Nucleus replacement has recently come into favor as a possible treatment for Degenerative Disc Disease. Replacing degenerative nucleus tissue with a synthetic material that mimics healthy nucleus tissue may restore normal function and biomechanics to the disc and delay or obviate the need for more invasive procedures such as total disc replacement and fusion. This thesis evaluated a novel protein polymer hydrogel composed of silk and elastin as a nucleus replacement material. There are three experimental components; one in vivo and two in vitro portions. In the first experimental portion, a large animal model was developed to evaluate the biocompatibility of the material as well as the effect on surrounding boney and soft tissues. Three discs were evaluated in each animal; sham, discectomy and discectomy treated with hydrogel. Discs were evaluated at 4, 26 and 52 weeks. The hydrogel group showed a quiet cellular response, as well as decreased boney remodeling and fewer degenerative changes when compared to the discectomy group. The second experimental portion evaluated the biomechanics of 9 cadaveric motion segments loaded in axial rotation, lateral bending, flexion/extension (FE) and compression. Specimens were tested sequentially in the intact state, following annulotomy, discectomy and after hydrogel treatment. Range of Motion (ROM) in FE was shown to increase from the intact state (8.50+/-1.44˚) to the discectomy state (9.86+/-1.77˚) and decrease following hydrogel treatment (8.66+/-0.76˚) to be similar to the intact ROM. The third experimental portion investigates the effect of three commonly applied testing conditions on the mechanical properties of spinal segments. 27 motion segments were tested at 18˚C wrapped with Phosphate Buffered Saline (PBS), at 37˚C in a PBS bath, and at 37˚C and 100% humidity. Specimens were tested hourly for 6 hours. The heated conditions were shown to have lower stiffness and increased range of motion when compared 18 ˚C tests. Repeated testing with time increased neutral zone and ROM for all modes of bending. As tests are repeated over time, tissue properties change and may mask the ability of a nucleus replacement to restore biomechanics.

Compounds that interact with Group II metabotropic glutamate receptors (mGluRs) have antipsychotic effects in animal models. These drugs have also shown efficacy in the treatment of schizophrenia in humans. The mechanism of action is believed to arise from a reduction of glutamatergic transmission in limbic and forebrain regions commonly associated with this disorder. Previous anatomical tracer and lesion studies have revealed that neurons of the paraventricular nucleus of the thalamus (PVT) are an important source of the glutamatergic drive to these specific regions. However, the function of Group II mGluRs in the PVT remains to be determined. Whole-cell recordings from PVT neurons reveal that activation of these receptors has two interesting effects; it reduces calcium entry through voltage-gated calcium channels and it causes neurons to hyperpolarize. These two effects may contribute to affect the excitability of PVT neurons, an action that may underlie the effectiveness of Group II mGluR-activating compounds.

Mechanical low back pain is a disabling condition often associated with degenerative disc disease (DDD). Treatment for DDD includes non-operative pain management, total disc arthroplasty and nucleus pulposus (NP) replacement. A thiol-modified hyaluronan elastin-like polypeptide (TMHA/EP) composite has been under consideration as a NP replacement and has shown promise in vitro. This thesis aims to determine the effects of TMHA/EP composite augmentation on spinal motion segment mechanics in healthy and induced early stage DDD porcine intervertebral discs (IVD). Healthy IVD augmentation on average increased axial compressive stiffness, while bending and rotational stability decreased. Early stage DDD porcine IVD had compromised mechanical integrity in comparison to healthy controls. TMHA/EP augmentation of the mechanically compromised IVDs through two injection techniques worked to restore spinal stability, exhibiting mechanical properties similar to healthy IVDs. This work demonstrates the potential of the injectable TMHA/EP composite in providing initial structural stabilization in early stages of DDD.

Mechanical low back pain is a disabling condition often associated with degenerative disc disease (DDD). Treatment for DDD includes non-operative pain management, total disc arthroplasty and nucleus pulposus (NP) replacement. A thiol-modified hyaluronan elastin-like polypeptide (TMHA/EP) composite has been under consideration as a NP replacement and has shown promise in vitro. This thesis aims to determine the effects of TMHA/EP composite augmentation on spinal motion segment mechanics in healthy and induced early stage DDD porcine intervertebral discs (IVD). Healthy IVD augmentation on average increased axial compressive stiffness, while bending and rotational stability decreased. Early stage DDD porcine IVD had compromised mechanical integrity in comparison to healthy controls. TMHA/EP augmentation of the mechanically compromised IVDs through two injection techniques worked to restore spinal stability, exhibiting mechanical properties similar to healthy IVDs. This work demonstrates the potential of the injectable TMHA/EP composite in providing initial structural stabilization in early stages of DDD.

Compounds that interact with Group II metabotropic glutamate receptors (mGluRs) have antipsychotic effects in animal models. These drugs have also shown efficacy in the treatment of schizophrenia in humans. The mechanism of action is believed to arise from a reduction of glutamatergic transmission in limbic and forebrain regions commonly associated with this disorder. Previous anatomical tracer and lesion studies have revealed that neurons of the paraventricular nucleus of the thalamus (PVT) are an important source of the glutamatergic drive to these specific regions. However, the function of Group II mGluRs in the PVT remains to be determined. Whole-cell recordings from PVT neurons reveal that activation of these receptors has two interesting effects; it reduces calcium entry through voltage-gated calcium channels and it causes neurons to hyperpolarize. These two effects may contribute to affect the excitability of PVT neurons, an action that may underlie the effectiveness of Group II mGluR-activating compounds.

Diverse forms of life have evolved 24-hour or circadian timekeeping systems serving to coordinate internal biological events with the daily solar cycle. The generation of circadian rhythms by this timekeeping system ensures that internal processes occur at the appropriate time of day or night in relation to the environmental cycle and to other functionally-affiliated events. For mammals, endogenous oscillations in gene expression are a prevalent feature of oscillatory cells residing in the suprachiasmatic nucleus (SCN) and non-SCN tissues. To determine whether immortalized cells derived from the rat SCN (SCN2.2) retain the intrinsic rhythm-generating properties of the SCN, oscillatory behavior of the SCN2.2 transcriptome was analyzed and compared to that found in the rat SCN in vivo. In SCN2.2 cells, 116 unique genes and 46 ESTs or genes of unknown function exhibited circadian fluctuations for 2 cycles. Many (35%) of these rhythmicallyregulated genes in SCN2.2 cells also exhibited circadian profiles of mRNA expression in the rat SCN in vivo. To screen for output signals that may distinguish oscillatory cells in the mammalian SCN from peripheral-type oscillators, the rhythmic behavior of the transcriptome in forskolin-stimulated NIH/3T3 fibroblasts was analyzed and compared relative to SCN2.2 cells in vitro and the rat SCN in vivo. Similar to the circadian profiling of the SCN2.2 and rat SCN transcriptomes, NIH/3T3 fibroblasts exhibited rhythmic fluctuations in the expression of the core clock genes and 323 (2.6%) functionally diverse transcripts. Overlap in rhythmically expressed transcripts among these different oscillator models was limited to the clock genes and four genes that function in metabolism or transcription. Coupled with evidence for the rhythmic regulation of the inducible isoform of nitric oxide synthase (Nos) in SCN2.2 cells and the rat SCN but not in fibroblasts, studies examining the effects of antisense oligonucleotide-mediated inhibition of Nos2 suggest that the gaseous neurotransmitter nitric oxide may play a key role in SCN pacemaker function. Thus, our comparative analysis of circadian gene expression in SCN and non-SCN cells has important implications in the selective analysis of circadian signals involved in the coupling of SCN oscillators and regulation of rhythmicity in downstream cells.

Thesis--M. Phil., University of Hong Kong, 1980.

Thesis--Ph. D., University of Hong Kong, 1979.

Degenerative disc disease (DDD) is a common medical issue among human adults, leading to back pain and potentially, disability, decreasing an individual’s quality of life. In the United States alone, huge economic impacts are apparent with an estimated $50- 100 billion attributed to lost productivity and medical costs related to DDD. Spinal degeneration occurs in the intervertebral disc (IVD) and once damaged, the IVD is incapable of adequate self-repair. A regenerative therapy incorporating nucleus pulposus (NP) tissue engineering may provide an answer to spinal degeneration. The objective of this in vitro study was to evaluate the potential of a thiol-modified hyaluronan (TMHA) and elastin-like polypeptide (ELP) as a hydrogel scaffold for nucleus pulposus tissue engineering. Two materials, one composed of TMHA only and one a 3:1 TMHA/ELP, crosslinked with polyethylene glycol diacrylate (PEGDA), were seeded with cultured human NP cells and cyclic hydrostatic loading was applied at 1MPa for 3 hours a day for 3 consecutive days. Cell viability and gene expression were analyzed. A decreasing trend in cell viability with time and cyclic hydrostatic pressure loading was observed and statistically significant differences were observed between the TMHA unloaded treatment group at day 0 and the TMHA loaded treatment group at day 4 and between the TMHA unloaded treatment group at day 0 and the 3:1 TMHA/ELP loaded group at day 4. Comparisons between TMHA only and 3:1 TMHA/ELP hydrogels for the same treatment indicate similar trends and no statistically significant differences in biological effects were observed. Gene expression analysis indicated low frequency expression of NP extracellular matrix (ECM) molecules regardless of time point or cyclic hydrostatic pressure application. These results are revealing in that the 3:1 TMHA/ELP hydrogel did not support NP cells significantly better than the TMHA hydrogel, though cell source and hydrostatic pressure generation issues may have impacted this finding. Additional studies with alternative cell type and a refined hydrostatic pressure application method may better illuminate the efficacy of a 3:1 TMHA/ELP hydrogel as for NP tissue engineering. / Thesis (Master, Chemical Engineering) -- Queen's University, 2011-03-17 14:16:28.83

Metallothioneins (MTs) have a major role in metal metabolism and may also protect DNA against oxidants. MT protein has been found localized in the nucleus during S-phase. The mRNA encoding for the MT-1 isoform is found localized around the nucleus and associated with the cytoskeleton; this is due to targeting signals within the 3'untranslated region (3'UTR). Using cells transfected with gene constructs differing in their 3'UTRs, the role of perinuclear mRNA localization in facilitating MT synthesis close to its site of function and subsequent import of protein into the nucleus has been investigated, as well as the role of MT protein in the nucleus. We transfected CHO cells, which have a low constitutive level of MT expression, with either the full MT-gene (MTMT) or with MR 5'UTR and coding region linked to the 3'UTR of glutathione peroxidase (MTGSH). Immunocytochemistry showed that MT protein was localized in the perinuclear cytoplasm in the MTMT cells whereas no distinct localization was found in the MTGSH cells. The cells were then synchronised in S-phase by serum depletion/repletion. After serum repletion, MT was found in the nucleus of MTMT cells but not in the MTGSH cells. This suggests that perinuclear localization of MT-1 mRNA and its association with the cytoskeleton is necessary for MT protein localization, particularly for the shuttling of MT protein into the nucleus during S-phase. Functional studies demonstrated that the extent of oxidative stress and DNA damage was lower in the MTMT than the MTGSH, showing that a loss of MT protein localization led to a reduced protection of the cell. Therefore, it seems that perinuclear localization of mRNAs coding for MT is necessary for subsequent transport and targeting of proteins into the nucleus and that the localization of the protein within the cell is important for its function.