Nerve regeneration in transplanted organs and tracer imaging studies: A review

Sympathetic reinnervation in cardiac transplant recipients: Prevalence, time course, and association with long-term survival

BACKGROUND

Partial cardiac sympathetic reinnervation after cardiac transplant has been extensively investigated and evidenced. However, there have been no large-scale, long-term studies evaluating the prevalence, time-course, and association with long-term survival of sympathetic reinnervation of the heart.

METHODS

Cardiac transplant recipients (n = 232) were recruited from outpatient clinic at a single transplant center in the United Kingdom. Participants were each tested once for the presence of sympathetic reinnervation of the sinus node using the low-frequency component of power spectral analysis of heart rate variability, with a cutoff defined as 2 standard deviations above the mean for denervated participants (those tested <56 days posttransplant). Time course was calculated based on the timing of testing posttransplant. Patients were then followed up over a period of up to 27 years after transplant for survival analysis.

RESULTS

The overall prevalence of cardiac sympathetic reinnervation in the 225 patients tested >56 days posttransplant was 64.9%. Sympathetic reinnervation primarily occurred in the first 18 months after transplant, with a plateau thereafter. The prevalence in participants tested >18 months posttransplant was 69.6%. In Kaplan-Meier survival analysis, sympathetic reinnervation was associated with significantly improved survival (Log-rank p = 0.019), with a median survival time for reinnervated patients of 19.9 years compared with 14.4 years for the denervated group.

CONCLUSIONS

Sympathetic reinnervation of the sinus node occurs mostly within 18 months of transplant, is found in 70% of cardiac transplant recipients tested >18 months posttransplant, and is associated with significantly improved long-term survival.

Advances in tissue engineering of peripheral nerve and tissue innervation - a systematic review

Although various options are available to treat injured organs and peripheral nerves, none is without limitations. Auto- and allografts are the first choice of treatment, but tissue survival or functionality is not guaranteed due to often limited vascular and neural networks. In response, tissue-engineered solutions have been developed, yet clinical translations is rare. In this study, a systematic review was performed on tissue-engineered advancements for peripheral nerves and tissues, to aid future developments in bridging the gap toward the clinic by identifying high-potential solutions and unexplored areas. A systematic search was performed in PubMed, Embase, Web of Science, and Scopus until November 9, 2023. Search terms involved "tissue engineering," "guided," "tissue scaffold," and "tissue graft," together with "innervation" and "reinnervation." Original in vivo or in vitro studies meeting the inclusion criteria (tissue-engineered peripheral nerve/innervation of tissue) and no exclusion criteria (no full text available; written in foreign language; nonoriginal article; tissue-engineering of central nervous system; publication before 2012; insufficient study quality or reproducibility) were assessed. A total of 68 out of 3626 original studies were included. Data extraction was based on disease model, cell origin and host species, biomaterial nature and composition, and external stimuli of biological, chemical or physical origin. Although tissue engineering is still in its infancy, explored innervation strategies of today were highlighted with respect to biomaterials, cell types, and external stimuli. The findings emphasize that natural biomaterials, pre-seeding with autologous cell sources, and solutions for reproductive organs are beneficial for future research. Natural biomaterials possess important cues required for cell-material interaction and closely resemble native tissue in terms of biomechanical, geometrical and chemical composition. Autologous cells induce biomaterial functionalization. As these solutions pose no risk of immunorejection and have demonstrated good outcomes, they are most likely to fulfill the clinical demands.

The role of the nervous system in liver diseases

The nervous system significantly participates in maintaining homeostasis, and modulating repair and regeneration processes in the liver. Moreover, the nervous system also plays an important role in the processes associated with the development and progression of liver disease, and can either potentiate or inhibit these processes. The aim of this review is to describe the mechanisms and pathways through which the nervous system influences the development and progression of liver diseases, such as alcohol-associated liver disease, nonalcoholic fatty liver disease, cholestatic liver disease, hepatitis, cirrhosis, and hepatocellular carcinoma. Possible therapeutic implications based on modulation of signals transduction between the nervous system and the liver are also discussed.

Organ Neuroprosthetics: Connecting Transplanted and Artificial Organs with the Nervous System

Implantable neural interfaces with the central and peripheral nervous systems are currently used to restore sensory, motor, and cognitive functions in disabled people with very promising results. They have also been used to modulate autonomic activities to treat diseases such as diabetes or hypertension. Here, this study proposes to extend the use of these technologies to (re-)establish the connection between new (transplanted or artificial) organs and the nervous system in order to increase the long-term efficacy and the effective biointegration of these solutions. In this perspective paper, some clinically relevant applications of this approach are briefly described. Then, the choices that neural engineers must implement about the type, implantation location, and closed-loop control algorithms to successfully realize this approach are highlighted. It is believed that these new "organ neuroprostheses" are going to become more and more valuable and very effective solutions in the years to come.

The Sympathetic-Immune Milieu in Metabolic Health and Diseases: Insights from Pancreas, Liver, Intestine, and Adipose Tissues

Sympathetic innervation plays a crucial role in maintaining energy balance and contributes to metabolic pathophysiology. Recent evidence has begun to uncover the innervation landscape of sympathetic projections and sheds light on their important functions in metabolic activities. Additionally, the immune system has long been studied for its essential roles in metabolic health and diseases. In this review, the aim is to provide an overview of the current research progress on the sympathetic regulation of key metabolic organs, including the pancreas, liver, intestine, and adipose tissues. In particular, efforts are made to highlight the critical roles of the peripheral nervous system and its potential interplay with immune components. Overall, it is hoped to underscore the importance of studying metabolic organs from a comprehensive and interconnected perspective, which will provide valuable insights into the complex mechanisms underlying metabolic regulation and may lead to novel therapeutic strategies for metabolic diseases.