Stimulating effect of thyroid hormones in peripheral nerve regeneration: research history and future direction toward clinical therapy

Age and Gender Adjusted FT3 Levels as Novel Predictors of Survival

CONTEXT

Lower levels of free T3 (FT3) occur during acute illness, as part of "euthyroid sick syndrome." A chronic form of this syndrome also exists.

OBJECTIVE

To determine whether thyroid hormone levels predict long-term survival.

DESIGN AND SETTING

This was a "big-data" study of thyroid function tests from samples taken between 2008 and 2014. Data were crossed with electronic health records for morbidity and mortality. Test results were converted to age- and gender-adjusted percentiles (AGAPs). The hazard ratio for death was crossed with ranges of initial AGAPs and change in AGAPs for 2 subgroups: "not healthy" (subjects with at least 1 of 5 chronic conditions registered in their electronic health chart) and "healthy" (all others).

PARTICIPANTS

2 453 091 sets of thyroid function tests from 365 965 distinct patients were evaluated. 258 695 sets remained after excluding patients registered as taking thyroid preparations or anti-thyroid drugs.

MAIN OUTCOME MEASURE

Hazard ratio for death, planned before data collection.

RESULTS

The cohort included 151 868 not healthy and 106 827 healthy people. After a median of 6.8 years, 5865/151 868 (10.4%) of the not healthy had died and 2504/106 827 (2.3%) of healthy participants. Low initial FT3 AGAPs were predictive of poor survival. The hazard ratio for survival compared between the lowest 5 and highest 50 percentiles of initial FT3 AGAPs for not healthy participants was 5.71 [confidence interval (CI) 5.23-6.26, P < .001] and for healthy was 3.92 (CI 3.06-5.02, P < .001).

CONCLUSION

Low FT3 AGAPs predicted poor survival, most strongly among not healthy people.

Wiring the ocular surface: A focus on the comparative anatomy and molecular regulation of sensory innervation of the cornea

The cornea is richly innervated with sensory nerves that function to detect and clear harmful debris from the surface of the eye, promote growth and survival of the corneal epithelium and hasten wound healing following ocular disease or trauma. Given their importance to eye health, the neuroanatomy of the cornea has for many years been a source of intense investigation. Resultantly, complete nerve architecture maps exist for adult human and many animal models and these maps reveal few major differences across species. Interestingly, recent work has revealed considerable variation across species in how sensory nerves are acquired during developmental innervation of the cornea. Highlighting such species-distinct key differences, but also similarities, this review provides a full, comparative anatomy analysis of sensory innervation of the cornea for all species studied to date. Further, this article comprehensively describes the molecules that have been shown to guide and direct nerves toward, into and through developing corneal tissue as the final architectural pattern of the cornea's neuroanatomy is established. Such knowledge is useful for researchers and clinicians seeking to better understand the anatomical and molecular basis of corneal nerve pathologies and to hasten neuro-regeneration following infection, trauma or surgery that damage the ocular surface and its corneal nerves.

Low T3 syndrome is associated with peripheral neuropathy in patients with type 2 diabetes mellitus

INTRODUCTION/AIMS

Diabetic peripheral neuropathy (DPN) is one of the most common chronic complications of diabetes mellitus. Diabetic patients often have thyroid dysfunction. The aim of this study was to investigate the association between low triiodothyronine (T3) syndrome and DPN in patients with type 2 diabetes mellitus (T2DM).

METHODS

A retrospective review was performed of 928 patients with T2DM for whom data was available for clinical manifestations and nerve conduction studies (NCS), and of 134 non-diabetic controls. The composite Z scores of conduction velocity and amplitude were calculated. Low T3 syndrome was defined as T3 levels below the lower limit of the reference interval.

RESULTS

Among the patients with T2DM, 632 (68.1%) had DPN, and a larger proportion of these patients presented with low T3 syndrome than patients without DPN. After adjusting for potential confounders, low T3 syndrome was independently associated with the occurrence of DPN (odds ratio [OR] = 2.049, 95% confidence interval [CI] 1.319-3.181, p = .001) and the severity of DPN (OR = 1.597, 95% CI 1.030-2.476, p = .036). Adding the criterion of low T3 syndrome improved the prognostic performance of the traditional model (age + gender + diabetic duration + glycated hemoglobin [HbA1c]) for predicting DPN.

DISCUSSION

Low T3 syndrome is associated with a higher risk and increased severity of DPN in patients with T2DM. These findings suggest that low T3 syndrome could be a predictor for risk stratification in patients with T2DM.

Thyroid Function and Metabolic Syndrome in Children and Adolescents with Neuromotor Disability

Thyroid function plays a crucial role in nervous system integrity and metabolic homeostasis. We evaluated the pattern of TSH, FT4 and FT3 release in children with neuromotor impairment (NI) in relationship with metabolic syndrome (MS). We enrolled 55 patients with NI and 30 controls. Clinical parameters, thyroid function and MS presence were recorded. Principal component analysis (PCA), cluster analysis, and logistic regression models were performed. MS was detected in 54.5% of patients. Four clusters were identified: the first one included only controls and, contrasting with cluster 4, was exclusively characterized by children with disability and MS. This latter showed increased FT4 and FT3 and decreased TSH levels. Cluster 2, characterized by disability without MS showed high FT4 and FT3, whereas cluster 3 with low FT4 and FT3 mainly included disability (90%) and showed prevalent MS (57%). The association between TSH and NI is represented by a U-shape structure. The TSH, FT3 and FT4 release patterns may reflect thyrotropic adaptation, allostatic response and compensatory mechanisms. These mechanisms, found in both MS and disability, show that the odds of having a condition of NI with or without MS increase as the TSH values deviate, in both directions, from a value of 2.5 mLU/mL.

Upregulation of Neurotrophic Factors and Myelin Basic Protein in Schwann-like Cells by T3 Hormone Following Transdifferentiation of Human Adipose-derived Stem Cells

Peripheral nerve regeneration is a complicated phenomenon. Thyroid hormones are known as critical regulators in the nervous system development. The Schwann cells have the regenerative potency in the peripheral nervous system. In this study, the human adipose-derived stem cells were assessed in vitro, for transdifferentiation potency into Shwann-like cells (SLCs) as a candidate source for clinical cell therapy, under the treatment of triiodothyronine (T3) hormone, and compared with the untreated cells. The cell viability rate, myelination and neurotrophic factors expression of SLCs were evaluated two weeks post- induction by MTT assay, immunocytochemistry and real-time RT-PCR techniques, respectively. The obtained results revealed a significant decrease in SLCs viability, compared to the adipose-derived stem cells (P < 0.001). Immunocytochemistry technique was applied to detect SLCs markers, such as S100β, GFAP and myelin basic proteins (MBP) in the presence and absence of T3 treatment. The results indicated that administering T3 can significantly increase the differentiation and myelination potency of SLCs (P < 0.01). The findings of real-time RT-PCR technique indicated that the expression of Schwann cells markers, MBP, brain-derived neurotrophic factor and glial cell-derived neurotrophic factor were upregulated significantly with T3 hormone administration in comparison with the untreated cells (P < 0.05). The SLCs were able to express the neurotrophic factors and myelination related genes in the presence of T3 hormone. Furthermore, T3 administration improved myelination potency of adipose-derived stem cells, in vitro. Further in vivo experiments are necessary to confirm the advantages of using a combination of autologous SLCs and T3 hormone for peripheral nerve injury recovery.

Sulforaphane, a Chemopreventive Compound Induces Necrotic Behavior and Inhibits S-phase of Cell Cycle in Human Kidney Cells in Vitro

Sulforaphane (SFN) is an organosulfur product of found isothiocyanates in vegetables. The chemopreventive effects of SFN have revealed that there is a link between excessive consumption of SFN-rich vegetables and cancer formation without possible toxicological consequences. We aimed to evaluate the cellular outcome of SFN from a toxicological perspective, particularly for renal cells including clear cell adenocarcinoma (769-P) and human embryonic renal epithelial (293T) cells. The viability/cytotoxicity experiments were performed with methyl thiazole diphenyl tetrazolium (MTT) and lactate dehydrogenase (LDH) assays. IC₅₀-dependent, non-cytotoxic concentrations were used for the determination of cell cycle status and apoptosis by using flow cytometry and western blot. A certain concentration of SFN effectively altered apoptotic/necrotic behavior in 769-P compared to the control group 293T. Cell cycle status remained stable while showing a decreased proliferation profile for 769-P cells. The percentage of the S phase from the cell cycle in 293T cells significantly reduced without affecting proliferation status. The use of SFN as an alternative to traditional treatments might be considered for the battle against renal cell carcinoma but the current findings showed that caution should be applied particularly for renal cells. Our study will provide a basis for future in vivo studies to support traditional cancer therapies.

Related Fluoxetine and Methylprednisolone Changes of TNF-α and IL-6 Expression in The Hypothyroidism Rat Model of Spinal Cord Injury

Objective

Spinal cord injury (SCI) is a serious clinical condition that leads to disability. Following primary injury, pro- inflammatory cytokines play an important role in the subsequent secondary events. The thyroid hormone (TH) is known as the modulator of inflammatory cytokines and acts as a neuroprotective agent. Methylprednisolone (MP) is used for the early treatment of SCI. Fluoxetine (FLX), also is known as a selective serotonin reuptake inhibitor (SSRI), has therapeutic potential in neurological disorders. The aim of the present study was to investigate the combined effects of MP and FLX on SCI in the rat hypothyroidism (hypo) model.

Materials and Methods

In this experimental study, 48 male Wistar rats with hypothyroidism were randomly divided into 6 groups (n=8/group): control (Hypo), Hypo+Surgical sham, Hypo+SCI, Hypo+SCI+MP, Hypo+SCI+FLX, and Hypo+SCI+MP+FLX. SCI was created using an aneurysm clip and Hypothyroidism was induced by 6-Propyl-2-thiouracil (PTU) at a dose of 10 mg/kg/day administered intraperitoneally. Following SCI induction, rats received MP and FLX treatments via separate intraperitoneal injections at a dose of 30 and 10 mg/kg/day respectively on the surgery day and FLX continued daily for 3 weeks. The expression levels of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) were quantified by Real-time polymerase chain reaction (PCR) and Western blotting. Myelination and glutathione (GSH) levels were analyzed by Luxol Fast Blue (LFB) staining and ELISA respectively.

Results

Following combined MP and FLX treatments, the expression levels of TNF-α and IL-6 significantly decreased and GSH level considerably increased in the trial animals.

Conclusion

Our results show the neuroprotective effects of MP and FLX with better results in Hypo+SCI+MP+FLX group. Further study is required to identify the mechanisms involved.

In vitro differentiation of human bone marrow stromal cells into neural precursor cells using small molecules

BACKGROUND

Neurogenic differentiation of human marrow stromal stem cells (hMSCs) into neural precursor cells (NPCs) offers new hope in many neurological diseases. Stromal cells can be differentiated into NPCs using small molecules acting as chemical inducers. The aim of this study is to formulate an efficient, direct, fast and safe protocol to differentiate hMSCs into NPCs using different inducers: b-mercaptoethanol (BME), triiodothyronine (T3), and curcumin (CUR). NEW METHOD: hMSCs were subjected to either 1 mM BME, 0.5 µM T3, or 5 µM CUR. Neurogenic differentiation was determined by assessing the protein expression of PAX6, SOX2, DLX2, and GAP-43 with flow cytometry and immunofluorescence, along with Nissl staining of differentiated cells.

RESULTS AND COMPARISON WITH EXISTING METHOD

It was revealed that T3 and CUR are 70-80% better than BME in terms of efficiency and safety, and surprisingly BME was a good promoting factor for cell preconditioning with limited effects on neural trans-differentiation related to its toxic effects on cell viability.

CONCLUSION

Reprogramming of bone marrow stromal cells into neural cells gives hope for treating different neurological disorders. Our study shows that T3 and CUR were effective in generation of NPCs from hMSCs with preservation of cell viability. BME was a good promoting factor for cell preconditioning with limited effects on neural transdifferentiation related to its toxic effects on cell viability.

Regional Difference in Myelination in Monocarboxylate Transporter 8 Deficiency: Case Reports and Literature Review of Cases in Japan

Background: Monocarboxylate transporter 8 (MCT8) is a thyroid hormone transmembrane transporter protein. MCT8 deficiency induces severe X-linked psychomotor retardation. Previous reports have documented delayed myelination in the central white matter (WM) in these patients; however, the regional pattern of myelination has not been fully elucidated. Here, we describe the regional evaluation of myelination in four patients with MCT8 deficiency. We also reviewed the myelination status of previously reported Japanese patients with MCT8 deficiency based on magnetic resonance imaging (MRI).

Case Reports: Four patients were genetically diagnosed with MCT8 deficiency at the age of 4–9 months. In infancy, MRI signal of myelination was observed mainly in the cerebellar WM, posterior limb of internal capsule, and the optic radiation. There was progression of myelination with increase in age.

Discussion: We identified 36 patients with MCT8 deficiency from 25 families reported from Japan. The available MRI images were obtained at the age of <2 years in 13 patients, between 2 and 4 years in six patients, between 4 and 6 years in three patients, and at ≥6 years in eight patients. Cerebellar WM, posterior limb of internal capsule, and optic radiation showed MRI signal of myelination by the age of 2 years, followed by centrum semiovale and corpus callosum by the age of 4 years. Most regions except for deep anterior WM showed MRI signal of myelination at the age of 6 years.

Conclusion: The sequential pattern of myelination in patients with MCT8 deficiency was largely similar to that in normal children; however, delayed myelination of the deep anterior WM was a remarkable finding. Further studies are required to characterize the imaging features of patients with MCT8 deficiency.

A cross-species analysis of systemic mediators of repair and complex tissue regeneration

Regeneration is an elegant and complex process informed by both local and long-range signals. Many current studies on regeneration are largely limited to investigations of local modulators within a canonical cohort of model organisms. Enhanced genetic tools increasingly enable precise temporal and spatial perturbations within these model regenerators, and these have primarily been applied to cells within the local injury site. Meanwhile, many aspects of broader spatial regulators of regeneration have not yet been examined with the same level of scrutiny. Recent studies have shed important insight into the significant effects of environmental cues and circulating factors on the regenerative process. These observations highlight that consideration of more systemic and possibly more broadly acting cues will also be critical to fully understand complex tissue regeneration. In this review, we explore the ways in which systemic cues and circulating factors affect the initiation of regeneration, the regenerative process, and its outcome. As this is a broad topic, we conceptually divide the factors based on their initial input as either external cues (for example, starvation and light/dark cycle) or internal cues (for example, hormones); however, all of these inputs ultimately lead to internal responses. We consider studies performed in a diverse set of organisms, including vertebrates and invertebrates. Through analysis of systemic mediators of regeneration, we argue that increased investigation of these "systemic factors" could reveal novel insights that may pave the way for a diverse set of therapeutic avenues.

Effects of endocrine disrupting chemicals on myelin development and diseases

In the central and peripheral nervous systems, myelin is essential for efficient conduction of action potentials. During development, oligodendrocytes and Schwann cells differentiate and ensure axon myelination, and disruption of these processes can contribute to neurodevelopmental disorders. In adults, demyelination can lead to important disabilities, and recovery capacities by remyelination often decrease with disease progression. Among environmental chemical pollutants, endocrine disrupting chemicals (EDCs) are of major concern for human health and are notably suspected to participate in neurodevelopmental and neurodegenerative diseases. In this review, we have combined the current knowledge on EDCs impacts on myelin including several persistent organic pollutants, bisphenol A, triclosan, heavy metals, pesticides, and nicotine. Besides, we presented several other endocrine modulators, including pharmaceuticals and the phytoestrogen genistein, some of which are candidates for treating demyelinating conditions but could also be deleterious as contaminants. The direct impacts of EDCs on myelinating cells were considered as well as their indirect consequences on myelin, particularly on immune mechanisms associated with demyelinating conditions. More studies are needed to describe the effects of these compounds and to further understand the underlying mechanisms in relation to the potential for endocrine disruption.

Silicone tubes with thyroid hormone (Τ3) and BDNF as an alternative to autografts for bridging neural defects

The way thyroid hormone works in peripheral nerve regeneration has not been fully elucidated, although studies have shown that it has a strong positive effect on nerve regeneration. It is argued that its action is probably stronger than the neurotrophic factors that have been used for some time. It is hypothesized that the use of thyroid hormone in the nerve tubes has a beneficial effect on nerve regeneration to the extent that the results of its use are comparable to those of the autograft technique in bridging small nerve deficits. In this experimental study, we examined the effect of thyroid hormone and BDNF (Brain Derived Neurotrophic Factor) on the repair of 10 mm nerve defects when administered within silicone nerve tubes and compared the results with the autograft method. Thyroid hormone promotes nerve regeneration mainly by increasing its speed and its effect on the maturation of nerve fibers compared to the other groups where the nerve deficit was bridged by entubulation. Also, better organization and the absence of intraneural fibrosis, compared to the other groups, may argue for the action of thyroid hormone in regulating the inflammatory response. Functionally, the AG group showed better results compared to the other groups by the end of the study (16 weeks).

Effects of Growth Hormone Treatment and Rehabilitation in Incomplete Chronic Traumatic Spinal Cord Injury: Insight from Proteome Analysis

Despite promising advances in the medical management of spinal cord injury (SCI), there is still no available effective therapy to repair the neurological damage in patients who experience this life-transforming condition. Recently, we performed a phase II/III placebo-controlled randomized trial of safety and efficacy of growth hormone (GH) treatment in incomplete chronic traumatic spinal cord injury. The main findings were that the combined treatment of GH plus rehabilitation treatment is feasible and safe, and that GH but not placebo slightly improves the SCI individual motor score. Moreover, we found that an intensive and long-lasting rehabilitation program per se increases the functional outcome of SCI individuals. To understand the possible mechanisms of the improvement due to GH treatment (motor score) and due to rehabilitation (functional outcome), we used a proteomic approach. Here, we used a multiple proteomic strategy to search for recovery biomarkers in blood plasma with the potential to predict response to somatropin treatment and to delayed intensive rehabilitation. Forty-six patients were recruited and followed for a minimum period of 1 year. Patients were classified into two groups based on their treatment: recombinant somatropin (0.4 mg) or placebo. Both groups received rehabilitation treatment. Our strategy allowed us to perform one of the deepest plasma proteomic analyses thus far, which revealed two proteomic signatures with predictive value: (i) response to recombinant somatropin treatment and (ii) response to rehabilitation. The proteins implicated in these signatures are related to homeostasis, inflammation, and coagulation functions. These findings open novel possibilities to assess and therapeutically manage patients with SCI, which could have a positive impact on their clinical response.

Improvement of the clinical signs of gait abnormality after treatment with levothyroxine in a horse with shivering and hypothyroidism

An 11-year-old Hanoverian gelding used for jumping was evaluated for gait abnormalities and hoof problems in the hindlimbs. Clinical examinations revealed signs consistent with shivers. A thyroid gland enlargement was noticed, baseline serum thyroid hormone (TH) concentrations were low, and a low response to thyrotropin-releasing hormone administration was observed. Hypothyroidism was suspected. The horse was treated with levothyroxine for 1 year. TH concentrations returned to the normal range by week 4 of treatment. Thirty weeks after the initiation of levothyroxine therapy, the gait abnormality improved. Our findings suggest that the assessment of thyroid status and especially of the subclinical thyroid gland disorders in horses affected with shivering, as well as evaluation of the effects of levothyroxine on the improvement of clinical signs could be promising in establishing the aetiopathogenesis and/or treatment of shivering in horses.

Unique and overlapping effects of triiodothyronine (T3) and thyroxine (T4) on sensory innervation of the chick cornea

Multiple aspects of cornea development, including the innervation of the cornea by trigeminal axons, are sensitive to embryonic levels of thyroid hormone (TH). Although previous work showed that increased TH levels could enhance the rate of axonal extension within the cornea in a thyroxine (T4)-dependent manner, details underlying the stimulatory effect of TH on cornea innervation are unclear. Here, by examining the effects throughout all stages of cornea innervation of the two main THs, triiodothyronine (T3) and T4, we provide a more complete characterization of the stimulatory effects of TH on corneal nerves and begin to unravel the underlying molecular mechanisms. During development, trigeminal axons are initially repelled at the corneal periphery and encircle the cornea in a pericorneal nerve ring prior to advancing into the corneal stroma radially from all along the nerve ring. Overall, exogenous T3 led to pleiotropic effects throughout all stages of cornea innervation, whereas the effects of exogenous T4 was confined to timepoints following completion of the nerve ring. Specifically, exogenous T3 accelerated the formation of the pericorneal nerve ring. By utilizing in vitro neuronal explants studies we demonstrated that T3 acts as a trophic factor to directly stimulate trigeminal nerve growth. Further, exogenous T3 caused disorganized and precocious innervation of the cornea, accompanied by the downregulation of inhibitory Robo receptors that normally act to regulate the timing of nerve advancement into the Slit-expressing corneal tissues. Following nerve ring completion, the growth rate and branching behavior of nerves as they advanced into and through the cornea were found to be stimulated equally by T3 or T4. These stimulatory influences of T3/T4 over nerves likely arose as secondary consequences brought on by TH-mediated modulations to the corneal extracellular matrix. Specifically, we found that the levels of nerve-inhibitory keratan- and chondroitin-sulfate containing proteoglycans and associated sulfation enzymes were dramatically altered in the presence of exogenous T3 or T4. Altogether, these findings uncover new roles for TH on corneal development and shed insight into the mechanistic basis of both T3 and T4 on cornea innervation.

Differential expression of circular RNAs in the proximal and distal segments of the sciatic nerve after injury

To investigate the functions of circular RNAs (circRNAs) in axonal regeneration and degeneration after injury, circRNA expression profiles in the injured peripheral nerves were determined using a circRNA-based microarray. The results showed that 281 upregulated and 261 downregulated circRNAs were found in the proximal stump of the sciatic nerve after injury. In the distal stump after injury, 217 circRNAs were upregulated and 224 circRNAs were downregulated. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment and gene ontology (GO) analysis of circRNAs after injury were associated with axon regeneration pathways, including thyroid hormone, Ras signaling, endocytosis, and the ErbB signaling pathway, as well as with Schwann cell differentiation and proliferation, including the axon guidance, focal adhesion, Glutamatergic synapse, and MAPK signaling pathway. To verify the microarray results, among the regulated circRNAs, the upregulation of circRNA 012142 in both proximal and distal segments was validated using quantitative PCR analysis. The biological function of the circRNA 012412/microRNA/mRNA network based on GO analysis and KEGG pathway was identified in cell differentiation, phosphorylation, intracellular signaling transduction, and focal adhesion, the Rap1 signaling pathway. Thus, circRNAs after nerve injury may be involved in these biological functions during nerve regeneration and degeneration.

The progress of biomaterials in peripheral nerve repair and regeneration

Repair and regeneration of the injured peripheral nerve (PN) is a challenging issue in clinics. Although the regeneration outcome of large PN defects is currently unsatisfactory, recently, the study of PN repair has considerably progressed. In particular, biomaterials for repairing PNs, such as nerve guidance conduits and nerve repair membranes, have been well developed. Herein, we summarize the anatomy of the PN, the pathophysiological features of the nerve injury, and the repair process post injury. Then, we highlight the progress in the development of natural and synthetic biomaterials and summarize the applications, advantages, and disadvantages of these materials. These materials can be used as nerve repair membranes and nerve conduits in the field of PN repair. Finally, we discuss the challenges encountered and development strategies for PN repair in the future.

Endocrine Regulation of Epimorphic Regeneration

Studies aiming to uncover primary mechanisms of regeneration have predominantly focused on genetic pathways regulating specific stages in the regeneration process: wound healing, blastema formation, and pattern formation. However, studies across organisms show that environmental conditions and the physiological state of the animal can affect the rate or quality of regeneration, and endocrine signals are likely the mediators of these effects. Endocrine signals acting directly on receptors expressed in the tissue or via neuroendocrine pathways can affect regeneration by regulating the immune response to injury, allocation of energetic resources, or by enhancing or inhibiting proliferation and differentiation pathways involved in regeneration. This review discusses the cumulative knowledge in the literature about endocrine regulation of regeneration and its importance in future research to advance biomedical research.

Endocrine regulation of regeneration: Linking global signals to local processes

Regeneration in amphibians and reptiles has been explored since the early 18th century, giving us a working in vivo model to study epimorphic regeneration in vertebrates. Studies aiming to uncover primary mechanisms of regeneration have predominantly focused on genetic pathways regulating specific stages of the regeneration process: wound healing, blastema formation and growth, and pattern formation. However, studies across organisms show that environmental conditions and physiological state of the animal can affect the rate or quality of regeneration, and endocrine signals are likely the mediators of these effects. Endocrine signals working/acting directly on receptors expressed in the structure or via neuroendocrine pathways can affect regeneration by modulating immune response to injury, allocation of energetic resources, or by enhancing or inhibiting proliferation and differentiation pathways in regenerating tissue. This review discusses the cumulative knowledge known about endocrine regulation of regeneration and important future research directions of interest to both ecological and biomedical research.

Repair of peripheral nerve defects by nerve transposition using small gap bio-sleeve suture with different inner diameters at both ends

During peripheral nerve transposition repair, if the diameter difference between transposed nerves is large or multiple distal nerves must be repaired at the same time, traditional epineurial neurorrhaphy has the problem of high tension at the suture site, which may even lead to the failure of nerve suture. We investigated whether a small gap bio-sleeve suture with different inner diameters at both ends can be used to repair a 2-mm tibial nerve defect by proximal transposition of the common peroneal nerve in rats and compared the results with the repair seen after epineurial neurorrhaphy. Three months after surgery, neurological function, nerve regeneration, and recovery of nerve innervation muscle were assessed using the tibial nerve function index, neuroelectrophysiological testing, muscle biomechanics and wet weight measurement, osmic acid staining, and hematoxylin-eosin staining. There was no obvious inflammatory reaction and neuroma formation in the tibial nerve after repair by the small gap bio-sleeve suture with different inner diameters at both ends. The conduction velocity, muscle strength, wet muscle weight, cross-sectional area of muscle fibers, and the number of new myelinated nerve fibers in the bio-sleeve suture group were similar to those in the epineurial neurorrhaphy group. Our findings indicate that small gap bio-sleeve suture with different inner diameters at both ends can achieve surgical suture between nerves of different diameters and promote regeneration and functional recovery of injured peripheral nerves.