New Findings
What is the central question of this study?
Do peripheral sensory neurons metabolize fat‐based fuel sources, and does a ketogenic diet modify these processes?
What is the main finding ...and its importance
We show that peripheral axons from mice fed a ketogenic diet respond to fat‐based fuel sources with reduced respiration and H2O2 emission compared with mice fed a control diet. These results add to our understanding of the responses of sensory neurons to neuropathy associated with poor diet, obesity and metabolic syndrome. These findings should be incorporated into current ideas of axonal protection and might identify how dietary interventions may change mitochondrial function in settings of sensory dysfunction.
Metabolic syndrome and obesity are increasing epidemics that significantly impact the peripheral nervous system and lead to negative changes in sensation and peripheral nerve function. Research to understand the consequences of diet, obesity and fuel usage in sensory neurons has commonly focused on glucose metabolism. Here, we tested whether mouse sensory neurons and nerves have the capacity to metabolize fat‐based fuels (palmitoyl‐CoA) and whether these effects are altered by feeding of a ketogenic (90% kcal fat) diet compared with a control diet (14% kcal fat). Male C57Bl/6 mice were placed on the diets for 10 weeks, and after the mice were killed, the dorsal root ganglion (DRG) and sciatic nerve (SN) were placed in an Oroboros oxygraph‐2K to examine diet‐induced alterations in metabolism (respiration) of palmitoyl‐CoA and H2O2 emission (fluorescence). In addition, RNAseq was performed on the DRG of mice fed a control or a ketogenic diet for 12 weeks, and genes associated with mitochondrial respiratory function were analysed. Our results suggest that the sciatic nerves from mice fed a ketogenic diet display reduced O2 respiration and H2O2 emission when metabolizing palmitoyl‐CoA compared with mice fed a control diet. Assessments of changes in mRNA gene expression reveal alterations in genes encoding the NADH dehydrogenase complex and complex IV, which could alter production of reactive oxygen species. These new findings highlight the ability of sensory neurons and axons to oxidize fat‐based fuel sources and show that these mechanisms are adaptable to dietary changes.
Hematopoietic stem cells (HSCs) reside predominantly in bone marrow, but low numbers of HSCs are also found in peripheral blood. We examined the fate of blood-borne HSCs using genetically marked ...parabiotic mice, which are surgically conjoined and share a common circulation. Parabionts rapidly established stable, functional cross engraftment of partner-derived HSCs and maintained partner-derived hematopoiesis after surgical separation. Determination of the residence time of injected blood-borne progenitor cells suggests that circulating HSCs/progenitors are cleared quickly from the blood. These data demonstrate that HSCs rapidly and constitutively migrate through the blood and play a physiological role in, at least, the functional reengraftment of unconditioned bone marrow.
Abstract Background Overuse of clinical laboratory testing in the inpatient setting is a common problem. The objective of this project was to develop an inexpensive and easily implemented ...intervention to promote rational laboratory use without compromising resident education or patient care. Methods The study comprised of a cluster-randomized, controlled trial to assess the impact of a multifaceted intervention of education, guideline development, elimination of recurring laboratory orders, unbundling of laboratory panels, and redesign of the daily progress note on laboratory test ordering. The population included all patients hospitalized “general medicine” was duplicated during 2 consecutive months on a general medicine teaching service within a 999-bed tertiary care hospital in Boston, Massachusetts. The primary outcome was the total number of commonly used laboratory tests per patient day during 2 months in 2008. Secondary outcomes included a subgroup analysis of each individual test per patient day, adverse events, and resident and nursing satisfaction. Results A total of 5392 patient days were captured. The intervention produced a 9% decrease in aggregate laboratory use (rate ratio, 0.91; P = .021; 95% confidence interval, 0.84-0.98). Six instances of delayed diagnosis of acute kidney injury and 11 near misses were reported in the intervention arm. Conclusions A bundled educational and administrative intervention promoting rational ordering of laboratory tests on a single academic general medicine service led to a modest but significant decrease in laboratory use. To our knowledge, this was the first study to examine the daily progress note as a tool to limit excessive test ordering. Unadjudicated near misses and possible harm were reported with this intervention. This finding warrants further study.
•Mechanical and thermal thresholds were altered in both A/J and C57Bl/6 mice following burn injury.•Stress by itself increased mechanical allodynia, independent of burn injury.•Behaviors consistent ...with chronic pain after burn injury were apparent in both stressed and non-stressed A/J and C57Bl/6 mice.•Anxiety-prone A/J mice exposed to stress had a shorter recovery time with regard to mechanical allodynia compared to C57BL/6 mice.
Acute pain is prevalent following burn injury and can often transition to chronic pain. Prolonged acute pain is an important risk factor for chronic pain and there is little preclinical research to address this problem. Using a mouse model of second-degree burn, we investigated whether pre-existing stress influences pain(sensitivity) after a burn injury. We introduced a contribution of stress in two different ways: (1) the use of foot-shock as a pre-injury stressor or (2) the use of A/J mice to represent higher pre-existing stress compared to C57Bl/6 mice. C57Bl/6 and A/J mice were exposed to repeated mild foot shock to induce stress for 10 continuous days and mice underwent either burn injury or sham burn injury of the plantar surface of the right hind paw. Assessments of mechanical and thermal sensitivities of the injured and uninjured paw were conducted during the shock protocol and at intervals up to 82-day post-burn injury. In both strains of mice that underwent burn injury, thermal hypersensitivity and mechanical allodynia appeared rapidly in the ipsilateral paw. Mice that were stressed took much longer to recover their hind paw mechanical thresholds to baseline compared to non-stressed mice in both burn and non-burn groups. Analysis of the two mouse strains revealed that the recovery of mechanical thresholds in A/J mice which display higher levels of baseline anxiety was shorter than C57Bl/6 mice. No differences were observed regarding thermal sensitivities between strains. Our results support the view that stress exposure prior to burn injury affects mechanical and thermal thresholds and may be relevant to as a risk factor for the transition from acute to chronic pain. Finally, genetic differences may play a key role in modality-specific recovery following burn injury.
Intraepidermal nerve fiber density (IENFD) has become an important biomarker for neuropathy diagnosis and research. The consequences of reduced IENFD can include sensory dysfunction, pain, and a ...significant decrease in quality of life. We examined the extent to which IENFD is being used as a tool in human and mouse models and compared the degree of fiber loss between diseases to gain a broader understanding of the existing data collected using this common technique.
We conducted a scoping review of publications that used IENFD as a biomarker in human and non-human research. PubMed was used to identify 1,004 initial articles that were then screened to select articles that met the criteria for inclusion. Criteria were chosen to standardize publications so they could be compared rigorously and included having a control group, measuring IENFD in a distal limb, and using protein gene product 9.5 (PGP9.5).
We analyzed 397 articles and collected information related to publication year, the condition studied, and the percent IENFD loss. The analysis revealed that the use of IENFD as a tool has been increasing in both human and non-human research. We found that IENFD loss is prevalent in many diseases, and metabolic or diabetes-related diseases were the most studied conditions in humans and rodents. Our analysis identified 73 human diseases in which IENFD was affected, with 71 reporting IENFD loss and an overall average IENFD change of -47%. We identified 28 mouse and 21 rat conditions, with average IENFD changes of -31.6% and -34.7%, respectively. Additionally, we present data describing sub-analyses of IENFD loss according to disease characteristics in diabetes and chemotherapy treatments in humans and rodents.
Reduced IENFD occurs in a surprising number of human disease conditions. Abnormal IENFD contributes to important complications, including poor cutaneous vascularization, sensory dysfunction, and pain. Our analysis informs future rodent studies so they may better mirror human diseases impacted by reduced IENFD, highlights the breadth of diseases impacted by IENFD loss, and urges exploration of common mechanisms that lead to substantial IENFD loss as a complication in disease.
In mammalian cells, DNA double-strand breaks (DSBs) are mainly repaired by nonhomologous end joining (NHEJ) pathway. Ku (a heterodimer formed by Ku70 and Ku80 proteins) and DNA ligase IV are the core ...NHEJ factors. Ku could also be involved in other cellular processes, including telomere length regulation, DNA replication, transcription, and translation control.
, an early branching eukaryote and the causative agent of leishmaniasis, has no functional NHEJ pathway due to its lack of DNA ligase IV and other NHEJ factors but retains Ku70 and Ku80 proteins. In this study, we generated Leishmania donovani Ku70 disruption mutants and Ku70 and Ku80 double gene (Ku70/80) disruption mutants. We found that
Ku is still involved in DSB repair, possibly through its binding to DNA ends to block and slowdown 5' end resections and Ku-Ku or other protein interactions. Depending on location of a DSB between the direct repeat genomic sequences,
Ku could have an inhibiting effect, no effect or a promoting effect on the DSB repair mediated by single strand annealing (SSA), the most frequently used DSB repair pathway in
. Ku70/80 proteins are also required for the healthy proliferation of
cells. Interestingly, unlike in Trypanosoma brucei and L. mexicana, Ku70/80 proteins are dispensable for maintaining the normal lengths of telomeres in L. donovani. We also show it is possible to reconstitute the two components (Ku and Ligase D) NHEJ pathway derived from Mycobacterium marinum in
. This improved DSB repair fidelity and efficiency in
and sets up an example that the bacterial NHEJ pathway can be successfully reconstructed in an NHEJ-deficient eukaryotic parasite.
Nonhomologous end joining (NHEJ) is the most efficient double-stranded DNA break (DSB) repair pathway in mammalian cells. In contrast, the protozoan parasite
has no functional NHEJ pathway but retains the core NHEJ factors of Ku70 and Ku80 proteins. In this study, we found that
Ku heterodimers are still participating in DSB repair possibly through blocking 5' end resections and Ku-Ku protein interactions. Depending on the DSB location, Ku could have an inhibiting or promoting effect on DSB repair mediated by the single-strand annealing repair pathway. Ku is also required for the normal growth of the parasite but surprisingly dispensable for maintaining the telomere lengths. Further, we show it is possible to introduce Mycobacterium marinum NHEJ pathway into
. Understanding DSB repair mechanisms of
may improve the CRISPR gene targeting specificity and efficiency and help identify new drug targets for this important human parasite.
Exercise is recommended for people with diabetes, but little is known about exercise in people with diabetic peripheral neuropathy (DPN).
The primary purpose of this preliminary study was to examine ...adverse events (AEs) during moderate-intensity, supervised aerobic exercise in people with DPN. The secondary purpose was to examine changes in fatigue, aerobic fitness, and other outcomes after intervention.
This was a single-group preliminary study.
The setting was an academic medical center.
Participants were 18 people who were sedentary and had type 2 diabetes and peripheral neuropathy (mean age=58.1 years, SD=5).
The intervention was a supervised 16-week aerobic exercise program (3 times per week at 50% to >70% oxygen uptake reserve).
Adverse events were categorized as related or unrelated to the study, anticipated or unanticipated, and serious or not serious. Outcomes included fatigue (Multidimensional Fatigue Inventory), cardiovascular fitness (peak oxygen uptake), body composition (dual-energy x-ray absorptiometry), sleep quality, plasma metabolic markers, and peripheral vascular function.
During the study, 57 nonserious AEs occurred. Improvements were found in general fatigue (mean change=-3.5; 95% confidence interval 95% CI=-1.3, -5.3), physical fatigue (mean change=-3.1; 95% CI=-1.2, -5.0), peak oxygen uptake (mean change=1.1 mL·kg(-1)·min(-1); 95% CI=0.2, 1.9), total body fat (mean change=-1%; 95% CI=-0.3, -1.7), fat mass (mean change=-1,780 g; 95% CI=-616.2, -2,938.7), and peripheral blood flow (mean change=2.27%; 95% CI=0.6, 4.0).
This was a small-scale, uncontrolled study. A future randomized controlled trial is needed to fully assess the effects of exercise on the outcomes.
This study provides new support for supervised aerobic exercise in people with DPN. However, it is important for physical therapists to carefully prescribe initial exercise intensity and provide close monitoring and education to address the anticipated AEs as people who are sedentary and have DPN begin an exercise program.
Large-fiber diabetic polyneuropathy (DPN) leads to balance and gait abnormalities, placing patients at risk for falls. Large sensory axons innervating muscle spindles provide feedback for balance and ...gait and, when damaged, can cause altered sensorimotor function. This study aimed to determine whether symptoms of large-fiber DPN in type 1 and type 2 diabetic mouse models are related to alterations in muscle spindle innervation. In addition, diabetic mice were treated with insulin to assess whether sensorimotor and spindle deficits were reversible.
Behavioral assessments were performed in untreated and treated streptozotocin (STZ)-injected C57BL/6 mice to quantitate diabetes-induced deficits in balance and gait. Quantification of Ia axon innervation of spindles was carried out using immunohistochemistry and confocal microscopy on STZ-injected C57BL/6 and db/db mice.
STZ-injected C57BL/6 mice displayed significant and progressive sensorimotor dysfunction. Analysis of Ia innervation patterns of diabetic C57BL/6 spindles revealed a range of abnormalities suggestive of Ia axon degeneration and/or regeneration. The multiple abnormal Ia fiber morphologies resulted in substantial variability in axonal width and inter-rotational distance (IRD). Likewise, db/db mice displayed significant variability in their IRDs compared with db(+) mice, suggesting that damage to Ia axons occurs in both type 1 and type 2 diabetes models. Insulin treatment improved behavioral deficits and restored Ia fiber innervation in comparison with nondiabetic mice.
Similar to small fibers, Ia axons are vulnerable to diabetes, and their damage may contribute to balance and gait deficits. In addition, these studies provide a novel method to assay therapeutic interventions designed for diabetes-induced large-fiber dysfunction.
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