAS knockout (cGAS-/-) male and female mice designed to characterize basic metabolic and inflammatory phenotypes and examine the impact of high-fat diet (HFD) on metabolic, inflammatory, and cognitive parameters. Results: cGAS-/- mice displayed normal metabolic profiles and retained the ability to respond to inflammatory stimuli, as indicated by an increase in plasma inflammatory cytokine production in response to lipopolysaccharide injection. HFD feeding caused expected increases in body weight and decreases in glucose tolerance, although onset was accelerated in females versus males. While HFD did not increase plasma or hippocampal inflammatory cytokine production, it did alter microglial morphology to a state indicative of activation, particularly in female cGAS-/- mice. However, HFD negatively impacted cognitive outcomes in male, but not female animals. Discussion: Collectively, these results suggest that cGAS-/- mice display sexually dimorphic responses to HFD, possibly based on differences in microglial morphology and cognition.

Regional interneuron transcriptional changes reveal pathologic markers of disease progression in a mouse model of Alzheimer's disease.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and leading cause of dementia, characterized by neuronal and synapse loss, amyloid-ß and tau protein aggregates, and a multifactorial pathology involving neuroinflammation, vascular dysfunction, and disrupted metabolism. Additionally, there is growing evidence of imbalance between neuronal excitation and inhibition in the AD brain secondary to dysfunction of parvalbumin (PV)- and somatostatin (SST)-positive interneurons, which differentially modulate neuronal activity. Importantly, impaired interneuron activity in AD may occur upstream of amyloid-ß pathology rendering it a potential therapeutic target. To determine the underlying pathologic processes involved in interneuron dysfunction, we spatially profiled the brain transcriptome of the 5XFAD AD mouse model versus controls, across four brain regions, dentate gyrus, hippocampal CA1 and CA3, and cortex, at early-stage (12 weeks-of-age) and late-stage (30 weeks-of-age) disease. Global comparison of differentially expressed genes (DEGs) followed by enrichment analysis of 5XFAD versus control highlighted various biological pathways related to RNA and protein processing, transport, and clearance in early-stage disease and neurodegeneration pathways at late-stage disease. Early-stage DEGs examination found shared, e.g ., RNA and protein biology, and distinct, e.g ., N-glycan biosynthesis, pathways enriched in PV-versus somatostatin SST-positive interneurons and in excitatory neurons, which expressed neurodegenerative and axon- and synapse-related pathways. At late-stage disease, PV-positive interneurons featured cancer and cancer signaling pathways along with neuronal and synapse pathways, whereas SST-positive interneurons showcased glycan biosynthesis and various infection pathways. Late-state excitatory neurons were primarily characterized by neurodegenerative pathways. These fine-grained transcriptomic profiles for PV- and SST-positive interneurons in a time- and spatial-dependent manner offer new insight into potential AD pathophysiology and therapeutic targets.

Palmitate and glucose increase amyloid precursor protein in extracellular vesicles: Missing link between metabolic syndrome and Alzheimer's disease.

The metabolic syndrome (MetS) and Alzheimer's disease share several pathological features, including insulin resistance, abnormal protein processing, mitochondrial dysfunction and elevated inflammation and oxidative stress. The MetS constitutes elevated fasting glucose, obesity, dyslipidaemia and hypertension and increases the risk of developing Alzheimer's disease, but the precise mechanism remains elusive. Insulin resistance, which develops from a diet rich in sugars and saturated fatty acids, such as palmitate, is shared by the MetS and Alzheimer's disease. Extracellular vesicles (EVs) are also a point of convergence, with altered dynamics in both the MetS and Alzheimer's disease. However, the role of palmitate- and glucose-induced insulin resistance in the brain and its potential link through EVs to Alzheimer's disease is unknown. We demonstrate that palmitate and high glucose induce insulin resistance and amyloid precursor protein phosphorylation in primary rat embryonic cortical neurons and human cortical stem cells. Palmitate also triggers insulin resistance in oligodendrocytes, the supportive glia of the brain. Palmitate and glucose enhance amyloid precursor protein secretion from cortical neurons via EVs, which induce tau phosphorylation when added to naïve neurons. Additionally, EVs from palmitate-treated oligodendrocytes enhance insulin resistance in recipient neurons. Overall, our findings suggest a novel theory underlying the increased risk of Alzheimer's disease in MetS mediated by EVs, which spread Alzheimer's pathology and insulin resistance.

Quantification and Proximal-to-Distal Distribution Pattern of Tibial Nerve Lesions in Relapsing-Remitting Multiple Sclerosis : Assessment by MR Neurography.

PURPOSE: Recent studies suggest an involvement of the peripheral nervous system (PNS) in multiple sclerosis (MS). Here, we characterize the proximal-to-distal distribution pattern of peripheral nerve lesions in relapsing-remitting MS (RRMS) by quantitative magnetic resonance neurography (MRN). METHODS: A total of 35 patients with RRMS were prospectively included and underwent detailed neurologic and electrophysiologic examinations. Additionally, 30 age- and sex-matched healthy controls were recruited. 3T MRN with anatomical coverage from the proximal thigh down to the tibiotalar joint was conducted using dual-echo 2­dimensional relaxometry sequences with spectral fat saturation. Quantification of PNS involvement was performed by evaluating microstructural (proton spin density (ρ), T2-relaxation time (T2app)), and morphometric (cross-sectional area, CSA) MRN markers in every axial slice. RESULTS: In patients with RRMS, tibial nerve lesions at the thigh and the lower leg were characterized by a decrease in T2app and an increase in ρ compared to controls (T2app thigh: p < 0.0001, T2app lower leg: p = 0.0040; ρ thigh: p < 0.0001; ρ lower leg: p = 0.0098). An additional increase in nerve CSA was only detectable at the thigh, while the semi-quantitative marker T2w-signal was not altered in RRMS in both locations. A slight proximal-to-distal gradient was observed for T2app and T2-signal, but not for ρ. CONCLUSION: PNS involvement in RRMS is characterized by a decrease in T2app and an increase in ρ, occurring with proximal predominance at the thigh and the lower leg. Our results indicate microstructural alterations in the extracellular matrix of peripheral nerves in RRMS and may contribute to a better understanding of the pathophysiologic relevance of PNS involvement.

Single-cell RNA sequencing identifies hippocampal microglial dysregulation in diet-induced obesity.

Obesity is a growing global concern in adults and youth with a parallel rise in associated complications, including cognitive impairment. Obesity induces brain inflammation and activates microglia, which contribute to cognitive impairment by aberrantly phagocytosing synaptic spines. Local and systemic signals, such as inflammatory cytokines and metabolites likely participate in obesity-induced microglial activation. However, the precise mechanisms mediating microglial activation during obesity remain incompletely understood. Herein, we leveraged our mouse model of high-fat diet (HFD)-induced obesity, which mirrors human obesity, and develops hippocampal-dependent cognitive impairment. We assessed hippocampal microglial activation by morphological and single-cell transcriptomic analysis to evaluate this heterogeneous, functionally diverse, and dynamic class of cells over time after 1 and 3 months of HFD. HFD altered cell-to-cell communication, particularly immune modulation and cellular adhesion signaling, and induced a differential gene expression signature of protein processing in the endoplasmic reticulum in a time-dependent manner.

Human neural stem cells restore spatial memory in a transgenic Alzheimer's disease mouse model by an immunomodulating mechanism.

INTRODUCTION: Stem cells are a promising therapeutic in Alzheimer's disease (AD) given the complex pathophysiologic pathways involved. However, the therapeutic mechanisms of stem cells remain unclear. Here, we used spatial transcriptomics to elucidate therapeutic mechanisms of human neural stem cells (hNSCs) in an animal model of AD. METHODS: hNSCs were transplanted into the fimbria fornix of the hippocampus using the 5XFAD mouse model. Spatial memory was assessed by Morris water maze. Amyloid plaque burden was quantified. Spatial transcriptomics was performed and differentially expressed genes (DEGs) identified both globally and within the hippocampus. Subsequent pathway enrichment and ligand-receptor network analysis was performed. RESULTS: hNSC transplantation restored learning curves of 5XFAD mice. However, there were no changes in amyloid plaque burden. Spatial transcriptomics showed 1061 DEGs normalized in hippocampal subregions. Plaque induced genes in microglia, along with populations of stage 1 and stage 2 disease associated microglia (DAM), were normalized upon hNSC transplantation. Pathologic signaling between hippocampus and DAM was also restored. DISCUSSION: hNSCs normalized many dysregulated genes, although this was not mediated by a change in amyloid plaque levels. Rather, hNSCs appear to exert beneficial effects in part by modulating microglia-mediated neuroinflammation and signaling in AD.

Human neural stem cells restore spatial memory in a transgenic Alzheimer's disease mouse model by an immunomodulating mechanism.

Introduction: Stem cells are a promising therapeutic in Alzheimer's disease (AD) given the complex pathophysiologic pathways involved. However, the therapeutic mechanisms of stem cells remain unclear. Here, we used spatial transcriptomics to elucidate therapeutic mechanisms of human neural stem cells (hNSCs) in an animal model of AD. Methods: hNSCs were transplanted into the fimbria fornix of the hippocampus using the 5XFAD mouse model. Spatial memory was assessed by Morris water maze. Amyloid plaque burden was quantified. Spatial transcriptomics was performed and differentially expressed genes (DEGs) identified both globally and within the hippocampus. Subsequent pathway enrichment and ligand-receptor network analysis was performed. Results: hNSC transplantation restored learning curves of 5XFAD mice. However, there were no changes in amyloid plaque burden. Spatial transcriptomics showed 1,061 DEGs normalized in hippocampal subregions. Plaque induced genes in microglia, along with populations of stage 1 and stage 2 disease associated microglia (DAM), were normalized upon hNSC transplantation. Pathologic signaling between hippocampus and DAM was also restored. Discussion: hNSCs normalized many dysregulated genes, although this was not mediated by a change in amyloid plaque levels. Rather, hNSCs appear to exert beneficial effects in part by modulating microglia-mediated neuroinflammation and signaling in AD.