Dedifferentiation: inspiration for devising engineering strategies for regenerative medicine

Cell dedifferentiation is the process by which cells grow reversely from a partially or terminally differentiated stage to a less differentiated stage within their own lineage. This extraordinary phenomenon, observed in many physiological processes, inspires the possibility of developing new therapeutic approaches to regenerate damaged tissue and organs. Meanwhile, studies also indicate that dedifferentiation can cause pathological changes. In this review, we compile the literature describing recent advances in research on dedifferentiation, with an emphasis on tissue-specific findings, cellular mechanisms, and potential therapeutic applications from an engineering perspective. A critical understanding of such knowledge may provide fresh insights for designing new therapeutic strategies for regenerative medicine based on the principle of cell dedifferentiation.

Midkine promotes articular chondrocyte proliferation through the MK-LRP1-nucleolin signaling pathway

Osteoarthritis (OA) is the most common disease of joint tissues; unfortunately, there are currently no curative therapies available for OA. Chondrocytes, the only cell type residing in cartilage, secrete many types of collagen (the mainly one is type II collagen) and aggrecan, which are the main components of the cartilage matrix. Chondrocyte apoptosis can lead to OA degenerative progression. We previously indicated that recombinant human midkine (rhMK), as a chondrocyte growth factor has a significant reparative effect on cartilage injury animal models. However, the molecular mechanism of this restorative function remains under investigation. Herein, we focused on the molecular mechanism underlying the role of MK in promoting the proliferation of chondrocytes cultured in vitro. Chondrocytes from rats and OA patients were successfully isolated by the digestion of articular cartilage using type II collagenase, and their proliferation was evaluated by a CCK8 assay and flow cytometry. rhMK stimulated the proliferation of chondrocytes from both OA patients and rats. Furthermore, qRT-PCR, shRNA-mediated knockdown, Western blot and immunoprecipitation (IP) assays were performed to identify the receptor and key elements responsible for the role of MK in promoting chondrocyte proliferation. Low-density lipoprotein receptor-related protein 1 (LRP1) was identified as the dominant MK receptor in chondrocytes that, as a translocator, mediates the endocytosis of MK. After being transferred into chondrocytes, MK was shown to form a complex with nucleolin that interacts with the active form of K-Ras. Upon the activation of ERK1/2, cyclin D1 expression was upregulated, promoting the chondrocyte cell cycle. Our data reveal for the first time the role of the MK-LRP1-nucleolin signaling pathway in facilitating MK-induced chondrocyte proliferation, thus providing a strong theoretical foundation for the further use of MK in OA clinical therapy.

Midkine is overexpressed in acute pancreatitis and promotes the pancreatic recovery in L-arginine-induced acute pancreatitis in mice

BACKGROUND AND AIM

Midkine (MK) is involved in the pathogenesis of numerous malignancies, but the expression and effect of MK in acute pancreatitis (AP) have not been well studied and documented.

METHODS

In this study, the expression of MK was assayed in mice with L-arginine-induced AP. A recombinant human MK (rhMK) was introduced in this study to test the effect of MK on the L-arginine-induced AP. Serum amylase and lipase were assayed. Pancreas tissue samples were also collected for the evaluation of histological injury. Western blot and immunochemical staining of α-amylase and proliferating cell nuclear antigen were applied for the study of acinar regeneration in the pancreas.

RESULTS

The elevation of MK expression was found in mice with AP induced by L-arginine. After rhMK administration, rhMK did not affect the severity of acute pancreatic injury in acute phase in L-arginine-induced pancreatitis in mice, in accordance with changes of serum amylase and lipase and the histological evaluation. But during the recovery phase, the area of remaining acinar cells was increased and the fibrosis was reduced in rhMK-treated mice. Furthermore, the expression of proliferating cell nuclear antigen and α-amylase was also upregulated after rhMK treatment.

CONCLUSION

Midkine is over-expressed during AP in the animal model. Recombinant MK could promote the recovery of L-arginine-induced pancreatitis in mice. Therefore, MK may be involved in the regeneration of acinar cells in AP, and rhMK may be a possible therapeutic intervention for the repairment of AP.

Antagonizing midkine accelerates fracture healing in mice by enhanced bone formation in the fracture callus

BACKGROUND AND PURPOSE

Previous findings suggest that the growth and differentiation factor midkine (Mdk) is a negative regulator of osteoblast activity and bone formation, thereby raising the possibility that a specific Mdk antagonist might improve bone formation during fracture healing.

EXPERIMENTAL APPROACH

In the present study, we investigated the effects of a monoclonal anti-Mdk antibody (Mdk-Ab) on bone healing using a standardized femur osteotomy model in mice. Additional in vitro experiments using chondroprogenitor and preosteoblastic cells were conducted to analyse the effects of recombinant Mdk and Mdk-Ab on differentiation markers and potential binding partners in these cells.

KEY RESULTS

We demonstrated that treatment with Mdk-Ab accelerated bone healing in mice based on increased bone formation in the fracture callus. In vitro experiments using preosteoblastic cells showed that Mdk-Ab treatment abolished the Mdk-induced negative effects on the expression of osteogenic markers and Wnt/β-catenin target proteins, whereas the differentiation of chondroprogenitor cells was unaffected. Phosphorylation analyses revealed an important role for the low-density lipoproteinLDL receptor-related protein 6 in Mdk signalling in osteoblasts.

CONCLUSIONS AND IMPLICATIONS

We conclude that Mdk-Ab treatment may be a potential novel therapeutic strategy to enhance fracture healing in patients with orthopaedic complications such as delayed healing or non-union formation.

The therapeutic effect of rhMK on osteoarthritis in mice, induced by destabilization of the medial meniscus

Osteoarthritis (OA) is a worldwide disease in aged people, causing not only physical suffering to the patients themselves, but also a great burden on their families and on society. Here we used a mouse OA model induced by destabilization of the medial meniscus (DMM), and studied the therapeutic effect of recombinant human midkine (rhMK) on this OA model. Our results indicated that the DMM surgery induced mechanical allodynia and locomotor activity obstacles, together with cartilage injury in the C57BL/6 mice. The rhMK treatment mitigated the OA related mechanical allodynia, improved locomotor activity capacity, and prevented degradation of the cartilage. Considering the safety issue of rhMK used as a biologic, we also inspected the main organs in the rhMK treated mice throughout the process and found no pathological change. These results suggest that rhMK could be used as a biologic to treat OA or OA related pain.

Prokaryotic Expression, Refolding and Purification of High-Purity Mouse Midkine in Escherichia coli

To evaluate the clinic safety of human Midkine as an articular protective agent, recombinant mouse Midkine (rmMK) was prepared in prokaryotic system for the pre-clinic long-term studies in mice. The open reading frame of mouse Midkine (mMK) was sub-cloned onto expression vector pET30a (+) and transformed into Escherichia coli BL21 (DE3) strain line. The rmMK protein, with a Met fused at N terminus of native mMK for expression initiating, proved to be expressed in inclusion bodies and turned out to be soluble post-denaturation and renaturation. The soluble rmMK was purified successfully with ion exchange and affinity chromatography and characterised good enough to meet the requirements for animal use. Eventually, 13.2-mg rmMK with high quality and bioactivity was obtained from 1 L LB culture, and the total recovery was 11.4%. The present work laid a good foundation for pilot- or large-scale production of rmMK in prokaryotic system.