Lari Hakkinen

Professor

Research Classification

Cell Therapy
Cell Signaling
Connective Tissue

Research Interests

Wound Healing
Tissue regeneration
Fibroblasts, MSC
Extracellular matrix
Cell to cell communication
Oral mucosa and skin

Relevant Degree Programs

 

Research Methodology

tissue engineering
cell culture
Animal models
Cell Biology
Proteomics
molecular biology
Microscopy
Histology

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Master's students
Doctoral students
2019
2020

Wound healing, cell communication, fibroblast biology, cell therapy

I support public scholarship, e.g. through the Public Scholars Initiative, and am available to supervise students and Postdocs interested in collaborating with external partners as part of their research.
I am open to hosting Visiting International Research Students (non-degree, up to 12 months).

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
Role of connexin 43 in regulating wound healing-related gene expression in human skin and gingival fibroblasts (2018)

Wound healing in human oral mucosal gingiva is faster and results in significantly reduced scar formation as compared to similar skin wounds. Fibroblasts are the most abundant group of connective tissue cells that play a key role in wound healing and scar formation. It is possible that differential healing outcomes in skin and gingiva may relate to the distinct phenotypic features of fibroblasts residing in these tissues. In fibroblasts, cells-to-cell communication occurs partly through connexin (Cx) hemichannels (HCs) and gap junctions (GJs). Findings from previous studies have shown that functional blockage of connexin 43 (Cx43), the most ubiquitous Cx in skin (SFBLs) and gingival fibroblasts (GFBLs), accelerates wound closure in skin and may alleviate scarring, but the mechanisms are poorly understood and may involve modulation of Cx43 function in fibroblasts. In the present dissertation, we show that (1) Cx43 was the most abundant Cx present in cultured human SFBLs and GFBLs. (2) Its abundance was potently downregulated at the early stage of human gingival wound healing. (3) Cx43 assembled into GJ and HC plaques in skin and gingival epithelium and connective tissue fibroblasts, although its distribution into GJs or HCs was markedly different in these two tissues. (4) Cx43 mainly assembled into HCs in GFBLs while in SFBLs only a few HCs were present in vivo and in vitro. (5) Using an in vivo-like 3D culture model and Cx43 mimetic peptides to block its function, we showed that the GJ, HC, and channel-independent functions of Cx43 distinctly upregulate anti-fibrotic and downregulate profibrotic wound healing-related genes in GFBLs and SFBLs. (6) In GFBLs this response was mainly mediated by activation of ERK1/2 pathway via Cx43 HC blockage. Thus, Cx43 assembly into GJs and HCs and its function are distinct in SFBLs and GFBLs, which may contribute to the different wound healing outcomes in these tissues. Furthermore, specific blockage of Cx43 HC functions may provide a novel target to promote wound healing and alleviate scar formation.

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Method development for the comprehensive analysis of post translational modifications by mass spectometry (2008)

Signal Transduction is mediated by protein complexes whose spatial- and temporal-distribution, composition and function within cells are often regulated by different post-translational modifications (PTM). As PTMs add or subtract a specific mass difference to a protein, mass spectrometry becomes very amenable for modification analysis. These modifications have conventionally been monitored by fragmenting the modified protein or peptide by collision induced dissociation (CID) within the mass spectrometer, and then screening for the characteristic neutral fragment or fragment ion (marker ion), which is particular to the modification in question. Unfortunately, there are two major issues with respect to the traditional mass spectrometric analysis of PTMs: (1) as there are over 300 known types of modifications, the characteristic fragmentation of only a fraction of these modifications has been studied and (2) the traditional mass spectrometric approaches can only monitor these modifications sequentially, and thus comprehensive modification analysis would be unfeasible considering the breadth of PTMs. The following work aims to address these issues by (1) analyzing PTMs that have never been characterized mass spectrometrically and (2) developing a multiplexed technique for comprehensive PTM monitoring by simultaneously screening for all known characteristic fragments. With respect to the first issue, the characteristic fragmentation of lipid modifications and HNO-induced modifications was investigated. The most prevalent indicator(s) of the modification within the mass spectra are as follows: fragmentation of N-terminal myristoylated peptides produced marker ions at 240 and 268 Th, fragmentation of cysteine farnesylated peptides produced a marker ion at 205 Th and a neutral fragment of 204 Da, and fragmentation of cysteine palmitoylated peptides produced a neutral fragment of 272 Th. For HNO-induced modifications, fragmentation of the sulfinamide- and sulfinic acid-modified peptides produced a neutral fragment of 65 Da and 66 Da, respectively. With respect to the second issue, a multiplexed technique for monitoring modifications that fragment as neutral losses, termed Multiple Neutral Loss Monitoring (MNM), has been developed, successfully validated, and then shown to be the most sensitive approach for PTM analysis. MNM, combined with a second multiplexed approach, targeted Multiple Precursor Ion Monitoring, has been used to provide a comprehensive PTM analysis.

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Master's Student Supervision (2010 - 2018)
The role of fibroblast phenotype and pericellular matrix in wound healing (2013)

Scar formation as a result of wound healing in skin is associated with increased deposition of extracellular matrix (ECM) and reduced ECM turnover by fibroblasts. Remarkably, wound healing in the human oral mucosa results in scarless healing, while wound healing in the skin can often result in scarring. Therefore comparing fibroblast phenotype and interactions with their ECM niche in the gingiva and skin may provide novel information about the factors that regulate scar formation. To this end, a novel 3D cell culture model was utilized to yield a cellular microenvironment (niche) that closely mimics the in vivo situation and primary gingival (GFBL) and skin fibroblasts (SFBL) phenotype was characterized. Furthermore, fibroblasts were reseeded on cell-free 3D ECM derived from GFBL and SFBL and the effects of the 3D ECM on cell phenotype were analyzed. Interestingly, SFBL in 3D cultures had greater expression of ECM deposition associated genes, including collagens, matricellular proteins, SLRPs, TGF-β1 and CTGF, intracellular ECM degradation and myofibroblast differentiation and function-associated genes, while GFBL had a greater expression of matrix remodeling associated genes (MMPs). We also found that the 3D cultures showed a significant difference in expression of certain genes (MMPs and myofibroblast function-associated genes) between GFBL and SFBL compared to cells reseeded on the 3D ECM or 2D control substrate. Thus, the 3D culture conditions may differentially regulate expression of a subset of genes in these cells. Interestingly, SFBL had a greater expression of matrix deposition associated genes (collagens, SLRPs, tenascins) irrespective of the culture conditions, suggesting that expression of these genes is inherently distinct between GFBL and SFBL. This was associated with greater autogenous TGF-β expression and SMAD3 phosphorylation in SFBL than GFBL, which may partly explain the innate difference in gene expression. In addition, there was greater ERK1/2 phosphorylation in fibroblasts when seeded on 3D ECM compared to 2D substrate. Greater ERK1/2 phosphorylation may have promoted greater expression of AP-1-dependent MMPs seen in SFBL and GFBL on 3D ECM. In conclusion, reduced expression of matrix deposition associated genes and greater expression of matrix remodeling genes in GFBL may contribute to scarless healing in gingiva.

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Matrix metalloproteinases in scarless wound healing (2011)

Objectives: Wound healing in skin often results in scar formation, whereas wound healing in oral palatal mucosa is fast and rarely results in scarring. Understanding the mechanisms that promote oral scarless wound healing may provide novel approaches to prevent scar formation in skin. The goal of the study was to compare the abundance of the major collagenases MMP-1 and MMP-13 and gelatinases MMP-2 and MMP-9 in normal unwounded oral mucosa and skin and in experimental excisional wounds in skin (healing results to scar formation) and oral mucosa (wounds heal with minimal scar formation) at various time points post-wounding at the protein level. We hypothesized that the abundance of MMPs will be higher in scarless oral mucosal wound healing, compared to skin wound healing.Methods: Experimental wounds were created in oral palatal mucosa and dorsal skin of red Duroc pigs. Wound biopsies were collected before wounding and at various time points after wounding. The abundance of MMPs at the protein level was assessed by Western blotting and zymography. Results: All studied MMPs showed a significantly increased accumulation in the wound tissue already at day three post-wounding. Their abundance remained high until day 28 when MMP-9 and MMP-13 returned to the level of unwounded tissue, while MMP-1 and MMP-2 remained significantly elevated. Oral mucosal wounds showed in general a robust early up-regulation of MMP-1, MMP-2 and MMP-9 as compared to skin wounds already at day 3 after wounding. In contrast, the peak abundance of these MMPs occurred at day 14 in skin wounds. Unwounded oral mucosa showed significantly higher abundance of total MMP-2 and active MMP-9 as compared to unwounded skin. Thus, MMPs needed for early wound healing response are already present in higher abundance in oral mucosa as compared to skin before tissue injury possibly allowing a fast wound healing response. Conclusions: Results suggest that oral mucosal wound healing is associated with fast and robust regulation of MMPs. Rapid controlled processing of wound extracellular matrix may play a key role in scarless palatal wound healing. In addition, MMPs may regulate inflammatory reaction that plays a central role in scar formation.

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